Module 6 (Listeria)

What is the only pathogenic Listeria species for warm-blooded animals and humans?

Listeria monocytogenes

What is the Gram reaction and shape of Listeria monocytogenes?

Gram-positive, small rods

How does Listeria monocytogenes appear in older cultures?

Gram-negative in young cultures, almost entirely Gram-negative in old cultures

What type of motility does Listeria monocytogenes exhibit?

Tumbling motility with peritrichous flagella

What is a distinguishing feature of Listeria monocytogenes morphology?

Shows slight clubbing, diphtheroid appearance, and coccoid forms

On what media does Listeria monocytogenes grow?

Most ordinary media, though growth is never abundant

What is the appearance of Listeria monocytogenes colonies on blood agar?

Small, flat, bluish-white, transparent

What type of hemolysis does Listeria monocytogenes exhibit?

Beta-hemolysis with narrow zones

What is the characteristic growth pattern of Listeria monocytogenes in gelatin?

Inverted fir tree formation

How does Listeria monocytogenes differ from Erysipelothrix rhusiopathiae biochemically?

Produces catalase

How many O and H antigens does Listeria monocytogenes have?

15 O antigens, 5 H antigens

How many serotypes and subtypes exist for Listeria monocytogenes?

16 serotypes, 14 subtypes

How do the neural and visceral forms of Listeria monocytogenes infection differ?

Neural form: via trigeminal nerve; Visceral form: via ingestion

What is the major mode of infection for visceral Listeria monocytogenes infection?

Ingestion

What type of infections are most Listeria monocytogenes cases classified as?

Exogenous infections

What reproductive effect does Listeria monocytogenes have in cows and ewes?

Causes abortion without neural manifestations

What is the common presentation of Listeria monocytogenes in chickens and turkeys?

Septicemic form with necrotic foci in the liver and myocardium

Where is Listeria monocytogenes commonly found?

Ubiquitous in nature, present in animal and human feces

How does pH affect Listeria monocytogenes survival?

Survival is poor below pH 5

Why is Listeria monocytogenes more heat-tolerant than most non-sporeforming bacteria?

It has increased resistance to environmental conditions

Where is Listeria monocytogenes commonly harbored in swine?

Tonsils

What enables Listeria monocytogenes to invade host cells?

Surface protein internalin interacts with E-cadhedrin

How does Listeria monocytogenes escape from the phagosome?

Produces hemolysin listeriolysin O

What is the role of listeriolysin O?

Lyses cholesterol-containing membranes of eukaryotic cells

How does Listeria monocytogenes move within host cells?

Induces actin polymerization to push against the cell membrane

What are filopods in Listeria monocytogenes infection?

Protrusions formed by bacterial movement within cells

Why is it difficult to recover Listeria monocytogenes from brain tissue?

Requires prolonged cold enrichment up to 12 weeks

What temperature is used for cold enrichment of Listeria monocytogenes?

Refrigerator temperature

On what medium is Listeria monocytogenes routinely isolated?

Blood agar

What environmental conditions stimulate Listeria monocytogenes growth?

5-10% CO2

What is the appearance of Listeria monocytogenes colonies under transmitted light?

Round, entire, glistening, bluish

How does Listeria monocytogenes survive in the environment?

Resistant to drying

Where can Listeria monocytogenes persist for months?

Food, straw, soil, shavings

What immune response is most important in Listeria monocytogenes infections?

T-cell mediated activation of macrophages

What is the role of humoral immunity in Listeria monocytogenes infections?

Not clearly understood

Is immunization commonly practiced against Listeria monocytogenes?

No, immunization is not widely practiced

What antibiotics are effective against Listeria monocytogenes?

Chloramphenicol, tetracycline, sulfonamides, penicillin

What are the preferred treatments for Listeria monocytogenes infections in humans?

Erythromycin and ampicillin