Efeito de extratos de folhas de yacon e nisina sobre a viabilidade de Staphylococcus aureus in vitro e em leite

Abstract

Staphylococcus aureus is an opportunistic pathogen and some strains are capable of producing toxins, an important virulence factor. S. aureus was identified as the etiological agent in 12.9% of outbreaks of Waterborne and Foodborne Diseases in Brazil between 2012 and 2021. Foods most commonly involved in cases and outbreaks of staphylococcal intoxication are milk and dairy products, among others animal products. In addition to rigorous monitoring of hygienic-sanitary conditions when handling milk and dairy products, the use of natural antimicrobials as sanitizing agents has shown promising results in controlling microbial development in foods, which also pleases consumers who are increasingly looking for food more natural and safe. This work aimed to verify the effect of yacon leaf extract, a potential natural antimicrobial, and nisin A and V, on the growth of S. aureus ATCC 25923 in vitro and in milk. The minimum inhibitory concentration (MIC) was determined in polystyrene 96-well plates using the microdilution technique in BHI broth. The effect of the yacon extract and nisin A on the viability of S. aureus in milk was evaluated by the pathogen cultivation in the food matrix supplemented with different concentrations of both antimicrobials at 37 ºC. On time points 0, 2, 4, 6, and 24 h, aliquots were removed, diluted and plated on BHI agar. The MIC of yacon extract, nisin A and nisin V was 35 µg/mL, 1.4 µM and 1.8 µM, respectively. The effect of the plant extract and the bacteriocin on the bacteria in milk was not conclusive and consistent with results previously reported in the literature. Both yacon extract and acidified isoprapon-2ol showed similar behavior on the staphylococcal inhibition. Nisin also was not able to inhibit bacterial growth in milk. Although in milk results were not as expected, the antimicrobial potential of yacon and nisin is significant in BHI broth, requiring further studies on the subject so that its efficiency in milk and derivatives can be better evaluated.