Letters in Applied Microbiology
The susceptibility of the cell-wall free bacterial pathogens Ureaplasma spp. to Manuka honey was examined. The minimum inhibitory concentration (MIC) of Manuka honey for four Ureaplasma urealyticum and four Ureaplasma parvum isolates was determined. Sensitivity to honey was also compared to clinical isolates with resistance to tetracycline, macrolide and fluoroquinolone antibiotics. Finally step-wise resistance training was utilised in an attempt to induce increased tolerance to honey.
The MIC was dependent on the initial bacterial load with 7.5% and 18.0% w/v honey required to inhibit U. urealyticum at 1 and 106 colour changing units (CCU), respectively, and 4.8% and 15.3% w/v required to inhibit U. parvum at 1 and 106 CCU, respectively. MIC values were consistently lower for U. parvum compared with U. urealyticum. Antimicrobial activity was seen against tetracycline resistant, erythromycin resistant and ciprofloxacin resistant isolates at 105 CCU. No resistance to honey was observed with fifty consecutive challenges at increasing concentrations of honey.
This is the first report of the antimicrobial activity of Manuka honey against a cell-wall free bacterial pathogen. The antimicrobial activity was retained against antibiotic resistant strains and it was not possible to generate resistant mutants.