Legionella
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Legionella: Characteristics, Culture, Identification, and Control of L. pneumophila, Study notes of Microbiology
Detailed information about Legionella, a genus of aquatic saprophytes that includes the species L. pneumophila, which causes both community-acquired and nosocomial pneumonia. the morphology, culture, biochemical reactions, susceptibility to physical and chemical agents, molecular diagnosis, and treatment of Legionella infections. It also discusses prevention and control methods.
What you will learn
- What is the morphology of L. pneumophila?
- What are the recommended treatments for Legionella infections?
- What are the prevention and control methods for Legionella infections?
- How is L. pneumophila identified in clinical specimens?
Typology: Study notes
2021/2022
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Legionella
- (^) Legionella are ubiquitous aquatic saprophytes present worldwide. Many of these species are found in the environment and are also associated with human infections. L. pneumophila is an important species, which causes both community-acquiredand nosocomial pneumonia.
- (^) Family Legionellaceae consists of one genus, Legionella which contains 39 genetically defined species and more than 60 serogroups. Many of these species cause infections in humans. Legionellosis is the term used for infections caused by different Legionella species. Legionnaire’s disease is the term used to describe the pneumonia caused by L. pneumophila.
- (^) Culture
- (^) L. pneumophila is a strict aerobe, grows at an optimum temperature of 35°C and an optimum pH of 6.9. It is nutritionally fastidious and grows on the medium supplemented with iron salts and L-cysteine.
- (^) Buffered charcoal yeast extract (BCYE) agar: The agar containing buffered charcoal, yeast extract, and cysteine is a useful medium for growth of L. pneumophila. It is a slowgrowingn bacterium and may take 3–5 days to produce visible colonies. The colonies on BCYE agar are circular, gray, or grayblue and low convex with a slightly irregular margin. Under the microscope, the colonies typically have a ground glass appearance.
- (^) Biochemical reactions
- (^) L. pneumophila shows following biochemical properties:
- (^) It is mostly nonfermenter and derives its energy from the metabolism of amino acids.
- (^) It does not ferment any sugars and is urease and nitrate test negative.
- (^) It is catalase positive, oxidase variable, and liquefies gelatin.
- (^) It hydrolyzes starch and hippurate.
- (^) Molecular Diagnosis
- (^) Polymerase chain reaction (PCR) is a specific method for detection of Legionella spp. in urine, serum, and bronchoalveolar lavage fluid. The main advantage of this method is that it can detect infections caused by Legionella species other than L. pneumophila serogroup 1.
- (^) Prevention and Control
- (^) Hyperchlorination of water and superheating of water to 70–80°C has proved to be of value in preventing the disease. Complete elimination of bacteria from water, however, is difficult.