Adaptação de Staphylococcus aureus aos estresses químicos: óleos essenciais, antibióticos e pH

Abstract

Staphylococcus aureus is a pathogenic Gram-positive bacterium that does not produce spores, which can develop in a wide temperature range and cause food toxinfection, is the most important agent in hospital infections. Due to their high resistance to commercial antimicrobials, alternatives have been proposed, especially those of natural origin, mainly essential oils (EO) and their major components. The objective of this study was to evaluate the ability of direct adaptation and cross-adaptation of S. aureus to EO, antibiotics and pH. The minimum bactericidal concentrations (MBC) of the essential oils of cinnamon, oregano, peppermint and lavender on S. aureus were determined: 0.062; 0.25; 1.0 and 2.0% (v / v), respectively. Afterwards the bacterial cells were submitted to the sublethal stresses generated by EO at concentrations of 1/4 MBC, 1/8 MBC and 1/16 MBC, for 6 and 24h. The adapted cells were exposed to different concentrations of essential oils and the antibiotic sensitivity test (cefuroxime, chloramphenicol, norfloxacin, novobiocin, tetracycline). After determination of minimum inhibitory pH and minimum growth, 4.5 and 5.0, respectively, S. aureus was submitted to acid stress (pH 5) for 6 and 24h. The cells were then submitted to the antibiotic sensitivity test. The direct adaptation of S. aureus was observed only at concentrations of 1/4 and 1/8 of the MBC of cinnamon oil after 6h of exposure. Peppermint oil, after 6h exposure to sublethal stress and oregano oil, in both times, led to the reduction of the sensitivity of the cells to EO. The pre-exposure of the cells for 24 hours only led to direct adaptation in peppermint oil. The strain was not able to adapt to lavender EO at any of the sublethal concentrations used. The cross-adaptation between EO and antibiotics was dependent not only on the essential oil and antibiotic used but also on the time of exposure to stress. The increase in cell sensitivity to novobiocin after pre-exposure to 1/4 MBC of cinnamon oil for 6 hours and 1/16 MBC of peppermint oil was observed for 24 hours. In general, it can be concluded that the strain studied presented capacity to respond to the stresses evaluated.