Microbiology Research Journal International

Aims: To discover an alternative chemical that could potentially be used in combination with antibiotics to inhibit the growth of Staphylococcus epidermidis RP62A.

Study Design: The studies of the growth inhibition in both the biofilm forming strain of S. epidermidis RP62A and the wild-type strain ATCC 12228, were conducted with different concentrations of rifampicin and D-limonene using the measurement of the optical density.

Place and Duration of Study: All experiments were conducted in the Department of Biology at Manhattanville College between September 2015 and December 2019.

Methodology: Different concentrations of rifampicin (0.0025 µg/mL, 0.005 µg/mL, 0.01 µg/mL and 0.02 µg/mL) and D-limonene (152.8 µg/mL, 305.6 µg/mL, 611.2 µg/mL and 1222.4 µg/mL) were used in the study. The minimal inhibitory concentrations (MIC) of rifampicin and D-limonene on RP62A and ATCC 12228 were obtained. The combination of rifampicin and D-limonene on the inhibition of the growth of RP62A and ATCC 12228 was conducted using a microtiter plate by measuring optical density. The alamarBlue^® assay was further used to evaluate the viability of RP62A and ATCC 12228 with the combination treatment. The biofilm assay was then conducted on RP62A with the combination treatment of rifampicin and D-limonene.

Results: The MIC of the combination treatment of rifampicin and D-limonene on RP62A was found to be 0.01 µg/mL and 1222.4 µg/mL respectively. A combination treatment of 0.005 µg/mL of rifampicin with 611.2 µg/mL of D-limonene significantly inhibited the growth and biofilm formation of RP62A than the same concentration of rifampicin.

Conclusion: The addition of the D-limonene to the rifampicin was found to be effective in inhibiting the growth and biofilm formation of RP62A. This indicates that the combination of alternative mineral oil may have the potential to lower the antibiotic concentration in the inhibition of the growth of the bacteria S. epidermidis.