Prevalence of Extended-Spectrum β-Lactamases CTX-M-8 and CTX-M-2-Producing Salmonella Serotypes from Clinical and Nonhuman Isolates in Brazil.

Abstract

We characterized extended-spectrum β-lactamases (ESBL) enzymes among Salmonella strains isolated in Brazil from 2009 to 2014. Salmonella recovered from both clinical and nonhuman (food, poultry, and environment) sources were subjected to antimicrobial susceptibility testing. β-lactamases genes were detected by polymerase chain reaction/sequencing; plasmid profiles and transferability were assessed by S1-pulsed field gel electrophoresis (PFGE). Genetic diversity was evaluated by XbaI-PFGE. Out of 630 Salmonella strains screened, 46 displayed ESBL phenotype, distributed across 11 different serotypes. blaCTX-M-8 and blaCTX-M-2 genes were detected at frequencies of 47% and 41%, respectively. blaSHV-5 and blaSHV-2 were also detected but in lower frequencies (4%, 2%). blaTEM-1 gene was detected in 22% of the strains. Most of the ESBL genes were transferable by conjugation, and the respective blaESBL gene was detected in the recipient strain, indicating the location of ESBL determinants on transferable plasmids. XbaI-PFGE revealed genomic diversity of Salmonella Typhimurium bearing blaCTX-M-2, blaCTX-M-8, blaTEM-1, and blaSHV-2 genes. Salmonella Muenchen (harboring blaCTX-M-2) and Salmonella Corvallis (blaCTX-M-8 and blaSHV-5) showed clonal relatedness within respective serotypes. Our findings underscore the occurrence of diverse ESBL genes in several Salmonella serotypes, reinforcing the need for continuous surveillance of resistance genes circulating in human and nonhuman sources.