Effect of ceftazidime, amikacin and ciprofloxacin on biofilm formation by some enterobacterial clinical isolates.

The effect of sub-minimal inhibitory concentrations of antimicrobial agents on the biofilm formationto polystyrene by Escherichia coli, Proteus vulgaris, Providencia stuartii, and Morganella morganii was investigated by examining eight clinical strains. All the isolates tested were efficient biofilm-forming strains in the microtiter plate assay, with crystal violet staining (OD595 nm) ranging from 0.13 +/- 0.01 for P. stuartii ER21870 to 1.23 +/- 0.02 for P. vulgaris ER50120. The biofilm formation of the majority of the strains was affected in the presence of ceftazidime or ciprofloxacin: biofilm formation significantly decreased for all the E. coli and P. vulgaris strains in the presence of either of the two antibiotics, it also decreased for M. morganii ER89472 in the presence of ceftazidime but increased for P. stuartii ER21870 and M. morganii ER89472 in the presence of ciprofloxacin. Amikacin decreased only the biofilm formation of P. stuartii ER08274. In addition to their antibacterial activity, ceftazidime and ciprofloxacin could be effective in preventing the biofilm formation of E. coli and P. vulgaris.