Atividade antimicrobiana e mecanismos de ação do óleo essencial de Plectranthus amboinicus frente a cepas multirresistentes de Klebsiella pneumoniae

Abstract

This work describes the first study about the antimicrobial activity and mechanisms of action of the subinihibitory and inhibitory concentrations essential oil from leaves of Plectranthus amboinicus against standard strain of Klebsiella pneumoniae and multresistant clinical isolates of the bacterium. The minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC), the rate of killing and the pH sensitivity of the essential oil were determined through microplate-microdilution tests. Subinihibitory and inhibitory concentrations of Plectranthus amboinicus essential oil were tested in order to check their action on K. pneumoniae membrane permeability, capsule expression, urease activity and cell morphology. The MIC and MBC of the essential oil were 0.09± 0.01% and resulted remarkably in complete inhibition of the bacterial growth after 2 hours, when the bacteria were exposed to twice the MIC of the essential oil. A better MIC was found when neutral or alkaline pH broth was used. Cristal violet uptake which represented altered permeability was considered to be significant when twice the MIC of the essential oil was used compared to the untreated group (p<0.05); Reduction of the urease activity could be found when all the subinihibitory concentrations were tested compared to the untreated group (p< 0.001). Is the result was an indicative that there was alteration on the capsule expression and membrane leakage, which could be demonstrated by the Anthony´s method and atomic force microscopy, respectively.