title: Effect of subinihibitory and inhibitory concentrations of Plectranthus amboinicus (Lour.) Spreng essential oil on Klebsiella pneumoniae.
abstract: 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. 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. Subinhibitory and inhibitory concentrations of the essential oil were tested in order to check its 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%. A complete inhibition of the bacterial growth was observed after 2 h of incubation with twice the MIC of the essential oil. A better MIC was found when neutral or alkaline pH broth was used. 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. The urease activity could be prevented when all the subinhibitory concentrations were tested in comparison to the untreated group (p<0.001). Alteration of the bacterial morphology besides inhibition of the capsule expression was verified by atomic force microscopy, and Anthony's stain method, respectively. Our data allow us to conclude that the essential oil of P. amboinicus can be a good candidate for future research.
authors: Departamento de Análises Clínicas e Toxicológicas, Faculdade de Farmácia, Odontologia e Enfermagem, Universidade Federal Ceará, Rua Capitão Francisco Pedro 1210, CEP 60430-370, Fortaleza, Ceará, Brazil. thially@gmail.com
authors: Thially Braga
authors: TB
authors: Gonçalves
authors: Milena Aguiar
authors: MA
authors: Braga
authors: Francisco F M
authors: FF
authors: de Oliveira
authors: Gilvandete M P
authors: GM
authors: Santiago
authors: Cibele B M
authors: CB
authors: Carvalho
authors: Paula
authors: P
authors: Brito e Cabral
authors: Thiago
authors: T
authors: de Melo Santiago
authors: Jeanlex S
authors: JS
authors: Sousa
authors: Eduardo Bedê
authors: EB
authors: Barros
authors: Ronaldo Ferreira
authors: RF
authors: do Nascimento
authors: Aparecida T
authors: AT
authors: Nagao-Dias
mesh_terms: D000900:Anti-Bacterial Agents / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D002463:Cell Membrane Permeability / Q000187:drug effects; D024901:Drug Resistance, Multiple, Bacterial; D006863:Hydrogen-Ion Concentration; D007711:Klebsiella pneumoniae / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology; D008826:Microbial Sensitivity Tests; D050296:Microbial Viability / Q000187:drug effects; D009822:Oils, Volatile / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D018515:Plant Leaves / Q000737:chemistry; D010938:Plant Oils / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D031346:Plectranthus / Q000737:chemistry*; D014510:Urease / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D009822:Oils, Volatile; D010938:Plant Oils; D014510:Urease