Bacteriology exam prep :Erysipelothrix, Cornyebacterium, Listeria

Genus Erysipelothrix

• 6 species, 28 serotypes
• Only species with veterinary significance is Erysipelothrix rhusiopathiae

Characteristics

• Gram +’ve
• Non-motile
• Facultative anaerobe
• Mesophilic (optimal in moderate temperatures)
• Non-spore forming
• Catalase -’ve
• Oxidase -’ve

Erysipelothrix Rhusiopathiae

• Most commonly associated with pigs (tonsils & intestinal tract lymphoid tissues)
• Healthy carriers: bacteria carried in tonsils and GIT lymph tissue
• Ubiquitous in nature & persists at low temperatures, alkaline pH within organic matter
• Can survive for long periods without replicating in soil and marine environments
• Isolated from many species: mammals, birds, reptiles, fish

Causes Erysipelas in

• Swine
• Poultry
• Sheep & lambs (sporadic infections)

Transmission

• Pigs shed bacteria in feces and bodily secretions, contaminating environment
• Transmission via ingestion of contaminated material: food, water, soil, feces
• Transmission via wound infection: epidermal breaches, arthropod bites
• Pigs between 3 months to 3 years of age are most susceptible

Predisposing Factors

• Environmental stress
• Abrupt dietary changes
• Fatigue
• Subclinical aflatoxicosis
• Intoxication of toxins caused by a variety of mold species

Swine Erysipelas

• After oral or percutaneous infection, bacteria proliferate in the portal of entry
• Approximately 3-5 days of incubation, bacteria disseminate throughout the host
• Four forms: septicemic, acute, chronic arthritis, vegetative endocarditis

Septicemic Form

• Some animals die before symptoms develop
• High mortality rate, pregnant sows may abort
• Acute cases: fever, anorexia, stiff gait, depression, vomiting, reluctance to walk
• Cutaneous lesions: diamond skin, abdomen, thighs, ears, tail, necrosis, sloughing off skin

Acute Form

• Fever, depression, anorexia
• Cutaneous lesions: pink/purple raised areas of skin, diamond/rhomboid shaped, erythematous plaques
• Plaque size and number vary
• Generalized coagulopathy: thrombosis, invasion of vascular endothelium, deposition of fibrin perivascular tissues

Chronic Arthritis

• May occur as a result of acute disease or persistent infection by low virulence strains
• Presents with stiffness, lameness or reluctance to weight-bear on affected limbs
• Localized joint infections: fibrinous exudation, pannus, proliferative changes due to immune response
• Joint lesions: erosion of articular cartilage, fibrosis, ankylosis

Vegetative Endocarditis

• Less common than joint involvement
• Initiated by bacterial emboli and vascular inflammation
• Lesions lead to valvular insufficiency, congestive heart failure, or release of emboli
• Mitral valves most commonly affected
• Chronic condition, many animals asymptomatic
• Symptoms: manifestations of cardiac insufficiency, sudden death

Genus Listeria

• 10 species, 2 of which are pathogenic: Listeria monocytogenes and Listeria ivanovii
• Widely distributed in the environment, frequently found in cold and temperate climates
• Primary habitat is soil and decaying vegetation; isolated from over 50 species, including ruminants, swine, horses, dogs, cats, and various avian species

Characteristics

• Gram-positive, small, coccobacilli rods (up to 2µm)
• Facultative anaerobes, facultative intracellular, non-spore forming, and motile at 25ºC

Transmission

• Ruminants are the most frequently affected species, with poor quality silage (pH > 5.5) commonly associated with transmission
• Multiple modes of transmission: ingestion, inhalation, and mucous membrane wound contamination
• Asymptomatic carriers are indirect sources of infection, leading to persistent environmental contamination

Listeria Pathogenesis

• Ingestion of bacteria, attachment to M cells in Peyer's patches, and transport to lamina propria
• Phagocytic cells uptake, dissemination via bloodstream, and escape from phagosome to become motile
• Avoidance of host immune mechanisms and continued infection of other cells

Forms of Listeria

• Septicemia (Visceral): most common in monogastric species, affecting organs other than the brain
• Meningoencephalitis (Neural): primarily affects sheep, cattle, and goats, with localized, asymmetric infection of the brainstem
• Abortions: L. monocytogenes invades fetoplacental tissues, causing abortions in various species
• Mastitis: subclinical to severe suppurative mastitis, with Listeria as an environmental agent

Listeria in Humans

• Zoonotic, food-borne pathogen causing severe infections in immunocompromised, pregnant, and neonatal populations
• Manifests from mild gastroenteritis to severe cases of sepsis, meningitis, encephalitis, or abortion
• Common forms include meningitis, meningoencephalitis, and hydrocephalus in newborns

Genus Corynebacterium

• Part of the CMNR group, which includes Mycobacterium, Nocardia, Rhodococcus, and Actinomycetes class, and family Corynebacteriaceae
• Found on skin, udders, mucous membranes of the nasopharynx and intestinal tract of animals and humans
• Both pathogenic and non-pathogenic species with biotech applications

Characteristics

• Gram +ve
• Non-motile
• Pleomorphic, irregular or club-shaped
• Non-sporulating
• Mycolic acid layer (corynomycolic acids) covering the cell wall, functionally equivalent to outer membrane of Gram -ve bacteria

Species of Veterinary Relevance

• Corynebacterium pseudotuberculosis
• Corynebacterium renale group
  • C. renale
  • C. cystitidis
  • C. pilosum

Transmission and Pathogenesis of C. pseudotuberculosis

• Transmission: superficial wound contamination, bacteria enter and spread through the host body via the lymphatic system to lymph nodes and other organs
• Pathogenesis: bacteria invades neutrophils and macrophages, multiplies intracellularly, and causes host cells to degenerate and necrose, leading to a host response of forming granulomas and abscesses

Caseous Lymphadenitis (CLA)

• Causes significant economic loss in sheep and goat industries due to decreases in wool, milk, meat, and quality of leather due to scarring
• Two forms:
  • Granulomatous: necrosis of superficial lymph nodes and subcutaneous lesions
  • Visceral: lesions in internal organs and lymph nodes, such as lungs, kidneys, spleen, liver, and intestines

Ulcerative Lymphangitis

• Affects cattle and horses
• Cattle: develops skin infections with lymph node involvement, most common on lateral body walls with trauma allowing for bacterial invasion
• Horses: rare, but can present in three forms:
  • Ulcerative lymphangitis: manifests as nas cellulitis ascending the lymphatics, forming abscesses that rupture and result in ulcers
  • Internal abscessation: difficult to recognize, with symptoms of weight loss, fever, depression, and colic
  • External form (Pigeon Breast/Pigeon Fever/Breast Bone Fever): most common form, usually a single, large abscess with a thick capsule on the underside of the abdomen or pectoral region

Other Pathogenic Corynebacterium species

• C. auriscanis: causes otitis externa in dogs and cats
• C. bovis: causes mastitis in cattle
• C. kutscheri: commensal in rodent oral cavities, causes pseudotuberculosis in immunosuppressed mice
• C. diphtheriae, C. striatum, and C. ulcerans: zoonotic, may colonize animals without causing serious disease, and infected animals can act as a source of infection for humans