RESUMO
Microbial adherence to host cells is an early key step in the establishment of infection. During the course of Legionnaire's disease, Legionella interactions with host cells are best documented for resident macrophages. However, L. pneumophila can also replicate within type I and type II pneumocytes, which cover almost the entire alveolar surface. In the presence of zinc, we observed a significant and concentration-dependent increase in L. pneumophila adherence to and invasion of type II pneumocytes. The zinc-dependent adherence mechanism seemed to be host-cell-independent, as a similar increase in cytoadherence was observed with macrophages. We also found that zinc-dependent adherence of L. pneumophila appears to involve recognition of zinc-binding pneumocyte receptors by a bacterial adhesin, and heparan-sulfated host cell receptors, but not type IV pili.
Assuntos
Adesinas Bacterianas/efeitos dos fármacos , Legionella pneumophila/fisiologia , Doença dos Legionários/fisiopatologia , Macrófagos Alveolares/efeitos dos fármacos , Zinco/farmacologia , Adesinas Bacterianas/fisiologia , Linhagem Celular , Células Epiteliais/microbiologia , Células Epiteliais/patologia , Humanos , Legionella pneumophila/metabolismo , Macrófagos Alveolares/microbiologia , Alvéolos Pulmonares/imunologia , Receptores de Complemento/fisiologia , Receptores Imunológicos/metabolismoRESUMO
We evaluated a ready-to-use real-time quantitative Legionella pneumophila PCR assay system by testing 136 hot-water-system samples collected from 55 sites as well as 49 cooling tower samples collected from 20 different sites, in parallel with the standard culture method. The PCR assay was reproducible and suitable for routine quantification of L. pneumophila. An acceptable correlation between PCR and culture results was obtained for sanitary hot-water samples but not for cooling tower samples. We also monitored the same L. pneumophila-contaminated cooling tower for 13 months by analyzing 104 serial samples. The culture and PCR results were extremely variable over time, but the curves were similar. The differences between the PCR and culture results did not change over time and were not affected by regular biocide treatment. This ready-to-use PCR assay for L. pneumophila quantification could permit more timely disinfection of cooling towers.