Actinobacillus species

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Overview

• Mainly pathogens of farm animals
• Commensals of mucosa of upper respiratory tract and oral cavity
• Cannot survive long in the environment, therefore carrier animals are important in their transmission
• Cause granulomatous inflammation

Actinobacillus characteristics

• Small Gram negative coccobacilli
• Oxidase negative
• Do not grow on MacConkey
• Non-motile
• Facultative anaerobes which ferment carbohydrates to produce acid

Actinobacillus lignieresii

• Pathogenesis and pathogenicity:
  • Commensal in the mouth and intestinal tract of cattle and sheep
  • Penetrates damaged mucosa to cause chronic granulomatous inflammation of soft tissues, a condition known as Actinobacillosis
  • Enodogenous, sporadic infection
  • Lesions in the tongue, cheek, lips and sometimes in the lower gut and lungs from aspiration
  • Often spreads from the site of infection to lymphatics, and may cause pyogranulomatous lymphadenitis
  • Myositis and formation of fibrous tissue in the lesions lead to hardening of the tissue, hence the condition is known as 'wooden tongue' in cattle
  • In sheep abscesses with thick walls are produced
  • Feeding is impaired, causing loss of condition
  • Infection in the oesophageal groove can cause tympany and enlargement of the retropharyngeal lymph node, causing difficulty in swallowing and breathing
  • Cutaneous lesions in cattle and sheep
  • Contamination of the environment via ulcerating lesions
• Diagnosis:
  • Induration of tongue
  • Tissue sections may demonstrate pyogranulomatous foci containing club colonies
  • Gram negative rods may be present in smears from exudates
  • Cultures on blood agar and MacConkey agar, incubated for 24-72 hours
  • Blood agar: small, sticky, non-haemolytic clonies
  • MacConkey agar: slow lactose fermentation
• Treatment:
  • Sodium iodide parenterally, or potassium iodide orally
  • Potentiated sulphonamides or a penicillin/streptomycin combination
  • Rough feed should be avoided

Actinobacillus pleuropneumoniae

• Contagious porcine pleuropneumonia especially of pigs under 6 months
• Endemic in UK
• 12 serotypes causing the same disease
• Different serotypes in different regions, with serotypes 3,6 and 8 the most common in the UK
• Pathogenesis and pathogenicity:
  • Virulent strains possess capsules which are antiphagocytic and immunogenic
  • Fimbriae allow the bacteria to attach to cells of the respiratory tract
  • Damaged neutrophils in the lungs produce lytic enzymes
  • The sustained inflammatory response causes tissue necrosis
  • Lungs consolidated and necrotic with fibrinous pleuisy at post mortem
  • Produce three cytotoxins which belong to the repeats-in-structural-toxin (RTX) cytolysin family
  • RTX toxins:
    • Several peptide repeats within the molecules
    • Produced by various Gram-negative bacteria
    • Possess four contiguous genes, A, B, C and D
    • A is the structural gene; B and D are required for secretion; C allows post-translational activation of the gene product of A into a functional product
    • ApxI is a strong haemolysin with cytolytic activity
    • ApxII is a weak haemolysin
    • ApxIII is a cytotoxin
    • Different Actinobacillus pleuropneumonia serotypes secrete a particular combination of toxins; American serotypes secrete ApxI and II; European serotypes secrete ApxII and III
    • Toxins introduce pores into cell membranes
• Clinical signs and epidemiology:
  • Acute disease in susceptible herds with high morbidity and mortality (up to 50%)
  • In acute outbreaks, pigs may be dyspnoeic, pyrexic or anorexic
  • Blood-stained froth surrounding nose and mouth
  • Cyanosis
  • Pregnant sows abort
  • Causes pneumonia in pigs
  • Carrier herds have some immunity, protecting from acute disease, where lesions are often subclinical, and deaths sporadic
  • Lung scarring and pleural adhesions in many recovered animals
  • Solid immunity develops in recovered animals to all serotypes
  • The disease is spread between herds by carrier pigs
• Diagnosis:
  • Haemorrhagic consolidation close to the main bronchi and fibrinous pleuritis may be suggestive
  • Specimens are cultured on chocolate agar and blood agar in 5-10% carbon dioxide for 2-3 days
  • Small colonies surrounded by clear haemolysis
  • No growth on MacConkey agar
  • Positive CAMP reaction with Staphylococcus aureus
  • Most strains are NAD-dependent (grow on Heated Blood agar)
  • Immunofluorescent- or PCR-based techniques
  • The bacteria on the palatine tonsil may remain undetected by serological tests and swabbing, and can therefore cause an outbreak in naive pigs
• Treatment:
  • Antibiotics depending on the strain of bacteria
  • Prophylactic antibiotics for in-contact pigs
• Control:
  • Killed and polyvalent bacterin vaccines as well as a subunit vaccine are available
  • Improve ventilation, avoid chilling and overcrowding

Actinobacillus equuli

• Commensal of the equine intestinal and reproductive tract
• Pathogenesis and clinical signs:
  • Foals infected in utero or or after birth via the umbilicus
  • Infection at birth causes severe enteritis and septicaemia within 24 hours, known as sleepy foal disease
  • Foals become pyrexic and recumbent
  • Death usually occurs within 1-2 days
  • In foals that survive neonatal infection the condition progresses to cause joint infections and purulent nephritis, enteritis or pneumonia
  • A. equuli in arthritis of horses
  • Abortion, septicaemia and peritonitis in horses
• Diagnosis:
  • Specimens cultured on blood agar and MacConkey agar and incubated aerobically for 1-3 days
  • Sticky colonies with variable haemolysis on blood agar
  • Lactose-fermenting colonies on MacConkey agar
• Treatment and control:
  • Antimicrobials ineffective unless early in course of disease
  • Blood trasfusion and administration of colostrum
  • Good hygiene
  • Consider prophylactic antibiotics for new-born foals
  • Bacteria susceptible to streptomycin, tetracyclines and ampicillin
• In other animals:
  • Septicaemia in piglets
  • Arthritis and enteritis in pigs
  • Enteritis in calves
  • RTX group cytotoxin present

Actinobacillus suis

• May be present in upper respiratory tract of sows
• Pathogenicity and clinical signs:
  • Infection of piglets via aerosol or possibly skin abrasions
  • Fatal septicaemia in piglets 1-8 weeks old
  • Mortality up to 50% in some litters
  • Fever, respiratory distress, prostration and paddling of forelimbs seen in piglets
  • Petechial and ecchymotic haemorrhages in many organs
  • Interstitial pneumonia, pleuritis, meningoencephalitis, myocarditis and arthritis
  • Causes abscesses in joints and lungs of older pigs
  • Carried in the nasopharynx of pigs and nose of horses
  • Carriage may confer immunity to the more severe pleuropneumonia
• Diagnosis:
  • Specimens cultured on blood agar and MacConkey agar for 1-3 days
  • Sticky haemolytic colonies
  • Pink, lactose-fermenting colonies on MacConkey agar
• Treatment and control:
  • Bacteria usually susceptible to ampicillin, carbenicillin, potentiated sulphonamides and tetracyclines
  • Disinfect contaminated pens
• Other animals:
  • Septicaemia and pneumonia in foals
  • Pneumonia in pigs and horses

Actinobacillus seminis

• Epididymitis in young rams (4-8 months)
• Polyarthritis in lambs
• Organism found in prepuce
• Opportunistic infection causing abscesses in epididymides
• May be purulent discharge onto scrotal skin
• Specimens cultured on blood agar and incubated aerobically for 1-3 days produce pin-point haemolytic colonies which are catalase-positive; no growth on MacConkey agar

Actinobacillus actinomycetemcomitans

• Epididymitis in rams