Possible connections between the antibiotic-related plasmids of potentially probiotic Lactobacillus strains and the antibiotic resistance

The tolerances of 5 potentially probiotic lactobacilli strains to antibiotics were investigated with K-B paper-diffusion method. The antibiotic-related resistance genes obtained from PCR were sequenced. Five lactobacilli strains showed their susceptibility to tetracycline, but tolerated to 7 antibiotics including bacitracin, polymyxin B, kanamycin, and nalidixic acid. All of five strains, Lactobacillus pentosus CH8 was used as case for further study. After both SDS and SDS-heating methods were chosen to remove the plasmids from strain CH8 cells, this strain showed its susceptibility to cephalothin and chloromycetin. Analysis of the PCR products, targeted from the primers of β-lactam resistance-related genes including blr, ECP-1569 and nps-1 as well as chloromycetin resistance-related genes including cmlA, cat and cmlA1, indicated that the plasmid of L. pentosus CH8 contained the blr gene that caused this bacteria to tolerate cephalothin. The elimination of plasmids by SDS or SDS -heating confirmed that there might be the potential relationship between the plasmid ’s presence of these strains and their antibiotic resistances. The detection of the plasmid’s presence should provide a novel way for the safety evaluation of potential probiotic lactobacilli bacteria, and thus be helpful for the further investigation of resistance gene transferability in human body at a molecular level.