N-acetyl-cysteine increases the replication of Chlamydia pneumoniae and prolongs the clearance of the pathogen from mice.

Purpose. Within the community, 10 % of acquired pneumonia is caused by Chlamydia pneumoniae. N-acetyl-cysteine (NAC) is one of the most commonly used mucolytics in respiratory diseases, but its effect on C. pneumoniae infection has not yet been investigated. In this study, our aim was to investigate whether NAC influences the replication of C. pneumoniae. After determining that NAC does have an effect on C. pneumoniae replication, the effect of an alternative drug called Ambroxol (Ax) was investigated. Methodology. The in vitro effect of NAC and Ax was studied on C. pneumoniae-infected A549 and McCoy cells. Furthermore, the influence of NAC and Ax was examined in mice infected intranasally with C. pneumoniae. Results. NAC treatment resulted in approximately sixfold more efficient C. pneumoniae growth in tissue culture compared to the untreated control cells, and this effect was shown to be based on the increased binding of the bacterium to the host cells. The C. pneumoniae-infected mice to which NAC was given had prolonged and more severe infections than the control mice. Ax decreased C. pneumoniae replication in vitro, which was partially associated with the increased expression of indolamine 2,3-dioxygenase. In animals, using the adapted usual human dose, Ax did not alter the number of recoverable C. pneumoniae. Conclusion. Based on our results, it might be recommended that a mucolytic agent other than NAC, such as Ax, be used in respiratory diseases suspected to be caused by C. pneumoniae.