Extended-spectrum β-lactamase-producing Salmonella serovars among healthy and diseased chickens and their public health implication

Objectives: This study investigated the occurrence of extended-spectrum beta-lactamase (ESBL)-producing Salmonella and the associated virulence genes among farmed chickens. Methods: Cloacal swab samples were collected from apparently healthy and diseased chickens and were cultured for Salmonella using conventional methods. The isolates were serotyped using slide agglutination tests and were examined by polymerase chain reaction (PCR) for the virulence genes invA, stn, svpC and pefA and the outer membrane protein-encoding genes ompA and ompE Screening for ESBL resistance was performed using the disk-diffusion test, the combinational-disk test with clavulanic acid, and multiplex PCR for bla(TEM), bla(SHV), bla(CTX-M) and bla(OXA). The presence of the AmpC bla(CMy-2) was tested among the ESBL-negative isolates by uniplex PCR. The resistant isolates were partially sequenced based on the stn gene. Results: The Salmonella isolation rate was 3.4% (6/175) from healthy and 11.1% (14/126) from diseased chickens. The 20 isolates belong to serotypes with public health significance like Typhimurium, Kentucky and Infantis. All the isolates possess invA, stn, svpC and ompF genes; 16 isolates harboured ompA, and one carried pefA. Of the 20 isolates,19 were resistant to more than one antibiotic. Of these 19 isolates,16 were ESBL-producing with the majority carrying bIa(TEM) and bla(SHV) genes. The four ESBL-negative isolates carried bla(CMY-2). Partial-stn-sequencing of the isolates revealed a high genetic relatedness to Salmonella strains from patients in Egypt and Asia. Conclusions: Virulent ESBL-producing Salmonella was isolated from healthy and diseased chickens; the strains have a close relationship to human strains, posing a public health threat. (C) 2020 The Author(s). Published by Elsevier Ltd on behalf of International Society for Antimicrobial Chemotherapy.