Abstract

Significance and Impact of the Study

Mastitis can be caused by Staphylococcus aureus, which is hard to be eradicated, especially when it formed biofilm. This situation has made searching for novel antimicrobial agents urgent. Present study demonstrates the anti-bacteria and anti-biofilm inhibitory activity of essential oils on S. aureus alone and combined with rifaximin. Combinations of rifaximin and mint oil can not only inhibit S. aureus from growing on abiotic material, but also restrain its invasion into cells. Results of the present study gave an insight into the promising alternatives for killing S. aureus and treating mastitis.

Abstract

This study intended to explore whether rifaximin and EOs (mint oil (MEO), eucalyptus oil (EEO), and EO of Houttuynia cordata (HEO)) alone and combined can inhibit the biofilm formation and invasion ability of S. aureus. Firstly, minimal inhibitory concentration (MIC) of 9 strains were investigated. Otherwise, checkerboard microdilution assays were used to measure FICI of rifaximin and EOs of S. aureus- 2. Lastly, the influence of the sub-MIC of EOs alone and combined with rifaximin on the biofilm formation and invasion of S. aureus were tested. MEO exhibited the greatest efficacy against planktonic cells. The results demonstrated that combination of rifaximin and MEO was additive, and the others showed indifferent. Almost all EOs alone and combined with rifaximin effectively reduced the S. aureus biofilm formation to some extent. Meanwhile, combination of rifaximin and MEO showed the strong inhibitory effect on invasion, and 0.5MIC rifaximin +0.125MIC MEO can inhibit bacteria from invasion. These results suggested rifaximin alone and combined with EOs, in particular MEO, can be the alternative therapies for bovine mastitis.

Keywords: Staphylococcus aureus; Invasion; Rifaximin; Biofilm; Essential oils; Combination