Inhibitory effect of N-acetylcysteine on adherence of Streptococcus pneumoniae and Haemophilus influenzae to human oropharyngeal epithelial cells in vitro

Respiration. 2000;67(5):552-8. doi: 10.1159/000067473.


Background: Bacterial adherence to mucosal and epithelial cell structures is of importance for the persistence of bacteria in the airways. Cigarette smoking and chronic bronchitis are associated with increased bacterial adherence. N-Acetylcysteine (NAC) medication reduces the number of infectious exacerbations in patients with chronic bronchitis, and NAC medication has been associated with low intrabronchial bacterial numbers.

Objective: We investigated whether NAC influences bacterial adherence as a possible mechanism behind its clinical effects.

Methods: Highly adhering test strains of Streptococcus pneumoniae and Haemophilus influenzae were used to investigate the influence of four pharmacological compounds on adherence to oropharyngeal epithelial cells in vitro. Adhesion assays were performed both during short-term exposure to, as well as after long-time incubation with, NAC, lidocaine, hydrocortisone and terbutaline at concentrations not inhibiting bacterial growth.

Results: Only NAC showed a significant inhibitory effect on adhesion of H. influenzae during short-term incubation. After long-term incubation, both NAC and hydrocortisone inhibited bacterial adhesion for both strains in a dose-dependent manner. When NAC's effect on three different strains of S. pneumoniae and four strains of H. influenzae was studied, inhibition of bacterial adhesion was found for three strains of each species.

Conclusions: NAC lowers bacterial adhesion in vitro to oropharyngeal epithelial cells in doses equivalent to that is being used clinically. This effect might be a contributory mechanism behind the reduction of infectious exacerbations in chronic bronchitis patients.

MeSH terms

  • Acetylcysteine / pharmacology*
  • Bacterial Adhesion / drug effects*
  • Cells, Cultured
  • Epithelial Cells
  • Expectorants / pharmacology*
  • Haemophilus influenzae / drug effects*
  • Humans
  • Mouth Mucosa / cytology
  • Pharynx / cytology
  • Streptococcus pneumoniae / drug effects*


  • Expectorants
  • Acetylcysteine