Bacteriology exam prep Pasteurella, Manheimia, Actinobacillus, Pseudomonas

Family of Pasteurellaceae

• Gram-negative, facultative anaerobes, and usually oxidase-positive
• Distinguishes them from the Enterobacteriaceae family
• Many species are commensal in the upper respiratory tract and gastrointestinal tract
• Opportunistic pathogens, with over 30 genera including:
  • Actinobacillus
  • Glaeserella
  • Haemophilus
  • Histophilus
  • Manheimia
  • Pasteurella

Genus Pasteurella

• Natural habitat in birds, mammals, and reptiles
• Found in the upper respiratory tract and gastrointestinal tract
• Pasteurella multocida is the primary pathogenic species

Pasteurella multocida

• Isolated from healthy dogs, cats, reptiles, marine mammals, and livestock
• Carriers are reservoirs for transmission to naive or immunocompromised animals
• Transmission occurs through:
  • Saliva
  • Bites
  • Open wound exposure
  • Respiratory secretions
  • Inhaled air
  • Direct contact with contaminated feces or carcasses
• Causes diseases including:
  • Fowl cholera
  • Hemorrhagic septicemia
  • Mucopurulent rhinosinusitis
  • Atrophic rhinitis
  • Respiratory infections
  • Bite wound-associated infections

Fowl Cholera

• Generally manifests as acute septicemia or chronic localized infection
• Systemic infection in birds with four forms:
  • Peracute: no clinical signs, high mortality
  • Acute: lasts for several days, listlessness, anorexia, diarrhea, nasal and ocular discharge, lower mortality
  • Subacute: mostly respiratory signs, mucopurulent nasal discharge
  • Chronic: caseous lesions in joints, middle ear, ovaries, or wattles

Hemorrhagic Septicemia

• Acute systemic infection in cattle, water buffalo, and other species
• Important disease in Asia, Africa, and the Middle East
• Causes vascular damage resulting in:
  • Hemorrhage
  • Focal necrosis in parenchymatous organs
  • Ulcerations of mucous membranes
  • Fluid loss
  • Generalized hemorrhagic lymphadenopathy
• Signs and outcomes are due to severe systemic inflammatory response and multi-organ infections
• High fever, depression, subcutaneous edema, hypersalivation, diarrhea, and sudden death
• All excretions are highly infectious

Mucopurulent Rhinosinusitis

• 'Snuffles' in rabbits
• Infection develops after stressful events
• Coinfections with other pathogens, especially Bordetella bronchiseptica, may exacerbate disease
• Complications include:
  • Bronchopneumonia
  • Middle and inner ear infections
  • Conjunctivitis
  • Septicemia

Atrophic Rhinitis

• Chronic, synergistic infection by P. multocida and Bordetella bronchiseptica
• Affects pigs 3-7 months old
• Clinical signs:
  • Sneezing
  • Epistaxis
  • Staining on the face from tear duct obstruction
  • Nasal, skeletal abnormalities
• Lateral deviation or wrinkling of the snout due to rostro-caudal compression
• Secondary pneumonia
• Histologically, fibrinous tissue replaces osseous tissue, bony atrophy, and varying acuteness of inflammation

Virulence Factors

• Capsule
• Cell wall (LPS and Endotoxin)
• Dermonecrotic toxin (P. multocida toxin)
• Adhesins
• Hemagglutinins
• Pili
• Outer Membrane Proteins
• Siderophores
• Function similarly to adhesins
• Resistance to bactericidal effects of serum

Virulence Factors

• Capsule is a virulence factor
• Cell wall consists of Lipopolysaccharide (LPS) and Endotoxin
• Dermonecrotic toxin is produced by P. multocida and affects cell-signaling processes, leading to:
  • Increased levels of inflammatory cytokines
  • Proliferation of osteoclasts, disrupting turbinate structures
  • Reduction of osteoblasts, responsible for rebuilding turbinate structures
• Adhesins, Hemagglutinins, Pili, and Outer Membrane Proteins facilitate colonization
• Siderophores help resist bactericidal effects of serum

Genus Mannheimia

• Gram-negative, bipolar staining, non-motile, and variable morphology (rods and coccobacilli)
• Mucosal commensals and pathogens for domestic and wild ruminants and other species
• 7 species, with Mannheimia haemolytica being the most important
• Natural habitat: nasal cavity and nasopharynx of cattle and sheep

Mannheimia haemolytica

• Opportunistic pathogen causing pneumonia as part of the Bovine Respiratory Disease (BRD) complex
• Does not cause disease by itself in immunocompetent hosts
• Can cause fibrinous pneumonia under certain conditions

Predisposing Factors for Disease

• Weaning
• Animal transport (shipping fever pneumonia)
• Castration
• Dehorning
• Commingling with animals from different places
• Deprivation of food and water
• Abrupt dietary changes
• Weather changes
• Other illnesses (e.g., BRSV, BHV-1, BPIV, BoCV, BVDV)

Pathogenesis of Pasteurella and Mannheimia

• Infections typically transmitted through inhalation, ingestion, and bite or scratch wounds
• Many infections are likely to be endogenous and manifest in three ways:
  • Respiratory tract diseases
  • Atrophic rhinitis
  • Acute hemi-hemolytic infection

Respiratory Tract Diseases

• Pneumonia or pleuropneumonia, most frequent in ruminants with predisposing factors and lowered immunity
• Commensal bacteria migrate to lower respiratory tract and deposit in lungs
• Virulence factors (LPS, leukotoxin, etc.) initiate intense inflammatory response
• Results in fibrin deposition, thrombosis, and inflammation

Shipping Fever/Bovine Respiratory Disease Complex (BRDC)

• Typically seen 1-2 weeks post transport
• Clinical signs:
  • Fever
  • Inappetence
  • Listlessness
  • Respiratory signs (nasal discharge, cough, respiratory distress)
  • Inconsistently present
  • Abnormal lung sounds may be detected over apical lung lobes

Pasteurella multocida

• Most commonly isolated from older cows and young dairy cows with pneumonia
• Unlike Mannheimia haemolytica, does not cause airway and alveolar neutrophil infiltration, necrosis, or fibrin deposition

Mannheimia haemolytica-induced Acute Hemi-hemolytic Infection

• Severe fibrinous necrotizing pleural pneumonia with exudate and proteinaceous fluid in the pleural space
• Microscopically, inflammatory response causes gross lesions with massive neutrophil infiltration, necrosis, hemorrhage, fibrin deposition, and thrombi

Atrophic Rhinitis

• Chronic, synergistic infection by P. multocida + Bordetella bronchiseptica
• B. bronchiseptica first attaches to nasal mucosa and secretes Dermonecrotic toxin (DNT), causing mild damage to nasal epithelium
• P. multocida then attaches and secretes Pasteurella multocida toxin (PMT), leading to destruction of turbinates

Bacteremic & Septicemic Diseases

• Caused by P.multocida infections in ruminants and avian species
• Hemorrhagic septicemia: acute systemic infection with P.multocida in cattle
• Important disease in cattle and water buffalo in Asia, Africa, and the Middle East
• Sporadic cases occurring in other species and locations
• Causes vascular damage, leading to severe systemic inflammatory response and multi-organ infections
• All excretions are highly infectious

Trauma-Related Diseases

• Caused by "mouth microorganisms" inoculated into bite wounds or by licking wounds
• Most commonly caused by P.multocida

Genus Actinobacillus

• 16 species and 2 subspecies
• Several species associated with diseases in animals
• Associated species: A.pleuropneumoniae, A.lignieresii, A.suis, A.equuli, A.seminis
• Natural habitat: commensal of mucosal surfaces (except A.pleuropneumoniae)
• Respiratory tract, alimentary tract, and genital tracts

Actinobacillus: Transmission & Pathogenesis

• Transmission: aerosols, close contact, epidermal breaches
• Neonatal infections originate from mothers
• Primarily endogenous
• Pathogenesis:
  • Deposition of actinobacillus into a normal sterile environment
  • Initiation of inflammatory response
  • Interference of host phagocytic processes
  • Cytotoxic toxin production
  • Neutrophil and macrophage destruction
  • Release of neutrophilic cellular contents
  • Resulting in tissue damage

Actinobacillus spp. Associated with Animal Diseases

• A.lignieresii: oropharynx of cattle and sheep, causing "wooden tongue"
• A.suis: septicemia and localized infections, sometimes causing pleuropneumonia in horses and pigs
• A.equuli: purulent nephritis and arthritis, especially in foals and piglets, sometimes causing pleuropneumonia
• A.pleuropneumoniae: nasal cavities and tonsillar crypts of healthy pigs, causing acute pleuropneumonia disease outbreaks in pigs

A.pleuropneumoniae in Swine

• Occurs worldwide with 19 serotypes
• All serotypes can cause pleuropneumonia in pigs if conditions are optimal
• Clinical pleuropneumonia can occur at any age in susceptible animals
• Most commonly affects 2-4 month old piglets, but can occur in animals as young as 3 weeks
• Passive immunity from the sow begins to wane around the 2-4 month mark, making piglets more susceptible to infection
• Transmission via aerosols, inducing clinical disease in as little as 24 hours
• Disease occurrence and severity influenced by facility production practices, environmental temperature, and ventilation
• Produces necrotizing, fibrinohemorrhagic pneumonia with pleuritis and serosanguinous thoracic effusion
• Resulting death likely due to respiratory failure

Actinobacillus spp. Pathogenesis

• Reduced ventilation facilitates the migration of microorganisms from palatine tonsillar crypts to the lower respiratory tract, leading to inflammation, coughing, and aerosol transmission.

A. suis in Swine

• May be difficult to distinguish from pleuropneumonia.
• Can cause pleuropneumonia in older pigs.
• Causes septicemia, arthritis, petechial hemorrhage, and endocarditis in younger pigs.
• Clinical characteristics include sudden death of piglets and prolonged disease in older pigs.
• Pathological changes include vasculitis, leading to cutaneous petechial hemorrhages in kidneys, heart, and lungs.

A. lignieresii in Cattle

• Causes 'Wooden tongue', a chronic granuloma in the soft facial tissues and tongue of ruminants.
• Infection spreads to lymph nodes, producing granulomas along the lymph vessels.
• Tongue involvement is not typical, but if involved, proliferative tissue reaction causes tongue to protrude from mouth.
• Lesions may contain plant fiber, indicating external penetration and coalescence.

A. equuli in Horses

• Sporadic, infrequent, and often fatal.
• Animals that survive the first few days typically develop umbilical infections and lameness due to polyarthritis and/or purulent nephritis.
• Global occurrence, naturally present in the oral cavity of mares.
• Infects neonates during or immediately following birth through aerosols or umbilicus, causing 'Sleepy foal' disease.
• Clinical characteristics include neonatal septicemia, fever, inappetence, prostration, and diarrhea.
• Disease strongly associated with colostrum deprivation.

A. seminis in Sheep

• One of the bacterial species that can cause epididymitis in rams.
• Normally resides in the prepuce and is an opportunistic pathogen that ascends to cause infection.
• Affects all parts of the genital tract, with greatest severity in the epididymis.
• Causes fibrinosuppurative and necrotic infection involving both epididymides.
• Prolonged infections can lead to enlargement of the epididymis, herniation through the scrotal wall, and becoming fibrinotic.

Genus Pseudomonas

• Consists of over 200 species and subspecies
• Gram-negative, rod-shaped, and aerobic

Habitat and Distribution

• Found in soil, water, plants, and sewage
• Present on skin, mucous membranes, and feces of healthy animals
• Not part of normal microbiota, but rather transient
• Can be opportunistic pathogens in compromised host immune systems

Pathogenic Mechanism of P. aeruginosa

• Contaminates areas with reduced normal flora, replacing it
• Disruption of normal flora often due to antimicrobial agents
• Resistant to commonly used antimicrobials
• Breaches the first line of defense and invades tissues
• Releases toxins and enzymes, causing tissue destruction
• Infection potential dependent on quorum sensing and T6SS virulence factors

P. aeruginosa Infections in Animals

Cattle

• Pneumonia
• Metritis
• Mastitis
• Enteritis (in calves)
• Dermatitis

Sheep

• Pneumonia
• Mastitis
• Fleece-rot
• Dermatitis
• Otitis media

Pigs

• Respiratory infections
• Otitis

Horses

• Pneumonia
• Endometritis
• Genital tract infections
• Ulcerative keratitis
• Conjunctivitis

Dogs and Cats

• Pneumonia
• Cystitis
• Lower UTI
• Pyoderma
• Ulcerative keratitis
• Ocular infections
• Otitis externa

Other Animals

• Mink: Hemorrhagic pneumonia, Septicemia
• Chinchillas: Pneumonia, Septicemia
• Rabbits: Moist dermatitis ('blue fur disease')
• Reptiles: Necrotic stomatitis