Combined Application of Essential Oil Compounds and Bacteriophage to Inhibit Growth of Staphylococcus aureus In Vitro

Staphylococcus aureus is considered an important human pathogen. This study aimed to investigate the combination of essential oil compounds (EOCs) and bacteriophage as alternative antimicrobials to control S. aureus in vitro. Here, four EOCs (alpha-pinene, 3-carene, (+)-limonene, (1S)-(−)-β-pinene) were evaluated by disc diffusion assay (DDA) and growth inhibition assay (GIA) to determine inhibitory effects against five strains of S. aureus. Phage adsorption assays were performed with phage K up to 120 h at 6, 13, and 37 °C to determine lytic activity. Combinations of phage K and EOCs against S. aureus were also evaluated at 37 °C. Alpha-pinene exhibited significantly greater inhibition towards S. aureus strains when compared to other EOCs tested by the DDA. GIAs indicate that all S. aureus strains exhibited significantly reduced growth (P < 0.006) over a 48-h period when exposed to EOCs. Phage adsorption assays indicate that phage K has high lytic activity at 37 °C with at least a 1.5-log increase in the number of plaque-forming units (PFU) over 6 h when compared to 6 and 13 °C. S. aureus strains showed significantly reduced growth (P < 0.05) when treated with combined phage K and EOCs. Results from the combined effect of EOC and phage indicate that phage alone inhibits S. aureus in vitro at 37 °C as effectively as EOCs alone or in combination with phage with variability between strains. The results from DDA, GIA, and phage adsorption assays indicate that select EOCs and phage K can be used as antimicrobials against S. aureus in vitro with potential application in situ.