Prevalence, drug resistance, and virulence genes of potential pathogenic bacteria in pasteurized milk of Chinese Fresh Milk Bar.

Fresh Milk Bar (FMB), an emerging dairy retail franchise, is used to instantly produce and sell pasteurized milk and other dairy products in China. However, the quality and safety of pasteurized milk in FMB have received little attention. The objective of this study is to investigate the prevalence, antimicrobial resistance, and virulence genes of Escherichia coli (E. coli) , Staphylococcus aureus (S. aureus) , and Streptococcus in 205 pasteurized milk samples collected from FMBs in China. Four (2.0%) isolates of E. coli , seven (3.4%) isolates of S. aureus , and three (1.5%) isolates of S. agalactiae  were isolated and identified. The E. coli  isolates were resistant to amikacin (100%), streptomycin (50%), and tetracycline (50%). Their detected resistance genes include  aac(3)-III (75%), blaTEM  (25%), aadA  (25%), aac(3)-II  (25%), catI  (25%) and qnrB (25%). The S. aureus  isolates were mainly resistant to penicillin G (71.4%), trimethoprim-sulfamethoxazole (71.4%), kanamycin (57.1%), gentamicin (57.1%), amikacin (57.1%) and clindamycin (57.1%).  blaZ (42.9%),  mecA (28.6%), ermB (14.3%) and ermC  (14.3%) were detected as their resistance genes. The Streptococcus strains were mainly resistant to tetracycline (66.7%) and contained resistance genes:  pbp2b (33.3%) and tetM (33.3%). The virulence genes eae  and stx2  were only found in one E. coli  strain (25%), and sec  was detected in two S. aureus strains(28.6%), while bca  was detected in one  S. agalactiae  strain (33.3%) .  The results of this study indicate that bacteria with drug resistance and virulence genes isolated from the pasteurized milk of FMB are a potential risk to consumers' health.