Background: Streptococcus pyogenes is a common nosocomial pathogen capable causing skin and soft tissue infections. Successful treatment of these infections has become increasingly complicated with the emergence of bacterial resistance to conventional antibiotics and there is a growing demand for novel treatments. Manuka honey has been shown to inhibit several species of pathogenic organisms, including S. pyogenes (Maddocks et al 2012), and in combination with various antibiotics it has been shown to act synergistically against other species (Jenkins et al 2013; Muller et al 2013). This study aimed to test whether manuka honey and selected antibiotics were synergistic for S. pyogenes.
Method: A reference strain of S. pyogenes (NCTC 10085) and a clinical isolate of S. pyogenes (74721) were challenged with each of eleven antibiotics with and without manuka honey. The antibiotics tested were: ampicillin, azithromycin, cepalexin, ciprofloxacin, clarithromycin, erythromycin, lymecycline, oxacillin, penicillin, rifampicin and tetracycline at concentrations ranging from 512 mg/l – 0.0078 mg/l, and manuka honey (Medihoney, Comvita, NZ) was also tested. The British Society for Antimicrobial Chemotherapy guidelines were used to determine MICs with the broth dilution method in microtitre plates. Sensitivity was also determined for antibiotics and honey alone and in combination by the disc diffusion method. The fractional inhibitory concentrations for each antimicrobial were the determined. Tests were done in triplicate.
Results: Combining each of the antibiotics with manuka honey resulted in either synergistic or additive activity for both test organisms. The clinical isolate was more sensitive than the reference strain, exhibiting lower FIC values overall, with 8 antibiotics showing synergy and 3 antibiotics gave additive results. The reference strain showed 6 synergistic and 5 additive combinations.
Conclusion: Combining antibiotics and manuka honey led to improved activity of antibiotics against S. pyogenes. Honey could potentially be used to increase efficacy of topical antibiotic therapy in clinical practice.