Difference between revisions of "Bacillus species"

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===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 outgrowths from 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 - WikiBlood|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, [[Haemostasis - Pathology#Haemorrhagic Disease Due To Vascular Fragility|haemorrhagic disease]] and oedema lead to death of the animal
 
**Severe systemic disease that can result in [[Intestines Fibrinous/Haemorrhagic Enteritis - Pathology#Bacterial septicaemia and enteritis|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
 
***[[Peritoneal Cavity Inflammatory - Pathology#In pigs|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 found 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
 
**Blood smear from an ear or tail vein of ruminants, or peritoneal fluid from pigs stained with polychrome methylene blue
 
**Chains of square-ended blue rods surrounded by mauve capsules
 
**Culture on blood and MacConkey agar (no growth on MacConkey)
 
**Biochemical tests
 
*Treatment:
 
**High doses of penicillin G or oxytetracylcine
 
*Control:
 
**Report suspected cases - notifiable
 
**Spores destroyed by sterilisation
 
**Endemic regions:
 
***Live Sterne spore vaccine which produces toxin but has no capsule, therefore is non-pathogenic; stimulates protective antibody
 
***Chemoprophylaxis with long-acting penicillin
 
**Non-endemic regions after an outbreak:
 
***Movement restrictions
 
***Footbath with sporicidal disinfectant
 
***Fumigate buildings with formaldehyde
 
***Dispose carcases and contaminated material
 
***Isolate in-contact animals
 
 
 
===''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
 
 
 
 
 
*''CAR bacillus'' in [[Respiratory Bacterial Infections - Pathology#CAR bacillus|URT infection in cattle]] and [[Respiratory Bacterial Infections - Pathology#In Rabbits|URT infection in rabbits]]
 

Latest revision as of 20:41, 10 May 2010