LEGIONELLA - World Health Organization

• other Legionella species that do not cause legionellosis produce colonies on the medium,
as does L. pneumophila
• the culture technique often fails to detect some other disease-causing Legionella species
(e.g. L. bozemanii and L. micdadei)
• residual disinfectant in the system may affect the cultivation of legionellae
• if the sample collection bottles do not contain a neutralizing agent, Legionella may be
killed (Wiedenmann, Langhammer & Botzenhart, 2001).
These uncertainties and differences in susceptibility of Legionella populations make it difficult
to interpret the colony count values for Legionella in relation to disease risk. However, culture
results, together with the percentage of samples containing Legionella, provide useful information
about the degree of amplification of Legionella in a system. A high degree of amplification
results in a higher exposure, which may be related to a higher infection risk.
When using L-cysteine dependence to confirm legionellae, it is worth remembering that
some bacteria produce extracellular cysteine that can support the growth of legionellae, which
then appear as satellite colonies on the cysteine-free medium (Wadowsky & Yee, 1983). Some
pseudomonads can grow with Legionella within water systems; however, their presence can
reduce Legionella growth on artificial media. When this occurs and the pseudomonads cannot
be removed by pretreatment or dilution, the results must be interpreted carefully.
LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS