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Federico A Zumaya-Estrada,1 Alfredo Ponce-de-León-Garduño,2 Edgar Ortiz-Brizuela,2 Juan Carlos Tinoco-Favila,3 Patricia Cornejo-Juárez,4 Diana Vilar-Compte,4 Alejandro Sassoé-González,5 Pedro Jesus Saturno-Hernandez,6 Celia M Alpuche-Aranda1 1Center for Infectious Diseases Research (CISEI), National Institute of Public Health (INSP), Cuernavaca, C.P. 62100, Morelos, México; 2Infectology Department, National Institute of Medical Sciences and Nutrition “Salvador Zubirán”, Ciudad de México, C.P. 14080, México; 3Infectology Department, Hospital General 450, Secretary of Health of Durango, Durango, C.P. 34206, Durango, México; 4Infectious Diseases Department, National Institute of Cancer (INCan), Ciudad de México, C.P. 14080, México; 5Epidemiological Intelligence Unit, High Specialty Regional Hospital of Ixtapaluca, Estado de México, C.P. 56530, México; 6Center for Evaluation and Surveys Research (CIEE), National Institute of Public Health (INSP), Cuernavaca, C.P. 62100, Morelos, MéxicoCorrespondence: Celia M Alpuche-ArandaCenter for Infectious Diseases Research (CISEI), National Institute of Public Health (INSP), Cuernavaca, C.P. 62100, Morelos, MéxicoTel +52 777-329-3000 ext. 2101Email celia.alpuche@insp.mxPedro Jesus Saturno-HernandezCenter for Evaluation and Surveys Research (CIEE), National Institute of Public Health (INSP), Cuernavaca, C.P. 62100, Morelos, MéxicoTel +52 777-329-3000 ext. 4332Email pedro.saturno@insp.mxPurpose: To describe the antimicrobial use in four tertiary care hospitals in Mexico.Patients and Methods: Point prevalence surveys (PPSs) were conducted on medical records of hospitalized patients with prescribed antimicrobials (AMs) in four tertiary care hospitals in Mexico in 2019. Prevalence estimates and descriptive statistics were used to present the collected data on antimicrobial prescribing and microbiological studies.Results: The prevalence of patients with prescribed AMs among the hospitals ranged from 47.1% to 91.3%. Antibiotics for systemic use (J01s) were the most prescribed (84.6%, [95% CI: 81.5– 87.3]), mainly extended-spectrum J01s: third-generation cephalosporins 19.8% [95% CI: 16.8– 23.1], and carbapenems 17.0% [95% CI: 14.2– 20.2]. Antibiotic treatments were largely empirical, with no planned duration or review dates. The ceftriaxone use was excessive and prolonged. No formal reference guidelines for antimicrobial prescribing were available in the hospitals. Multidrug-resistant Escherichia coli and ESKAPE pathogens were identified in all hospitals.Conclusion: This study describes the extensive use of antimicrobials and broad-spectrum antibiotics for systemic use in Mexican hospitals, along with the presence of resistant pathogens to the antibiotics frequently used in the hospitals surveyed.Keywords: PPSs, antimicrobial use, antibiotics, Mexican hospitals

Astroviruses are highly divergent and infect a wide variety of animal hosts. In 2009, a genetically divergent human astrovirus (HAstV) strain VA1 was first identified in an outbreak of acute gastroenteritis. This strain has also been associated with fatal central nervous system disease. In this work, we report the isolation of three high-affinity neutralizing monoclonal antibodies (Nt-MAbs) targeting the capsid spike domain of HAstV-VA1. These antibodies (7C8, 2A2, 3D8) were used to select individual HAstV-VA1 mutants resistant to their neutralizing activity and a HAstV-VA1 triple mutant that escapes neutralization from all three Nt-MAbs. Sequencing of the virus genome capsid region revealed escape mutations that map to the surface of the capsid spike domain, define three potentially independent neutralization epitopes, and help delineate four antigenic sites in human astroviruses. Notably, two of the escape mutations were found to be present in the spike sequence of the HAstV-VA1-PS strain isolated from an immunodeficient patient with encephalitis, suggesting that those mutations arose as a result of the immune pressure generated by the patient's immunotherapy. In agreement with this observation, human serum samples exhibiting strong neutralization activity against wild-type HAstV-VA1 had a 2.6-fold reduction in neutralization titer when evaluated against the triple-escape HAstV-VA1 mutant, suggesting that both mouse and human antibody responses target shared neutralization epitopes. The isolated Nt-MAbs reported in this work will help to characterize the functional domains of the virus during cell entry and have the potential for developing a specific antibody therapy for the neurological disease associated with HAstV-VA1., Importance: Human astroviruses (HAstVs) have been historically associated with acute gastroenteritis. However, the genetically divergent HAstV-VA1 strain has been associated with central nervous system disease. In this work high-affinity neutralizing monoclonal antibodies directed to HAstV-VA1 were isolated and characterized. The proposed binding sites for these antibodies and for neutralizing antibodies against classical HAstVs suggest that there are at least four neutralization sites on the capsid spike of astroviruses. Our data show that natural infection with human astrovirus VA1 elicits a robust humoral immune response that targets the same antigenic sites recognized by the mouse monoclonal antibodies and strongly suggests the emergence of a variant HAstV-VA1 virus in an immunodeficient patient with prolonged astrovirus infection. The isolated Nt-MAb reported in this work will help to define the functional sites of the virus involved in cell entry and hold promise for developing a specific antibody therapy for the neurological disease associated with HAstV-VA1., Competing Interests: The authors declare no conflict of interest.

The metagenomic surveillance of antimicrobial resistance in wastewater has been suggested as a methodological tool to characterize the distribution, status, and trends of antibiotic-resistant bacteria. In this study, a cross-sectional collection of samples of hospital-associated raw and treated wastewater were obtained from February to March 2020. Shotgun metagenomic sequencing and bioinformatic analysis were performed to characterize bacterial abundance and antimicrobial resistance gene analysis. The main bacterial phyla found in all the samples were as follows: Proteobacteria , Bacteroides , Firmicutes , and Actinobacteria . At the species level, ESKAPEE bacteria such as E. coli relative abundance decreased between raw and treated wastewater, but S. aureus , A. baumannii , and P. aeruginosa increased, as did the persistence of K. pneumoniae in both raw and treated wastewater. A total of 172 different ARGs were detected; bla OXA , bla VEB , bla KPC , bla GES , mphE , mef , erm , msrE , AAC(6') , ant(3″) , aadS , lnu , PBP-2 , dfrA , vanA-G , tet , and sul were found at the highest abundance and persistence. This study demonstrates the ability of ESKAPEE bacteria to survive tertiary treatment processes of hospital wastewater, as well as the persistence of clinically important antimicrobial resistance genes that are spreading in the environment.

Objective: Estimate COVID-19 vaccine booster uptake and identify sociodemographic profiles associated with vaccine booster uptake in Mexican adults aged 60 and older., Methods: Using data from the 2022 National Health and Nutrition Survey, we estimated COVID-19 booster uptake in Mexican adults 60 and older. We conducted a latent class analysis using sociodemographic characteristics and then estimated group-specific booster prevalence., Results: Adults aged 60 and older with a completed vaccination schedule had 80.3% booster coverage. Two groups showed the lowest coverage: 1) unemployed and informal working men with elementary education with low socioeconomic status (73.8% boosted), and 2) female homekeepers with elementary education or less living in rural areas (77.0% boosted)., Conclusions: Our analysis points to the need to reach out to men and women with elementary education or less who live in rural areas to strengthen booster campaigns in the future., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Tonatiuh Barrientos-Gutierrez reports financial support was provided by Centers for Disease Control and Prevention. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paperless., (Copyright © 2024 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

The objective of the study was to detect multidrug-resistant Staphylococcus sp. and Enterococcus sp. isolates in municipal and hospital wastewater and to determine their elimination or persistence after wastewater treatment. Between August 2021 and September 2022, raw and treated wastewater samples were collected at two hospital and two community wastewater treatment plants (WWTPs). In each season of the year, two treated and two raw wastewater samples were collected in duplicate at each of the WWTPs studied. Screening and presumptive identification of staphylococci and enterococci was performed using chromoagars, and identification was performed with the Matrix Assisted Laser Desorption Ionization Time of Flight mass spectrometry (MALDI-TOF MS ® ). Antimicrobial susceptibility was performed using VITEK 2 ® automated system. There were 56 wastewater samples obtained during the study period. A total of 182 Staphylococcus sp. and 248 Enterococcus sp. were identified. The highest frequency of Staphylococcus sp. isolation was in spring and summer (n = 129, 70.8%), and for Enterococcus sp. it was in autumn and winter (n = 143, 57.7%). Sixteen isolates of Staphylococcus sp. and sixty-three of Enterococcus sp. persisted during WWTP treatments. Thirteen species of staphylococci and seven species of enterococci were identified. Thirty-one isolates of Staphylococcus sp. and ninety-four of Enterococcus sp. were multidrug-resistant. Resistance to vancomycin (1.1%), linezolid (2.7%), and daptomycin (8.2%/10.9%%), and a lower susceptibility to tigecycline (2.7%), was observed. This study evidences the presence of Staphylococcus sp. and Enterococcus sp. resistant to antibiotics of last choice of clinical treatment, in community and hospital wastewater and their ability to survive WWTP treatment systems.

Objetivo: Describir la prevalencia de anticuerpos contra SARS-CoV-2, vacunación, barreras y rechazo a la vacunación Covid-19 en población mexicana. Material y métodos. Se utilizó información de los integrantes del hogar de uno y más años, incluidos en la Encuesta Nacional de Salud y Nutrición Continua 2022 (Ensanut Continua 2022) realizada de agosto-noviembre. Se estimó la prevalencia de anticuerpos antiproteínas N y S de SARS-CoV-2 en muestras de sangre capilar, dosis reportadas de vacunación a Covid-19 y las razones de barreras y rechazo a la vacunación., Resultados: La prevalencia de anticuerpos anti-N fue de 94.4% y de anti-S 98.1%. La prevalencia de anticuerpos anti-S fue mayor en personas vacunadas con una, dos o tres o más dosis que en no vacunadas. Dentro de la población elegible a vacunación, 20.2% no estaba vacunada, 16.2% tenía una dosis, 30% dos dosis y 33.6% tres dosis o más. El 11.2% de la población elegible rechazó la vacunación, 5.5% reportó una barrera y 3.2% reportó que la vacuna no había llegado a su localidad. Conclusión. La prevalencia de anticuerpos por infección natural y por vacunación Covid-19 es alta en México. Las variaciones de rechazo y barreras a la vacunación entre grupos de edad y regiones deben tomarse en cuenta para intensificar esfuerzos específicos para la vacunación.

Objective: To estimate vaccine uptake and assess sociodemographic conditions associated with vaccination barriers and refusal and to explore the effect of a monetary incentive to overcome them., Materials and Methods: We used data from adults from the 2021 National Continuous Health and Nutrition Survey conducted during August-October 2021. We evaluated if an hypothetical monetary incentive between 50-650 MXN (~2.5-31 USD) would overcome barriers or refusal., Results: 73.9% were vaccinated with at least one dose, 7.5% refused, 4.8% reported barriers and 13.8% were ineligible at the time of the survey. Refusal and barriers were more frequent in men, older age, lower education and socioeconomic status, unemployed and informal workers. In people with barriers and refusal, the hypothetical incentive increased the acceptance in 57.6% (95%CI 50.7,64.4%) and 17.4% (95%CI 13.2,21.7%) in people with barriers and refusal, respectively., Conclusion: Understanding the reasons for barriers and refusal is crucial for future Covid-19 vaccination campaigns or epidemics. A monetary incentive might increase vaccination uptake, although, cost-effectiveness analyses are needed.

Dengue and Zika are arthropod-borne viral diseases present in more than 100 countries around the world. In the past decade, Zika emerged causing widespread outbreaks in new regions, where dengue has been endemic-epidemic for a long period. The wide and extensive dissemination of the mosquito vectors, Aedes aegypti , and Ae. albopictus , favor the co-existence of both infections in the same regions. Together with an important proportion of asymptomatic infections, similar clinical manifestations, and a short time window for acute infection confirmatory tests, it is difficult to differentially estimate both dengue and Zika incidence and prevalence. DENV and ZIKV flavivirus share high structural similarity, inducing a cross-reactive immune response that leads to false positives in serological tests particularly in secondary infections. This results in overestimation of recent Zika outbreaks seroprevalence in dengue endemic regions. In this review, we address the biological basis underlying DENV and ZIKV structural homology; the structural and cellular basis of immunological cross reactivity; and the resulting difficulties in measuring dengue and Zika seroprevalence. Finally, we offer a perspective about the need for more research to improve serological tests performance., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Gaspar-Castillo, Rodríguez, Ortiz-Navarrete, Alpuche-Aranda and Martinez-Barnetche.)

Bacterial meningitis is one of the diseases that, despite the introduction of several vaccines, remains a serious public health concern. Streptococcus pneumoniae (Spn), Neisseria meningitidis (Nm), and Haemophilus influenzae (Hi) are responsible for most cases diagnosed in children, adolescents, and adult population. Rapid, sensitive, and specific laboratory assays are critical for effective diagnosis and treatment, particularly in countries like Mexico in which culture positivity rates are very low due to the use of antibiotics prior to sample collection and to delay in transporting samples to the laboratory. The aim of this study was to evaluate the use of real-time polymerase chain reaction (RT-PCR) of cerebrospinal fluid (CSF) as a rapid diagnostic test for bacterial meningitis and compare these results with bacterial culture in three general hospitals in Mexico. During a 5-year period (2014-2018), a total of 512 CSF samples obtained from patients in whom infectious meningitis was suspected as initial clinical diagnosis were tested with RT-PCR with species-specific targets for the three pathogens. For Spn, 5.07% samples were RT-PCR positive; 0.39% for Nm and none for Hi. Only five RT-PCR Spn positive samples had a positive culture. Sensitivity and specificity estimates for RT-PCR are 100% and 95.46%, respectively. DNA amplification methods can provide better sensitive diagnostic tests than the reference standard, which is culture, particularly when antimicrobial treatment is initiated before clinical samples can be obtained., (© 2022. The Author(s) under exclusive licence to Sociedade Brasileira de Microbiologia.)

Objective: Evaluate spatially and temporally simultaneous presence of clusters of dengue and Zika clinical cases and their relationship with expected dengue transmission risk., Materials and Methods: A classification of dengue risk transmission was carried out for whole country, and spatial autocorrelation analyses to identify clusters of confirmed clinical cases of dengue and Zika from 2015 to 2018 was conducted using Moran's Index statistics., Results: Clusters of both diseases were identified in dengue-high risk munici-palities at the beginning of the outbreak, but, at the end of the outbreak, Zika clusters occurred in dengue low-risk mu-nicipalities., Conclusion: This study identified Zika clusters in low-risk dengue areas suggesting participation of several factors that favor virus introduction and dissemination, such as differences in entomological and control interventions, and the possibility of cross-immunity in the population.

The objective of this study was to determine the presence and persistence of antimicrobial-resistant enterobacteria and their clonal distribution in hospital wastewater. A descriptive cross-sectional study was carried out in wastewater from two Mexico City tertiary level hospitals. In February and March of 2020, eight wastewater samples were collected and 26 isolates of enterobacteria were recovered, 19 (73.1%) isolates were identified as E. coli , 5 (19.2%) as Acinetobacter spp. and 2 (7.7%) as Enterobacter spp. Antimicrobial susceptibility profiles were performed using the VITEK 2 ® automated system and bacterial identification was performed by the Matrix-Assisted Laser Desorption/Ionization-Time of Flight mass spectrometry (MALDI-TOF MS ® ). ESBL genes were detected by polymerase chain reaction (PCR) and clonal distributions of isolates were determined by pulsed-field gel electrophoresis (PFGE). E. coli susceptibility to different classes of antimicrobials was analyzed and resistance was mainly detected as ESBLs and fluoroquinolones. One E. coli strain was resistant to doripenem, ertapenem, imipenem and meropenem. The analysis by PCR showed the presence of specific β-lactamases resistance genes ( bla KPC , bla CTX-M ). The PFGE separated the E. coli isolates into 19 different patterns (A-R). PFGE results of Acinetobacter spp. showed the presence of a majority clone A. Surveillance of antimicrobial resistance through hospital wastewater is an important tool for early detection of clonal clusters of clinically important bacteria with potential for dissemination.

In this research, a review of antimicrobial resistance (AMR) is conducted as part of the One Health approach. A review of publications, which included "antimicrobial resistance" and "One Health," was conducted. Among the global health problems, AMR is the one that most clearly illustrates the One Health approach. AMR is a critical global problem affecting humans, the environment, and animals. This is related to each of these three components due to the irresponsible and excessive use of antimicrobials in various sectors (agriculture, livestock, and human medicine). Improper management of antimicrobials, inadequate control of infections, agricultural debris, pollutants in the environment, and migration of people and animals infected with resistant bacteria facilitate the spread of resistance. The study aimed to analyze the problem of AMR from a health perspective to analyze the different actors involved in One Health., Competing Interests: The authors declare that they have no competing interests., (Copyright: © Velazquez-Meza, et al.)

The objective of this study was to investigate the presence and persistence of carbapenemase-producing Klebsiella spp. isolated from wastewater and treated wastewater from two tertiary hospitals in Mexico. We conducted a descriptive cross-sectional study in two hospital wastewater treatment plants, which were sampled in February 2020. We obtained 30 Klebsiella spp. isolates. Bacterial identification was carried out by the Matrix-Assisted Laser Desorption/Ionization-Time of Flight mass spectrometry (MALDI-TOF MS ® ) and antimicrobial susceptibility profiles were performed using the VITEK2 ® automated system. The presence of carbapenem resistance genes (CRGs) in Klebsiella spp. isolates was confirmed by PCR. Molecular typing was determined by pulsed-field gel electrophoresis (PFGE). High rates of Klebsiella spp. resistance to cephalosporins and carbapenems (80%) were observed in isolates from treated wastewater from both hospitals. The molecular screening by PCR showed the presence of bla KPC and bla OXA-48-like genes. The PFGE pattern separated the Klebsiella isolates into 19 patterns (A-R) with three subtypes (C1, D1, and I1). Microbiological surveillance and identification of resistance genes of clinically important pathogens in hospital wastewater can be a general screening method for early determination of under-detected antimicrobial resistance profiles in hospitals and early warning of outbreaks and difficult-to-treat infections.

México cuenta con más de tres décadas de gran experiencia en la aplicación de Encuestas Nacionales de Salud. La primera Encuesta de Salud fue realizada por la Secretaría de Salud (SS) en el año de 1986; tan sólo dos años después se llevó a cabo la primera Encuesta Nacional de Nutrición, enfocada al área materno-infantil. Posteriormente, la Secretaría de Salud encargó al Instituto Nacional de Salud Pública (INSP) que realizara en 1999 una segunda Encuesta Nacional de Nutrición materno-infantil y, en el año 2000, una Encuesta Nacional de Salud. En 2006, bajo el esfuerzo del INSP y de la SS, se unen ambas encuestas, lo que da origen a la primera Encuesta Nacional de Salud y Nutrición (Ensanut), la cual incluye, en un mismo operativo, la evaluación de la nutrición y de la salud en toda la población a nivel nacional y estatal.

Objetivo. Describir el diseño de la Encuesta Nacional de Salud y Nutrición 2021 (Ensanut 2021). Material y métodos. La Ensanut 2021 es una encuesta probabilística de hogares que forma parte de la serie de Ensanut Continua 2020-2024. En esta ocasión se describen el alcance, el muestreo, la medición y la organización logística. Resultados. Se planea obtener al menos 12 060 entrevistas de hogar completas a nivel nacional y 9 837 muestras para determinar seropositividad a SARS-CoV-2 a nivel nacional. Conclusiones. La Ensanut 2021 permitirá realizar inferencias regionales sobre la prevalencia de seropositividad a SARS-CoV-2 y también acumular información para realizar inferencias estatales en el año 2024.

Background: Low vaccination rates and under-detection of pertussis infections in adolescents and young adults have an impact on the transmission of pertussis to infants. In this study, the proportion of adolescents and young adults with IgG antibodies against B. pertussis antigens, representing recent infection or vaccination, was estimated in a population-based probabilistic survey in Mexico., Methods: Sera and data from 1,581 subjects, including 1,102 adolescents and 479 young adults (10-19 and 20-25 years old, respectively) randomly selected from Mexico's 2012 National Health and Nutrition Survey, were analyzed. IgG antibodies against pertussis toxin (PT) were measured with the CDC/FDA ELISA. A subset of 234 samples was additionally tested with Bp-IgG PT ELISA kit (EUROIMMUN AG, Lubeck, Germany). Threshold values from corresponding test kits were used to identify recent infection or vaccination., Results: Overall anti-PT IgG seroprevalence was 3.9% (95% CI: 2.3-6.3); 3.1% (95% CI: 1.9-5.0) in adolescents, and 4.9% (95% CI: 2.2-11) in young adults. Seroprevalence did not significantly vary by sex, socioeconomic status, region or rural/urban location. Compared to the CDC/FDA ELISA, the EUROIMMUN test showed a 76% sensitivity and 88% specificity. The weighted estimates represent a considerable burden of recent infection in adolescents and young adults; however, most adolescents and adults were seronegative and, therefore, susceptible to pertussis infection., Conclusion: Since booster vaccination to B. pertussis after toddlerhood is not recommended in the Mexican national policy, anti-PT IgG seropositivity may be reasonably attributed to recent infection. Assessing pertussis seroprevalence requires careful consideration of the diagnostic test threshold interpretation and epidemiological model used., Competing Interests: Declaration of Competing Interest EOB and MYCA are employees of the GSK group of companies and hold shares in the GSK group of companies as part of their employee remuneration. RCA and RDA were employees and disclosed shares of the GSK group of companies during the conduct of the study. EOB, MYCA, RCA and RDA declare no other financial and non-financial relationships and activities. HLG, GEA, MASA, SGC, MLT, LCP, MRM, MOP and CMAA declare no financial and non-financial relationships and activities and no conflicts of interest., (Copyright © 2021. Published by Elsevier Ltd.)

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Objective: To estimate the willingness to vaccinate against Covid-19 (acceptance) in the Mexican population and to iden-tify socioeconomic factors associated with vaccine hesitancy and refusal., Materials and Methods: We estimated the acceptance, refusal and hesitancy proportions using data from the Covid-19 National Health and Nutrition Survey conducted from August to November 2020. Factors associated with re-fusal and hesitancy were explored using multinomial logistic regression., Results: Covid-19 vaccination acceptance was 62.3%, refusal 28.2% and hesitancy 9.5%. Refusal and hesitancy were associated with being female, having older age, lower educational level, lower socioeconomic status and working in the informal sector., Conclusion: National campaigns to incentivize vaccine acceptance need to consider specific subgroups were the likelihood of hesitancy and refusal is high. In Mexico, refusal and hesitancy were higher in vulnerable groups, and people at a higher risk of Covid-19 complica-tions and death.

Point prevalence surveys (PPSs) are a useful option for collecting antimicrobial prescription data in hospitals where regular monitoring is not feasible. The methodology recommended by the World Health Organization (WHO) for conducting PPSs (WPPS), which targets low- and middle-income countries (LMICs), attempts to respond to the lag in these regions to generate estimates for antimicrobial use. However, based on our experience in four third-level public hospitals in Mexico, we identified substantial gaps in the WPPS guide with regards to addressing common challenges for the implementation of PPSs. While the oversimplified narrative of WPPS could facilitate the adoption of this methodology and extend its use, it underestimates the efforts and potential pitfalls for survey preparation, coordination, and reliable implementation. Conducting rigorous pilot studies could reduce the WPPS deficiencies and strengthen the reliability and comparability of the estimates for antimicrobial use., (Copyright © 2021 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Objective: Determine the frequency of diarrheagenic Escherichia coli pathotypes colonizing swine., Materials and Methods: E. coli strains isolated of fecal samples from 280 swine, produced for local consumption, in a semi-technical farm of Morelos state, (central Mexico) were tested to identify the diarrheagenic E. coli pathotypes by multiplex PCR., Results: Of the 521-diarrheagenic E. coli isolates examined, 50 (9.6%) were positive for at least one virulence gene in 42 different animals. Thus, 15% (42/280) of the swine in this farm were colonized with pathogenic E. coli. Among the E. coli isolates, the pathotype EPEC (6.5%) was the most frequently, followed by EHEC (2.3%), ETEC and EIEC (0.4%)., Conclusions: In this study, four different E. coli pathotypes were found among swine colonized by E. coli in this farm. Thus, these swine are reservoirs for these virulent bacteria and there is potential risk of causing diarrhea in swine and in the population consuming the meat.

In April 2009, Mexican, American, and Canadian authorities announced a novel influenza that became the first pandemic of the century. We report on lessons learned in Mexico. The Mexican Pandemic Influenza Preparedness and Response Plan, developed and implemented since 2005, was a decisive element for the early response. Major lessons-learned were the need for flexible plans that consider different scenarios; the need to continuously strengthen routine surveillance programs and laboratory capacity and strengthen coordination between epidemiological departments, clinicians, and laboratories; maintain strategic stockpiles; establish a fund for public health emergencies; and collaboration among neighboring countries. Mexico responded with immediate reporting and transparency, implemented aggressive control measures and generous sharing of data and samples. Lessons learned induced changes leading to a better response to public health critical events.

Objective: To assess the magnitude of the Mexican epidemic of Zika virus infection and the associated risk of microcephaly., Methods: From the reported number of laboratory-confirmed symptomatic infections among pregnant women and the relevant birth rate, we estimated the number of symptomatic cases of infection that occurred in Mexico between 25 November 2015, when the first confirmed Mexican case was reported, and 20 August 2016. We used data from the birth certificates to compare mean monthly incidences of congenital microcephaly before (1 January 2010-30 November 2015) and after (1 December 2015-30 September 2017) the introduction of Zika virus, stratifying the data according to whether the mother's place of residence was at an altitude of at least 2200 m above sea level. We used Poisson interrupted time series, statistical modelling and graphical analyses., Findings: Our estimated number of symptomatic cases of infection that may have occurred in the general population of Mexico between 25 November 2015 and 20 August 2016, 60 172, was 7.3-fold higher than the corresponding number of reported cases. The monthly numbers of microcephaly cases per 100 000 live births were significantly higher after the introduction of the virus than before (incidence rate ratio, IRR: 2.9; 95% confidence interval, CI: 2.3 to 3.6), especially among the babies of women living at altitudes below 2200 m (IRR: 3.4; 95% CI: 2.9 to 3.9)., Conclusion: The Mexican epidemic appears to be much larger than indicated by estimates based solely on counts of laboratory-confirmed cases, and to be associated with significantly increased risk of microcephaly.

Objective: To estimate the seroprevalence of CHKV antibodies and assess correlates of seropositivity at a small geographical scale., Materials and Methods: A community-based serosurvey of 387 households in Puente de Ixtla, Morelos (central Mexico). Serum IgG antibodies to CHKV were detected by immunoassay., Results: From 27 April to 29 May 2016, we interviewed and collected blood samples from 387 individuals at the same number of households. A total of 114 (29.5%) participants were seropositive to CHK, 36 (31.6%) of them reported no symptoms of CHKV infection within 12 months before the survey., Conclusions: The estimated seroprevalence to CHKV antibodies was higher than expected by the small number of confirmed cases of CHKV infection reported in Mexico by the National Surveillance System., Competing Interests: Declaration of conflict of interests. The authors declare that they have no conflict of interests.

Background: Acute respiratory infections are the leading cause of mortality in children worldwide, especially in developing countries. Pneumonia accounts for 16% of all deaths of children under 5 years of age and was the cause of death of 935000 children in 2015. Despite its frequency and severity, information regarding its etiology is limited. The aim of this study was to identify respiratory viruses associated with community-acquired pneumonia (CAP) in children younger than 5 years old., Methods: One thousand four hundred and four children younger than 5 years of age with a clinical and/or radiological diagnosis of CAP in 11 hospitals in Mexico were included. Nasal washes were collected, placed in viral medium, and frozen at -70°C until processing. The first 832 samples were processed using the multiplex Bio-Plex/Luminex system and the remaining 572 samples using the Anyplex multiplex RT-PCR. Clinical data regarding diagnosis, clinical signs and symptoms, radiographic pattern, and risk factors were obtained and recorded., Results: Of the samples tested, 81.6% were positive for viruses. Respiratory syncytial virus (types A and B) was found in 23.7%, human enterovirus/rhinovirus in 16.6%, metapneumovirus in 5.7%, parainfluenza virus (types 1-4) in 5.5%, influenza virus (types A and B) in 3.6%, adenovirus in 2.2%, coronavirus (NL63, OC43, 229E, and HKU1) in 2.2%, and bocavirus in 0.4%. Co-infection with two or more viruses was present in 22.1%; 18.4% of the samples were negative. Using biomass for cooking, daycare attendance, absence of breastfeeding, and co-infections were found to be statistically significant risk factors for the presence of severe pneumonia., Conclusions: Respiratory syncytial virus (types A and B), human enterovirus/rhinovirus, and metapneumovirus were the respiratory viruses identified most frequently in children younger than 5 years old with CAP. Co-infection was present in an important proportion of the children., (Copyright © 2017 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Background:  After decades of obscurity, Zika virus (ZIKV) has spread through the Americas since 2015 accompanied by congenital microcephaly and Guillain-Barré syndrome. Although these epidemics presumably involve transmission by Aedes aegypti, no direct evidence of vector involvement has been reported, prompting speculation that other mosquitoes such as Culex quinquefasciatus could be involved., Methods:  We detected an outbreak of ZIKV infection in southern Mexico in late 2015. Sera from suspected ZIKV-infected patients were analyzed for viral RNA and antibodies. Mosquitoes were collected in and around patient homes and tested for ZIKV., Results:  Of 119 suspected ZIKV-infected patients, 25 (21%) were confirmed by RT-PCR of serum collected 1-8 days after the onset of signs and symptoms including rash, arthralgia, headache, pruritus, myalgia, and fever. Of 796 mosquitoes collected, A. aegypti yielded ZIKV detection by RT-PCR in 15 of 55 pools (27.3%). No ZIKV was detected in C. quinquefasciatus ZIKV sequences derived from sera and mosquitoes showed a monophyletic relationship suggestive of a point source introduction from Guatemala., Conclusions:  These results demonstrate the continued, rapid northward progression of ZIKV into North America with typically mild disease manifestations, and implicate A. aegypti for the first time as a principal vector in North America., (© The Author 2016. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail journals.permissions@oup.com.)

As new vaccines against diseases that are prevalent in low- and middle-income countries gradually become available, national health authorities are presented with new regulatory and policy challenges. The use of CYD-TDV - a chimeric tetravalent, live-attenuated dengue vaccine - was recently approved in five countries. Although promising for public health, this vaccine has only partial and heterogeneous efficacy and may have substantial adverse effects. In trials, children who were aged 2-5 years when first given CYD-TDV were seven times more likely to be hospitalized for dengue, in the third year post-vaccination, than their counterparts in the control group. As it has not been clarified whether this adverse effect is only a function of age or is determined by dengue serostatus, doubts have been cast over the long-term safety of this vaccine in seronegative individuals of any age. Any deployment of the vaccine, which should be very cautious and only considered after a rigorous evaluation of the vaccine's risk-benefit ratio in explicit national and subnational scenarios, needs to be followed by a long-term assessment of the vaccine's effects. Furthermore, any implementation of dengue vaccines must not weaken the political and financial support of preventive measures that can simultaneously limit the impacts of dengue and several other mosquito-borne pathogens.

Background: The 2009 H1N1 influenza pandemic initially affected Mexico from April 2009 to July 2010. By August 2010, a fourth of the population had received the monovalent vaccine against the pandemic virus (A(H1N1)pdm09). To assess the proportion of the Mexican population who remained potentially susceptible to infection throughout the summer of 2010, we estimated the population seroprevalence to A(H1N1)pdm09 in a serosurvey of blood donors., Methods: We evaluated baseline cross-reactivity to the pandemic strain and set the threshold for seropositivity using pre-pandemic (2005-2008) stored serum samples and sera from confirmed A(H1N1)pdm09 infected individuals. Between June and September 2010, a convenience sample serosurvey of adult blood donors, children, and adolescents was conducted in six states of Mexico. Sera were tested by the microneutralization (MN) and hemagglutination inhibition (HI) assays, and regarded seropositive if antibody titers were equal or exceeded 1:40 for MN and 1:20 for HI. Age-standardized seroprevalence were calculated using the 2010 National Census population., Results: Sera from 1,484 individuals were analyzed; 1,363 (92%) were blood donors, and 121 (8%) children or adolescents aged ≤19 years. Mean age (standard deviation) was 31.4 (11.5) years, and 276 (19%) were women. A total of 516 (35%) participants declared history of influenza vaccination after April 2009. The age-standardized seroprevalence to A(H1N1)pdm09 was 48% by the MN and 41% by the HI assays, respectively. The youngest quintile, aged 1 to 22 years, had the highest the seroprevalence; 61% (95% confidence interval [CI]: 56, 66%) for MN, and 56% (95% CI: 51, 62%) for HI., Conclusions: Despite high transmission of A(H1N1)pdm09 observed immediately after its emergence and extensive vaccination, over a half of the Mexican population remained potentially susceptible to A(H1N1)pdm09 infection. Subsequent influenza seasons with high transmission of A(H1N1)pdm09, as 2011-2012 and 2013-2014, are compatible with these findings.

Dengue is a major global public health problem affecting Latin America and Mexico Prevention and control measures, focusing on epidemiological surveillance and vector control, have been partially effective and costly, thus, the development of a vaccine against dengue has created great expectations among health authorities and scientific communities worldwide. The CYD-TDV dengue vaccine produced by Sanofi-Pasteur is the only dengue vaccine evaluated in phase 3 controlled clinical trials. Notwithstanding the significant contribution to the development of a vaccine against dengue, the three phase 3 clinical studies of CYD-TDV and the meta-analysis of the long-term follow up of those studies, have provided evidence that this vaccine exhibited partial vaccine efficacy to protect against virologically confirmed dengue and lead to four considerations: a) adequate vaccine efficacy against dengue virus (DENV) infections 3 and 4, less vaccine efficacy against DENV 1 and no protection against infection by DENV 2; b) decreased vaccine efficacy in dengue seronegative individuals at the beginning of the vaccination; c) 83% and 90% protection against hospitalizations and severe forms of dengue, respectively, at 25 months follow-up; and d) increased hospitalization for dengue in the vaccinated group, in children under nine years of age at the time of vaccination, detected since the third year of follow-up. The benefit of the CYD-TDV vaccine can be summarized in the protection against infection by DENV 3 and 4, as well as protection for hospitalizations and severe cases in people over nine years, who have had previous dengue infection, working mainly as a booster. In this review we identified elements on efficacy and safety of this vaccine that must be taken into account in the licensing process and potential inclusion in the national vaccination program of Mexico. The available scientific evidence on the CYD-TDV vaccine shows merits, but also leads to relevant questions that should be answered to properly assess the safety profile of the product and the target populations of potential benefit. In this regard we consider it would be informative to complete the 6-year follow-up after starting vaccination, according to the company's own study protocol recommended by the World Health Organization. As with any new vaccine, the potential licensing and implementation of the CYD-TDV as part of Mexico's vaccination program, requires a clear definition of the balance between the expected benefits and risks. Particularly with a vaccine with variable efficacy and some signs of risk, in the probable case of licensing, the post-licensed period must involve the development of detailed protocols to immediately identify risks or any health event associated with vaccination.

Since chikungunya virus (CHIKV) was introduced into the Americas in 2013, its geographic distribution has rapidly expanded. Of 119 serum samples collected in 2014 from febrile patients in southern Mexico, 79% were positive for CHIKV or IgM against CHIKV. Sequencing results confirmed CHIKV strains closely related to Caribbean isolates.

Objective: To assess the risks factors for urinary tract infections (UTIs) caused by Extended-Spectrum Beta-Lactamases (ESBLs)-producing E. coli and the molecular characterization of ESBLs., Materials and Methods: A case-control study was performed to identify risk factors in consecutively recruited patients with UTIs caused by ESBLs or non-ESBLs-producing E. coli in a tertiary hospital in Mexico., Results: ESBLs-producing E. coli were isolated from 22/70 (31%) patients with E. coli UTIs over a three month period. All isolates were resistant to cephalosporins and quinolones but susceptible to carbapenems, amikacin and nitrofurantoin. Prior antibiotic treatment with more than two antibiotic families (OR=6.86; 95%CI 1.06-157.70; p=0.028), recurrent symptomatic UTIs (OR=5.60; 95%CI 1.88-17.87; p=0.001) and previous hospitalization (OR=5.06; 95%CI 1.64-17.69; p=0.002) were significant risk factors. Sixteen isolates harbored the beta-lactamase (bla)CTX-M-15 gene and five the blaTEM-1 gene., Conclusions: One of every three patients presented UTIs with ESBLs-producing beta-lactams and fluoroquinolone resistant E. coli. Risk factors and resistance patterns must be taken into account for developing antibiotic use policies in these settings.

Salmonella infects and survives within B cells, but the mechanism used by the bacterium to promote its survival in these cells is unknown. In macrophages, flagellin secreted by Salmonella activates the Nod-like receptor (NLR) family CARD domain containing protein 4 (NLRC4) inflammasome, leading to the production of IL-1β and pyroptosis of infected cells. In this study, we demonstrated that the NLRC4 inflammasome is functional in B cells; however, in Salmonella-infected B cells, IL-1β secretion is prevented through the downregulation of NLRC4 expression. A functional Salmonella pathogenicity island 1 type III secretion system appears to be required for this process. Furthermore, infection induces Yap phosphorylation and promotes the interaction of Yap with Hck, thus preventing the transcriptional activation of NLRC4. The ability of Salmonella to inhibit IL-1β production also prevents B cell death; thus, B cells represent an ideal niche in which Salmonella resides, thereby promoting its persistence and dissemination.

Background: Acinetobacter baumannii has evolved from an opportunistic pathogen into a common and persistent nosocomial bacterium capable of causing severe infections during endemic and epidemic periods., Methods: The study period extended from January 1999 to December 2011 and involved patients hospitalized at the Hospital Civil de Guadalajara, Fray Antonio Alcalde, Jalisco, Mexico. From each patient, a single isolate was obtained, and a total of 3,680 unique isolates were collected. Susceptibility tests were performed according to the guidelines of the Clinical and Laboratory Standards Institute., Results: A. baumannii has disseminated throughout the Hospital Civil de Guadalajara, Fray Antonio Alcalde, since 1999. A. baumannii isolates obtained from patients treated in the adult intensive care unit represent the majority of the isolates that have been collected. In addition, A. baumannii was isolated from the adult neurosurgical ward and the adult internal medicine ward, and these isolates were frequently obtained from secretions. A persistent decrease in the susceptibility of A. baumannii isolates to meropenem (92% in 1999 to 12% in 2011), imipenem and amikacin has been observed., Conclusions: A. baumannii became an endemic nosocomial pathogen during the study period at the Hospital Civil de Guadalajara, Fray Antonio Alcalde, and has exhibited a persistent decrease in susceptibility to all categories of antimicrobial agents over the past 13 years., (Copyright © 2013 S. Karger AG, Basel.)

Background: The 2009 H1N1 outbreak provides an opportunity to identify strengths and weaknesses of disease surveillance and notification systems that have been implemented in the past decade., Methods: Drawing on a systematic review of the scientific literature, official documents, websites, and news reports, we constructed a timeline differentiating three kinds of events: (1) the emergence and spread of the pH1N1 virus, (2) local health officials' awareness and understanding of the outbreak, and (3) notifications about the events and their implications. We then conducted a "critical event" analysis of the surveillance process to ascertain when health officials became aware of the epidemiologic facts of the unfolding pandemic and whether advances in surveillance notification systems hastened detection., Results: This analysis revealed three critical events. First, medical personnel identified pH1N1in California children because of an experimental surveillance program, leading to a novel viral strain being identified by CDC. Second, Mexican officials recognized that unconnected outbreaks represented a single phenomenon. Finally, the identification of a pH1N1 outbreak in a New York City high school was hastened by awareness of the emerging pandemic. Analysis of the timeline suggests that at best the global response could have been about one week earlier (which would not have stopped spread to other countries), and could have been much later., Conclusions: This analysis shows that investments in global surveillance and notification systems made an important difference in the 2009 H1N1 pandemic. In particular, enhanced laboratory capacity in the U.S. and Canada led to earlier detection and characterization of the 2009 H1N1. This includes enhanced capacity at the federal, state, and local levels in the U.S., as well as a trilateral agreement enabling collaboration among U.S., Canada, and Mexico. In addition, improved global notification systems contributed by helping health officials understand the relevance and importance of their own information.

The aim of the present study was to determine the bacteriological prevalence of subclinical non-typhi Salmonella infections in zoo animals and to determine the most frequently isolated serovars of the bacteria. A total of 267 samples were analyzed, including fecal samples from zoo animals and rodents, insects (Musca domestica and Periplaneta americana) and samples of the zoo animal's food. Salmonella was detected in 11.6% of the samples analyzed. Characterization of the isolates was performed with serotyping and pulsed-field gel electrophoresis. The following serovars were isolated: S. San Diego, S. Oranienburg, S. Weltevreden, S. Braenderup, S. Derby, S. 6,7, H:en x:- and S. 3,10, H:r:-. The isolates showed seven pulsed-field gel electrophoresis patterns with a Jaccard coefficient≥0.75 indicating a possible common origin. The prevalence of asymptomatic infections caused by Salmonella spp. in zoo animals was high. These findings demonstrate the diversity of Salmonella serovars in several captive wild animal species., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

We have previously reported that Salmonella infects B cells and survives within endosomal-lysosomal compartments. However, the mechanisms used by Salmonella to enter B cells remain unknown. In this study, we have shown that Salmonella induces its own entry by the induction of localized ruffling, macropinocytosis, and spacious phagosome formation. These events were associated with the rearrangement of actin and microtubule networks. The Salmonella pathogenesis island 1 (SPI-1) was necessary to invade B cells. In contrast to macrophages, B cells were highly resistant to cell death induced by Salmonella. These data demonstrate the ability of Salmonella to infect these non-professional phagocytic cells, where the bacterium can find an ideal intracellular niche to support persistence and the possible dissemination of infection., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Background: Pandemic influenza A (H1N1) virus emerged during 2009. To help clinicians triage adults with acute respiratory illness, a scoring system for influenza-like illness (ILI) was implemented at Hospital Civil de Guadalajara, Mexico., Methods: A medical history, laboratory and radiology results were collected on emergency room (ER) patients with acute respiratory illness to calculate an ILI-score. Patients were evaluated for admission by their ILI-score and clinicians' assessment of risk for developing complications. Nasal and throat swabs were collected from intermediate and high-risk patients for influenza testing by RT-PCR. The disposition and ILI-score of those oseltamivir-treated versus untreated, clinical characteristics of 2009 pandemic influenza A (H1N1) patients versus test-negative patients were compared by Pearson's Chi(2), Fisher's Exact, and Wilcoxon rank-sum tests., Results: Of 1840 ER patients, 230 were initially hospitalized (mean ILI-score = 15), and the rest were discharged, including 286 ambulatory patients given oseltamivir (median ILI-score = 11), and 1324 untreated (median ILI-score = 5). Fourteen (1%) untreated patients returned, and 3 were hospitalized on oseltamivir (median ILI-score = 19). Of 371 patients tested by RT-PCR, 104 (28%) had pandemic influenza and 42 (11%) had seasonal influenza A detected. Twenty (91%) of 22 imaged hospitalized pandemic influenza patients had bilateral infiltrates compared to 23 (38%) of 61 imaged hospital test-negative patients (p<0.001). One patient with confirmed pandemic influenza presented 6 days after symptom onset, required mechanical ventilation, and died., Conclusions: The triaging system that used an ILI-score complimented clinicians' judgment of who needed oseltamivir and inpatient care and helped hospital staff manage a surge in demand for services.

Since its identification in April 2009, an A(H1N1) virus containing a unique combination of gene segments from both North American and Eurasian swine lineages has continued to circulate in humans. The lack of similarity between the 2009 A(H1N1) virus and its nearest relatives indicates that its gene segments have been circulating undetected for an extended period. Its low genetic diversity suggests that the introduction into humans was a single event or multiple events of similar viruses. Molecular markers predictive of adaptation to humans are not currently present in 2009 A(H1N1) viruses, suggesting that previously unrecognized molecular determinants could be responsible for the transmission among humans. Antigenically the viruses are homogeneous and similar to North American swine A(H1N1) viruses but distinct from seasonal human A(H1N1).

A novel influenza A (H1N1) virus has spread rapidly across the globe. Judging its pandemic potential is difficult with limited data, but nevertheless essential to inform appropriate health responses. By analyzing the outbreak in Mexico, early data on international spread, and viral genetic diversity, we make an early assessment of transmissibility and severity. Our estimates suggest that 23,000 (range 6000 to 32,000) individuals had been infected in Mexico by late April, giving an estimated case fatality ratio (CFR) of 0.4% (range: 0.3 to 1.8%) based on confirmed and suspected deaths reported to that time. In a community outbreak in the small community of La Gloria, Veracruz, no deaths were attributed to infection, giving an upper 95% bound on CFR of 0.6%. Thus, although substantial uncertainty remains, clinical severity appears less than that seen in the 1918 influenza pandemic but comparable with that seen in the 1957 pandemic. Clinical attack rates in children in La Gloria were twice that in adults (<15 years of age: 61%; >/=15 years: 29%). Three different epidemiological analyses gave basic reproduction number (R0) estimates in the range of 1.4 to 1.6, whereas a genetic analysis gave a central estimate of 1.2. This range of values is consistent with 14 to 73 generations of human-to-human transmission having occurred in Mexico to late April. Transmissibility is therefore substantially higher than that of seasonal flu, and comparable with lower estimates of R0 obtained from previous influenza pandemics.

Macrophages respond to Salmonella typhimurium infection via Ipaf, a NACHT-leucine-rich repeat family member that activates caspase-1 and secretion of interleukin 1beta. However, the specific microbial salmonella-derived agonist responsible for activating Ipaf is unknown. We show here that cytosolic bacterial flagellin activated caspase-1 through Ipaf but was independent of Toll-like receptor 5, a known flagellin sensor. Stimulation of the Ipaf pathway in macrophages after infection required a functional salmonella pathogenicity island 1 type III secretion system but not the flagellar type III secretion system; furthermore, Ipaf activation could be recapitulated by the introduction of purified flagellin directly into the cytoplasm. These observations raise the possibility that the salmonella pathogenicity island 1 type III secretion system cannot completely exclude 'promiscuous' secretion of flagellin and that the host capitalizes on this 'error' by activating a potent host-defense pathway.

We describe the prevalence and molecular characteristics of extended-spectrum beta -lactamase (ESBL)-producing Klebsiella pneumoniae causing nosocomial bacteremia and urinary tract infections in a Mexican general hospital. We analyzed 82 episodes of bacteremia (approximately 60% of episodes) and urinary tract infection (approximately 40% of episodes) due to K. pneumoniae during a 23-month surveillance period. The neonatal intensive care unit accounted for 49% of all episodes. All strains were imipenem susceptible; 62.2% of the strains were resistant to ceftazidime, cefotaxime, and aztreonam; 69.5% were resistant to amikacin; 58.5% were resistant to gentamicin; and 7.3% were resistant to ciprofloxacin. All strains were associated with 28 pulsed-field gel electrophoresis patterns, and dissemination of 2 ceftazidime-resistant clones produced 44% of the cases. The ESBL phenotype in these clones was transferred by identical or highly related megaplasmids. The ESBL activity corresponded to SHV-5 and TLA-1. Cross-transmission of 2 ceftazidime-resistant clones and the horizontal spread of identical or highly related megaplasmids explain the high prevalence of ESBL phenotype in these infections.

We describe a case-control study of a small outbreak of nosocomial sepsis and pneumonia with high mortality due to clonal dissemination of a multiresistant Klebsiella pneumoniae in the neonatal intensive care unit of a Mexican institution. Our study helped to change nosocomial infection control policy in this hospital.

Light microscopic studies indicated a correlation between the virulence for mice of different Salmonella serotypes and the ability to form or maintain spacious phagosomes (SP) within mouse macrophages. Although Salmonella typhimurium induced membrane ruffling, macropinocytosis, and SP formation in macrophages from BALB/c mice, serotypes which are nonpathogenic for mice produced markedly fewer SP. SP formation correlated with both serotype survival within mouse macrophages and reported lethality for mice. Time-lapse video microscopy demonstrated that the human pathogen S. typhi induced generalized macropinocytosis and SP formation in human monocyte-derived macrophages, indicating a similar morphology for the initial phases of this host-pathogen interaction. In contrast to bone marrow-derived macrophages from BALB/c mice, macrophages from S. typhimurium-resistant outbred (CD-1) and inbred (CBA/HN) mice did not initiate generalized macropinocytosis after bacterial infection and formed markedly fewer SP. These deficiencies were not due to the Ihy resistance genotype of these mice, as macrophages from mice that were congenic except for the Ihy locus demonstrated equal SP formation in response to S. typhimurium. The observation that S. typhimurium-resistant CD-1 and CBA/HN mice are deficient in the ability to form and/or maintain SP indicates that a variable host component is important for SP formation and suggests that the ability to induce or form SP affects susceptibility to S. typhimurium. When serotypes nonpathogenic for mice were used to infect BALB/c macrophages, or when CD-1 or CBA/HN mouse macrophages were infected by S. typhimurium, some of the SP that formed shrank within seconds. This rapid shrinkage suggests that SP maintenance is also important for S. typhimurium survival within macrophages. These studies indicate that both host and bacterial factors contribute to SP formation and maintenance, which correlate with Salmonella intracellular survival and the ability to cause lethal enteric (typhoid) fever.

The PhoP/PhoQ two-component system regulates Salmonella typhimurium genes that are essential to bacterial virulence and survival within macrophages. The best characterized of these PhoP-activated genes (pag) is pagC, which encodes a 188-amino-acid envelope protein (W. S. Pulkkinen and S. I. Miller, J. Bacteriol. 173:86-93, 1991). We here report the identification of four genes (pagD, envE, msgA, and envF) located 5' to pagC. Each gene is transcribed from its own promoter, two of which (msgA and pagD) were defined by primer extension analysis. Three of these genes (pagD, envE, and envF) are predicted to encode envelope proteins. The pagD gene is transcribed in a direction opposite from that of and adjacent to pagC and is positively regulated by PhoP/PhoQ. Transposon insertions within pagD and msgA attenuate bacterial virulence and survival within macrophages; however, deletion of pagD has no effect on virulence. The product of the envF gene is predicted to be a lipoprotein on the basis of the presence of a consensus lipid attachment site. The low G + C content of these genes and the homology of msgA to Shigella plasmid DNA suggest that this region may have been acquired by horizontal transmission.