Heterogeneity of macrolide-lincosamide-streptogramin phenotype & conjugal transfer of erm(B) in Pediococcus pentosaceus

BACKGROUND & OBJECTIVES: Pediococcus pentosaceus has been reported to cause clinical infections while it is being promoted as probiotic in food formulations. Antibiotic resistance (AR) genes in this species are a matter of concern for treating clinical infections. The present study was aimed at understanding the phenotypic resistance of P. pentosaceus to macrolide-lincosamide-streptogramin B (MLS(B)) antibiotics and the transfer of AR to pathogens. METHODS: P. pentosacues isolates (n=15) recovered from fermented foods were screened for phenotypic resistance to MLS(B) antibiotics using disc diffusion and microbroth dilution methods. Localization and transferability of the identified resistance genes, erm(B) and msr(C) were evaluated through Southern hybridization and in vitro conjugation methods. RESULTS: Four different phenotypes; sensitive (S) (n=5), macrolide (M) (n=7), lincosamide (L) (n=2) and constitutive (cMLS(B)) (n=1) were observed among the 15 P. pentosaceus isolates. High-level resistance (>256 μg/ml) to MLS(B) was observed with one cMLS(B) phenotypic isolate IB6-2A. Intermediate resistance (8-16 μg/ml) to macrolides and lincosamides was observed among M and L phenotype isolates, respectively. Cultures with S phenotype were susceptible to all other antibiotics but showed unusual minimum inhibitory concentration (MIC) values of 8-16 μg/ml for azithromycin. Southern hybridization studies revealed that resistance genes localized on the plasmids could be conjugally transferred to Enterococcus faecalis JH2-2. INTERPRETATION & CONCLUSIONS: The study provides insights into the emerging novel resistance patterns in P. pentosaceus and their ability to disseminate AR. Monitoring their resistance phenotypes before use of MLS antibiotics can help in successful treatment of Pediococcal infections in humans.