Antibiotic Resistance of Lactobacillusspp. and Streptococcus thermophilusIsolated from Chinese Fermented Milk Products

AbstractThe aim of the present study was to investigate the phenotypic and genotypic antimicrobial resistance and the transferability of resistance markers in 87 lactic acid bacterial strains recovered from fermented milk products obtained from different areas of China. The isolates were identified as 21 Lactobacillus bulgaricus, 8 Lactobacillus casei, 6 Lactobacillus rhamnosus, 3 Lactobacillus paracasei, 2 Lactobacillus acidophilus, and 47 Streptococcus thermophilusstrains. High levels of intrinsic resistance were revealed among the tested species. The following resistance genes were detected in strains isolated from fermented milk products: tet(M) in two L. bulgaricusand two S. thermophilusisolates, strAand strBin nine and seven S. thermophilusisolates, respectively; sul1in six L. bulgaricusand seven S. thermophilusisolates, sul2in one S. thermophilusisolate, aac(6′)-aph(2″)in two L. bulgaricusisolates, and aph(3″)-IIand aph(3″)-IIIin one S. thermophilusand two L. bulgaricusisolates, respectively. Transfer of the monitored antibiotic resistance genes was not observed in the filter mating assays of this study. To our knowledge, the strA, strB, sul1, sul2, and aph(3″)-IIgenes in S. thermophilus, and the sul1and aac(6′)-aph(2″)genes in L. bulgaricuswere identified for the first time. These results indicate the potential risks posed by lactic acid bacteria (LAB) in fermented milk products in expanding the antibiotic resistance gene reservoir and transferring antibiotic resistance genes among bacteria. Further investigations are required to identify the potential sources of contamination and the dissemination routes of antibiotic resistance genes among LAB in fermented milk products.