Homologous and heterologous adaptation and thermochemical inactivation of Staphylococcus aureus to cinnamaldehyde

Staphylococcus aureus causes food intoxication and can become resistant to a large number of drugs. Thus, there is a growing interest in understanding the mechanisms involved in the adaptation of bacterial cells to environmental stresses or to antimicrobial agents. In this context, we evaluated the cinnamaldehyde (CIN) MBC for two contaminating food strains of S. aureus (GL 5674 and GL 8702) and tested the hypothesis that the exposure of these strains to sublethal concentrations of CIN and pH could increase their resistance to this antimicrobial, to acid stress and also to stress at high temperatures. Thus, the ability of the strains to adapt to CIN and acid stress was evaluated, as well as the cross adaptation between acid stress and CIN. The strains GL 5674 and GL 8702 of S. aureus are sensitive to CIN in MBCs of 0.25% and 0.5% respectively, proving the antibacterial potential of this compound, but we proved the hypothesis of homologous adaptation to CIN. The strains grew in concentrations higher than the MBC after being previously exposed to sublethal concentrations of CIN. It was also observed heterologous adaptation of the strains, which, after exposure to the minimum pH of growth, were able to grow in concentrations greater than the MBC of CIN. GL 5674 showed greater adaptive plasticity, considerably reducing its minimum inhibitory pH and increasing its MBC after adaptation. Our results show a positive effect of adaptation to CIN, on the resistance of S. aureus (p <0.0001) to CIN, at a temperature of 37 ° C. However, in the absence of adaptation, the presence of CIN in S. aureus cultures maintained at 37 ° C, associated with increased exposure time showed an efficient bactericidal effect. Our results call attention to the conscious use of CIN as an antimicrobial agent and presents the possibility of using CIN, associated with the temperature of 37 ºC and the exposure time of 35 min, as a promising measure for the elimination of pathogenic strains .