The Inhibitory Effects of 2 Commercial Probiotic Strains on the Growth of Staphylococcus aureus and Gene Expression of Enterotoxin A

Background: Food-borne intoxications are current problems in human society and most of them are caused by the enterotoxins of Staphylococcus aureus. Staphylococcal enterotoxin A (SEA) is the most frequently responsible for staphylococcal food poisoning outbreaks. From a food safety and human health point of view, lactic acid bacteria (LAB) may provide a promising strategy to combat the pathogenic bacteria, particularly S. aureus. Objective: The objective of this study was to evaluate the inhibitory activity of two commercial lactobacillus strains on growth and enterotoxin A production by S. aureus. Moreover, the inhibitory effect of these strains on gene expression of enterotoxin type A was assessed using realtime Polymerase chain reaction (PCR). Materials and Methods: In this study the inhibitory effect of two commercial probiotic strains, Lactobacillus acidophilus (LA5) and Lactobacillus casei 01 on the growth and enterotoxin production of S. aureus was evaluated at 25 and 35°C. The gene expression of SEA of S. aureus was also evaluated by real time (RT) PCR technique. Results: The lactobacillus strains decreased the bacterial count at both temperatures compared with the control group. This reduced effect was greater at 25°C (3 log/CFU) than 35°C (2 log/CFU). The production of SEA, SEC and SEE was inhibited by the lactobacillus strains. Furthermore, the gene expression of SEA was significantly suppressed in S. aureus co cultured with studied lactobacillus strains and the greatest downregulation of sea (10.31 fold) was observed in coincubation of S. aureus with LC01 at 25°C. Conclusion: This research raises important implications for the potential use of LAB as a natural preservative in foodstuffs by correct microbial ecology of the environment and a new approach for biocontrol of S. aureus.