BACKGROUND: Staphylococcal foodborne intoxication is the most common cause of foodborne illnesses by Staphylococcus aureus strains and most are caused by the enterotoxins of S. 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 in the fight against S. aureus.OBJECTIVES: Increasing product shelf life, and enhancing the safety of food and human health using natural microflora are the aims of this study. METHODS: In this study we evaluate the inhibitory effects of three lactobacillus strains isolated from yoghurt, namely lactobacillus acidophilus, lactobacillus fermentum and lactobacillus paracasei, on the growth and enterotoxin production of Staphylococcus aureus by co-incubating each strain with enterotoxigenic S. aureus at two temperatures: 25 and 35°C. Expression of the SEA gene of S. aureus was assessed by real-time PCR. RESULTS: All the strains decreased the bacterial count at both temperatures compared to the control. This effect was greater at 25°°C than at 35°C. The production of SEA, SEC and SEE was inhibited by all the isolates tested. Furthermore, expression of the sea gene was significantly suppressed in S. aureus co-cultured with the lactobacillus isolates and the greatest impact was on Lactobacillus acidophilus at 35 ° C. CONCLUSINS: This research highlights the potential of lactic acid bacteria isolated from traditional foods for use as natural preservatives in foodstuffs and suggests a new approach for biocontrol of Staphylococcus aureus.

BACKGROUND: Bacterial resistance to antibiotics is a crucial public health problem. Essential oils (EOs) possess antimicrobial effects and have been screened as potential natural antimicrobial compounds. OBJECTIVES: This study was conducted to compare the effects of Eugenia caryophyllus (clove) and Origanum compactum (oregano) EOs on the growth of Staphylococcus aureus and the expression of the SEA, SEC and SEE genes. METHODS: The minimum inhibitory concentrations (MIC) of EOs and growth of bacterium at subMIC levels of EOs was determined. Enterotoxin detection was done using a commercial SE visual immunoassay kit after 18, 24, 48 and 72 h. Gene expression of enterotoxins was evaluated through RNA extraction, DNA synthesis and performing real time-PCR using specific primers for each SE. RESULTS: MIC of clove and oregano were 2 µl/ml and 1µ l/ml, respectively. Colony counts at 48 and 72h of cultures grown at 75% MIC of clove oil showed the growth rate was reduced 1.67 and 1.83 log10 cfu/ml compared to the control, and in the case of oregano at 75% MIC the decreases in growth rate were 2.25 and 2.68 log10 cfu/ml, respectively. When the target bacterium is cultured in the presence 75% subMIC of EOs, the transcript levels of sea, sec, see and the regulatory gene (agrA) were decreased 8.81, 9.13, 9.08 and 8.32 fold in the case of clove, and 11.56, 9.96, 11.07 and 11.15 fold in the case of oregano, compared to the control. CONCLUSIONS: The growth, gene expression and as a result secretion of enterotoxins A, C and E by S. aureus were decreased significantly at subMIC levels of EOs, especially at 75% MIC.