Purpose: The objective of this study was to verify growth suppression of methicillin-resistant Staphylococcus aureus (MRSA) involved in ventilator-associated pneumonia (VAP) aggravation by the probiotic candidate bacterium Lactobacillus gasseri (L. gasseri) in the oral cavity. Materials and Methods: L. gasseri YIT 12321 (Lg YIT 12321) and MRSA JCM 8702 (MRSA-JCM) were used as test bacteria. Both Lg YIT 12321 and MRSA-JCM were cultured in lactobacilli MRS medium, and MRSA-JCM was also cultured

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... TS medium anaerobically at 37˚C for 18-24 hours. The antibacterial activity of Lg YIT 12321 against MRSA-JCM was examined by competition assay and radial diffusion assay (RDA). A fraction obtained from the Lg YIT 12321 culture supernatant by 50% (w/v) saturated ammonium sulfate (50% sat. ammonium) precipitation was examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Results: In the competition assay, inhibition of MRSA-JCM proliferation by Lg YIT 12321 was observed. Moreover, it was confirmed that the growth of MRSA-JCM was inhibited by neutralized culture supernatant of Lg YIT 12321 in the RDA, suggesting that the growth of MRSA-JCM was suppressed by an antibacterial substance produced by Lg YIT 12321. Conclusion: Lg YIT 12321 is a candidate probiotic that produces a class II bacteriocin that suppresses the growth of MRSA-JCM. (Asian Pac J Dent 2020; 20: 1-8.)