Comprehensive Study Notes: Listeria and Erysipelothrix week10pt1
Introduction to Gram-Positive Rods: Listeria and Erysipelothrix
This lecture covers two specific genera of Gram-positive rods: Listeria and Erysipelothrix.
There is one species of primary interest within each genus:
Listeria monocytogenes (Genus Listeria).
Erysipelothrix rusiopathiae (Genus Erysipelothrix).
Both are significant pathogens in animals and humans.
Key areas of focus include laboratory features, virulence factors, host interactions, environmental interactions, and disease management.
Listeria monocytogenes: Microbiological and Laboratory Features
Morphology: A Gram-positive rod with a uniform shape; it is not pleomorphic.
Distribution: Widely distributed in nature; it is a common saprophytic organism that survives and replicates easily in the environment.
Commensal Status: It is frequently acquired as a commensal within the gut through ingestion.
Temperature Tolerance (Psychrotrophic Properties):
Listeria can grow across a wide range of temperatures but has a preference for cold climates.
It is classified as a psychrotrophic bacterium, meaning it can grow between .
This ability allows it to survive and proliferate in refrigerated conditions, making it a major food safety concern for both human and animal public health (e.g., cold storage of animal feed or human food).
Motility: It is a motile organism but lacks flagella; it utilizes internal propulsion mechanisms.
Metabolism: It is a facultative anaerobe.
Biochemical Tests:
Catalase Test: Positive.
Esculin Hydrolysis: It hydrolyzes esculin, creating a byproduct that results in a black reaction on media. These colonies fluoresce under UV light due to the breakdown process.
CAMP Test: Shows a positive reaction when streaked against Rhodococcus equi.
Hemolysis: Exhibits a narrow zone of complete (beta) hemolysis on sheep blood agar.
Pathogenesis and Virulence Factors of Listeria
Facultative Intracellular Parasitism: Its primary parasitic property is the ability to live inside host cells. It can cross from cell to cell without lysing them, thereby avoiding exposure to host antibodies.
Intracellular Life Cycle and Enzymes:
Invasion: Expresses the protein internalin, which allows the bacteria to invade non-phagocytic cells.
Survival: Produces Listeriolysin O, which prevents phagosome-lysosomal fusion, allowing the organism to survive within the phagosome.
Movement: Expresses Act A, which induces the formation of an "actin tail." This tail propels the bacteria laterally within the cytoplasm of the host cell.
Cell-to-Cell Spread: Produces lecithinase, which allows the organism to exit one cell and enter a neighboring cell.
Immune Response: Because the pathogen stays intracellular, cell-mediated immune responses are critical for clearance; extracellular defenses like antibody responses are largely ineffective.
Clinical Manifestations of Listeriosis
Visceral Form:
Occurs when the organism is ingested and enters the bloodstream (septicemia).
Spread leads to granulomatous foci and internal abscesses in various organs.
In pregnant animals (especially ruminants) and humans, it can reach the fetus and cause abortion or stillbirth.
Neonates are highly susceptible due to immature cell-mediated immunity.
Neural Form (Meningoencephalitis):
More common in animals (cattle and sheep) than humans.
Gains entry through damage to oral, nasal, or oculomucosal membranes.
The bacteria migrate up peripheral nerves (e.g., the trigeminal nerve) to the brain.
Circling Disease: A classic sign where animals circle toward the side of the brain lesion (e.g., if the right side of the brain is infected, they circle left; if the left side is infected, they circle right).
Transmission Scenarios:
Exogenous: Ingestion of soil-contaminated feed.
Endogenous: Septicemia triggered by stress in asymptomatic enteric carriers.
Environmental and Public Health Risks of Listeria
Sources: Soil, sewage, decaying vegetative material, water, and animal feces.
Silage Quality: Silage is fermented fodder. If the fermentation process is poor and the pH is above , Listeria will proliferate. High-quality silage should have a pH below .
The Rock Melon Outbreak (Australia, ~8 years ago):
Contamination occurred during heavy rain events; mud accumulated on the jagged, honeycomb skins of the melons.
Washing was insufficient to sanitize the surface.
Cutting the melon transferred the bacteria from the skin to the flesh.
Resulted in 7 deaths and 1 miscarriage.
Biofilms in Food Processing:
Listeria can form biofilms on equipment like meat slicers.
Example: A Canadian nursing home outbreak where over 200 meat products were contaminated because slicers were not disassembled and cleaned with hot soapy water, leading to 22 deaths.
Dietary Warnings for At-Risk Groups (Elderly, Pregnant, Immunocompromised):
Avoid soft cheeses, unpasteurized dairy, unwashed raw vegetables, and refrigerated pre-packaged meats.
The organism survives down to and can even persist in freezers if conditions are not optimal.
Erysipelothrix rusiopathiae: Microbiology and Virulence
Morphology: Gram-positive short rod; can also appear in a filamentous (rough) form.
Motility: Non-motile.
Metabolism: Facultative anaerobe.
Biochemical Tests:
Catalase: Negative.
Hemolysis: Produces pinpoint colonies with a greenish tinge (alpha-hemolysis/incomplete hemolysis).
Gelatin Slab: Exhibits a characteristic "bottle brush" appearance.
Serotyping: Typed based on peptidoglycan cell wall components, similar to Lancefield typing in Streptococci.
Virulence Factors:
Protective Antigen (Glycoprotein complex): Prevents phagocytosis.
Adhesins: Facilitate attachment to intestinal epithelial cells.
Neuraminidases: Associated with vascular damage and thrombosis; high concentrations correlate with high virulence.
Capsule: Antiphagocytic.
Intracellular Survival: Uses phospholipases and antioxidant enzymes to survive the oxidative burst in phagocytes.
Erysipelas in Pigs and Other Species
Affected Species: Primarily pigs, but also seen in fish, dolphins, walruses, and various birds (psittacines).
Disease Forms:
Acute Septicemia: Fatal form caused by highly virulent strains.
Skin Form (Diamond Skin Disease): Characterized by diamond-shaped lesions. These are a result of an Arthur’s reaction (an immune-mediated/allergic reaction) causing thrombosis in the skin.
Arthritis: Chronic form where the pathogen localizes in the joints, leading to lameness.
Vegetative Endocarditis: Chronic form where the bacteria colonize and damage the heart valves, resulting in congestive heart failure.
Public Health (Zoonosis): Known as Erysipeloid in humans (to distinguish it from Streptococcal Erysipelas). It causes non-suppurative, localized skin swelling, typically after handling contaminated carcasses or fish.
Management and Prevention of Erysipelas
Treatment: Penicillin is the drug of choice. In food animals, strict adherence to withholding periods is necessary to avoid drug residues in meat.
Hygiene and Husbandry:
Minimize overcrowding and stress, which can trigger endogenous infections.
Dispose of infected carcasses via heat treatment.
Quarantine new animals for a incubation period.
Vaccination:
Killed vaccines are available and widely used in piggeries.
They are effective at preventing acute septicemic disease and death (protecting the farmer's investment).
They are less effective at preventing chronic forms like arthritis or skin lesions.
Vaccinating sows and gilts helps transfer maternal antibodies to piglets.
This lecture covers two specific genera of Gram-positive rods: Listeria and Erysipelothrix.
The species of primary interest within each genus are:
Listeria monocytogenes (Genus Listeria), a pathogenic bacterium known for causing listeriosis in humans and animals.
Erysipelothrix rusiopathiae (Genus Erysipelothrix), known for causing Erysipelas in animals, and has zoonotic potential.
Both organisms are significant pathogens in animals and humans, capable of causing severe illness and public health concerns.
Key areas of focus include detailed laboratory features, specific virulence factors that enable pathogenicity, interactions with host immune responses, environmental adaptations, and strategies for effective disease management and prevention.
Listeria monocytogenes: Microbiological and Laboratory Features
Morphology: A Gram-positive rod characterized by its uniform shape; it does not exhibit pleomorphism, which distinguishes it from other rod-shaped bacteria that may vary in appearance.
Distribution: Listeria monocytogenes is widely distributed in various environments, including soil, water, and decaying plant materials. As a saprophytic organism, it possesses the ability to survive and replicate in harsh conditions, making it a persistent environmental contaminant. Additionally, it thrives in nutrient-rich environments such as animal feces and nameless processed foods.
Commensal Status: It often colonizes the gastrointestinal tract of many animals, including humans, and can be acquired through the consumption of contaminated food products.
Temperature Tolerance (Psychrotrophic Properties): - Listeria is particularly noted for its psychrotrophic properties, allowing growth within a temperature range of .
This adaptation is critical for its survival in refrigerated foods and contributes significantly to its risk as a foodborne pathogen; it can grow under refrigeration conditions, which allows it to contaminate food products that are typically considered safe.
Motility: This organism is motile but lacks flagella. Instead, it employs a unique internal propulsion mechanism involving the host's actin cytoskeleton.
Metabolism: It operates as a facultative anaerobe, allowing it to thrive in both aerobic and anaerobic environments.
Biochemical Tests:
Catalase Test: Positive, confirming it can neutralize hydrogen peroxide.
Esculin Hydrolysis: This bacterium can hydrolyze esculin, leading to a black color change on appropriate media, with colonies showing fluorescence under UV light due to this biochemical breakdown.
CAMP Test: Demonstrates a positive reaction when streaked alongside Rhodococcus equi, confirming its identification.
Hemolysis: Exhibits β-hemolysis on sheep blood agar, distinguished by a narrow zone of complete hemolysis.
Pathogenesis and Virulence Factors of Listeria
Facultative Intracellular Parasitism: Its most notable pathogenic feature is its facultative intracellular lifestyle, allowing Listeria monocytogenes to evade the host's immune defenses and persist within host cells.
Intracellular Life Cycle and Enzymes:
Invasion: The surface protein internalin facilitates entry into non-phagocytic cells by binding to host cell receptors.
Survival: The production of Listeriolysin O is crucial for the bacterium's survival inside phagocytes, preventing the fusion of phagosomes with lysosomes and enabling it to thrive within this protected niche.
Movement: By expressing Act A, it employs the host cell’s actin polymerization machinery to form an