EVALUATION OF THE EFFECT OF PHOSPHOMYCIN ALONG WITH THYMUS VULGARIS ESSENTIAL OIL ON METHICILLIN RESISTANT STAPHYLOCOCCUS AUREUS

Most of the methicillin resistant S.aureus isolates are resistant to many other
antibiotics as well, so they can cause refractory infections. Therefore monitoring and control of these
resistant isolates is always a necessity. Phosphomycin is an extended-spectrum antibiotic that inhibits
synthesis of bacterial cell wall peptidoglycan and is helpful for controlling methicillin resistant
S.aureus infections. However, because of bacteria’s ability of resisting to antibiotics and adaption and
survival in antibiotic-containing environments, studies for finding of natural antibacterial compounds
for treatment of such infections is essential Antibacterial effects of thymus vulgaris on Methicillin
resistant S.aureus has already been shown. In this study the in vitro effects of phosphomycin along
with thymus vulgaris essential oil on methicillin resistant S.aureus isolates were investigated.
Materials & Methods: Forty six Methicillin resistant S.aureus isolates from clinical specimens were
obtained. Minimum inhibitory concentration and minimum bactericidal concentration of
phosphomycin was determined by serial dilutions of antibiotic in broth with concentrations ranging
between 0.25-125 mg/L for each isolate. Also minimum bactericidal concentration of essential oil was
obtained by adding 10-0.078 V/V of it in broth medium. The effect of antibiotic along with essential
oil was measured by adding different concentrations of essential oil in Mueller-Hinton broth medium
in the presence of sub-MBC doses of antibiotic then by adding 1/5 × 106 CFU of each isolate and
incubating test tubes overnight in 37° C. Minimum inhibitory concentration of phosphomycin along
with thyme essential oil was determined for each isolate.
Results: Out of 46 isolates of methicillin-resistant S.aureus, 15% were sensitive to all investigated
concentrations of phosphmycin and 2% were resistant, in total 43.5% of isolates were considered as
resistant and 56.5% as sensitive. Isolates were sensitive to different concentrations of thyme essential
oil. Synergism has been observed in 97.4% of isolates between phosphomycin and thyme essential oil,
in respect of their antibacterial effects.
Conclusion: Regarding to the antimicrobial effects of thyme essential oil and synergistic effect of it
with phosphomycin on most of the methicillin resistant isolates, more investigations for using this
combination as an effective antimicrobial agent at least in topical antimicrobialgents formulations is
advised