Abstract:

In order to investigate the potential public health risk of resistance genes in lactic acid bacteria (LAB), LAB
strains isolated from commercial yogurts were identified and investigated for antibiotic resistance profiles and the
prevalence of streptomycin, gentamycin, sulfamethoxazole, and tetracycline resistance genes by PCR amplification. A total
of 56 LAB strains were isolated from 25 yogurt samples, including Lactobacillus delbrueckii subsp. bulgaricus (n = 26),
Lactobacillus plantarum (n = 3), Lactobacillus acidophilus (n = 2), and Streptococcus thermophilus (n = 25). Antimicrobial
susceptibility tests showed that 31 Lactobacillus strains were frequently resistant to streptomycin (87.1%), gentamycin
(80.6%), ciprofloxacin (74.2%), and tetracycline (61.3%), whereas cephalosporin exhibited good activity against the strains.
25 Streptococcus thermophilus also showed the highest resistance rate to streptomycin (76.0%), followed by vancomycin
(32.0%), ciprofloxacin (32.0%) and tetracycline (20.0%). Five different resistance genes were detected among the tested
strains, including ant(6) (accounting for 1.8% of the strains), aac(6')-aph(2'') (7.1%), tetM (5.4%), sul I (14.3%), and sul II
(1.8%). Of the 56 LAB strains, thirteen were positive for resistance genes, among which four strains harbored two different
resistance genes, indicating LAB strains which have been recognized as safe and widely used in fermented foods for a long
time may act as a reservoir of resistance genes.

Key words: yogurt, lactic acid bacteria, antimicrobial resistance, resistance gene