Antibacterial activity of Thymus vulgaris essential oil alone and in combination with cefotaxime against BLAESBL producing multidrug resistant enterobacterial strains

The dissemination of multi drug-resistant enterobacterial strains is considered a worldwide public health problem. Among the resistance mechanisms, extended-spectrum beta-lactamases (ESBLs) are now widespread in enterobacterial strains, leading to serious problems for the antimicrobial management of infections. The purpose of this work was to study the antibacterial effects of Slovakian origin Thymus vulgaris essential oil (TVEO) both alone and combined with cefotaxime against blaESBL producing enterobacterial strains. Gas chromatograph-mass spectrometer (GC/MS) was used for the determination of TVEO composition. In the current study, the effect of TVEO was studied on eight multidrug resistant enterobacterial strains, including blaESBL (blaCTX-M-!) and blaSHV-12) producing multi drug resistant enterobacterial strains, which were previously characterized. Antibacterial activity of TVEO against the enterobacterial strains was investigated by disc diffusion assay and minimum inhibitory concentration (MIC). The synergistic interaction between TVEO and cefotaxime was determined by checkerboard test. GC/MS analysis identified thymol, p-cymene and linalool as the major components present in the TVEO. TVEO showed an unexpected high antibacterial activity against all the studied multi drug resistant enterobacterial strains, including blaESBL producing isolates, with inhibition zones and MIC values in the range of 24-40 mm/10 microL and 2.87-11.5 micro/mL, respectively. TVEO showed variation in the synergistic effects in combination with cefotaxime on blaESBL producing isolates. These results confirm the potential of TVEO to be used alone against ESBL- and non ESBL producing multidrug resistant enterobacterial isolates, and in combination with cefotaxime against some blaESBL producing enterobacterial isolates.