Effect of subinhibitory antibiotic concentrations on polysaccharide intercellular adhesin expression in biofilm-forming Staphylococcus epidermidis

Biofilm production is an important step in the pathogenesis of Staphylococc us epidermidis polymer-associated infections and depends on the expression of the icaADBC operon leading to the synthesis of a polysaccharide intercel lular adhesin. A chromosomally encoded reporter gene fusion between the ica promoter and the beta-galactosidase gene lacZ from Escherichia coil was co nstructed and used to investigate the influence of both environmental facto rs and subinhibitory concentrations of different antibiotics on ica express ion in S. epidermidis. It was shown that S, epidermidis biofilm formation i s induced by external stress (i.e., high temperature and osmolarity). Subin hibitory concentrations of tetracycline and the semisynthetic streptogramin antibiotic quinupristin-dalfopristin were found to enhance ica expression 9- to Ii-fold, whereas penicillin, oxacillin, chloramphenicol, clindamycin, gentamicin, ofloxacin, vancomycin, and teicoplanin had no effect on ica ex pression. A weak (i.e., 2.5-fold) induction of ica expression was observed far subinhibitory concentrations of erythromycin. The results were confirme d by Northern blot analyses of ica transcription and quantitative analyses of biofilm formation in a colorimetric assay.