Effect of Lactobacillus rhamnosus on growth of Listeria monocytogenes and Staphylococcus aureus in a probiotic Minas Frescal cheese

Abstract

This study aimed to evaluate the effect of Lactobacillus rhamnosus GG on growth of Staphylococcus aureus and Listeria monocytogenes, inoculated alone or in combination on surface of Minas Frescal cheeses, during storage for 21 days at 7 °C. Survival percentages of each individual bacterial species after exposure to in vitro simulated gastrointestinal conditions (SGC) were also determined. The addition of L. rhamnosus did not affect (P > 0.05) pH, moisture, fat, protein and texture profile of Minas Frescal cheeses. L. rhamnosus was able to survive in suitable counts (>6 Log CFU/g) in cheeses from the 7th day of storage, with high survival (>74.6-86.4%) after SGC. An inhibitory effect of L. rhamnosus on L. monocytogenes was observed in cheeses (decrease of 1.1-1.6 Log CFU/g) and after SGC (20% reduction in the survival). No inhibitory effect of L. rhamnosus was observed on S. aureus counts (P > 0.05), and this microorganism did not survive the exposure to SGC. In conclusion, the addition of L. rhamnosus in Minas Frescal cheese has a potential for L. monocytogenes inhibition. Further studies are necessary to elucidate the mechanisms involved in the inhibition process and determine the survival ability of the bacterial species evaluated in in vivo experiments.

Keywords: Cheese; L. monocytogenes; L. rhamnosus; Probiotic; S. aureus.