Assessing the drug resistance profiles of oral probiotic lozenges.

Background: Probiotic lozenges have been developed to harvest the benefits of probiotics for oral health, but their long-term consumption may encourage the transfer of resistance genes from probiotics to commensals, and eventually to disease-causing bacteria.

Aim: To screen commercial probiotic lozenges for resistance to antibiotics, characterize the resistance determinants, and examine their transferability .

Results: Probiotics of all lozenges were resistant to glycopeptide, sulfonamide, and penicillin antibiotics, while some were resistant to aminoglycosides and cephalosporins. High minimum inhibitory concentrations (MICs) were detected for streptomycin (>128 µg/mL) and chloramphenicol (> 512 µg/mL) for all probiotics but only one was resistant to piperacillin (MIC = 32 µg/mL). PCR analysis detected erythromycin ( or ) and fluoroquinolone ( or ) resistance genes in some lozenges although there were no resistant phenotypes. The , and or genes conferring resistance to trimethoprim, chloramphenicol, quinupristin/dalfopristin, vancomycin, and streptomycin, respectively, were detected in resistant probiotics. The rifampicin resistance gene was also present. We found no conjugal transfer of streptomycin resistance genes in our co-incubation experiments.

Conclusion: Our study represents the first antibiotic resistance profiling of probiotics from oral lozenges, thus highlighting the health risk especially in the prevailing threat of drug resistance globally.