Antimicrobial activity and chemical composition of the essential oil of Hofmeisteria schaffneri

Objectives The aims of this study were to establish the antimicrobial potential of Hofmeisteria schaffneri essential oil and its chemical composition. Methods The essential oils of Hofmeisteria schaffneri harvested at flowering (batches I and IV) and non-flowering (batches II and III) seasons were prepared by hydrodistillation and analysed by GC and GC-MS. The aqueous and organic (CH2Cl2-MeOH 1 : 1) extracts were prepared by using infusion and maceration techniques, respectively. The in-vitro antimicrobial activity of the preparations and compounds against Candida albicans and some bacteria (Gram-negative and Gram-positive) was assessed using the broth dilution method in 96-microplate wells. Key findings Forty-four compounds, representing similar to 90% of the total constituents, were identified in the essential oil of Hofmeisteria schaffneri collected in flowering (batches I and IV) and non-flowering (batches II and III) seasons. In all cases, several thymol analogues were the major components of the oils (similar to 65%); some small differences in the relative proportions of these constituents were observed. The infusion exhibited an antibacterial activity against Staphylococcus aureus and Bacillus subtilis, with a MIC value of 64 mu g/ml in each case. The essential oil batches were active against Staphylococcus aureus, with MIC ranging from 48 to 192 mu g/ml. They were, however, inactive against Gram-negative bacteria, including Pseudomonas aeruginosa, Escherichia coli and Salmonella typhi (MIC > 1024 mu g/ml). On the other hand, the infusion of the plant as well as the oil from batch I displayed anti-Candida albicans activity, with MIC of 128 and 192 mu g/ml, respectively. Finally, the organic extract did not displayed significant activity against the tested microorganisms (MIC >= 1024 mu g/ml). Some of the compounds isolated from the plant were also tested. Compounds 8 and 38, which were present in the essential oils, displayed the best antibacterial effect against Gram-positive bacteria (MIC ranging between 32 and 64 mu g/ml). Compounds 6 (present in the infusion) and 10 (present in all preparations) showed higher activity against the yeast (MIC = 128 mu g/ml) than the remaining compounds, with MIC values ranging from 256 to 512 mu g/ml. Conclusions The composition and antimicrobial activity of the oils changed slightly from flowering to non-flowering seasons. The results of the present investigation provide in-vitro scientific support for the use of the plant against skin infections in Mexican folk medicine.