LEGIONELLA - World Health Organization

Chapter 11 Laboratory
aspects of Legionella
Britt Hornei, Santiago Ewig, Martin Exner, Igor Tartakovsky, Louise Lajoie, Susanne Surman-Lee,
Norman Fry, Barry Fields
This chapter provides:
• background information about Legionella biology and staining (Section 11.1)
• information on diagnostic tests for legionellosis (Section 11.2), including:
– culture (Section 11.2.1)
– detection of bacterial antigen (Section 11.2.2)
– detection of bacterial DNA (deoxyribonucleic acid) (Section 11.2.3)
• particular considerations for diagnosing patients with health-care associated (nosocomial)
pneumonia (Section 11.2.4)
• approaches to the environmental sampling of Legionella (Section 11.3)
• methods for identifying and differentiating Legionella species (Section 11.4).
11.1 Legionella biology and staining
11.1.1 Biology
Legionella are 0.3–0.9 µm wide and 2–20 µm long, depending on the age of the culture —fresh
cultures of Legionella produce coccobacilli about 2–6 µm long, whereas older cultures may
produce filamentous forms up to 20 µm long. L. pneumophila usually has limited motility, and
some strains are completely non-motile (Harrison & Taylor, 1988). The bacterium has one
or two polar flagellae, the expression of which may depend on temperature (Ott et al., 1991).
In contrast to other aquatic bacteria, L. pneumophila requires iron salts and the amino acid Lcysteine
to grow on laboratory media. Occasionally, rare clinical isolates of three Legionella species
(L. jordanis, L. oakridgensis and L. spiritensis) may lose their L-cysteine growth dependence (Orrison
et al., 1983). This characteristic only develops after serial passage, when Legionella from an
infected host is used to infect a second host — a process that often results in the mutation of
Legionella genes not essential for survival. However, legionellae that are not L-cysteine dependent
still grow more vigorously on media containing L-cysteine.
LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS