Plasmid-Mediated Antibiotic-Resistant Pattern of Lactobacillus spp. Isolated From Dairy Products

Microorganisms have potent activity for transferring antibiotic-resistant genes with either chromosomally- or plasmid-mediated characteristics. The purpose of this study was to isolate Lactobacillus from different commercial products and evaluate their potential in antibiotic-resistant development. Chromosomallyor plasmid-mediated resistant genes were investigated as well.

In total, Lactobacillus strains were isolated from 20 commercial dairy product samples such as cheese and yoghurt. The isolates were phenotypic and molecularly identified and their antibiotic-resistant properties were assessed by the disk-diffusion method. Finally, the plasmid-mediated antibiotic resistant characters of the isolates were evaluated by plasmid curing via evaluated temperatures and acridine orange methods.

Five strains Lactobacillus paracasei, L. rhamnosus, L. casei, L. plantarum, and L. fermentum were isolated different products. The results of the antibiotic susceptibility assay indicated that all strains were susceptible to amoxicillin and imipenem and resistant to ciprofloxacin and vancomycin. Furthermore, different responses were observed among the isolates against streptomycin and gentamicin. The evaluation of plasmid-mediated antibiotic resistance in the isolates revealed that streptomycin and gentamicin-resistant characters were of plasmid-mediated type in L. rhamnosus and L. plantarum strains.

In general, our finding demonstrated that some commercial Lactobacillus strains harboured antibiotic-resistant genes. These genes can be located either in chromosome or plasmid group. Hence, the frequency of antibiotic-resistant pathogenic bacteria might be increased after consuming some dairy products because of the horizontal transfer of antibiotic-resistance genes among the bacteria.