Laboratory diagnosis of genus legionella
The laboratory diagnosis of genus Legionella involves several steps. These steps include:
1. Collection of samples: The first step is to collect samples from potential sources of Legionella. This can include water sources, such as hot water taps, cooling towers, and decorative fountains, as well as other sources like respiratory secretions or lung tissue in cases of suspected Legionella pneumonia.
2. Culture: Legionella bacteria are fastidious and require specialized culture media for growth. One commonly used medium is the Buffered Charcoal Yeast Extract (BCYE) agar. The samples are streaked onto BCYE agar plates and incubated at 35-37°C with enhanced carbon dioxide levels. Legionella colonies appear as glistening, convex, and opaque colonies after 2-7 days of incubation.
3. Identification: Once colonies are obtained, further tests are performed for identification. These tests can include gram staining, which reveals Gram-negative bacteria with a characteristic rod shape. Biochemical tests, such as oxidase positivity, catalase positivity, and nitrate reduction, can also be performed to help identify Legionella.
4. Serological testing: Serological testing involves checking for the presence of specific antibodies against Legionella in the patient's blood. This can be done using methods such as indirect immunofluorescence assay (IFA) or enzyme-linked immunosorbent assay (ELISA). A significant rise in antibody titer between acute and convalescent phase samples can be suggestive of Legionella infection.
5. Molecular testing: Molecular methods, such as polymerase chain reaction (PCR), can be used to directly detect the presence of Legionella DNA in samples. This method can provide rapid and highly sensitive results. PCR can be performed on respiratory secretions, lung tissue, or water samples.
6. Urinary antigen test: Legionella pneumophila serogroup 1 is the most common cause of Legionnaires' disease. Urinary antigen testing is a rapid and specific method for detecting Legionella pneumophila serogroup 1 antigen in urine samples. This test can provide a presumptive diagnosis of Legionnaires' disease within a few hours.
7. Whole-genome sequencing: Whole-genome sequencing can provide a detailed analysis of the genetic characteristics of Legionella strains. It can be used for epidemiological investigations to determine the relatedness of different strains and track outbreaks.
It is important to note that laboratory diagnosis of Legionella requires specialized facilities and trained personnel to handle the bacteria safely.