Purpose: The aim of this study was to investigate the presence of Extended-spectrum β-lactamases (ESBLs) genes of the CTX-M family in S. Infantis isolates recovered from poultry at slaughterhouse in southern Brazil.
Methods: As part of a local surveillance study conducted for resistance genes monitoring in poultry slaughterhouse, forty S. Infantis isolates were phenotypically investigated for the presence of ESBL resistance by Kirby-Bauer disc diffusion susceptibility and Etest. Phenotypically ESBL-positive isolates were screened by PCR and clonal relatedness was performed by PFGE. Furthermore, the blaCTX-M-8 positive isolate was characterized by whole genome sequencing (WGS).
Results: Out of 40 S. Infantis isolates screened, 4 displayed ESBL phenotype. Three isolates (7.5%) harboring blaTEM were confirmed by PCR and WGS revealed the presence of blaCTX-M-8 in only one isolate (2.5%). In addition, six isolates (15%) were multidrug resistant (MDR) and the disc diffusion method revealed eight resistance patterns. Regarding MLST, the ST of S. Infantis harboring blaCTX-M-8 was ST32. The blaCTX-M-8 was located on an approximately 97 kb IncI1 plasmid. IncI1 plasmid was submitted to plasmid multilocus sequence typing and was assigned to ST113. The conjugation experiments were successfully obtained from the blaCTX-M-8 -positive isolates. All isolates showed clonal relatedness based on PFGE.
Significance: In conclusion, we report in this study one ESBL-positive CTX-M-8 / ST32 and three ESBL-positive TEM-type. Although the frequency of ESBL genes were low in S. Infantis our findings underscore the wide spread of resistance markers on poultry production chain, reinforcing the need for continuous surveillance of resistance genes circulating in foods.