In vitro production of biofilm in a flow cell system in a strain of Pseudomonas aeruginosa and Staphylococcus aureus and determination of efficiency of ciprofloxacin against them

BACKGROUND: Microorganisms develop biofilm on various medical devices. The process is particularly relevant in public health since biofilm associated organisms are much more resistant to antibiotics and have a potential to cause infections in patients with indwelling medical devices. MATERIALS AND METHODS: To determine the efficiency of an antibiotic against the biofilm it is inappropriate to use traditional technique of determining Minimum Inhibitory Concentration (MIC) on the free floating laboratory phenotype. Thus we have induced formation of biofilm in two strains (Pseudomonas aeruginosa and Staphylococcus aureus, which showed heavy growth of biofilm in screening by Tube method) in a flow cell system and determined their antibiotic susceptibility against ciprofloxacin by agar dilution method in the range (0.25 mg/ml to 8 mg/ml). The MIC value of ciprofloxacin for the biofilm produced organism was compared with its free form and a standard strain as control on the same plates. OBSERVATIONS: Both the biofilm produced strains showed a higher resistance (MIC > 8 mg/ml) than its free form, which were 2 μg/ml for Pseudomonas aeruginosa and 4 mg/ml for Staphylococcus aureus. Thus biofilm can pose a threat in the patient treatment.