The Influence of Essential Oil Compounds on Antibacterial Activity of Mupirocin-Susceptible and Induced Low-Level Mupirocin-Resistant MRSA Strains

Because of the bacterial drug resistance development, it is reasonable to investigate chemical compounds capable of preventing the spread of resistance to mupirocin (MUP), commonly used in staphylococcal eradication. The objective of the study was to verify the influence of essential oil compounds (EOCs) on the antibacterial activity of MUP against mupirocin-susceptible (MupS) and induced low-level mupirocin-resistant (MupRL) methicillin-resistant Staphylococcus aureus (MRSA) strains. The following parameters were examined: MRSA(MupS) and MRSA(MupRL) susceptibility to EOCs (1,8-cineole, eugenol, carvacrol, linalool, (-)-menthone, linalyl acetate, and trans-anethole), the bacterial cell size distribution, and chemical composition by the use of Fourier Transform Infrared Spectroscopy (FTIR) and Raman spectroscopies. The MRSA(MupS) and MRSA(MupRL) strains were susceptible to all tested EOCs. 1,8-cineole and (-)- menthone showed synergistic activity against MRSA(MupS) in combination with mupirocin, whereas 1,8-cineole exhibited synergistic activity against MRSA(MupRL) as well. In-depth analysis showed that both MRSA(MupS) and MRSA(MupRL) displayed similar distributions of the bacterial cell size. The FTIR and Raman spectra of the MRSAMupS and MRSA(MupRL) strains showed differences in some regions. New bands in the MRSA(MupRL) Raman spectrum were observed. It was concluded that the use of 1,8-cineole in combination with mupirocin can increase the mupirocin activity against the MRSA(MupS) and MRSA(MupRL) strains.