Dynamics of Legionella spp. and bacterial populations during the proliferation of L. pneumophila in a cooling tower facility

The dynamics of Legionella spp. and of dominant bacteria were investigated in water from a cooling tower plant over a 9-month period which included several weeks when Legionella pneumophila proliferated. The structural diversity of both the bacteria and the Legionella spp. was monitored using a fingerprint technique, single strand conformation polymorphism (SSCP), and Legionella spp. and L. pneumophila were quantified using real-time quantitative PCR. The structure of the bacterial community did not change over time, but it was perturbed periodically by chemical treatment or biofilm detachment. In contrast, the structure of Legionella spp. population changed at different periods, its dynamics at times showing stability but also a rapid, major shift during the proliferation of L. pneumophila in July. The dynamics of the Legionella spp. and of dominant bacteria were not correlated. In particular, no change in the bacterial community structure was observed during the proliferation of L. pneumophila. Legionella spp. present in the cooling tower system were identified by cloning and sequencing of 16S rDNAs. A high diversity of Legionella spp. was observed before proliferation, including L. lytica, L. fallonii, other Legionella-like amoebal pathogen types, along with as-yet-undescribed species. During the proliferation by L. pneumophila, Legionella spp. diversity decreased significantly, L. fallonii and L. pneumophila being the main species recovered