Difference between revisions of "Bacillus species"
Jump to navigation
Jump to search
| Line 39: | Line 39: | ||
**Endospores survive decades in the soil | **Endospores survive decades in the soil | ||
**Outbreaks in herbivores grazing pastures contaminated by spores from buried carcases | **Outbreaks in herbivores grazing pastures contaminated by spores from buried carcases | ||
| − | **Infection usually by ingestion of spores | + | **Infection usually by ingestion of spores and penetration through damaged mucosa |
*Pathogenesis and pathogenicity: | *Pathogenesis and pathogenicity: | ||
| + | **Spores germinate at site of entry and spread via lymphatics to bloodstream, where they multiply and produce toxin | ||
**Capsule and toxin (encoded by separate plasmids) required for virulence | **Capsule and toxin (encoded by separate plasmids) required for virulence | ||
**Capsule composed of homopolymer of D-isomer of glutamic acid allows survival in the body by resisting phagocytosis | **Capsule composed of homopolymer of D-isomer of glutamic acid allows survival in the body by resisting phagocytosis | ||
| Line 60: | Line 61: | ||
***Pyrexia, depression, congested mucous membranes and petechiae before death | ***Pyrexia, depression, congested mucous membranes and petechiae before death | ||
***Abortion, subcutaneous oedema and dysentry in animals surviving more that one day | ***Abortion, subcutaneous oedema and dysentry in animals surviving more that one day | ||
| − | |||
**Pigs: | **Pigs: | ||
***Subacute anthrax with oedematous swelling of throat, head and regional lymph nodes | ***Subacute anthrax with oedematous swelling of throat, head and regional lymph nodes | ||
***Intestinal form with high mortality - dysentry due to haemorrhagic enteric lesions | ***Intestinal form with high mortality - dysentry due to haemorrhagic enteric lesions | ||
| − | + | ***[[Peritoneal cavity - inflammatory#In pigs|Peritonitis]] | |
**Horses: | **Horses: | ||
***Subacute anthrax with subcutaneous oedema of thorax, abdomen and legs following entrance of spores into abrasions | ***Subacute anthrax with subcutaneous oedema of thorax, abdomen and legs following entrance of spores into abrasions | ||
| Line 70: | Line 70: | ||
**Dogs | **Dogs | ||
***Rarely affected, but similar disease to that foung in pigs | ***Rarely affected, but similar disease to that foung in pigs | ||
| − | + | **Humans | |
| + | ***Cutaneous anthrax - localised lesion from entrance into abrasion which can cause septicaemia | ||
| + | ***Pulmonary anthrax - inhalation of spores | ||
| + | ***Intestinal anthrax - ingestion of infective material | ||
| + | *Diagnosis: | ||
| + | **Post mortem: bloat, incomplete rigor mortis, ecchymoses, oedema, dark unclotted blood from orifices, blooy fluid in body cavities, splenomegaly | ||
| + | ** | ||
Revision as of 13:30, 17 May 2008
- CAR bacillus in URT infection in cattle and URT infection in rabbits
Overview
- Mostly non-pathogenic environmental organisms
- Bacillus anthracis causes anthrax
- Anthrax is a severe disease affecting all mammals worldwide
- Ruminants are highly susceptible to anthrax, dying of a septicaemic form
- Pigs and horses are moderately susceptible, but carnivores are fairly resistant
- Bacillus licheniformis may cause shoradic abortions in cattle and sheep
- Bacillus cereus causes food poisoning in humans and mastitis in cows
Characteristics
- Large, Gram positive rods
- Produce endospores
- Aerobes or facultative anaerobes
- Grow on non-enriched media
- Motile
- Catalase positive, oxidase negative
- Bacillus anthracis colonies are up to 5mm diameter, flat, dry, grey, with a ground-glass appearance; curled outgrowth sfrom the edge of the colony give a 'medusa head' appearance; non-haemolytic (differentiate from Bacillus cereus)
- Bacillus licheniformis forms dull, rough, wrinkled colonies, with hair-like outgrowths
- Biochemical tests for identification
- Can often tolerate adverse environmental conditions
Bacillus anthracis
- Epidemiology:
- Saprophyte in soil
- Endospore formation allows persistence and spread
- Endospores survive decades in the soil
- Outbreaks in herbivores grazing pastures contaminated by spores from buried carcases
- Infection usually by ingestion of spores and penetration through damaged mucosa
- Pathogenesis and pathogenicity:
- Spores germinate at site of entry and spread via lymphatics to bloodstream, where they multiply and produce toxin
- Capsule and toxin (encoded by separate plasmids) required for virulence
- Capsule composed of homopolymer of D-isomer of glutamic acid allows survival in the body by resisting phagocytosis
- Capsule stains mauve with polychrome methylene blue in the MacFadyean's reaction - identify anthrax in blood samples
- Bacilli appear as chains of dark blue, square-ended rods surounded with the capsule
- Extracellular toxin (holotoxin) composed of oedema factor, protective antigen and lethal factor
- Oedema factor is an adenylate cyclase which increases intracellular cAMP concetrations, causing fluid accumulation and damaging neutrophils
- Lethal factor causes release of cytokines from macrophages
- Protective antigen binds to the cell receptor to allow action of the other factors
- The toxin kills phagocytes, increases capillary permeability and interferes with clotting cascade
- Capillary thrombosis; leakage of fluid through damaged capillary endothelium
- Systemic shock from circulatory collapse, haemorrhagic disease and oedema lead to death of the animal
- Severe systemic disease that can result in enteritis
- Causes tissues to darken and swell due to oedema and necrosis
- Clinical signs:
- Cattle/sheep:
- Fatal peracute septicaemia
- Animals usually found dead
- Pyrexia, depression, congested mucous membranes and petechiae before death
- Abortion, subcutaneous oedema and dysentry in animals surviving more that one day
- Pigs:
- Subacute anthrax with oedematous swelling of throat, head and regional lymph nodes
- Intestinal form with high mortality - dysentry due to haemorrhagic enteric lesions
- Peritonitis
- Horses:
- Subacute anthrax with subcutaneous oedema of thorax, abdomen and legs following entrance of spores into abrasions
- Septicaemia with colic and dysentry due to haemorrhagic enteritis from ingestion of spores; ecchymoses and splenomegaly
- Dogs
- Rarely affected, but similar disease to that foung in pigs
- Humans
- Cutaneous anthrax - localised lesion from entrance into abrasion which can cause septicaemia
- Pulmonary anthrax - inhalation of spores
- Intestinal anthrax - ingestion of infective material
- Cattle/sheep:
- Diagnosis:
- Post mortem: bloat, incomplete rigor mortis, ecchymoses, oedema, dark unclotted blood from orifices, blooy fluid in body cavities, splenomegaly
Bacillus licheniformis
- Widespread in the environment
- Associated with food spoilage
- Abortion in cattle and sheep, possibly from spoiled silage or hay
Bacillus cereus
- Mastitis in cattle
- Food poisoning and eye infections in humans