12 – Bacillus Flashcards
Microbial characteristics
- vary of biocontainment levels
o B. anthracis=level 3 - large, spore forming, gram-positive rods
- aerobic, facultative anaerobic
- form large, irregular colonies
Natural host or habitat
- Ubiquitous (found in environment, water, soil)
- Spores survive for decades
o Highly resistant to desiccation, heat, radiation and disinfectants
o Can survive for decades (or longer!)
B. anthracis morphological characteristics
- “medusa heads” on gram stain
Virulence factors
- Virulent ones are encapsulated
- Protective antigen
- Edema toxin
- Lethal toxin
- *these 3 on own=inactive
- Protective antigen
Protective antigen
- Forms heptameric pores in cell wall
o Edema factor (EF) or lethal factor(LF) then bind to enter cell and create toxins
Lethal factor (LF)
- Inactivates MAPK kinases
- Disrupts cell signalling=leading to apoptosis
Edema factor (EF)
- Calmodulin dependent adenylate cyclase
- Increased intracellular cAMP leads to edema
B. cereus: virulence factors
- exotoxins which are responsible for gastroenteritis
B. thuringiensis (insect pathogens): virulence factors
- crystal toxins (disruption of gut)
- digestion of crystal liberates Cry toxin
- used as a larvicide in mosquito control
B. subtilis virulence factors
- largely non-pathogenic
Susceptibility ladder of species to B. anthracis
- most: cattle, sheep, goats
- intermediate: horses, humans
- lowest: pigs, birds, carnivores
Why might some species be more resistant to B. anthracis?
- Carnivores eat lots of dead animals
- *lifestyle and dietary choices
B. anthracis (ruminants)
- acquired by ingesting endospores
- often seen when drought followed by heavy rainfall
- sudden death
- *if suspect, do NOT perform necropsy and call CFIA
B. anthracis (ruminants): sudden death
- Incomplete rigor migor, splenomegaly
- Failure to clot: if cut carcass=blood flows freely
- **On exposure to oxygen, it will sporulate and are extremely resistant to disinfection
B. anthracis (horse)
- Presents as acute intestinal disease
o Colic, diarrhea, fever, depression - Localized lesions can be seen
o Due to insect transmission - may see dependent edema (thorax, abdomen, prepuce, mammary gland)
- followed by fatal septicemia
Anthrax outbreak in SK in 2006
- ante-moretm: not really an pathognomic clinical signs
o depression, SQ edema, skin lesions - post-mortem: dripping blood, failure to clot or darken blood)
B. anthracis (pigs and meat)
- oral/pharyngeal lesions most common
o ulceration at site of entry
o regional lymphadenitis
o ulcerative and haemorrhagic enteritis
B. anthracis (carnivores)
- rarely affected
- when diseased, similar to pigs
- septicemia with massive exposure
B. anthracis (hippo)
- disease recognized as animal die-offs
- serious public health concern
o exposure to or consumption of carcases associated with human disease
4 distinct forms of B. anthracis in people
- Cutaneous (most common)
- Pulmonary
- Oropharyngeal
- Gastrointestinal
Cutaneous form of B. anthracis (people)
- Direct contact with infected animal tissues
- Lesions develop 2-5 days post exposure
- Mortality rate 10-20% if untreated
Pulmonary form of B. anthracis (people)
- Inhalation of endospores, phagocytosis in lungs
- Lethal toxin kills macrophages
- Hemorrhagic necrosis of mediastinum
- 1-3 day incubation period
- Mortality rate 80-90% if untreated
Oropharyngeal and gastrointestinal forms of B. anthracis (people)
- Associated with ingestion of spores or vegetative cells
- GI form: 2-7 day incubation period, fever, nausea, bloody vomiting
- Oropharyngeal form: cervical and oral pain and edema
- *if sepsis untreated=DEATH
B. cereus (humans)
- Acute, self-limiting gastroenteritis
- Emetic form
- Long incubation food poisoning
- *some strains grow at low temperature 4-7 degree C
Emetic form of B. cereus
- ingestion of cereulide toxin
- 1-6hr following ingestion
- Associated with rice, cream and milk products, pasta and infant formula
Long incubation food poisoning
- Ingestion of hemolysins
- Watery diarrhea, nausea, tenesmus (straining to defecate)
- Associated with meat, vegetables, cakes, sauces and dairy
Paenibacillus larvae
- Pathogen of honeybee larvae
- Causes American foulbrood disease
- Acts by multiplicity of mechanisms
- Antibiotic and probiotics for prevention
- Infection control is key
Paenibacillus larvae acts by multiplicity of mechanisms
- Chitin degrading enzymes
- Toxins leading to intestinal epithelial cell death
- S-layer proteins on cell surface, protect from insect immune system
Specimens to collect
- B. anthracis: do NOT perform necropsy
o Collect blood from ea
o If working in dusty environment, respiratory protection is ESSENTIAL - Non-anthracis species can be handled using standard precaution (milk, tissues from aborted fetuses)
Sample handling
- Do NOT freeze
Lab ID: B. anthracis
- MUST work in biosafety cabinet if suspect
- Direct microscopy
- Culture on blood agar
- Non-hemolytic colonies
Lab ID: non-antracis species
- Culture
Lab ID: blood from ear tip
- Microscopy useful to see spores
o Special staining (methylene blue) required
B. anthracis zoonotic/interspecies transmission
- Extremely difficult to get rid of from environment
o Removal of top 20cm of soil
o Disinfecting soil and equipment with FORMALIN
o Burn or bury contaminated disposables along with carcasses - **PPE is critical
Destroying spores in environment is very challenging
- Ounce of prevention (not performing necropsies) is worth a pound of cure (formalin!)
B. anthracis in beef cow example
- Affected quarter was swollen, darkened and necrotic appearing
- Milk was serosanguinous and watery
- Classical chains of rod shaped bacteria seen in staining of milk
Treatment of choice: B. anthracis
- High DOSE penicillins or tetracyclines
Drugs to avoid/intrinsic resistance: B. thuringiensis
- Intrinsically resistant to penicillins
Drugs to avoid/intrinsic resistance: B. anthracis
- Resistant to 2nd and 3rd generation cephalosporins and trimethoprim + sulfamethoxazole
Control measures
- B. anthracis vaccination
- Antimicrobial prophylaxis is some outbreak situations
- Control the area (keep animal scavengers out)
- Proper disposal of carcasses
- Prevent additional contamination of environment
