Listeriosis laboratory tests
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: João André Alves Silva, M.D. [2]
Overview
For symptomatic patients, diagnosis is confirmed only after isolation of Listeria monocytogenes from a normally sterile site, such as blood, spinal fluid (in the setting of nervous system involvement), or amniotic fluid/placenta (in the setting of pregnancy). Cultures from non-sterile sites, such as stool samples, are not recommended (1-15% carriage rate) but may still be useful in gastroenteritis with high suspicion of listeriosis. Listeria monocytogenes may be isolated readily on routine media. Since Listeria is an intracellular organism, only 1/3 of cultures yield positive Gram-stains. Selective enrichment media improve rates of isolation from contaminated specimens. The cultures typically require 1-2 days for growth. A negative culture does not rule out infection in the presence of strong clinical suspicion. Serological tests are unreliable and currently not recommended. Laboratory testing on asymptomatic patients (including high-risk asymptomatic patients) is not recommended.[1]
Laboratory Tests
The gold standard for the diagnosis of listeriosis is culture from sterile sites.
Culture
- Diagnosis of listeriosis is made by culturing Listeria from sterile sites (e.g. blood, spinal fluid).
- Cultures from non-sterile sites, such as stool culture or vaginal culture, are not helpful for the diagnosis of listeriosis (approximately 5% to 15% fecal carriage, especially among patients who receive PPI therapy).[2]
- Gram-stain may yield positive results in approximately 1/3 of infected patients (Listeria is an intracellular organism).
- Listeria grows on media such as Mueller-Hinton agar.
- Identification is enhanced if the primary cultures are performed on agar containing sheep blood given the characteristic small zone of hemolysis that can be observed around, and under the colonies.
- Isolation can be enhanced if the tissue is kept at 4°C for some days before inoculation into bacteriologic media.
- The motility at room temperature and hemolysin production are primary findings that help differentiate listeria from other organisms (e.g. coryneform bacteria).
Stool Cultures
- Stool cultures are not indicated in systemic listeriosis patients because routine culture media for enteric pathogens are not appropriate for the growth of Listeria.
- In cases of outbreaks of listeriosis or individual patients with suspected listerial gastroenteritis, special selected media can be used.
Listeriolysin O Titers
- Elevated titers of listeriolysin O titers may distinguish patients with active Listeria infections from those who are carriers of the organism.
- The use of listeriolysin O for the diagnosis of listeriosis is still controversial.[3][4]
References
- ↑ "Listeria".
- ↑ Lennon D, Lewis B, Mantell C, Becroft D, Dove B, Farmer K; et al. (1984). "Epidemic perinatal listeriosis". Pediatr Infect Dis. 3 (1): 30–4. PMID 6701102.
- ↑ Salamina G, Dalle Donne E, Niccolini A, Poda G, Cesaroni D, Bucci M; et al. (1996). "A foodborne outbreak of gastroenteritis involving Listeria monocytogenes". Epidemiol Infect. 117 (3): 429–36. PMC 2271639. PMID 8972666.
- ↑ Dalton CB, Austin CC, Sobel J, Hayes PS, Bibb WF, Graves LM; et al. (1997). "An outbreak of gastroenteritis and fever due to Listeria monocytogenes in milk". N Engl J Med. 336 (2): 100–5. doi:10.1056/NEJM199701093360204. PMID 8988887.