Análise metabolômica de bactérias sob estresse subletal de compostos naturais e seus produtos nanoemulsionados

Abstract

In the present study, the various aspects of microbial adaptation were analyzed in relation to the safety of food environments and the search for new technologies for natural antimicrobial products. Potential microbiological pathogens are constantly the focus of attention in terms of health safety due to cross-adaptation phenomena induced by sublethal doses of antibacterial solutions. Essential oils and their major components appear as an alternative to the usual disinfectants, although further studies are still needed to better understand their applicability. To prevent bacterial adaptation to sanitizers, a different approach was taken to identify, understand and predict the occurrence of tolerant bacteria. Thus, the first study aimed to evaluate the global metabolomic analyses of Salmonella enterica serovar Enteritidis previously exposed to sublethal doses of cinnamaldehyde, citral and linalool. Preliminary tests demonstrated phenotypes of coplanktonic cell adaptation and biofilms of S. Enteritidis when exposed to sublethal doses of linalool, resulting in tolerance to previously lethal citral concentrations. Subsequently, the relative frequency and abundance of metabolites of samples treated with sublethal doses of terpenes (citral and linalool) were similar exhibiting equivalent cellular responses. The discriminatory analysis of OPLS (orthogonal partial least squares) provided a comprehensive view of the similarity between treatments that lead to the conclusion that this model was adequate to detect and predict possible phenomena of adaptation between bacteria against essential oil components. The second study sought new options for prevention and elimination of pathogenic bacteria by bringing nanoemulsion technology to improve the antimicrobial effect and, equally pertinently, the need for a better understanding of the cellular mechanisms of stress induced by sublethal doses of antimicrobial agents. In addition, the combination of nisin usually provide additional shelf life to processed foods. However, it can negatively interfere in the efficiency of the major components of essential oils against pathogenic bacteria. In this sense, natural compounds such as cinnamaldehyde, citral and linalool were tested alone, associated with nisin, and both in nanoemulsified forms in sensitivity tests against Bacillus cereus and a metabolomic test to identify possible changes between treatments. The results showed morphological changes in the structure of B. cereus cells treated with nisin and antagonistic effect of nisin-associated treatments compared to isolated and nanoemulsified treatments. Sensitivity tests and liquid chromatography coupled with mass spectrometry (UHPLC-QTOF-MS) analyses indicated that nisin may react in conjunction with reduced bactericidal efficiency, while the citral effect was pointed out as unaffected by the nisin in nanoemulsions. Therefore, the nanoemulsions of natural compounds were of superior efficiency to the other antimicrobial agents tested and the metabolomic analyses proved useful in understanding the adaptive response induced by sublethal doses in pathogenic bacteria.