Adaptação homóloga e heteróloga e inativação termoquímica de Staphylococcus aureus ao cinamaldeído

Abstract

Stapylococcus aureus is a gram -positive, mesophilic, pathogenic bacterium capable of causing food toxin. Several species of Staphylococcus, including S. aureus, stand out for their ability to become resistant to large numbers of antibacterial drugs. Thereby, a growing interest in understanding the mechanisms involved in the adapt ation of microbial cells to environmental conditions has been observed, since antimicrobial adaptation mechanisms contribute to resistance. New measures in the control of microorganisms must be taken in order to find biocides with a broad spectrum of actio n. A possible alternative for the control of pathogenic and / or deteriorating microorganisms are the essential oils and their compounds, since their antimicrobial action has been proven. This study’s objective was to evaluate the antimicrobial activity, the adaptation and the thermochemical death curve of Staphylococcus aureus GL 5674 and Staphylococcus aureus GL 8702 when submitted to a sublethal concentration of cinnamaldehyde (CIN), and to evaluate the capacity of these bacteria of develop adaptation to acid stress and cross-matching between acid stress and CIN. The minimum bactericidal concentrations (MBC) of CIN were determined by the broth microdilution technique, in 96-well microplates. Final concentrations of CIN ranged from 0.05% to 2% (v / v). Minimum inhibitory pH and minimum growth were determined with the aid of lactic acid and pH 6.0; 5.0; 4,5; 4.0; 3.5; 3.0; 2.5 and 2.0. Bacteria were standardized at 10 8 UFC/mL. After, the adaptation of S. aureus to the CIN was performed. To evaluate this adaptation, the cells exposed to sublethal concentrations of cinnamaldehyde were submitted to different concentrations of the same compound (CMB / 2; CMB; 1.2CMB; 1.4CMB; 1.6CMB; 1.8CMB and 2CMB) at which culture was previously exposed. S. aureus cells were classified as capable of adapting when grown on plaques after culturing in the presence of the component at concentrations higher than CIN. Then, the adaptive capacity of S. aureus to CIN and acid stress, as well as their cross-adaptation between CIN and acid stress, was evaluated. For both adaptation and cross-adaptation evaluation cultures of S. aureus were performed in the presence of CIN and minimal growth pH at 37 ° C for 6 hours. A thermochemical deathtime curve of S. aureus GL 5674, when submitted to MBC of CIN, at 37 ° C and 7 ° C, at times of 5, 10, 20, 30 and 35 minutes was performed. The MBC of S. aureus GL 5674 and S. aureus 8702 were 0.25% and 0.5%, respectively. Both strains adapted to CIN, growing at higher concentrations than MBC, when they were previously exposed to sublethal concentrations of CIN. The minimum growth and minimum inhibitory pH values were 4 and 3.5, for both bacteria, which also showed ability to adapt to acid stress. The results showed that the pre-exposure of S. aureus to the sublethal concentrations of CIN and the minimum pH of growth promoted the adaptation and cross-adaptation of this bacterium. The death-time curve showed that when S. aureus is submitted to a MBC of CIN at 7 ° C, this compound does not have antimicrobial activity on this bacterium. When S. aureus was submitted to CIN at 37 ° C in 35 minutes of contact, no viable S. aureus cells were detected (reduction of 7,653 log UFC/mL). In this study, the profile of S. aureus proteins, when submitted to the sublethal concentration of CIN, was also carried out, suggesting that modifications in the bacterial proteome occur.