Prevalence, Risk Factors, Antimicrobial Resistance and Molecular Characterization of <i>Salmonella</i> in Northeast Tunisia Broiler Flocks

This study was conducted in northeastern Tunisia to estimate both the prevalence and the risk factors of <i>Salmonella</i> in broiler flocks as well as to characterize the isolated multidrug-resistant (MDR) <i>Salmonella</i> strains. In the present study, a total number of 124 farms were sampled; <i>Salmonella</i> isolates were identified by the alternative technique <i>VIDAS Easy Salmonella</i>. The susceptibility of <i>Salmonella</i> isolates was assessed against 21 antimicrobials using the disk diffusion method on Mueller–Hinton agar using antimicrobial discs. Some antimicrobial resistance genes were identified using PCR. The prevalence rate of <i>Salmonella</i> infection, in the sampled farms, was estimated at 19.9% (64/322). Moreover, a total number of 13 different serotypes were identified. High rate of resistance was identified against nalidixic acid (82.85%), amoxicillin (81.25%), streptomycin (75%), and ciprofloxacin (75%). Alarming level of resistance to ertapenem (12.5%) was noticed. A total of 87.5% (56/64) of isolated strains were recognized as MDR. Three MDR strains were extended-spectrum β-lactamases (ESBL)-producers and three MDR strains were cephalosporinase-producers. The <i>bla_CTX</i><i>_-M</i> gene was amplified in all the three ESBL strains. The <i>qnrB</i> gene was not amplified in fluoroquinolones-resistant strains. The <i>tetA</i> and <i>tetB</i> genes were amplified in 5% (2/40) and 2.5% (1/40) of tetracycline-resistant strains, respectively. The <i>dfrA1</i> gene was amplified in five of the 20 trimethoprim-resistant strains. The <i>mcr-1, mcr-2, mcr-3, mcr-4,</i> and <i>mcr-5</i> genes were not amplified in any of the phenotypically colistin-resistant strains. In terms of integrase genes int1 and int2, only gene class 2 was amplified in 11% (7/64) of analyzed strains. Risk factors, such as the poor level of cleaning and disinfection, the lack of antimicrobial treatment at the start of the breeding, and a crawl space duration lower than 15 days, were associated with high <i>Salmonella</i> infection in birds. These data should be considered when preparing salmonellosis control programs in Tunisian broiler flocks.