Community interactions promote Legionella pneumophila survival in drinking water biofilms

Abstract

Legionella pneumophila is a waterborne pathogen that can cause Pontiac Fever or Legionnaires’ disease, a type of pneumonia that can be fatal. Although L. pneumophila is not able to replicate in low nutrient environments, such as drinking water, it is known that heterotrophic biofilms have a crucial role in the survival of this pathogen in drinking water distribution systems. The aim of this work is to study the community interactions that influence the survival of L. pneumophila in biofilms. For that, mono and dual-species biofilms of L. pneumophila and the predominant biofilm isolates Variovorax paradoxus, Mycobacterium chelonae, Acidovorax spp., Sphingomonas spp., were formed on PVC surfaces and sessile cells quantified for total cells, viable and cultivable L. pneumophila and cultivable non-Legionellae. Results demonstrated that Acidovorax spp. and Sphingomonas spp. appear to have an antagonistic effect on L. pneumophila cultivability but not in the viability, leading to the formation of viable but noncultivable (VBNC) cells, while M. chelonae increased the cultivability of this pathogen. M. chelonae is one of the microorganisms commonly found in drinking water and this work demonstrates that this strain is able to promote L. pneumophila survival in these systems. It is also demonstrated that other species might stimulate this pathogen to enter a VBNC state and consequently be underestimated in the drinking water quality control, as drinking water safety assessment still relies on standard culture techniques. It is essential for future work to study other biofilm community members to understand their ecological interactions with L. pneumophila.