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4 - Characteristics of
Legionella
genus and species
The species of
Legionella
are gram-negative, aerobic, non-spore forming
bacilli with 0.3 to 0.9µm in width, which vary between short forms, with
1.5 to 2 µm in length, and filamentous forms, with greater length.
5 - Biochemical and nutritional characteristics
The species of
Legionella
are nutritionally demanding, requiring
L-cysteineand iron salts for the growth in culture media. The proper culture
media is the Buffered Charcoal Yeast Extract agar (BCYEa).
Growth in BCYEa and lack of growth in blood agar are the most useful
presumptive findings to guide on possible presence of a species of
Legionella
.
The species of
Legionella
do not ferment nor oxidize carbohydrates and
they weakly positive for catalase and peroxidase.
6 - Laboratory diagnosis
The clinical diagnosis of Legionellosis is difficult because the signs and
symptoms observed during the presentation of the disease are nonspecific.
However it is important to have a definitive diagnosis, enabling the proper
antimicrobial treatment to be started early.
The diagnosis of the Legionnaires’ disease in patients with pneumonia
is based on the use of laboratory methods for phenotypic detection of the
organism (culture, serology and search of the urinary antigen), as well as in
the use of methods for genotypic detection.
The molecular methods used for the genotypic detection are based on
the polymerase chain reaction (PCR).
