Prevalence, antimicrobial resistance, resistance genes and class 1 integrons of Salmonella serovars in leafy vegetables, chicken carcasses and related processing environments in Malaysian fresh food markets

This study was carried out to determine the prevalence, antibiotic resistance, resistance genes and class 1 integrons of Salmonella serovars in raw leafy vegetables, chicken carcasses and related environments. From April 2015 to May 2016, a total of 642 samples collected from fresh food markets in Peninsular Malaysia were examined. The overall occurrence of Salmonella species was 29.1% (187/642) with 37 different serovars detected. The most prevalent serovars were S. Corvallis (49/187), S. Brancaster (28/187), S. Weltevreden (17/187), S. Albany (15/187), S. Hvittingfoss (6/178), S. Paratyphi B (6/178) and S. Typhimurium (6/178). Among the Salmonella isolates, the highest antibiotic resistance was to streptomycin (66.6%), followed by tetracycline (44.3%), sulfonamides (44.3%), ampicillin (26.7%), chloramphenicol (29.1%) and trimethoprim-sulfamethoxazole (16.6%). All isolates of Salmonella were 100% susceptible to cephalothin. Fifty-five percent of the isolates (103/187) were multidrug-resistant. The multiple antibiotic resistance (MAR) index of Salmonella serovars ranged from 0.08 to 0.83, and the most prevalent resistance pattern was STeS₃. Eleven out of 16 resistant genes (tetA, tetB, blaTEM-1,temB, strA, strB, aadA, sul1, sul2, floR and cmlA) were detected among the resistant Salmonella isolates. None of the isolates was positive for tetC, tetG, cat1 and cat2. Seventeen isolates harboured class 1 integrons, which were grouped into 5 different integrons profiles (IPs). DNA sequencing analyses have identified dfrA1, dfrA12, aadA2, blaPSE−1, dfrA12-orf-aadA2 arrays of cassettes in variable regions on class 1 integrons.