Antibiotic Susceptibility, Biofilm-Forming Ability, and Incidence of Class 1 Integron of Salmonella spp., Escherichia coli, and Staphylococcus aureus Isolated from Various Foods in a School Canteen in China

In recent years, the food poisoning incidents from school canteens have aroused widespread concern in China. Microbial contamination to the foods is the main factor responsible for these food poisoning events. In this study, identification of microbial pathogens including Salmonella spp., Escherichia coli, and Staphylococcus aureus in samples (frozen pork, fresh pork, fresh chicken, and different fresh vegetables) of a school canteen in China during 2017 to 2018 was performed. The antibiotic susceptibility pattern, class 1 integron, and biofilm formation ability of the isolated pathogens were also investigated. In total, 96 strains were isolated (32 Salmonella spp., 32 E. coli, and 32 S. aureus). The antibiogram study results demonstrated that 61.5% strains were found resistant to at least one type of antibiotics, and 17.7% were resistant to three or more antibiotics. In addition, 31.3% strains possessed class 1 integron. Among the integron-positive isolates, 38.9% Salmonella spp. and 87.5% E. coli contained ∼800 or/and 1500 bp size gene cassette within the integrons. However, four S. aureus strains possessing class 1 integron without gene cassette were found. Although none of the isolated strains were found strong biofilm producer, 44.8% were found to have weak or moderate biofilm formation ability. Despite biofilm formation ability or not, the Salmonella spp. containing positive class 1 integron showed significant resistance to cefazolin and gentamicin. In addition, class 1 integron-positive E. coli isolates having the biofilm formation ability hardly showed sensitive to four antibiotics, such as amikacin, amoxicillin–clavulanate, cefazolin, and gentamicin. Therefore, it is necessary to reduce the prevalence of antibiotic resistance gene cassettes containing antibiotic resistance genes by the prudent use of antibiotics in livestock farms, and the improvement of food processing and storage environment.