Effect of antibiotics on bordetella pertussis adhering activity: hypothesis regarding mechanism of action

Microbial adherence to epithelial cell surfaces has been implicated as the first step in the initiation of several infectious diseases. The ability of antibiotics to affect the properties of bacterial adherence to cell surfaces may be a criterion in selecting antibiotics for therapy. This study was performed in order to investigate the activity of amoxicillin, chloramphenicol, and clarithromycin in modifying the adhering activity of Bordetella pertussis to human epithelial cells. The actions of antibiotics, alone or combined with aprotinin, were compared with that of trypsin, aprotinin and trypsin + aprotinin, to investigate the chemical nature of the ligand where antibiotics could act. The adhering activity was evaluated on human epithelial cells, collected from the oral mucosa, challenged with B. pertussis A2963 previously incubated in the presence of the tested substances for 1 h at 37°C in a shaker incubator. After staining, the percentage of mucosal cells with more than 50 adhering bacteria was evaluated. Under the described experimental conditions, trypsin significantly reduced the adherence of B. pertussis. Aprotinin had no effect but was able to counteract the inhibitory action of trypsin. Both clarithromycin and chloramphenicol markedly reduced adhering activity and their actions were not counteracted by aprotinin. Amoxicillin was without effect. It was hypothesized that chloramphenicol and clarithromycin, exerting their antimicrobial action by inhibiting bacterial protein synthesis, affected bacterial adhesion through an unknown mechanism without proteolytic effect.