RESUMO: "Atividade antibacteriana do óleo essencial de Origanum vulgare L. (Lamiaceae) contra bactérias multiressistentes isoladas de pacientes nosocomial". Os antibióticos permanecem como a principal opção terapêutica para tratar infecções bacterianas, no entanto, existe a desvantagem de aumentarem a resistência bacteriana, e como alternativa, destaca-se a pesquisa de antimicrobianos de origem vegetal. Neste trabalho objetivou-se determinar in vitro a atividade antibacteriana do óleo essencial de Origanum vulgare L. (Lamiaceae) (orégano), sobre bactérias multirresistentes isoladas de materiais biológicos. Foram usadas 24 linhagens de bactérias de origem hospitalar, divididas em seis espécies distintas, que foram inibidas pelo óleo essencial no "screening" preliminar, realizado utilizando-se a técnica de difusão em ágar. A CIM foi determinada pelo método de microdiluição, partindo-se de soluções com as concentrações finais: 8 até 0,125% com os seguintes resultados: As quatro amostras (100%) de Escherichia coli, Enterococcus faecalis e MRSA foram inibidas pelo óleo essencial na concentração de 0,125%. Três amostras (75%) de Acinetobacter baumannii por 0,125% e uma amostra (25%) por 0,5%; Klebsiella pneumoniae (75%) por 0,125% e 25% por 0,25%; Pseudomonas aeruginosa (75%) por 0,5% e 25% por 0,25%. A CIM variou de 78 a 83%. Concluiu-se com base nos dados obtidos, que não houve diferença na concentração bactericida mínima (0,5%) do referido óleo tanto para os microrganismos Gram positivos quanto para os Gram negativos. Unitermos: Origanum vulgare, infecções bacterianas, bactérias multirresistentes.ABSTRACT: Antibiotics are considered the main therapeutic option to treat bacterial infections; however, there is the disadvantage of increasing bacterial resistance. Thus, the research of antimicrobials of plant origin has been an important alternative. This work aimed at determining the in vitro antibacterial activity of the essential oil of Origanum vulgare L. (Lamiaceae) on multiresistant bacteria isolated from biological materials. 24 strains of nosocomial bacteria were used and divided into six different species that were inhibited by the essential oil in the preliminary "screening" which was accomplished by the diffusion technique in agar. MIC was determined by the microdilution method, beginning with solutions with the final concentrations: 8 up to 0.125% with the following results: The four samples (100%) of Escherichia coli, Enterococcus faecalis and MRSA were inhibited by the essential oil at the concentration of 0.125%. Three samples (75%) of Acinetobacter baumannii at 0.125% and a sample (25%) at 0.5%; Klebsiella pneumoniae (75%) at 0.125% and 25% at 0.25%; Pseudomonas aeruginosa (75%) at 0.5% and 25% at 0.25%. MIC varied from 78 to 83%. It was concluded through the obtained data that there was not difference in the minimum bactericidal concentration (0.5%) of the referred oil for Gram positive as well for Gram negative microorganisms.

Aim:To evaluate in vitro, the antimicrobial effect of Cymbopogon citrates (lemon grass), Plectranthusamboinicus (Mexican mint) and Conyzabonariensis (hairy fleabane) tinctures as well as pure and diluted commercial mouth washes (Malvatricin®, Periogard® and Listerine®) on wild isolates of Streptococcusmutans and reference strains of S. mutans, Streptococcus salivarius, Streptococcus oralis and Lactobacillus casei by determination of minimum inhibitory dilution (MID).Materials and Methods:0.12% chlorhexidine and 70% corn alcohol were used as positive and negative controls, respectively. Saliva samples were collected from 3 volunteers and seeded in MSB broth to obtain Streptococcus isolates after 72-hour incubation. Using the agar diffusion method, susceptibility tests were performed with overnight incubation in microaerophilia at 37°C. All tests were performed in duplicate.Results:The bacterial species were resistant to the tinctures and Listerine®, but were susceptible to 0.12% chlorhexidine, Malvatricin® and Periogard®, with MIDs ranging from 12.5% to 1.56%.Conclusions:Plectrantusamboinicus, Conyzabonariensis and Cymbopongoncitratus tinctures and Listerine® did not show inhibitory action against the tested biofilm-forming bacteria.

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