EFFECT ON PSEUDOMONAS-AERUGINOSA ALGINATE EXPRESSION OF DIRECT PLATING AND CULTURE OF FRESH CYSTIC-FIBROSIS SPUTUM ON TO PSEUDOMONAS ISOLATION AGAR CONTAINING SUBINHIBITORY CONCENTRATIONS OF ROXITHROMYCIN AND RIFAMPICIN

The effects of subinhibitory concentrations of roxithromycin (16 mg/L) or rifampicin (16 mg/L) on alginate production by Pseudomanas aeruginosa were investigated. The weight of purified alginate from antibiotic-free cultures was significantly greater (52.5 +/- 24.0 mg, range 22.4-109.5), compared with alginate from cultures bacteria exposed to sub-MIC of roxithromycin (21.9 +/- 17.0, 0.0-42.1 (P less than or equal to 0.037)) and to sub-MIC of rifampicin (28.6 +/- 15.0, 2.9-47.5 (P less than or equal to 0.038)). Chromatographic analysis of hydrolysed and chemically transformed sub-units of alginate revealed that the presence and the molar ratio of D-mannuronic acid and L-guluronic acid were not affected in the remnant alginate exposed to sub-MIC of roxithromycin in contrast to that in the remnant alginate exposed to sub-MIC of rifampicin.