LEGIONELLA - World Health Organization

Chapter 2 Ecology and
environmental sources
of Legionella
Susanne Surman-Lee, Barry Fields, Britt Hornei, Santiago Ewig, Martin Exner, Igor Tartakovsky,
Louise Lajoie, Friederike Dangendorf, Richard Bentham, Pierre André Cabanes, Pascal Fourrier,
Thierry Trouvet, France Wallet
A good understanding of the factors that affect Legionella survival and growth in the natural
environment is important in controlling the bacteria in artificial water systems. It allows the
areas most at risk from Legionella colonization in such systems to be identified, thereby indicating
the points at which control measures will be most effective; it also allows the control measures
that will be most effective to be identified (see Chapter 3).
This chapter discusses the relationship of Legionella with its natural environment, and provides
information on:
• natural sources of Legionella (Section 2.1)
• factors affecting Legionella growth — water temperature and presence of other microorganisms
(Section 2.2)
• how the formation of biofilms protects Legionella and supplies nutrients (Section 2.3)
• sources of Legionella infection — aerosols, other water sources and soil (Section 2.4).
2.1 Natural sources of Legionella
Understanding the ecology of Legionella (i.e. the way it interacts with its natural environment
and with other species) helps in understanding the factors that encourage the survival and
growth of legionellae in artificial water systems.
Legionellae are ubiquitous in natural and artificial water environments worldwide, and
survive in a range of environmental conditions (Fliermans et al., 1981).The bacteria are acidtolerant
(they can withstand exposure to pH 2.0 for short periods) and they have been isolated
from environmental sources ranging from a pH of 2.7 to 8.3 (Anand et al., 1983; Sheehan,
Henson & Ferris, 2005). Legionellae have been found in sources as diverse as water on plants
in rainforests, groundwaters (Riffard et al., 2001; Brooks et al., 2004) and seawater (Ortiz-
Roque & Hazen, 1987). The bacterium also survives in artificial sources of salt water (Heller
et al., 1998). In certain natural aquatic environments (e.g. in groundwater that is contaminated
by soils or subsoils and has a temperature below 20 ºC), legionellae may be present in concentrations
LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS