Characterization of extended-spectrum β-lactamase and ampc β-lactamase genes in nontyphoidal salmonella clinical isolates in Thailand

Abstract

The production of extended-spectrum β-lactamases (ESBLs) and plasmid-mediated AmpC β-lactamases in nontyphoidal Salmonella are increasingly reported worldwide and pose a serious threat for salmonellosis. Nevertheless, no prevalence data on ESBLs and AmpC β-lactamases in nontyphoidal Salmonella in Thailand have been reported. This study characterized genes encoding ESBLs and plasmid-mediated AmpC β-lactamases and investigated the prevalence of extended-spectrum cephalosporin (ESC) resistance in nontyphoidal Salmonella isolates. A total of 560 nontyphoidal Salmonella isolated from patients during 2005-2007 were included in this study. The resistance rates to cefoxitin, ceftazidime, cefotaxime, and ceftriaxone were 11.79%, 14.64%, 9.46%, and 12.50%, respectively. A total of 119 ESC-resistant isolates were detected for ESBL and AmpC phenotypes. The results showed that 52 isolates (43.70%), 66 isolates (55.46%), and 1 isolate (0.84%) were ESBL producers, AmpC producers, and ESBL and AmpC co-producer, respectively. Screening for the presence of bla genes revealed that 66 isolates (55.46%) carried blaCIT-like followed by 31 isolates (26.05%) with blaCTX-M-9 group, 14 isolates (11.76%) with blaCTX-M-1 group together with blaTEM-like, 7 isolates (5.88%) with blaCTX-M-9 group together with blaTEM-like, and 1 isolate (0.84%) with blaCTX-M-9 group blaTEM-like and blaCIT-like. DNA sequencing analysis of the entire bla genes from representative isolates showed that of the 14 blaCTX-M-1 group, 13 were blaCTX-M-55 and one was blaCTX-M-15 whereas all 10 blaCTX-M-9 group, 22 blaTEM-like, and 10 blaCIT-like were blaCTX-M-14, blaTEM-1, and blaCMY-2, respectively. ISEcp1 was present in the upstream regions of blaCTX-M and blaCIT in all isolates. ISEcp1-mediated -35 and -10 promoter sequences were found in all 34 representative isolates. This is the first report of the prevalence of ESBLs and plasmid-mediated AmpC β-lactamases in nontyphoidal Salmonella isolates in Thailand. Our results showed that the high rate of ESC resistance was attributed to the production of CTX-M-type ESBL and plasmid-mediated AmpC which CTX-M-9 group ESBLs and CIT-type AmpC were the most frequent β-lactamases. This was the first report of CTX-M-14 in S. Choleraesuis and also the first report of co-carrying CMY-2, CTX-M-14, and TEM-1 in nontyphoidal Salmonella.