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Antimicrobial resistance of pathogenic bacteria, including Salmonella spp., is an emerging problem of food safety. Antimicrobial use can result in selection of resistant organisms. The food chain is considered a route of transmission of resistant pathogens to humans. In many European countries, sulfonamides are one of the most commonly used antimicrobials. The aim of our investigation was to assess the prevalence of sul genes and plasmid occurrence among sulfonamide-resistant Salmonella spp. Eighty-four sulfonamide-resistant isolates were collected in 2008 and 2013 from retail products in Poland. Minimal inhibitory concentration of all of these isolates was ≥1024 μg/mL. Resistant isolates were tested for the presence of sul1, sul2, sul3, and int1 genes by using multiplex polymerase chain reaction. In total, 44.0% (37/84) isolates carried the sul1 gene, 46.4% (39/84) were sul2 positive, while the sul3 gene was not detected in any of the sulfonamide-resistant isolates tested. It was found that 3.6% (3/84) of resistant Salmonella spp. contained sul1, sul2, and intI genes. All 33 intI-positive isolates carried the sul1 gene. Eleven of the sulfonamide-resistant isolates were negative for all the sul genes. Most of the sulfonamide-resistant Salmonella spp. harbored plasmids; only in eight isolates were no plasmids detected. Generally, the size of the plasmids ranged from approximately 2 kb to ≥90 kb. Our results revealed a relatively a high prevalence of sulfonamides-resistant Salmonella spp. isolated from retail food. Additionally, we have detected a high dissemination of plasmids and class 1 integrons that may enhance the spread of resistance genes in the food chain.

Introduction and Objectives. Antimicrobial resistance of pathogenic bacteria can result in therapy failure, increased hospitalization, and increased risk of death. In Poland, Salmonella spp. is a major bacterial agent of food poisoning. The majority of studies on antimicrobial resistance in Salmonella spp. isolates from food have focused on meat products as the source of this pathogen. In comparison, this study examines the antimicrobial susceptibility of Salmonella spp. isolated from retail food products other than meat in Poland. Materials and Methods. A collection of 122 Salmonella spp. isolates were isolated in Poland in 2008-2012 from foods other than meat: confectionery products, eggs, fruits, vegetables, spices and others. The resistance of these isolates to 19 antimicrobial agents was tested using the disc diffusion method. Results. Salmonella Enteritidis was the most frequently identified serotype (84.4% of all tested isolates). In total, 42.6% of the Salmonella spp. isolates were resistant to antibiotics. The highest frequencies of resistance were observed in isolates from 2009 (60.0%) and 2012 (59.5%). Antibiotic resistance was most prevalent among Salmonella spp. isolated from egg-containing food samples (68.0%). Resistance to nalidixic acid was most common and was observed in 35.2% of all tested isolates. The isolates were less frequently resistant to sulphonamides (6.6%), ampicillin (4.9%), amoxicillin/clavulanic acid (2.5%) and to streptomycin, cefoxitin, gentamicin and tetracycline (1.6%). Only one isolate showed resistance to chloramphenicol. Four isolates displayed multiresistance. Conclusions. Although, the level of resistance and multiresistance of Salmonella spp. isolates from non-meat foods was lower than in those from meat products, the presence of these resistant bacteria poses a real threat to the health of consumers.

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