Synergistic effects of the methanol extract of Trichosanthes kirilowii with antibiotics against oral pathogens

Trichosanthes kirilowii is a traditional medicine used in East Asia for treating patients with diabetes, cancer-associated symptoms, hepatoprotective, coughing, breast abscesses, antibacterial, and antiviral activity. This study aimed to investigate the synergistic antibacterial activity of the methanol extract of Trichosanthes kirilowii (METK) with existing antimicrobial agents against oral pathogen. The synergistic effects and anti-biofilm of METK were evaluated against oral bacteria, either alone or with antibiotics, via broth dilution method and crystal violet assays. MIC/MBC values for METK, ampicillin, and gentamicin against all the tested bacteria ranged between 156-2500/313-5000 microg/mL, 0.25-64/0.25-64 microg/mL, and 0.5-256/1-512 microg/mL, respectively. The synergistic effects were exhitited on METK with antibiotics against oral bacteria at fractional inhibitory concentration index (FICI) <0.5. Moreover, METK and antibiotics were found to synergistically reduce biofilm formation. 1-6 hours of treatment with 1/2 MIC of METK with 1/2 MIC of antibiotics resulted from an increase of the rate of killing in units of CFU/mL to a greater degree than was observed with alone except S. sanguinis on ampicillin and S. criceti, S. anginosus, and S. gordonii on gentamicin. These results suggest that the methanol extract of Trichosanthes kirilowii (METK) is important in the antibacterial actions of oral pathogen agents.