Comparison of the effect of grapefruit essential oil on gene expression of two Staphylococcus aureus isolates in biofilms

Metabolic processes are associated with pathogenicity in Staphylococcus aureus and the metabolic states are different in planktonic cells and in biofilms. The effect of grapefruit essential oil (EO) on one S. aureus strain was previously found to increase metabolic activity using the XTT assay. In this study the effect of grapefruit EO (Citrus paradisi) on changes in gene expression of two S. aureus biofilms was investigated using the RT-PCR. Methods: Two S. aureus strains (CA MRSA MW2 and PVL CA MSSA) were grown in planktonic state in 10ml sterile polypropylene tubes for 6 hours in a shaking incubator at 37°C. The biofilms were formed in a microtitre plate for 24 hours, treated with grapefruit EO for another 24 hours under shaking conditions at 37°C. RNA extraction was performed using the Qiagen Rneasy kit and the PowerBiofilm™ RNA Isolation Kit. Gene expression of five target genes (icaA, icaD, cap8C, luxS and sodA) was performed using the using the Bio-Rad Mini Opticon™ System. Results: Gene expression was higher in planktonic cells than in biofilms and between the two strains, gene expression was higher in the CA MRSA MW2 strain than in the PVL CA MSSA. Following exposure to grapefruit EO, there were changes in gene expression in icaD, cap8C, luxS and sodA genes between the two strains. The SodA gene was upregulated in planktonic cells but down-regulated in CA MRSA MW2 biofilms while this gene was upregulated in the PVL CA MSSA strain. Conclusions: The data from this study highlights the multifactorial nature of gene expression in biofilms. The upregulation of the sodA the soda gene in the PVL CA MSSA biofilm might be as a result of oxidative stress.