Effects of Zataria multiflora Boiss. essential oil on growth and gene expression of enterotoxins A, C and E in Staphylococcus aureus ATCC 29213

Abstract

Staphylococcal food poisoning results from the consumption of food in which enterotoxigenic staphylococci have grown and produced toxins. The present study was conducted with three principal aims: i) to determine the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of Zataria multiflora Boiss. essential oil (EO) against Staphylococcus aureus ATCC 29213, ii) to evaluate the effect of subinhibitory concentrations (subMIC) of EO on the growth of bacteria over 72 h (at 25 and 35 °C), and iii) to investigate the expression of genes involved in the production of staphylococcal enterotoxins SEA, SEC and SEE over 72 h at 35 °C. The MIC and MBC of Z. multiflora Boiss. EO were 0.03 and 0.04%, respectively. Colony counting at 24, 48 and 72 h of 3 day cultures grown in the presence of 75%MIC of the EO showed that the growth rate was reduced 2.16, 2.78 and 2.91 log 10 cfu/ml at 25 °C, and 1.34, 2.35 and 2.57 log 10 cfu/ml at 35 °C, respectively, compared to control cultures. SubMIC levels of EO also significantly decreased the expression of staphylococcal enterotoxin (SE)-related genes and therefore the production of SEs in a dose dependent manner. For example, when cultured with 75% MIC, the transcriptional levels of sea, sec, see and agrA were decreased 11.7, 9.3, 10.45 and 10.3 fold after 18 h and 13.9, 11.21, 12.44 and 12.52 fold after 72 h in comparison to control, respectively.