Actinobacillus species

BACTERIA

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