Legionella

Legionella
Legionella sp. under UV light
Scientific classification
Domain:	Bacteria
Phylum:	Pseudomonadota
Class:	Gammaproteobacteria
Order:	Legionellales
Family:	Legionellaceae Brenner et al. 1979
Genus:	Legionella Brenner et al. 1979
Species
Legionella adelaidensis[1] Legionella anisa[1] Legionella beliardensis[1] Legionella birminghamensis[1] Legionella bozemanae[1] Legionella brunensis[1] Legionella busanensis[1] Legionella cardiaca[1] Legionella cherrii[1] Legionella cincinnatiensis[1] Legionella clemsonensis[2] Legionella donaldsonii[1] Legionella drancourtii[1] Legionella dresdenensis[1] Legionella drozanskii[1] Legionella dumoffii[1] Legionella erythra[1] Legionella fairfieldensis[1] Legionella fallonii[1] Legionella feeleii[1] Legionella geestiana[1] Legionella genomospecies 1 Legionella gormanii[1] Legionella gratiana[1] Legionella gresilensis[1] Legionella hackeliae[1] Legionella impletisoli[1] Legionella israelensis[1] Legionella jamestowniensis[1] Candidatus Legionella jeonii Legionella jordanis[1] Legionella lansingensis[1] Legionella londiniensis[1] Legionella longbeachae[1] Legionella lytica[1] Legionella maceachernii[1] Legionella maioricensis[1] Legionella massiliensis[1] Legionella micdadei[1] Legionella monrovica[1] Legionella moravica[1] Legionella nagasakiensis[1] Legionella nautarum[1] Legionella norrlandica[1] Legionella oakridgensis[1] Legionella parisiensis[1] Legionella pittsburghensis[1] Legionella pneumophila[1] Legionella quateirensis[1] Legionella quinlivanii[1] Legionella rowbothamii[1] Legionella rubrilucens[1] Legionella sainthelensi[1] Legionella santicrucis[1] Legionella shakespearei[1] Legionella spiritensis[1] Legionella steelei[1] Legionella steigerwaltii[1] Legionella saoudiensis[1] Legionella taurinensis[1] Legionella thermalis[1] Legionella tucsonensis[1] Legionella tunisiensis[1] Legionella wadsworthii[1] Legionella waltersii[1] Legionella worsleiensis[1] Legionella yabuuchiae[1] Legionella bononiensis[1]

Legionella is a genus of pathogenic gram-negative bacteria that includes the species L. pneumophila, causing legionellosis^[3] (all illnesses caused by Legionella) including a pneumonia-type illness called Legionnaires' disease and a mild flu-like illness called Pontiac fever.^[3]

Legionella may be visualized with a silver stain or cultured in cysteine-containing media such as buffered charcoal yeast extract agar. It is common in many environments, including soil and aquatic systems, with at least 50 species and 70 serogroups identified. These bacteria, however, are not transmissible from person to person;^[4] Furthermore, most people exposed to the bacteria do not become ill.^[5] Most outbreaks are traced to poorly maintained cooling towers.

The side chains of the cell wall carry the bases responsible for the somatic antigen specificity of these organisms. The chemical composition of these side chains both with respect to components and arrangement of the different sugars determines the nature of the somatic or O antigen determinants, which are essential means of serologically classifying many gram-negative bacteria.

Legionella acquired its name after an outbreak in 1976 of a then-unknown "mystery disease" made 221 people sick and caused 34 deaths. The outbreak was first noticed among attendees at a convention of the American Legion—an association of U.S. military veterans. The convention occurred in Philadelphia during the U.S. Bicentennial year on July 21–24, 1976. This epidemic among U.S. war veterans, occurring in the same city as—and within days of the 200th anniversary of—the signing of the Declaration of Independence, was widely publicized and caused great concern in the United States.^[6] On January 18, 1977, the causative agent was identified as a previously unknown bacterium subsequently named Legionella.