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

Abstract

ObjectivesThis study investigated the occurrence of extended-spectrum β-lactamase (ESBL)-producing Salmonella and the associated virulence genes among farmed chickens. MethodsCloacal 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 ompF. Screening for ESBL resistance was performed using the disk-diffusion test, the combinational-disk test with clavulanic acid, and multiplex PCR for blaTEM, blaSHV, blaCTX-M and blaOXA. The presence of the AmpC blaCMy-2 was tested among the ESBL-negative isolates by uniplex PCR. The resistant isolates were partially sequenced based on the stn gene. ResultsThe 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 blaTEM and blaSHV genes. The four ESBL-negative isolates carried blaCMY-2. Partial-stn-sequencing of the isolates revealed a high genetic relatedness to Salmonella strains from patients in Egypt and Asia. ConclusionsVirulent ESBL-producing Salmonella was isolated from healthy and diseased chickens; the strains have a close relationship to human strains, posing a public health threat.