Eradication of methicillin resistant S. aureus biofilm by the combined use of fosfomycin and β-chloro-L-alanine

BACKGROUND AND OBJECTIVES Biofilm formation is an important virulence factor for methicillin-resistant Staphylococcus aureus (MRSA). Fosfomycin is a borad-spectrum antibiotic with inhibitory effects on biofilm production and β-Chloro-L-alanine (β-CLA) is an amino acid analog. The aim of this study was to determine effect of the combination of fosfomycin and β-CLA on biofilm production by MRSA isolates. Also, the clonal relatedness of the isolates was evaluated. MATERIALS AND METHODS To determine the ability of biofilm production by 42 MRSA isolates, microtiter plate method was used. Antibacterial activities of fosfomycin and β-CLA were investigated by determining MICs and MBCs. Antibiofilm activities were measured in the presence of sub-MIC concentrations of fosfomycin, β-CLA or a combination of both. RAPD-PCR was used for investigating the clonal relationship between isolates by the two specific primers. RESULTS 21.4% of isolates were strong and 5% were moderate biofilm producers. The effect of fosfomycin plus β-CLA treatment on biofilm production was significantly different from non-treated, fosfomycin and β-CLA groups (p=0.00, 0.004 and 0.000 respectively). RAPD-PCR analysis revealed that the RAPD1 primer had more discriminatory power. The Sizes of RAPD-PCR bands ranged from 150 bp to 1500 bp and the number of bands varied from 1 to 13. CONCLUSION Clonal relatedness of isolates showed that the majority of biofilm producing isolates had identical pattern and only three isolates showed more than 80% similarity. The combination of fosfomycin and β-CLA could be introduced as an excellent mixture for eradication of MRSA biofilms in vitro.