TAILIEUCHUNG - Chapter 141. Legionella Infection

Legionellosis refers to the two clinical syndromes caused by bacteria of the genus Legionella. Pontiac fever is an acute, febrile, self-limited illness that has been serologically linked to Legionella species, whereas Legionnaires' disease is the designation for pneumonia caused by these species. Legionnaires' disease was first recognized in 1976, when an outbreak of pneumonia took place at a hotel in Philadelphia during the American Legion Convention. The causative agent proved to be a newly discovered bacterium, Legionella pneumophila, that was isolated from lung specimens obtained from the victims at autopsy. Microbiology The family Legionellaceae comprises more than 49 species. | Chapter 141. Legionella Infection Introduction Legionellosis refers to the two clinical syndromes caused by bacteria of the genus Legionella. Pontiac fever is an acute febrile self-limited illness that has been serologically linked to Legionella species whereas Legionnaires disease is the designation for pneumonia caused by these species. Legionnaires disease was first recognized in 1976 when an outbreak of pneumonia took place at a hotel in Philadelphia during the American Legion Convention. The causative agent proved to be a newly discovered bacterium Legionella pneumophila that was isolated from lung specimens obtained from the victims at autopsy. Microbiology The family Legionellaceae comprises more than 49 species with more than 64 serogroups. The species L. pneumophila causes 80-90 of human infections and includes at least 16 serogroups serogroups 1 4 and 6 are most commonly implicated in human infections. To date 18 species other than L. pneumophila have been associated with human infections among which L. micdadei Pittsburgh pneumonia agent L. bozemanii L. dumoffli and L. longbeachae are the most common. Members of the Legionellaceae are aerobic gram-negative bacilli that do not grow on routine microbiologic media. Buffered charcoal yeast extract BCYE agar is the medium used to grow Legionella. Antibiotics added to the medium suppress the growth of competing flora from nonsterile sites and dyes color the colonies and assist in identification. The direct fluorescent antibody DFA test can definitively identify a number of individual species. In the case of L. pneumophila the serogroup-specific antigen and antibodies detected by immunofluorescence are directed primarily at the lipopolysaccharide a prominent outer-membrane component. Both polyclonal and monoclonal DFA reagents are commercially available. The monoclonal reagent is less cross-reactive but is specific for L. pneumophila. Ecology and Transmission The natural habitats for L. pneumophila are aquatic

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