Antibiotic Resistance and the Mobility of Its Genetic Determinants in Lactobacillus fermentum

The work aimed to estimate the potential of transfer of resistance genes from Lactobacillus fermentum 5-1 to the Gram-negative intestinal microbiota. The sensitivity of antibiotics was assessed using the gradient agar method and microdilution method. Antibiotic resistance (AR) genes in bacterial genomic DNA were detected by PCR, followed by Sanger sequencing of the amplicons and BLASTn sequence analysis. Acinetobacter baumannii, Citrobacter freundii, and Escherichia coli had neither phenotypic nor genotypic resistance to tetracycline and therefore were selected among nine Gram-negative strains as recipients of the AR genes. The transferability of the AR genes from L. fermentum 5-1 to these bacteria was studied under cocultivation in a simulated colonic environment, in filter mating experiments, and using transformation of bacteria by electroporation. Based on the values of minimum inhibitory concentration (MIC), we found that this strain was resistant to vancomycin (MIC = 256 μg/mL), ciprofloxacin (MIC = 64 μg/mL), aminoglycosides (MIC = 54–256 μg/mL), and chloramphenicol (MIC = 8 μg/mL); sensitive to ampicillin (MIC = 0.5 μg/mL), rifampicin (MIC = 2 μg/mL), and cefotaxime (MIC = 0.12 μg/mL); and showed intermediate (low) resistance to erythromycin (MIC = 1 μg/mL) and tetracycline (MIC = 8 μg/mL). Using PCR analysis in the chromosomal DNA of L. fermentum 5-1, we detected the erythromycin resistance gene ermB, while two tetracycline resistance genes, tetM and tetK, were identified in plasmid DNA. Moreover, we demonstrated that L. fermentum 5-1 could transfer their tetK gene to C. freundii via electroporation and transformation with the plasmid DNA of the lactobacilli. Our results demonstrate that lactobacilli can negatively contribute to the problem of antibiotic resistance and warrant stricter control over the practical use of LAB.