Antiviral activity of Bifidobacterium adolescentis SPM1005-A on human papillomavirus type 16

Background: Probiotic lactic acid bacteria (LAB) support a functional and balanced immune system, and contribute to immune modulatory effects in combatting microbial pathogens, including viruses. Most cervical cancers are associated with anogenital region infection with high-risk (HR) human papillomavirus (HPV). In this study, we analyzed the antiviral activity of Bifidobacterium adolescentis SPM1005-A in the SiHa cervical cancer cell line expressing HPV type 16. Methods: We assessed the cellular toxicity of B. adolescentis SPM1005-A in SiHa cells by the Trypan blue dye exclusion assay. Cells (3.6 x 10(5)) in culture plates with or without B. adolescentis SPM1005-A in the same type of medium, were incubated with HPV type 16 at a concentration of 5.1 x 10(7) cfu/ml. For antiviral analysis, we performed quantitative real-time PCR (qRT-PCR) for E6 and E7 oncogene expressions and observed protein levels by immunoblotting. Results: The qRT-PCR results showed that E6 and E7 mRNA levels decreased simultaneously. Western blot analysis revealed that the E6 protein expression slightly decreased after 24 and 48 h, but the level of E7 protein expression appear unaffected compared with that in the control. Decreased HPV16 E6 and E7 mRNA transcript and protein levels were not associated with cell morphology or significant cytotoxic effects. Conclusions: This study showed that B. adolescentis SPM1005-A had antiviral activity through suppression E6 and E7 oncogene expression. The results suggest that B. adolescentis SPM1005-A could be potential applications of HPV-associated cervical cancer prevention.