Preliminary studies regarding antimicrobial effect of various kuwanon G – antibiotic combinations on some MRSA strains

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) is a constant therapeutic challenge in humans and animals, due to the limited range of antibiotics that can be used for the management of infections. This preliminary study is based on the assessment of the antibacterial activity of kuwanon G (a prenylated flavonoid present in white mulberry, Morus alba L., Moraceae) and its interactions with various antibiotics (oxacillin, amoxicillin, erythromycin and gentamicin) against four MRSA clinical isolates (MRSA T1 – T4). The sources of all clinical isolates resistant to cefoxitin and oxacillin were infections (recurrent otitis, pyoderma and laryngopharyngitis) in dogs. Minimum inhibitory concentrations (MICs) for kuwanon G and antibiotics were determined by the microdilution method. Interactions between kuwanon G and antibiotics were evaluated by the checkerboard method and time-kill assay. MICs varied between 6.25 and 12.5μg/mL for kuwanon G alone against all four MRSA clinical isolates. According to the calculated fractional inhibitory concentration index, various combinations were synergistic and additive. Microbicidial time has confirmed the synergy as the logarithmic reductions of colony-forming units obtained for the combinations of kuwanon G and some antibiotics were 2log10 lower than the logarithmic reductions obtained for the most potent/active component of the combination. The obtained results are promising, taking into account the antibacterial activity of kuwanon G, as well as its synergistic effects with the most used antibiotics. This study reports on the antibacterial activity of kuwanon G and suggests its ability to act synergistically with antibiotics; combinations effective in combating Gram-positive including MRSA infections might be developed.