In vitro anti-staphylococcal combinatory effect of Cinnamomum cassia essential oil and 8-hydroxyquinoline evaluated simultaneously in liquid and vapour phase

Staphylococcal infections are often difficult to treat due to increasing resistance to antibiotics, which is leading to a need for discovering of new drugs and alternative treatments. Plant essential oils are of great potential for the development of new antimicrobial preparations and furthermore, due to their volatility, they are suitable for inhalation therapy, which is an effective way for healing of respiratory diseases. However, compared to well-established methods for testing of antimicrobial combinatory effects in liquid media, there are no standardized assays for determination of interactions between volatile compounds in gaseous phase, although disk volatilization assay is probably the most frequently used method [1], [2]. In this study, we tested in vitro antimicrobial combinations of plant volatile compound 8-hydroxyquinoline (8-HQ) with Cinnamomum cassia essential oil (CCEO) in liquid and vapour phase by broth volatilization chequerboard method [3] developed in our laboratory based on combination of standard microdilution chequerboard method [4] and broth volatilization method [5]. Combinatory effect against S. aureus was evaluated according to means of fractional inhibitory concentration indices (ΣFICI) [4]. Results showed additive effects in both, liquid (broth) and solid (vapour) phases. The best combinatorial effects were obtained for S. aureus BAA 976 in vapour at combination of 145.8 µg/mL of CCEO and 8 µg/mL of 8-HQ (ΣFICI=0.672) and in broth for S. aureus 29213 at combination of 71.1 µg/mL of CCEO and 1 µg/mL of 8-HQ (ΣFICI=0.503). These results can be potentially applied in development of various pharmaceutical applications that are based on volatile antimicrobials.

• References

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