Abstract
An in vitro study was conducted on the effects of clindamycin (CLDM), erythromycin (EM), tobramycin (TOB), piperacillin (PIPC), ceftazidime (CAZ) and ofloxacin (OFLX) on biofilm formation, which is considered to be a contributing factor to the intractability of chronic respiratory infections caused by Pseudomonas aeryginosa. Alginic acid and extracellular polysaccharides produced by P.aeruginosa were determined as indices reflecting the level of biofilm formation. Alginic acid production by P. aeruginosa mucoid strains was investigated by determining alginic acid produced in standard agar culture medium using high performance liquid chromatography. Extracellular polysaccharide (glycocalyx) produced by non-mucoid strains was quantified by determining polysaccharides contained in biofilms formed on silicon strips using the tryptophan method. The effects of the antibiotics on these indices at concentrations below the minimum inhibitory concentration (sub-MIC) were investigated. The production of alginic acid was significantly inhibited at CLDM ≥ 1/16 MIC, EM ≥ 1/128 MIC and TOB ≥1/4 MIC (p<0.02), and that of glycocalyx at CLDM ≥ 1/16 MIC and EM ≥ 1/16 MIC (p<0.05). The indices were not affected by other drugs at sub-MIC concentrations. Observations under a scanning electron microscope showed inhibition of biofilm formation by CLDM at sub-MIC concentrations. These results suggested that CLDM as well as EM inhibit P. aeruginosa biofilm formation at sub-MIC concentrations.
