Bacillus Flashcards
Gram + or -? Spore producing? Aerobic or Anaerobic? How long for large colonies to form? Are the majority pathogenic or non-pathogenic in the environment?
Gram positive large rods
Resistant spores produced
Aerobes or facultative anaerobes
Grow very fast- Large colonies at 24 hours
Biochemically active
Majority non pathogenic environmental organisms
Which three species of Bacillus do we study? What are the primary diseases each cause?
B. anthracis- anthrax
B. cereus- food poisoning (emetic and diarrhoeal forms), eye and soft tissue infections (man) mastitis (cattle-rare)
B. licheniformis- sporadic abortion in cattle and sheep
Put these in order of susceptibility to anthrax, greatest to smallest: Birds, ruminants,carnivores, pigs, horses
Ruminants (most susceptible), Pigs and Horses (moderately), carnivores (fairly resistant), birds (almost completely resistant)
How long will spores live for in the environment?
How are they brought back to the surface?
What does ingestion of spores lead to?
<100 years in the soil
Flooding, excavation, subsidence, earthworm activity etc
INFECTION
What three methods of infection are possible?
Pulmonary (spore-laden dust)
Gastrointestinal (contaminated meat/vegetables)
Cutaneous (via lesion. From handling infected meat/ fly bite)
Pathogenesis
Virulence factors?
What will upregulate expression?
Toxin consists of which three antigenic components?
Virulence - presence of poly-D-glutamic acid capsule and complex toxin
Both virulence factors encoded on plasmids- pX01 and pX02
Expression upregulated by ^ host temperature and carbon dioxide
Capsule inhibits phagocytosis
Toxin consists of 3 antigenic components-(protective antigen, oedema factor, and lethal factor)
PA acts as the binding moiety for both oedema factor and lethal factor.
Describe the two effects of Protective Antigen
Oedema factor - calmodulin dependent adenylate cyclase - increases cAMP causes build up of fluid in tissue (tissue swells) - also inhibits neutrophil function
Lethal toxin is a zinc metalloprotease plus PA which acts as its binding domain
LF stimulates macrophages to release IL-1 beta and TNF alpha and cleaves MAP kinase
Local effects - swelling, darkening of tissue, oedema and necrosis
Septicaemia, leads to increased vascular permeability, haemorrhage, shock and death
Incubation period for B. anthrax?
Hours to Days
What is usually the first clinical sign of infection?
DEATH OH NO
In cattle and sheep it causes septicaemia, which is rapidly fatal
Septicaemia
Occurs in the last hours of life
At the point of death, numbers often exceed 108 bacilli/ml blood.
Anthrax Diagnosis
- carcass appearance?
- what is characteristic about their blood stain?
- colonial morphology?
Carcasses are bloated, putrify and do not exhibit rigor mortis
Bleeding issues from mouth, nostrils, anus
Blood collected from animal stained with polychrome methylene blue – blue bacteria, pink capsules – McFadyean’s capsule stain. Have a capsule and square ends.
Inoculate agar plates for growth- Characteristic colonial morphology- medusa head colonies form on blood agar
Biochemical tests
Anthrax and humans- which forms? What is the result?
3 forms of disease in man
Cutaneous (malignant pustule) – endospores enter abraded skin – septicaemia if untreated
Pulmonary – ‘woolsorters disease’ – inhalation of spores
Intestinal – ingestion of infective material
All fatal if not recognised early
Is there a vaccine available?
Yes- live spore vaccine, capsule minus toxin +ve - endemic regions
How should you dispose of an infected carcass?
Do not open carcass as this will facilitate spore formation and environmental contamination!
Report to regulatory authority
Carcasses incinerated or buried away from water courses
Contaminated material disinfected in 10% formalin or if appropriate incinerated
