Characterization of antimicrobial resistance in lactobacilli and bifidobacteria used as probiotics or starter cultures based on integration of phenotypic and in silico data

Lactic acid bacteria and bifidobacteria deliberately introduced into the food chain may act as a reservoir of antimicrobial resistance genes (ARGs), which is considered a safety concern. In the present study, resistance to antimicrobials of commercial probiotic strains, probiotic candidate strains, and starter cultures (n = 20) was characterised based on integration of phenotypic and in silico data. Minimum inhibitory concentrations (MICs) of 16 antimicrobials were determined for lactobacilli and bifidobacteria that were isolated from pharmaceutical products or obtained from the manufacturers or culture collections. Using different databases and bioinformatic tools, we predicted ARGs, mutations, genomic islands, and mobile genetic elements (MGEs) in their whole genome sequences. In addition, a comprehensive in silico analysis of the prevalence of the tetW gene and its genetic environment across lactobacilli and bifidobacteria (n = 1423) was conducted. Several strains exhibited phenotypic resistance to kanamycin, tetracycline, chloramphenicol, quinupristin-dalfopristin, ciprofloxacin, or neomycin. These resistances, however, did not always correspond to the presence of ARGs and vice versa. We detected an acquired tetW gene in four commercial strains of Bifidobacterium animalis subsp. lactis, whereas homologs of antimicrobial resistance (AR) proteins were predicted in all 20 proteomes. The prevalence of the tetW gene, which was often flanked by MGEs, was higher in analysed bifidobacteria (31.9%) than lactobacilli (6.3%). In addition, sequences flanking tetW were associated with putative genomic islands and were conserved in several strains, including potential pathogens. Our findings provide an insight into AR of probiotics, probiotic candidates, and starter cultures with an emphasis on tetracycline and into the safety of these strains in the context of AR.