Antimicrobial Susceptibility Testing Of Lactic Acid Bacteria Isolated From Yoghurts In Different Areas Of China

As a daily consumed dairy products, yoghurts have a good mouthfeel and various healthbenefits due to the fermentation of LAB. However, the main threat associated with these LABis that they may receive resistance genes from other bacteria or transfer resistance genes topathogentic bacteria in human gastrointestinal tract. Thus the acquired resistance or theincreasing antibiotic resistance will cause illness more difficulty to treat. Hence, the aim ofthis work was to study the occurrence of antimicrobial resistance and presence of selectedresistance genes among LAB isolated from yoghurts made in different places of China. Themain results were as follows:(1) A total of43strains of LAB, including18strains of Lactobacillus bulgaricus and25strains of Streptococcus thermophilus, were isolated from yoghurts collected from dairy plantslocated in different places of China. L. bulgaricus and S. thermophilus were used as startercultures. Recovered strains derived from yoghurts were isolated on MRS agar supplementedwith0.75%CaCO3. Isolates with dissolved calcium were initially identified by gram stainingand yoghurt coagulation test. The putative LAB identified were further confirmed byPCR-based16S rDNA sequencing.(2) The phenotypic antimicrobial resistance of a strain to each antibiotic tested wasdetermined as the minimum inhibitory concentration (MIC). Among the43LAB strains, allisolates were found resistant to kanamycin and97.7%(42/43) were resistant to neomycin,followed by gentamycin at90.7%(39/43), lincomycin at88.4%(38/43), chloramphenicol at88.4%(38/43), streptomycin at74.4%(32/43), tetracycline at65.1%(28/43),chlortetracycline at44.2%(19/43), ampicillin at34.9%(15/43), roxithromycin at27.9%(12/43), penicillin G at11.6%(5/43). Multidrug resistance was observed in most isolaotes anddifferent resistance was found in different isolates.(3) All the antibiotic-resistant strains were tested for the presence of antibiotic resistancegenes most frequently occurring in LABs by PCR amplification. The tet(M) gene wasdetected in three tetracycline-resistant LAB isolates (10.7%). Four (12.5%) of the thirty-twostreptomycin-resistant isolates were observed to contain the ant(6) gene while five (29.4%) of the fourty-three kanamycin-resistant isolates were found to contain the aph(3’)-IIIa gene.(4) Primer CRA23, which showed higher discriminatory ability, was selected for RAPDanalysis. Results showed that a notable genotypic heterogeneity among the43LAB isolateswas observed by RAPD fingerprinting and there is no evidence of direct correlation betweenantibiotic resistance phenotypes and genotypes.