Search

Delay in the results of standard phenotypic susceptibility tests is the main obstacle to adequate antibiotic treatment. For this reason, the European Committee for Antimicrobial Susceptibility Testing has proposed the Rapid Antimicrobial Susceptibility Testing for the disk diffusion method directly from blood culture. However, to date, there are no studies evaluating early readings of polymyxin B broth microdilution (BMD), the only standardized methodology for assessing susceptibility to polymyxins. This study aimed to evaluate modifications in the BMD technique for polymyxin B using fewer antibiotic dilutions and reading after an incubation time of 8–9 hr (early reading) in comparison to 16–20 hr of incubation (standard reading) for isolates of Enterobacterales, Acinetobacter baumannii complex, and Pseudomonas aeruginosa. A total of 192 isolates of gram-negative bacteria were evaluated and the minimum inhibitory concentrations were read after early and standard incubations. The early reading presented 93.2% of essential agreement and 97.9% of categorical agreement with the standard reading of BMD. Only three isolates (2.2%) presented major errors and only one (1.7%) presented a very major error. These results indicate a high agreement between the early and the standard reading times of BMD of polymyxin B. [ABSTRACT FROM AUTHOR]

The clinical importance of extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli has increased steadily over the years. The presence of the blaTEM, blaSHV, and blaCTX-M genes in the environment has been recently recognized as an important issue in the dissemination of resistance to cephalosporins. Food animals are considered important vectors for transfer of ESBL genes from the environment to humans. The objective of this study was to characterize the ESBL genes (blaTEM, blaSHV, and blaCTX-M types) that were most prevalent among 343 ceftazidime-resistant E. coli isolates (17 batches from 12 different farms) obtained from cloacal swabs of broiler chicken in southern Brazil. The blaSHV, blaCTX-M, blaTEM, blaIMP-type, blaVIM-type, blaNDM-1, blaKPC-type, blaGES-type, blaOXA-48, and mcr-1 genes were evaluated by polymerase chain reaction. A total of 27 (7.9%) E. coli isolates were positive for ESBL genes as follows: 24 for blaCTX-M (23 blaCTX-M-2 Group and 1 blaCTX-M-8) and 3 for blaSHV (2 blaSHV-2a and 1 blaSHV-18). A random sample of 32 ceftazidime/cefotaxime-resistant isolates that were negative for ESBL genes were evaluated for the presence of blaCMY-2 and 24 (75%) tested positive. We detected the blaCMY-2 gene in isolates from all farms. All isolates positive for ESBL or blaCMY-2 are considered multidrug resistant (resistant to at least three antibiotic classes). Our results suggest that broiler chickens are an important reservoir of blaCMY-2 and ESBL genes, including blaSHV-2a, described for the first time in animals originating from Brazil in this study, and blaSHV-18, which has never been described in Brazil before. This fact highlights the importance of controlling the use of antibiotics in animal production to reduce environmental sources of resistance genes. [ABSTRACT FROM AUTHOR]

Polymyxins (colistin and polymyxin B) have recently regained significant importance as last-line drugs to treat infectious diseases due to multidrug-resistant gram-negative bacteria. However, resistance to polymyxins has increased, and the recognition of plasmid-mediated resistance (by the mcr gene) has led to an epidemiological concern. We aimed to evaluate the reduction of the polymyxin B minimum inhibitory concentration (MIC) in the presence of EDTA or dipicolinic acid (DPA) by using the broth microdilution (BMD) method for phenotypic screening of acquired polymyxin resistance mediated by the mcr-1 gene. Overall, 94 Enterobacterales (48 polymyxin-resistant and 46 polymyxin-susceptible) were evaluated: 47 mcr-1 positive (36 Escherichia coli, 2 Klebsiella pneumoniae, and 9 Salmonella spp.) and 47 mcr-1 negative (3 E. coli and 44 K. pneumoniae—27 isolates with MIC from ≤0.125 to 8 μg/mL and 20 isolates with MIC from 16 to 64 μg/mL). Results were categorized as positive when the chelator decreased the original BMD MIC by ≥2 logs. The majority (95.7%) of mcr-1 positive isolates displayed at least a 3 log dilution decrease in the MIC of polymyxin B with EDTA or DPA. The EDTA-based BMD assay detected 45 mcr-1-positive isolates, with only one false-positive among the mcr-1-negative isolates (sensitivity [SN], 95.7%; specificity [SP], 97.9%), whereas the DPA-based BMD assay detected 44 mcr-1-positive isolates (SN, 93.6%; SP, 95.7%), with two false-positive results. The accuracy of EDTA- and DPA-based BMD assays were 97% and 95%, respectively. The EDTA- and DPA-based assays were demonstrated to be reliable methods to detect mcr-1 positive isolates with excellent accuracy. [ABSTRACT FROM AUTHOR]

Acinetobacter baumannii is considered an important pathogen of clinical significance that is responsible for a wide range of nosocomial infections. Carbapenem resistance among A. baumannii isolates has increased dramatically in the Past years because of the emergence and dissemination of specific epidemic clones. We aimed to characterize the population structure of A. baumannii isolates from Porto Alegre city, Southern Brazil, in two distinct periods: during the first carbapenem-resistant A. baumannii (CRAB) outbreak (2007–2008) and 5 years later when the CRAB reached endemic levels (2013–2014). The study included 49 CRAB isolates collected in two periods: 2007–2008 (31 isolates) and 2013–2014 (18 isolates). Multilocus sequence typing (MLST) was performed according to Institute Pasteur, followed by eBURST analysis. PCR was used to detect integrase gene, blaNDM, and oxacillinase genes, and also to detect the ISAba1 element upstream blaOXA-23. The eBURST analysis identified the clonal complexes (CCs) CC15, CC32, CC79, CC216, CC221, and CC464 in the first period (2007–2008) and CC1, CC2, CC15, CC79, and CC162 during the endemic period (2013–2014). Molecular analysis by MLST identified 13 new sequence types. As we found A. baumannii with the blaOXA-23 gene of several CCs, it can be concluded that the increase of CRAB infections are not related to a specific clone. Furthermore, the high-risk CC15 and CC79 were related to the first CRAB outbreak and these CCs persisted up to 2014 in Porto Alegre city. The international clones CC1 and CC2 were observed for the first time in only the second period (2013–2014), alerting to the emergence of these clones in Southern Brazil. [ABSTRACT FROM AUTHOR]