Abstract
Methicillin resistant Staphylococcus aureus (MRSA) is the etiologic agent of a wide range of diseases worldwide including the Middle East. Biofilm production is an important virulence attribute in the pathogenesis of device-related MRSA infection. Our aim was to study the bactericidal effect of cephalosporin/fluoroquinolone combinations against MRSA biofilm in vitro and in vivo. The minimal inhibitory concentrations (MICs) were evaluated by microdilution method. All studied MRSA strains were highly resistant to cephalosporins (MIC90, 500 -1,000 mu g/ml). Moxifloxacin showed higher activity than levofloxacin (MIC90, 6.25 and 12.5 mu g/ml, respectively). The combinations were studied using checkerboard technique. Ceftriaxone/moxifloxacin revealed 50% synergistic effect contrary to ceftriaxone/levofloxacin combination (16.7%). Rate of biofilm inhibition was determined by the time kill assay. When biofilm coated catheter was exposed to ceftriaxone and/or moxifloxacin, the combination showed 3-7.5 log reduction compared to the starting point after 24 h while it was only 1-3 and 2-4 log reduction with ceftriaxone and moxifloxacin, respectively. Levels of inflammatory markers as tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) were evaluated by Enzyme-linked immunosorbent assay (ELISA). Co-administration of both antibiotics to bacterial strain challenged rats showed significant reduction in TNF-alpha and IL-6 levels (P < 0.001).