The pathogenic bacterium Listeria monocytogenes is the source of listeriosis, a dangerous illness usually contracted by consuming tainted food. In order to distinguish Listeria monocytogenes from other bacteria, a battery of biochemical assays is frequently employed. Here are a few of the crucial exams.
Table of Contents
Key Test
1. Catalase Test
- Purpose: The goal is to find out if the catalase enzyme, which converts hydrogen peroxide into water and oxygen, is present.
- Result for L. monocytogenes: Positive (the addition of hydrogen peroxide causes bubbles to form).
2. Gram Stain
- Purpose: The goal is to separate bacteria according to the make-up of their cell walls.
- Result for L. monocytogenes: Gram-positive (purple-colored cocci or short rods) is the result for L. monocytogenes.
3. Motility Test
- Purpose: To assess bacterial motility.
- Result for L. monocytogenes: Positive (exhibits a characteristic tumbling motility at room temperature).
4. CAMP test
- Purpose: To determine the generation of CAMP factor, which increases hemolysis when Staphylococcus aureus is around.
- Result for L. monocytogenes: Positive (enhanced hemolysis observed).
5. Hemolysis on Blood Agar
- Purpose: To observe hemolysis patterns, which help in identification.
- Result for L. monocytogenes: Weakly beta-hemolytic; colonies are surrounded by a small hemolysis zone.
6. Esculin Hydrolysis
- Purpose: To test the ability to hydrolyze esculin.
- Result for L. monocytogenes: Positive (blackening of the medium).
7. Hippurate Hydrolysis
- Purpose: To test the ability to hydrolyze hippurate to glycine and benzoic acid.
- Result for L. monocytogenes: Positive (formation of a deep purple color).
8. Voges-Proskauer (VP) Test
- Purpose: Tpo determine the production of acetonin from glucose fermentation.
- Result for L. monocytogenes: Positive ( red color after addition of VP reagents).
9. Sugar Fermentation Tests
- Purpose: To assess the ability to ferment various sugars.
- Common sugars tested: Glucose, lactose, mannitol, and rhamnose.
- Result for L. monocytogenes:
Glucose: Positive (acid production)
Lactose: Negative (no acid production)
Mannitol: Variable
Rhamnose: Positive (acid production)
10. Nitrate Reduction Test
- Purpose: To determine the ability to reduce nitrate to nitrite or other nitrogenous compounds.
- Result for L. monocytogenes: Positive (red color after addition of nitrate reagents, indicating nitrite production).
11. Serological Test
- ELISA (Enzyme-Linked Immunosorbent Assay): This method uses organism-specific antibodies to find Listeria antigens in samples.
A facultative anaerobic Gram-positive bacteria, Listeria monocytogenes is frequently found in soil and food. It can result in listeriosis, a dangerous infection that is especially dangerous in susceptible groups like infants, expectant mothers, and people with weakened immune systems.
Summary Of Key Identifying Features
- Gram-positive: Purple coloration under a microscope.
- Catalase-positive: Presence of bubbles.
- Tumbling motility: Observed at room temperature.
- Beta-hemolysis: Narrow zone on blood agar.
- Positive CAMP and esculin hydrolysis tests: Characteristic of L. monocytogenes.
- Positive VP and hippurate hydrolysis tests: Differentiates from other species.
Important Consideration
- Adhering to appropriate laboratory protocols is essential in order to avoid cross-contamination and guarantee precise identification.
- Confirmation should come from many testing, particularly in cases of foodborne infections.
- Compared to conventional biochemical tests, molecular and serological diagnostics provide faster and more accurate results.
Frequently Asked Question(FAQ)
What test confirms Listeria monocytogenes?
Blood cultures are the best clinical specimens for suspected, symptomatic cases of listeriosis. It is not advised to test for Listeria in asymptomatic individuals who have consumed a recalled or contaminated food item. evaluation, two sets of standard blood cultures (which find Listeria spp.) may be taken into consideration.
Is Listeria monocytogenes catalase positive?
When cultivated on blood agar, Listeria monocytogenes is a facultative intracellular rod bacterium that is gram-positive, catalase positive, and beta-hemolytic.
How can Listeria monocytogenes be confirmed?
A laboratory test that finds Listeria in bodily tissue or fluid—such as blood, spinal fluid, or the placenta—is typically used to diagnose infections. The kind and degree of a person’s condition determine the course of treatment. Antibiotics are used to treat the majority of Listeria infections.
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