Dynamics of Legionella spp. and Bacterial Populations during the Proliferation of L. pneumophila in a Cooling Tower Facility

Abstract

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 by a fingerprint technique, single-strand conformation polymorphism, and Legionella spp. and L. pneumophila were quantified by 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 the Legionella sp. population changed in 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 rRNA genes. A high diversity of Legionella spp. was observed before proliferation, including L. lytica, L. fallonii, and other Legionella-like amoebal pathogen types, along with as-yet-undescribed species. During the proliferation of L. pneumophila, Legionella sp. diversity decreased significantly, L. fallonii and L. pneumophila being the main species recovered.

High Diversity and Abundance of Legionella spp. in a Pristine River and Impact of Seasonal and Anthropogenic Effects

“…The quantification data and the clone sequences in our study all show that L. pneumophila was not the most abundant member of the Legionella community in the Tech River. This may suggest that this species is able to proliferate and dominate the Legionella community only under specific conditions (e.g., higher temperatures characteristic of man-made systems), as already reported by Wéry et al (44).…”

“…Studies using qPCR quantification of Legionella have been mostly restricted to man-made systems such as drinking water distribution systems (hot sanitary) and cooling towers implicated in legionellosis outbreaks. Surprisingly, the Legionella abundances found close to the source of the Tech River, which could be considered a pristine environment, were comparable to those found in cooling towers (44).…”

“…A high number of sequences affiliated with not yet described Legionella species were also found in cooling towers (44), suggesting that cultured representatives are lacking for Legionella not only in natural reservoirs but also in man-made systems. Interestingly, although the Legionella community was initially diverse in these cooling towers, the Legionella sp.…”

“…One such genetic fingerprinting technique, single-strand conformation polymorphism (SSCP), is well suited to bacterial diversity analysis of large sample sets due to its rapidity, reproducibility, and low cost and was also used recently to study the dynamics of Legionella spp. in water from a cooling tower plant (44).…”

Detecção de bactérias do gênero Legionella em amostras de água de sistemas de ar condicionado<a href="#endereco"></a>

“…Nessas condições, os organismos podem permanecer viáveis, porém não cultiváveis. 9,23 Outro fator que pode ter influenciado no baixo número de isolamentos é que as amostras apresentaram valores de pH 6,0 em todas as ocasiões avaliadas. Embora a baixa temperatura e o pH de caráter ácido possam causar alterações fisiológicas nas células, estas podem permanecer viáveis mas não cultiváveis.…”