The oral care probiotic strain Weissella cibaria CMU (oraCMU) inhibits volatile sulphur compounds associated with halitosis, presumably by inhibiting the growth of associated oral pathogens. In the present study, we investigated whether oraCMU inhibits the production of these compounds by suppressing the expression of mgl . This gene encodes L-methionine-α-deamino-γ-mercaptomethane-lyase (METase) and is involved in the production of methyl mercaptan (CH3SH) by Porphyromonas gingivalis . Therefore, we specifically investigated the effects of oraCMU on the growth, CH3SH production, METase activity, and mgl expression of P. gingivalis . The minimum inhibitory concentrations of cell-free supernatant and secreted proteins from oraCMU were 125 mg/mL and 800 µg/mL, respectively. At sub-minimum inhibitory concentration levels, these metabolites inhibited CH3SH production, but they also reduced P. gingivalis viability. Only heat-killed oraCMU decreased CH3SH production without affecting P. gingivalis viability. Heat-killed oraCMU also inhibited METase activity toward L-methionine and mgl mRNA expression (p < 0.05). In summary, we demonstrated the inhibition of volatile sulphur compounds via the antimicrobial action of oraCMU and, for the first time, the inhibition of such compounds by heat-killed oraCMU, which occurred at the molecular level.

Introduction
Materials and Methods
    1. Bacterial strains and growth conditions
    2. Bacterial susceptibility assay
    3. Methyl mercaptan production assays
    4. XTT reduction assay
    5. L-methionine-α-deamino-γ-mercaptomethanelyaseassay
    6. Analysis of mgl expression by quantitative realtimepolymerase chain reaction (qRT-PCR)
    7. Statistical analysis
Results
    1. Determination of antibacterial activity of oraCMUagainst P. gingivalis
    2. Effects of oraCMU on the production of methylmercaptan
    3. Effects of HK-oraCMU on METase activity
    4. Effect of HK-oraCMU on mgl expression
Discussion
References

• Hyun-Jin Kim(Institute of Biomaterial Implant, Department of Oral Anatomy, School of Dentistry, Wonkwang University)
• Ji-Eun Yeu(Research Institute, OraPharm Inc/Department of Food and Nutrition, Hanyang University)
• Dong-Suk Lee(School of Nursing, Kangwon National University)
• Mi-Sun Kang(Research Institute, OraPharm Inc) Correspondence to