The aim of this study was to evaluate the effect of antibiotics at subminimal inhibitory concentrations (sub-MIC) on fluorescent pseudomonas adherence to A549 pneumocyte cells. Pseudomonas fluorescens MF0 isolated from contaminated raw milk and Pseudomonas aeruginosa NK125502 isolated from a cystic fibrosis patient’s lung adhered to A549 cells. As previously shown for P. aeruginosa, P. fluorescens bound to A549 cells in a dose-dependent manner over a wide range of bacterial concentrations. Bacterial growth in the presence of polymyxin B or gentamicin at MIC/2 had no effect on the adherence of NK125502 and MF0 to A549 cells. Instead, MIC/2 and MIC/8 of cefsulodin or chloramphenicol decreased the adherence of the two strains. A decrease in MF0 adherence was also observed with cefsulodin at MIC/32. We conclude that, in addition to their antibacterial activity, cefsulodin and chloramphenicol could be effective in preventing Pseudomonas adherence to respiratory epithelium.

Pseudomonas aeruginosa adherence to fibronectin has been shown to be important to bacterial colonization and infection. To better understand the mechanisms involved in this interaction, the role of the carbohydrate moiety of the fibronectin molecule in P. aeruginosa adhesion was studied. Strain NK 125 502 adhered to immobilized fibronectin with an adherence index of 4.8 x 10(5) CFU/ micro g. Periodic oxidation of fibronectin markedly reduced the adhesion of P. aeruginosa, while a neuraminidase treatment increased bacteria adhesion. N-Acetylgalactosamine, N-acetylglucosamine, sialic acid, and also lectin PA-IL worked as efficient inhibitors in adhesion assays: 59%, 70.7%, 100%, and 60% of inhibition, respectively. We have demonstrated here the involvement of a lectin-like process in the interaction of P. aeruginosa NK 125 502 with immobilized fibronectin.

Bacterial adherence is a complex phenomenon involving specific interactions between receptors, including matricial fibronectin, and bacterial ligands. We show here that fibronectin and outer membrane proteins of Pseudomonas fluorescens were able to inhibit adherence of P. fluorescens to fibronectin-coated wells. We identified at least six fibronectin-binding proteins with molecular masses of 70, 55, 44, 37, 32 and 28 kDa. The presence of native (32 kDa) and heat-modified forms (37 kDa) of OprF was revealed by immuno-analysis and the 44-kDa band was composed of three proteins, their N-terminal sequences showing homologies with Pseudomonas aeruginosa porins (OprD, OprE1 and OprE3).

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