Modulating effects of mucoregulating drugs on the attachment of Haemophilus influenzae.

Non-typable Haemophilus influenzae (NTHI) is one of the three major pathogens implicated in human respiratory infections. The ability to attach with pharyngeal epithelial cells is an important factor for infection and virulence. In the present study we describe the effects of two mucoregulating drugs, S-carboxymethylcysteine (S-CMC) and ambroxol, on the attachment of NTHI to pharyngeal epithelial cells. There was a significant (P<0.0001, <0.001 and <0.01) decrease of attachment (8.8±2.4, 9.2±2.5 and 15.4±5.7 bactreria/cell) compared with the control (17.5±2.9, 15.5±3.1 and 18.8±6.8 bacteria/cell) after cells were treated wth S-CMC at a dose of 100, 10 and 1 μg/ml. After attachment assay, cells treated with S-CMC (100 μg/ml) showed a significant decrease (P<0.01) of attached bacteria (3.1±0.8 bacteria/cell) compared with the control (5.9±1.8 bacteria/cell). Treatment of cells with ambroxol did not influence bacterial attachment. By scanning electron microscopic observation it was found that NTHI attaches to the surface elevations (microplicae) of human pharyngeal epithelial cells. Atomic force microscopic observation revealed that the surface potential of microplicae decreased significantly in cells treated with S-CMC compared with the untreated control cells. As bacteria with negative surface charge attach to the positively charged domain, i.e. microplicae of human pharyngeal epithelial cells, this study suggests that the decrease of attachment of NTHI with epithelial cells after treatment with S-CMC was possibly due to the decrease of surface charge. This study suggests that S-CMC decreases the episodes of respiratory infections in patients with respiratory diseases both by inhibiting the attachment of bacteria to the upper respiratory tract, and by detaching the adherent one.