Essential oil combinations against Clostridium perfringens and Clostridium septicum ‐ the causative agents of gas gangrene

AIMS The inhibitory and bactericidal effect of a wide range of essential oils, and their selected combinations against two pathogens (Clostridium perfringens and Clostridium septicum), the causative pathogens of gas gangrenous infections were investigated. Fractional inhibitory indices were also calculated to determine the interactions. METHODS AND RESULTS The Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) assays were used to determine the efficacy of the essential oils. Santalum austrocaledonicum demonstrated the highest activity inhibiting both Clostridial pathogens at the lowest concentration of 0·02 mg ml-1 . Santalum austrocaledonicum combined with Cymbopogon martinii had the strongest inhibition against C. perfringens (MIC 0·02 mg ml-1 ) and C. septicum (MIC 0·01 mg ml-1 ). Selected combinations demonstrated synergy (ΣFIC ≤ 0·50) in combination against both pathogens tested. Antagonism was also observed in many combinations. CONCLUSIONS Selected essential oils, when studied either individually or in combination, have high inhibitory and bactericidal effects against both Clostridial strains. Nine combinations have proven to be synergistic with 23 combinations additive; 96 indifferent and 77 having an antagonistic effect against the pathogenic strains. Some combinations demonstrated extreme antagonism and as such, careful consideration needs to be given to essential oil selection against these pathogens. SIGNIFICANT IMPACT OF THE STUDY Very few essential oils have been antimicrobially screened (MIC and MBC) against Clostridial strains and furthermore, the efficacies in combination are not known.