DETERMINATION OF THE EFFICACY OF PHOSPHOMYCIN ON CLINICAL ISOLATES OF METHICILLIN-RESISTANT STAPHYLOCOCCUS AUREUS

Staphylococcus aureus is a Gram-positive coccus that can cause a range of
infections. Methicillin resistance in these bacteria is often in companion with resistance to multiple
antibiotics. High prevalence of these isolates can cause treatment failure. Phosphomycin is a
Peptidoglycan biosynthesis inhibitor that is used in treating of infections caused by multi-drug
resistant bacteria .The aim of this study was the investigation of the effect of phosphomycin on clinical
isolates of methicillin-resistant S.aureus.
Materials & Methods: This study was conducted on 43 clinical isolates of methicillin-resistant
S.aureus that were collected and identified using standard methods. Susceptibility of isolates to
different antibiotics was tested by disk diffusion method. The minimum inhibitory and bactericidal
concentrations of phosphomycin serial dilutions of antibiotic were prepared in broth medium in
concentrations ranging between 0.25-128 mg/L after that isolates were inoculated to each tube. S.
aureus ATCC 25923 was used as reference strain.
Results: Among the strains, 16.3% were sensitive to all investigated concentrations and 11.6%were
resistant. The average amounts of minimum inhibitory and minimum bactericidal concentrations for
the other isolates were 57.16±51.05 and 74.70±49.72 μ/ml, respectively. Regarding the standard
definitions, a total of 44.2% of isolates were resistant and 55.8% were sensitive to phosphomycin.
Conclusion: Due to the higher resistance of isolates tested in this study, compared with others, it
seems that there is a need for exact evaluation of susceptibility tests and being cautious in using of
phosphomycin alone, as well as designing another studies in order to evaluate the use of the
combination of phosphomycin with other antibiotics against methicillin-resistant S. aureus.