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Background: Staphylococcus aureus may invade and persist intracellularly in prosthetic joint infections (PJIs). Despite optimized treatments with levofloxacin plus rifampin, the intracellular reservoir may lead to infection relapse. This study assessed the intracellular activity of levofloxacin and rifampin in an in-vitro model of human osteoblastic infection., Methods: Ten meticillin-susceptible S. aureus strains were used to infect osteoblastic MG63 cells. Osteoblasts were challenged with rifampin and levofloxacin at cortical and cancellous bone concentrations. Efficacy was measured as the intracellular counts of colony-forming units (log 10 CFU) compared with untreated controls. The emergence of small colony variants (SCVs) was determined, and the results were stratified according to the patient's prognosis (six cured and four with persistence/relapse)., Results: All regimes led to a significant decrease in CFU count compared with controls (1-2 log 10 CFU). Levofloxacin was the most effective treatment at both cortical and cancellous bone concentrations (-2.4 to -1.9 log 10 CFU, respectively). The addition of rifampin to levofloxacin did not improve performance (-1.9 log 10 CFU for cortical concentration and -1.8 log 10 CFU for cancellous concentration). An increase in SCVs was observed in the presence of rifampin. The efficacy of antimicrobials was higher and the formation of SCVs was lower against strains belonging to PJIs with a favourable outcome., Conclusions: Levofloxacin plus rifampin had good intracellular activity against S. aureus. However, from the intracellular perspective, the addition of rifampin to levofloxacin showed no benefit but could account for an increased number of SCVs., (Copyright © 2019 Elsevier B.V. and International Society of Chemotherapy. All rights reserved.)

Background: Recent studies have demonstrated improved survival when the management of Staphylococcus aureus bloodstream infection (BSI) is compliant with evidence-based therapeutic interventions. Whether this effect extends to low-risk sources, such as catheter-related BSI, remains unclear., Methods: We retrospectively included 225 episodes of methicillin-sensitive S. aureus catheter-related BSI diagnosed in our centre during two non-consecutive periods: 2002-2004 (first period (101 episodes)) and 2009-2013 (second period (124 episodes)). We evaluated the adherence (percentage of compliance = (no. of interventions performed/no. of interventions recommended) × 100) to the following bundle: early catheter removal (≤72 hours), early initiation of appropriate antibiotic therapy, adequate sampling of follow-up blood cultures, transthoracic echocardiography (TTE) during hospitalization and adequate duration of therapy., Results: Patients in the second period had a higher burden of comorbidities and more severe underlying conditions. All-cause 30-day mortality was 9.3%, with a significant difference between the first and second periods (13.9% versus 5.6%; p value = .035). Bundle adherence was significantly higher in the second period, particularly for follow-up blood cultures (26.7% versus 48.4%; p value = .001), performance of TTE (45.5% versus 84.7%; p value < .001) and appropriate duration of therapy (34.7% versus 50.0%; p value = .022). Bundle adherence ≥ 55% was associated with lower 30-day mortality (hazard ratio: 0.31; 95% confidence interval: 0.13-0.76). This effect remained significant across propensity score-based models adjusted for septic shock, study period and underlying conditions., Conclusions: There was a survival benefit in adhering to a bundle of evidence-based interventions in the specific setting of catheter-related BSI due to methicillin-sensitive S. aureus.

Background: The ability of Staphylococcus aureus to invade tissues and cause an infectious disease is the result of a multi-factorial process supported by the huge number of virulence factors inherent to this microorganism tightly regulated by the accessory gene regulator (agr). During antimicrobial therapy bacteria may be exposed to sub-inhibitory concentrations (subMICs) of antibiotics that may trigger transcriptional changes that may have an impact on the pathogenesis of infection. The objective of this study was to investigate the effect of oxacillin sub-MICs on agr system expression as the key component in the regulation of virulence in methicillin-susceptible (MSSA) and -resistant S. aureus (MRSA) strains. Furthermore, we studied the genetic basis of the agr locus and their potential association with the expression levels., Methods: We have examined the expression of RNAIII and agrA mRNA as biomarkers for agr expression in the presence and absence of oxacillin subMICs in 10 MSSA and 4 MRSA clinical strains belonging to 5 clonal complexes (CC45-agrI, CC8-agrI, CC5-agrII, CC15-agrII and CC30-agrIII) causing endovascular complications. The DNA sequences of agr locus were obtained by whole genome sequencing., Results: Our results revealed that exposure to subMICs of oxacillin had an impact on agr locus expression modifying the relative levels of expression with increases in 11 strains and with decreases in 3 strains. Thereby, the exposure to subMICs of oxacillin resulted in higher levels of expression of agr in CC15 and CC45 and lower levels in CC30. We also observed the presence of mutations in agrC and agrA in 13/14 strains with similar mutation profiles among strains within individual CCs except for strains of CC5. Although, agr expression levels differed among strains within CCs, the presence of these mutations was associated with differences in agr expression levels in most cases., Conclusions: Changes in agr expression induced by exposure to oxacillin subMICs should be considered because they could lead to changes in the virulence modulation and have an adverse effect on the course of infection, especially in certain clonal complexes.

Objectives: Limited data exist regarding the role of agr dysfunction in reducing susceptibility to vancomycin in methicillin-susceptible Staphylococcus aureus (MSSA). This study investigated the clinical and molecular epidemiology of MSSA causing bacteraemia, with emphasis on the reduced susceptibility to vancomycin (RSV) phenotype (MIC ≥ 1.5 mg/L) and its relationship with agr dysfunction., Methods: All MSSA bloodstream isolates obtained at our hospital during 2010 were analysed. Antimicrobial susceptibility was determined and time-kill experiments were performed for oxacillin. Multilocus sequence type and agr genotype were determined and DNA microarray analysis of virulence factors was performed. agr dysfunction was assessed phenotypically and by RT-PCR quantification of RNAIII., Results: Of 84 MSSA, 55 (65.5%) exhibited the RSV phenotype, comprising 13 clonal complexes. agr II polymorphism was more prevalent in RSV than non-RSV isolates (41.8% versus 17.2%, P = 0.023) and average levels of RNAIII gene expression were higher in RSV than non-RSV isolates (ΔCt 4.05 ± 3.29 versus 1.5 ± 2.11, P = 0.005), implying greater agr dysfunction in RSV MSSA., Conclusions: We demonstrated a correlation between RSV phenotype in MSSA and reduced agr expression, particularly in association with the agr II genotype. These results may help to understand the role of agr dysfunction in the increased mortality in MSSA infections.

Background: Staphylococcus aureus is the main pathogen causing nosocomial infections. Health professionals, including medical students, could be a source of transmission. The aims of the study were to determine the rate of nasal carriage of S.aureus susceptible and resistant to methicillin (MRSA) and evaluate the knowledge and adherence that students had about hand hygiene., Methods: The study included medical students attached to the Hospital Universitario 12 de Octubre (Madrid, Spain). We collected samples from both nasal vestibules, and the antimicrobial susceptibility was determined on all isolates. Data collection was performed using a self-administered questionnaire that included risk factors for colonization, hygiene habits and knowledge of hand hygiene protocols., Results: Of the 140 students included, 55 (39.3%) were colonized by S.aureus, and 3 (2,1%) by MRSA. The exposure to antibiotics in the last 3 months was lower in colonized students (12.3% vs. 25.9%, P=.03). Self-assessment showed that 56.4% of students almost never washed their hands before to attending to the first patient, and only 38.6% always washed after examining patients. More than a third (35.7%) ignored the hand hygiene protocol, and 38.6% had not received specific formation., Conclusions: Medical students should be included in hospital infection control programs. Hand hygiene training should be given to students before they begin their practices in the hospital., (Copyright © 2012 Elsevier España, S.L. All rights reserved.)

Introduction: Panton-Valentine leukocidin (PVL) is a toxin associated with community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) worldwide and also occurs in community-associated methicillin-susceptible S aureus (CA-MSSA) strains. The aims of the study were to determine the prevalence of PVL in community-onset S aureus skin and soft-tissue infections (SSTIs) and to analyse the influence of methicillin resistance and PVL presence on the clinical characteristics of these infections., Patients and Methods: We prospectively enrolled all children with S aureus community-onset SSTIs attending the emergency department of a tertiary hospital between 2007 and 2009. Results A total of 142 S aureus SSTIs were identified, 46 (32%) were PVL positive. The proportion of subjects in each group was: 89 (63%) PVL-MSSA, 33 (23%) PVL+MSSA, 13 (9%) PVL+MRSA and 7 (5%) PVL-MRSA. PVL+infections were more frequently abscesses (63% vs 39%, p<0.01), and more often required incision and drainage (p<0.01) and hospital admission (46% vs 26%, p=0.02). MRSA infections were also more frequently associated with abscesses but in a multivariable analysis only PVL remained independently related (OR 2.33; 95% CI 1.10 to 4.90)., Conclusions: Our study found a high prevalence of PVL presence in community-onset S aureus SSTIs in children in Spain. This toxin is associated with more abscess formation, regardless of methicillin resistance.

We conducted a retrospective study of 99 patients with methicillin-suseptible Staphylococcus aureus catheter-related bacteremia in which vancomycin MIC was determined by Etest. High vancomycin MIC (>1.5 ug/mL) was the only independent risk factor for development of complicated bacteremia caused by methicillin-susceptible S. aureus (odds ratio 22.9, 95% confidence interval 6.7-78.1).

Most Staphylococcus aureus small-colony variants (SCVs) are auxotrophs for menadione, hemin, or thymidine but rarely for CO(2). We conducted a prospective investigation of all clinical cases of CO(2)-dependent S. aureus during a 3-year period. We found 14 CO(2)-dependent isolates of S. aureus from 14 patients that fulfilled all requirements to be considered SCVs, 9 of which were methicillin resistant. The clinical presentations included four cases of catheter-related bacteremia, one complicated by endocarditis; two deep infections (mediastinitis and spondylodiscitis); four wound infections; two respiratory infections; and two cases of nasal colonization. Pulsed-field gel electrophoresis typing showed that the 14 isolates were distributed into 4 types corresponding to sequence types ST125-agr group II (agrII), ST30-agrIII, ST34-agrIII, and ST45-agrI. An array hybridization technique performed on the 14 CO(2)-dependent isolates and 20 S. aureus isolates with normal phenotype and representing the same sequence types showed that all possessed the enterotoxin gene cluster egc, as well as the genes for alpha-hemolysin and delta-hemolysin; biofilm genes icaA, icaC, and icaD; several microbial surface components recognizing adhesive matrix molecules (MSCRAMM) genes (clfA, clfB, ebh, eno, fib, ebpS, sdrC, and vw); and the isaB gene. Our study confirms the importance of CO(2)-dependent SCVs of S. aureus as significant pathogens. Clinical microbiologists should be aware of this kind of auxotrophy because recovery and identification are challenging and not routine. Further studies are necessary to determine the incidence of CO(2) auxotrophs of S. aureus, the factors that select these strains in the host, and the genetic basis of this type of auxotrophy.

Staphylococcus aureus is an important human pathogen that affects children worldwide. The number of publications discussing community-associated S. aureus infections, particularly in children, adolescents and young adults, has increased in recent years. This is related to the emergence and worldwide spread of community-associated methicillin-resistant S. aureus and the increase in severe life-threatening community-associated S. aureus infections. The increase in severity has been seen with both methicillin-resistant and methicillin-susceptible strains. This suggests that other virulence factors might be associated with the observed trend. Panton-Valentine leukocidin is a distinctive virulence factor associated with a highly aggressive and often fatal form of community-acquired infections. We propose that empiric treatment should be adapted to the type of infection and the resistance profile present in each country or region. In cases of severe infection, a combination of antibiotics, including at least one molecule active against protein synthesis such as clindamycin or linezolid, will be needed.

We report recurrent bacteremia due to mixed infection with two clonally derived isolates of Staphylococcus aureus in a patient with Sezary syndrome. The two isolates, one gentamicin resistant and methicillin susceptible and the other gentamicin susceptible and methicillin resistant, developed by the deletion of the mecA, ant(4')Ia, and aacA-aphD genes from a common gentamicin-resistant and methicillin-susceptible ancestor.

Molecular epidemiology of Staphylococcus aureus strains causing bacteremia in neonates during 2002 to 2005 revealed seven clones, with four MSSA clones responsible for 80% of the cases. Some clones persisted or reappeared throughout the study. Three bacteremic clones were found colonizing health care workers (HCWs), particularly clone C, which was harbored by at least 15% of HCWs.

Introduction: The observation of an increasing number of methicillin-resistant Staphylococcus aureus (MRSA) isolated from children prompted us to study the microbiological, epidemiological and clinical characteristics of these isolates. The possibility of some of them being community-acquired focused particularly our attention., Methods: A retrospective analysis of all children with MRSA isolated at the Doce de Octubre hospital between January 2002 and June 2005 was conducted. Infections were classified as community-acquired, hospital-acquired, or health-care associated. Isolates of MRSA were studied by pulsed-field gel electrophoresis (PFGE) and SSCmec typing. The presence of the gene encoding the Panton-Valentine leukocidin was also detected by PCR., Results: MRSA were isolated from 17 patients. Seven isolates (42.2%) were community-acquired, corresponding to four cases of skin or soft-tissue infections, two otitis cases and one bacteremic pyomyositis. Six of seven community-acquired isolates had the same ECP pattern (genotype D), presented a type IV SSCmec, and were LPV toxin-producing and methicillin-resistant with no other associated resistances., Conclusion: To our knowledge, this study shows the presence of these community-acquired MRSA strains for the first time in Spain. The evidence of an apparently clonal spreading of community-acquired MRSA infections in children has important implications for public health and treatment strategies.

A total of 15 of 101 (14.8%) nasal methicillin-resistant Staphylococcus aureus (MRSA) isolates exhibited mupirocin resistance (Mup(r)) compared with 1 of 154 (0.6%) methicillin-susceptible Staphylococcus aureus isolates. A total of 14 (93%) isolates exhibiting high-level Mup(r) belonged to a single clone. Horizontal plasmid transfer and transmission of Mup(r) strains contribute to a high incidence of Mup(r) MRSA at our institution.

Linezolid has good penetration to the meninges and could be an alternative for treatment of Staphylococcus aureus meningitis. We assessed the efficacy and safety of linezolid therapy for this infection. Retrospective multicenter cohort study of 26 adults treated with linezolid, derived from a cohort of 350 cases of S. aureus meningitis diagnosed at 11 university hospitals in Spain (1981-2015). There were 15 males (58%) and mean age was 47.3 years. Meningitis was postoperative in 21 (81%) patients. The infection was nosocomial in 23 (88%) cases, and caused by methicillin-resistant S. aureus in 15 cases and methicillin-susceptible S. aureus in 11. Linezolid was given as empirical therapy in 10 cases, as directed therapy in 10, and due to failure of vancomycin in 6. Monotherapy was given to 16 (62%) patients. Median duration of linezolid therapy was 17 days (IQR 12-22 days) with a daily dose of 1,200 mg in all cases. The clinical response rate to linezolid was 69% (18/26) and microbiological response was observed in 14 of 15 cases evaluated (93%). Overall 30-day mortality was 23% and was directly associated with infection in most cases. When compared with the patients of the cohort, no significant difference in mortality was observed between patients receiving linezolid or vancomycin for therapy of methicillin-resistant S. aureus meningitis (9% vs. 20%; p =.16) nor between patients receiving linezolid or cloxacillin for therapy of methicillin-susceptible S. aureus meningitis (20% vs 14%; p =.68). Adverse events appeared in 14% (3/22) of patients, but linezolid was discontinued in only one patient. Linezolid appears to be effective and safe for therapy of S. aureus meningitis. Our findings showed that linezolid may be considered an adequate alternative to other antimicrobials in meningitis caused by S. aureus. [ABSTRACT FROM AUTHOR]

Staphylococcus aureus bacteremia (SAB) is associated with high morbidity and mortality, which varies depending on the source of infection. Nevertheless, the global molecular epidemiology of SAB and its possible association with specific virulence factors remains unclear. Using DNA microarrays, a total of 833 S. aureus strains (785 SAB and 48 colonizing strains) collected in Spain over a period of 15 years (2002–2017) were characterized to determine clonal complex (CC), agr type and repertoire of resistance and virulence genes in order to provide an epidemiological overview of CCs causing bloodstream infection, and to analyze possible associations between virulence genes and the most common sources of bacteremia. The results were also analyzed by acquisition (healthcare-associated [HA] and community-acquired [CA]), methicillin-resistant (MRSA) and methicillin-susceptible (MSSA) strains, and patient age (adults vs. children). Our results revealed high clonal diversity among SAB strains with up to 28 different CCs. The most prevalent CCs were CC5 (30.8%), CC30 (20.3%), CC45 (8.3%), CC8 (8.4%), CC15 (7.5%), and CC22 (5.9%), which together accounted for 80% of all cases. A higher proportion of CC5 was found among HA strains than CA strains (35.6 vs. 20.2%, p < 0.001). CC5 was associated with methicillin resistance (14.7 vs. 79.4%, p < 0.001), whereas CC30, CC45, and CC15 were correlated with MSSA strains (p < 0.001). Pathogen-related molecular markers significantly associated with a specific source of bacteremia included the presence of sea, undisrupted hlb and isaB genes with catheter-related bacteremia; sed, splE , and fib genes with endocarditis; undisrupted hlb with skin and soft tissue infections; and finally, CC5, msrA resistance gene and hla gene with osteoarticular source. Our study suggests an association between S. aureus genotype and place of acquisition, methicillin resistance and sources of bloodstream infection, and provides a valuable starting point for further research insights into intrinsic pathogenic mechanisms involved in the development of SAB. [ABSTRACT FROM AUTHOR]

Staphylococcus aureus is amajor cause of bacteremia and, even with appropriate clinical management, causes highmorbidity, andmortality due to its involvement in endovascular complications and metastatic infections. Through different pathogenic in vivo and in vitro models we investigated the behavior of S. aureus most relevant clonal complexes (CCs) causing endovascular complications. We analyzed 14 S. aureus strains representing CC5, CC8, CC15, CC30, and CC45 that caused endovascular complications, including methicillin susceptible and resistant isolates and strains with different functionality of the agr global regulator. Their adherence to collagen, interaction with the endothelium, resistance to immune attack, capacity to form biofilm and virulence in the Galleria mellonella model were analyzed. CC30 and CC45 showed greater adhesion to collagen and CC8 showed a trend towards higher rate of intracellular persistence in endothelial cells. All CCs exhibited similar tolerance to neutrophil antimicrobial peptide hNP-1 and were capable of forming biofilms under static conditions. The virulence assay in the G.mellonellamodel demonstrated that CC15 and CC30 were themost and least virulent, respectively. The analysis of the genomic sequences of the most relevant virulence genes identified some CC15 specific gene patterns (absence of enterotoxins and sak gene) and variants (mainly in leucocidins and proteases), but did not reveal any gene or variant that could be responsible for the increased virulence detected for CC15 strains. Even though all the CCs were capable of causing endovascular complications, our results showed that different CCs are likely to produce these complications through different mechanisms which, if confirmed in more sophisticated models, would indicate the need to more specific management and therapeutic approaches. [ABSTRACT FROM AUTHOR]

A response by Jose Maria Aguado to a letter to the editor about his article on the relationship between vancomycin and outcome of Staphylococcus aureaus bacteremia in a previous is presented.