ABSTRACT
OBJECTIVES: The essential oil of Melaleuca alternifolia (tea tree oil) and its components have antimicrobial activity against a wide range of Gram-positive and Gram-negative bacteria, fungi and viruses. The mechanism(s) by which Pseudomonas aeruginosa NCTC 10662 maintains a decreased susceptibility to tea tree oil and components was investigated. RESULTS: Ethylene diamine tetraacetic acid enhanced the antimicrobial activity of tea tree oil and terpinen-4-ol against stationary phase P. aeruginosa while polymyxin B nonapeptide enhanced the activity of tea tree oil and gamma-terpinene. Pre-treatment with the protonophore carbonyl cyanide m-chlorophenylhydrazone increased the susceptibility of exponential phase cells to sub-inhibitory concentrations of tea tree oil, terpinen-4-ol and gamma-terpinene, indicating that intrinsic tolerance to tea tree oil and components is substantially energy dependent. CONCLUSIONS: Increased tolerance to tea tree oil in P. aeruginosa is directly related to the barrier and energy functions of the outer membrane, and may involve efflux systems.
Subject(s)
Anti-Infective Agents, Local/pharmacology , Bacterial Outer Membrane Proteins/drug effects , Bacterial Outer Membrane Proteins/metabolism , Energy Metabolism/drug effects , Polymyxin B/analogs & derivatives , Pseudomonas aeruginosa/drug effects , Tea Tree Oil/pharmacology , Anti-Infective Agents/pharmacology , Carbonyl Cyanide m-Chlorophenyl Hydrazone/pharmacology , Drug Resistance, Bacterial , Edetic Acid/pharmacology , Microscopy, Electron , Polymyxin B/pharmacology , Pseudomonas aeruginosa/ultrastructure , Time Factors , Uncoupling Agents/pharmacologyABSTRACT
AIM: Erysipelothrix rhusiopathiae causes the occupationally-related infection erysipeloid in humans, and may be responsible for infections in lobster fishermen in Western Australia. There are little recent data pertaining to antimicrobial susceptibility, or susceptibility to disinfectants that might be used in the environment. The aim of this study was to determine the susceptibility of E. rhusiopathiae from human, animal and environmental sources to various antimicrobial agents and disinfectants. METHODS: The susceptibility of 60 E rhusiopathiae isolates was determined using a recommended agar dilution procedure. Susceptibility to disinfectants was achieved using a broth microdilution method. RESULTS: Penicillin and ceftriaxone, with low minimum inhibitory concentrations (MICs) (MIC90 0.03 mg/l and 0.125 mg/l, respectively), remained active against E. rhusiopathiae and should continue to be recommended for treatment. Ciprofloxacin MICs were particularly low (MIC90 0.06 mg/l), offering an alternative agent for the penicillin allergic patient. Erysipelothrix rhusiopathiae is still resistant to vancomycin (MIC90 64 mg/l), highlighting the importance of early diagnosis of E. rhusiopathiae infection in cases of endocarditis. In addition, 31 E. rhusiopathiae isolates were tested against several commercially available home disinfectants. Most were effective in killing E. rhusiopathiae with minimum bactericidal concentrations of 0.001% for Pine O Cleen, and 0.03% for Domestos, Linely and the Wheelie Bin Phenyl Cleanser. CONCLUSIONS: There appeared to be no new emergence of antibiotic resistance in E. rhusiopathiae. Various disinfectants could be used following mechanical cleaning of work environments, such as fishing boats, and equipment, to reduce the risk of infection with E. rhusiopathiae.
