Bacteriology lecture--------------------------------------------------------------------------------------------Dr. Zina AL-Shami
Genus Actinobacillus
Actinobacillus is a genus of gram-negative, immotile and nonspore-forming, oval
to rod-shaped bacteria occurring as parasites or pathogens in mammals, birds, and
reptiles.
It is a member of the Pasteurellaceae family. The bacteria are
facultatively aerobic or anaerobic, capable of fermenting carbohydrates (without
production of gas) and of reducing nitrates. Actinobacillus , may present in several
different forms, depending on the specific agent and the host. Soft- tissue infections
are common, and lymph node involvement is frequently a step in systemic spread;
adjacent bony tissue may also be affected.
Virulence factors:
1- polysaccharide capsule (protect against phagocytosis and complement action).
2- pore forming endotoxines (RTX toxins) responsible for cell apoptosis or
necrosis
3- lipopolysaccharides (aid in cell adhesion and colonization).
4- Iron acquisition mechanisms (essential in bacterial metabolism).
5- Urease production (essential for obtaining ammonia as a source of nitrogen)
6- Secreted proteases (used in IgA degradation and mucosal spread).
7- Fambriae.
Pathogenesis:
A actinomycetemcomitans is a common agent of human periodontal disease, and a
rare cause of human endocarditis and ram epididymitis. It is found naturally on
mucous membranes.
A pleuropneumoniae (biotype 1&2) causes contagious pleuropneumonia in pigs.
Disease ranges from acute, severe pleuropneumonia to subacute or chronic
infection with pleuritis and pulmonary abscess. Infection is usually restricted to
pigs <5 mo of age. A pleuropneumoniae may be normal mucosal flora in pigs,
cattle, and sheep.
The natural host of A equuli is the horse; infections are seen in both foals and adult
horses. Disease in foals may manifest as diarrhea, followed by meningitis and
septicemia of neonatal foals called sleepy foal disease. Abortions, septicemia,
nephritis, and endocarditis may result from A equuli infection in adult horses.
Bacteriology lecture--------------------------------------------------------------------------------------------Dr. Zina AL-Shami
A lignieresii causes tumorous abscesses of the tongue, usually referred to as
wooden tongue. It is seen primarily in cattle but also in sheep, horses, pigs, and
dogs. It is a rare cause of disease in chickens. The organism may also cause
pyogranulomatous lesions in soft tissues associated with the head, neck, limbs, and
occasionally the lungs, pleura, udder, and subcutaneous tissue. The organism is part
of the normal mucosal flora of the upper GI tract and causes disease when it gains
access to adjacent soft tissue via penetrating wounds. It causes localized infections
and can spread via the lymphatics to other tissues. Pus from the abscesses may
contain microcolonies surrounded by club-like spicules of calcium phosphate,
giving the appearance of sulfur granules <1 mm diameter. This form of
actinobacillosis is found worldwide, but is sporadic and thus difficult to prevent.
A suis is part of the normal flora of the oral cavity of pigs. It causes septicemia in
young pigs and arthritis, pneumonia, and pericarditis in older pigs. Disease follows
a break in the integrity of the oral mucosa or may be associated with
immunosuppression.
Diagnosis:
1- Direct examination of gram stained smears of pus from tongue lesions may
reveal club-like spicules of calcium phosphate, giving the appearance of
sulfur granules <1 mm diameter that contain central masses of pleomorphic
G-ve rods. On stained slide they may appear as morse dot appearance (dots
and dashes).
2- Biochemical tests:
a- non motile , usually oxidase +ve, facultatively anaerobes, Co2 is required
for growth, they ferment charbohydrate without gas production (TSI=R/R).
b- Culture results:
- growth on MacConkey agar=small lactose fermenting colonies.
- Growth on blood agar show waxy or very sticky with variably
hemolytic colonies.
3- PCR Tecnique
Treatment:
Vaccines are available, and treatment usually involves use of penicillins,
tetracycline, erythromycin, spectinomycin, or cephalosporins. Surgical debridement
may be useful in treatment; potassium iodide can be administered PO (although not
to food-producing animals).