High Levels of Resistance to Cephalosporins Associated with the Presence of Extended-Spectrum and AmpC β-Lactamases in Escherichia coli from Broilers in Southern Brazil

The clinical importance of extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli has increased steadily over the years. The presence of the bla(TEM), bla(SHV), and bla(CTX-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 (bla(TEM), bla(SHV), and bla(CTX-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 bla(SHV), bla(CTX-M), bla(TEM), bla(IMP-type), bla(VIM-type), bla(NDM-1), bla(KPC-type), bla(GES-type), bla(OXA-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 bla(CTX-M) (23 bla(CTX-M-2) Group and 1 bla(CTX-M-8)) and 3 for bla(SHV) (2 bla(SHV-2a) and 1 bla(SHV)-18). A random sample of 32 ceftazidime/cefotaxime-resistant isolates that were negative for ESBL genes were evaluated for the presence of bla(CMY-2) and 24 (75%) tested positive. We detected the bla(CMY-2) gene in isolates from all farms. All isolates positive for ESBL or bla(CMY-2) are considered multidrug resistant (resistant to at least three antibiotic classes). Our results suggest that broiler chickens are an important reservoir of bla(CMY-2) and ESBL genes, including bla(SHV-2a), described for the first time in animals originating from Brazil in this study, and bla(SHV)-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.