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

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

The antibacterial activity and synergies between morusin and some antibiotics against MRSA strains – preliminary study

Mulberry (Morus alba L., Moraceae) is one of the most valuable and rich in phytochemicals plant. Morusin is a prenylated flavonoid present in mulberry roots and leaves. The in vitro antibacterial activity of morusin and its interactions with conventional antibiotics (oxacillin, amoxicillin and gentamicin) were evaluated against four methicillin resistant Staphylococcus aureus clinical isolates (MRSA T1 – T4) with resistance to oxacillin and cefoxitin which had been isolated from dogs with various pathologies. Minimum inhibitory concentrations (MICs) were determined by the microdilution method. The interactions were assessed by the chequerboard method - with interpretation through fractional inhibitory concentration index (FICI) and isobologram analysis. The interactions were confirmed by the time-kill assay. MICs varied between 3.125 and 6.25μg/mL for morusin alone against all four MRSA clinical isolates. Chequerboard method showed synergies for the combinations: morusin – oxacillin (FICI=0.024 - 0.27), morusin – amoxicillin (FICI=0.024 - 0.27) and morusin - gentamicin (FICI=0.05 - 0.12) against all four tested isolates. Time-kill assay determined synergies for the following combinations: morusin – oxacillin against MRSA T1, morusin – amoxicillin against MRSA T2 and morusin - gentamicin against all four isolates. Our preliminary study evaluated the antibacterial activity of morusin and its ability to act synergistically with antibiotics; these results suggest that morusin might be a promising strategy to overcome antibiotic resistence

Prenylated phenolics as promising candidates for combination antibacterial therapy: morusin and kuwanon G

Combination of antibiotics with natural products is a promising strategy for potentiating antibiotic activity and overcoming antibiotic resistance. The purpose of the present study was to investigate whether morusin and kuwanon G, prenylated phenolics in Morus species, have the ability to enhance antibiotic activity and reverse antibiotic resistance in Staphylococcus aureus and Staphylococcus epidermidis. Commonly used antibiotics (oxacillin, erythromycin, gentamicin, ciprofloxacin, tetracycline, clindamycin) were selected for the combination studies. Checkerboard and time-kill assays were used to investigate potential bacteriostatic and bactericidal synergistic interactions, respectively between morusin or kuwanon G and antibiotics. According to both fractional inhibitory concentration index and response surface models, twenty combinations (14 morusin-antibiotic combinations, six kuwanon G-antibiotic combinations) displaying bacteriostatic synergy were identified, with 4–512-fold reduction in the minimum inhibitory concentration values of antibiotics in combination. Both morusin and kuwanon G reversed oxacillin resistance of methicillin-resistant Staphylococcus aureus. In addition, morusin reversed tetracycline resistance of Staphylococcus epidermidis. At half of the minimum inhibitory concentrations, combinations of morusin with oxacillin or gentamicin showed bactericidal synergy against methicillin-resistant Staphylococcus aureus. Fluorescence and differential interference contrast microscopy and scanning electron microscopy showed an increase in the membrane permeability and massive leakage of cellular content in methicillin-resistant Staphylococcus aureus exposed to morusin or kuwanon G. Overall, our findings strongly indicate that both prenylated compounds are good candidates for the development of novel antibacterial combination therapies