Susceptibility and intrinsic tolerance of Pseudomonas aeruginosa to selected plant volatile compounds.
OBJECTIVE
To examine the causes for variations in sensitivity and intrinsic tolerance of Pseudomonas aeruginosa to plant volatile compounds.


RESULTS
Minimum inhibitory concentrations were determined for a selection of volatile phytochemicals against P. aeruginosa using a microdilution assay. Effects on growth were also assessed in 100-ml broth cultures. The two strains of P. aeruginosa included in the study exhibited intrinsic tolerance to all compounds, with the exception of carvacrol and trans-cinnamaldehyde. The protonophore carbonyl cyanide m-chlorophenylhydrazone increased P. aeruginosa sensitivity to all compounds except trans-cinnamaldehyde, implicating an ATP-dependent efflux mechanism in the observed tolerance. Outer membrane integrity following treatment with test compounds was assessed by measuring sensitization to detergents. Only carvacrol caused damage to the outer membrane of P. aeruginosa.


CONCLUSIONS
The intrinsic tolerance of P. aeruginosa strains to plant volatile compounds is associated with an active efflux mechanism and the barrier function of the outer membrane.


CONCLUSIONS
These findings offer an explanation for the intrinsic tolerance to plant volatile compounds exhibited by P. aeruginosa. The study also confirms that the outer membrane-permeabilizing action of carvacrol, previously reported for the gram-negative bacteria Escherichia coli and Salmonella, extends to monoterpene-tolerant strains of P. aeruginosa.
Cox
S D
SD
School of Science and Primary Industries, Charles Darwin University, Darwin, Australia. sean.cox@cdu.edu.au
Markham
J L
JL
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D000081007:Cymenes; D003902:Detergents / Q000494:pharmacology; D024881:Drug Resistance, Bacterial; D004357:Drug Synergism; D008826:Microbial Sensitivity Tests; D039821:Monoterpenes / Q000494:pharmacology; D009822:Oils, Volatile / Q000494:pharmacology*; D010938:Plant Oils / Q000494:pharmacology*; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000254:growth & development
D000900:Anti-Bacterial Agents; D000081007:Cymenes; D003902:Detergents; D039821:Monoterpenes; D009822:Oils, Volatile; D010938:Plant Oils; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; C073316:carvacrol