Legionella adelaidensis
Legionella anisa
Legionella beliardensis
Legionella birminghamensis
Legionella brunensis
Legionella busanensis
Legionella cherrii
Legionella cincinnatiensis
Legionella donaldsonii
Legionella drancourtii
Legionella drozanskii
Legionella erythra
Legionella fairfieldensis
Legionella fallonii
Legionella feeleii
Legionella geestiana
Legionella gratiana
Legionella gresilensis
Legionella hackeliae
Legionella israelensis
Legionella jamestowniensis
Legionella jordanis
Legionella lansingensis
Legionella londiniensis
Legionella longbeachae
Legionella lytica
Legionella monrovica
Legionella moravica
Legionella nautarum
Legionella oakridgensis
Legionella parisiensis
Legionella pneumophila
Legionella quateirensis
Legionella quinlivanii
Legionella rowbothamii
Legionella rubrilucens
Legionella sainthelensi
Legionella santicrucis
Legionella shakespearei
Legionella spiritensis
Legionella steigerwaltii
Legionella taurinensis
Legionella tucsonensis
Legionella wadsworthii
Legionella waltersii
Legionella worsleiensis Legionella is a Gram negative bacterium, including many species that cause legionellosis or Legionaires' disease, most notably L. pneumophilia. At least 46 species and 70 serogroups have been identified. On the side-chains of the cell wall are carried the bases for the somatic antigen specifity of these organisms. The chemical composition of these side chains both with respect to components as well as arrangement of the different sugars determines the nature of the somatic or O antigen determinants, which are such important means of serologically classifying many Gram-negative.

At least 14 different serovars of L. pneumophila have been described as well as several other species being subdivided into a number of serovars. Sera have been used both for slide agglutination studies as well as for direct detection of bacteria in tissues using fluorescent-labelled antibody. Specific antibody in patients can be determined by the indirect fluorescent antibody test. ELISA and microagglutination tests have also been successfully applied.

Legionella pneumophila is non-acid, fast non-capsulated rods, aerobic and do not hydrolyse gelatin or produce urease. They are non-fermentative. L. pneumophila is neither pigmented nor does it autofluoresce. It is oxidase and catalase positive, produces beta-lactamase.

L. pneumophila is an intracellar pathogen. The internalisation of the bacteria is enhanced by the presence of antibody and complement. A pseudopod coils around the bacterium in this unique form of phagocytosis. Once internalised, the bacteria surround themselves by a membrane-bound phagolysosome . This becomes a vescicle , within which the bacteria multiply. They produce a 39kDa metalloprotease into culture fluids, which is cytotoxic for some cultured tissue culture cells.