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.
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 log10 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.
Brady
Aaron
A
Clinical and Practice Research Group, School of Pharmacy, Queen's University Belfast, Medical Biology Centre, 97 Lisburn Road, Belfast BT9 7BL, UK.
Loughlin
Ryan
R
Clinical and Practice Research Group, School of Pharmacy, Queen's University Belfast, Medical Biology Centre, 97 Lisburn Road, Belfast BT9 7BL, UK.
Gilpin
Deirdre
D
Clinical and Practice Research Group, School of Pharmacy, Queen's University Belfast, Medical Biology Centre, 97 Lisburn Road, Belfast BT9 7BL, UK.
Kearney
Paddy
P
Microbiology Department, United Hospitals Trust, Antrim, BT41, UK.
Tunney
Michael
M
Clinical and Practice Research Group, School of Pharmacy, Queen's University Belfast, Medical Biology Centre, 97 Lisburn Road, Belfast BT9 7BL, UK.
D000891:Anti-Infective Agents, Local / Q000494:pharmacology*; D018441:Biofilms / Q000187:drug effects* / Q000254:growth & development; D003030:Coagulase; D006801:Humans; D008712:Methicillin / Q000494:pharmacology*; D016106:Methicillin Resistance; D008826:Microbial Sensitivity Tests; D010933:Plankton / Q000187:drug effects*; D013207:Staphylococcal Skin Infections / Q000382:microbiology*; D013210:Staphylococcus / Q000187:drug effects* / Q000201:enzymology / Q000502:physiology; D013211:Staphylococcus aureus / Q000187:drug effects; D020947:Tea Tree Oil / Q000494:pharmacology*
D000891:Anti-Infective Agents, Local; D003030:Coagulase; D020947:Tea Tree Oil; D008712:Methicillin