WHAT IS IT?
Listeria monocytogenes is a gram positive rod shaped (bacillus) bacterium. It is a a facultative intracellular pathogen.
Beta hemolytic when grown on agar plates
Tumbling motility can be observed with microscopy given this bacterium uses a flagella for movement. This occurs at 22°C (bacteria immobile at 37°C)
Growth in cold temperatures this organism is able to multiply at temperatures as low as 4°C. This is why it can contaminate refrigerated foods.
Listeriolysin O: pore forming toxin that is selectively activated within acidified phagosomes. This is how this organism can lyse vacuolar membranes when other cells ingest it by phagocytosis.
Rocket tails are formed by actin polymerization that allow the intracellular movement of these pathogens. This feature can also enable the cell-to-cell spread across cell membranes (which help avoid antibodies). The video below shows these “rocket tails” in action.
Endotoxin: this pathogen is the only gram positive bacterium that produces endotoxin.
Ingestion of contaminated foods (even refrigerated ones) are especially associated with Listeria infection:
- Unpasteurized milk/dairy products
- Cold deli meats
Transplacental transmission can occur between the mother and fetus.
Vaginal transmission can also occur during birth
Neurologic: meningitis (usually in immunocompromised individuals), neonatal meningitis,
Pregnancy related: amnionitis, spontaneous abortion, granulomatosis infantiseptica
Ampicillin is the antibiotic of choice for this pathogen.
Trimethoprim-sulfamethoxazole can also be sued for treatment.
OTHER HY FACTS
Not spore forming: this organism does not form spores.
Cell mediated immunity is important for combating this microbe (given its intra-cellular nature.
Intact cell mediated immunity is essential for elimination of this bacteria from the body.
ARCHIVE OF STANDARDIZED EXAM QUESTIONS
This archive compiles standardized exam questions that relate to this topic.
Page Updated: 07.23.2016