In vitro activity of tea-tree oil against clinical skin isolates of meticillin-resistant and -sensitive Staphylococcus aureus and coagulase-negative staphylococci growing planktonically and as biofilms

Abstract

The susceptibility of Staphylococcus aureus [meticillin-resistant (MRSA) and meticillin-sensitive (MSSA)] and coagulase-negative staphylococci (CoNS), which respectively form part of the transient and commensal skin flora, to tea-tree oil (TTO) was compared using broth microdilution and quantitative in vitro time-kill test methods. MRSA and MSSA isolates were significantly less susceptible than CoNS isolates, as measured by both MIC and minimum bactericidal concentration. A significant decrease in the mean viable count of all isolates in comparison with the control was seen at each time interval in time-kill assays. However, the only significant difference in the overall mean log 10 reduction in viable count between the groups of isolates was between CoNS and MSSA at 3 h, with CoNS isolates demonstrating a significantly lower mean reduction. To provide a better simulation of in vivo conditions on the skin, where bacteria are reported to grow as microcolonies encased in glycocalyx, the bactericidal activity of TTO against isolates grown as biofilms was also compared. Biofilms formed by MSSA and MRSA isolates were completely eradicated following exposure to 5 % TTO for 1 h. In contrast, of the biofilms formed by the nine CoNS isolates tested, only five were completely killed, although a reduction in viable count was apparent for the other four isolates. These results suggest that TTO exerts a greater bactericidal activity against biofilm-grown MRSA and MSSA isolates than against some biofilm-grown CoNS isolates.

<i>In vitro</i> Antibacterial and Chemical Properties of Essential Oils Including Native Plants from Brazil against Pathogenic and Resistant Bacteria

“…Although there was no significant difference, we observed that MSSA strains were more resistant or showed the same sensibility levels as the MRSA strains for most EO. Brady et al 45 reported similar results when they evaluated the susceptibility of MRSA and MSSA strains to tea tree EO Melaleuca alternifolia and reported MIC between 0.25 to 2.0 v/v and 0.5 -2.0 v/v, respectively, although statistically significant difference was not found for both S. aureus strains. The EO M. piperita has demonstrated antibacterial activity at concentrations of 0.064 to 0.128 mg/mL against MSSA and from 0.064 to 0.256 mg/ mL against MRSA strains, although no significant differences were found between the bacterial types tested 46 .…”

Control of Biofilm Formation: Antibiotics and Beyond

“…Biofilm formation was also inhibited when oregano essential oils, carvacrol and thymol, were used against S. aureus (99). Five of nine biofilms formed by coagulase-negative staphylococci (CoNS) strains were completely eradicated when 5% tea tree oil (TTO) was used, while the same concentration of TTO achieved complete eradication of methicillin-susceptible S. aureus (MSSA) and MRSA biofilm growth as microcolonies in glycocalyx during 1 h of treatment (100). The antimicrobial function of TTO was attributed to the disruption of the hydrophobic phospholipid bilayers in the cell membrane.…”

Treatment of acne with tea tree oil (melaleuca) products: A review of efficacy, tolerability and potential modes of action

“…In general, bacteria growing within biofilms are more difficult to eradicate than their planktonic counterparts and this may be one of the factors contributing to the relatively long time that it can take to improve acne after commencement of treatment [36]. Whilst no data exist for tea tree oil and P. acnes biofilms, the oil has activity against biofilms of other Gram-positive bacteria such as Staphylococcus aureus [37], suggesting that in principle it may also affect P. acnes biofilm.…”