Antibiotic resistance of lactic acid bacteria isolated from dairy products in Tianjin, China

Antibiotic resistance poses safety risk to public health. Limited studies have considered the spread of resistance due to bacteria used in food production. We conducted a study investigating the antibiotic resistance of lactic acid bacteria from fermented dairy products in Tianjin. A total of 9 strains (3 Lactobacillus bulgaricus and 6 Streptococcus thermophilus) were isolated from commercial yogurt and cheese. Antibiotic resistance to 4 antibiotics of all isolates was analyzed by disc diffusion method and the corresponding resistance genes were determined using PCR and sequencing. Eight of 9 isolates were identified to be resistant to at least one antibiotic and 6 isolates displayed multi-drug resistance. Occurrence rate of antibiotic resistant strains to vancomycin, neomycin, gentamycin and streptomycin were 11.1%, 77.8%, 66.7% and 44.4%, respectively. The presence of antibiotic resistance genes van, aph or aadA2 were identified in 6 resistant strains. Sequencing results of aph and aadA2 amplicon demonstrated 100% and 99% identity to the resistant genes in vector pEXKm4 and Lactococcus lactis subsp. cremoris, respectively. L. bulgaricus and S. thermophilus used in dairy products can harbour antibiotic resistance genes and disseminate the resistance through food. Screening for antibiotic resistance in fermented foods should be a routine inspection for food safety.