Legionella spp: non-pneumophilia species - MegaMicro

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Legionella spp: non-pneumophilia species

Micro > Bacteriology > Gram-negative bacteria
Legionella, other than L. pneumophilia

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Although more than 70 Legionella serotypes have been identified among 50 species, L. pneumophilia causes most legionellosis. L. pneumophilia serogroup 1 alone is responsible for 70-90% of the cases in adults. In a pediatric series, L. Pneumophilia serogroup 1 accounted for only 48% of cases, serogroup 6 accounted for 33%, and the remaining cases involved other serotypes and species. Legionella micdadei and L. dumoffii are the second and third most common species to cause Legionnaires disease in children, respectively.
Legionella species associated with human disease include L. pneumophilia, L. micdadei, L..bozemanii, L. dumoffii, L. gormanii, L. longbeachae, among others.
Gram stain or other staining characteristics: technically Gram-negative, although it does not retain staining well and is usually not visible on gram staining. Silver stain is typically required to demostrate in tissues. DFA is useful only for L pneumophilia type I
Morphology and structure: Slender, pleomorphic rods
Physiology: Facultative intracellular organism (inside alveolar macrophages)
Growth characteristics in the laboratory: Require charcoal yeast extract agar/media (with L-cysteine and iron); growth is enhanced by iron
Virulence factors:
·         Dot/lcm type IV secretion system inhibits macrophage phagosome/endo/lysosome fusions
·         Cu-Zn and catalase-peroxidase protects bacteria from macrophage superoxide and hydrogen peroxide oxidative burst
·         Pili and flagella promote attachment and invasion
·         Secretion of protein toxins like RNAase, phospholipase A, and phospholipase C
Pathobiology:
Legionella spp. are transmitted via aerosol transmission from environmental water source habitat (e.g. air conditioning systems, hot water tanks). There is no person-to-person transmission.
They are facultative intracellular bacteria that multiply in free-living amoebae in nature, and in alveolar macrophages, monocytes, and alveolar epithelial cells in infected hosts. This ability to infect and replicate in macrophages is critical.
The replicative cycle is initiated by binding complement component C3b to an outer membrane porin protein on the bacterial surface. The bacteria then binds to the CR3 complement receptors on mononuclear phagocytes, after which the organisms penetrate the cell through endocytosis. The bacteria survive intracellularly and are not killed in the cells by exposure to toxic superoxide, hydrogen peroxide, and hydroxyl radicals because phagolysosome fusion is inhibited.
Chemokines and cytokines released by the infected macrophages stimulate a robust inflammatory response that is characteristic of Legionella infections. The organisms proliferate in their intracellular vacuole and produce proteolytic enzymes that eventually kill the host cell when the vacuole is lysed.
Major associated diseases: pneumonia
Major medications or classes of medications that have therapeutic efficacy: Macrolides (e.g. azithromycin, clarithromycin) or fluoroquinolones (e.g. ciprofloxacin, levofloxacin) are the treatment of choice
Prevention: Decrease environmental exposure to reduce risk of disease; for environmental sources associated with disease, treat with hyper-chlorination, superheating, or copper-silver ionization
Epidemiology/Geography: Capable of sporadic, epidemic, and nosocomial infections; commonly found in natural bodies of water, cooling towers, condensers, and water systems (including hospital systems); patients at risk for symptomatic disease include patients with compromised pulmonary function and patients with decreased cellular immunity (particularly transplant patients).
Related concepts

1.       Gram Negative
2.       L-cysteine
3.       Facultative intracellular
4.       Pontiac fever
5.       Legionella
6.       Legionnaire’s disease
7.       L. micdadei
8.       L. bozemanii
9.       L. dumoffii
10.     L. gormanii
 
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