The urease activity could be prevented when all the subinhibitory concentrations were tested in comparison to the untreated group ( p < 0.001). Alteration in membrane permeability was found by the increase of crystal violet uptake when the bacteria were incubated with twice the MIC levels of the essential oil. A better MIC was found when neutral or alkaline pH broth was used. A complete inhibition of the bacterial growth was observed after 2 h of incubation with twice the MIC of the essential oil. The MIC and MBC of the essential oil were 0.09 ± 0.01%. pneumoniae membrane permeability, capsule expression, urease activity and cell morphology. Subinhibitory and inhibitory concentrations of the essential oil were tested in order to check its action on K. The minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC), the rate of kill and the pH sensitivity of the essential oil were determined by microdilution tests performed in 96-well plates. We evaluated the antimicrobial activity and some mechanisms used by subinhibitory and inhibitory concentrations of the essential oil, obtained from leaves of Plectranthus amboinicus, against a standard strain of Klebsiella pneumoniae and 5 multiresistant clinical isolates of the bacteria.
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