The susceptibility of a PVL-negative Staphylococcus aureus isolate to antibiotics and essential oils

Since the early reports of methicillin resistance in Staphylococcus aureus in the mid twentieth century, antibiotic resistance has been an important health issue. Multidrug resistance (MDR) has subsequently been identified as a problem in healthcare due to its association with increased treatment options and costs. Despite the problems of resistance, antibiotics remain an important therapeutic option for bacterial infections in humans. Antimicrobial properties have also been identified in various plants products including essential oils (EOs). In this study, a S. aureus isolate was screened for susceptibility to different antibiotic groups and EOs. Methods: Antibiotic susceptibility testing based on the BSAC guidelines was performed on the isolate. the antibiotics tested included cefoxitin, tetracycline, gentamicin, ciprofloxacin, erythromycin and rifampicin. Multiplex PCR was also performed to determine the presence/absence of the PVL gene and mecA in this isolate. The effect of EOs (lemongrass, grapefruit, lime, bergamot, citral, geranium, lemon and limonene) against the S. aureus strain was tested using disc diffusion assay and determination of MICs and MBCs. Results: The S. aureus isolate was resistant to four of six antibiotic groups including methicillin. However the isolate was inhibited by different EOs lemongrass, grapefruit, lime, bergamot, citral, geranium however lemon EO and limonene did not inhibit the S. aureus isolate. The most inhibitive activity (100%) was observed with Lemongrass EO and citral. The MIC of the EOs ranged between 0.03% and 2% (v/v), while the MBCs ranged between 0.06% and >4% (v/v). Conclusions: The EOs tested in this study demonstrated antimicrobial activity against a multi antibiotic resistant isolate and can be potentially used as a therapeutic option to reduce bacterial colonisation ex vivo.