Basic features of Bacillus spp.
- Gram-positive rods
- Spore forming:
- Endospores (dehydrated cells)
- Highly resistant to heat and other environmental exposures
- Can persist in soil in a dormant state for many years
- Catalase positive
- Bacillus anthracis (B. anthracis):
- Colonies show halo projections known as “medusa heads.”
- Form long chains when grown in culture
- Grow on blood agar at 37°C (98.6°F), non-hemolytic
- Have non-functional flagellae (defective flagellin proteins); non-motile
- Virulence factors:
- Polypeptide D-glutamate capsule (stains with India ink)
- Edema factor (EF)
- Lethal factor (LF)
- Protective antigen (PA)
- B. cereus
- Grow well on blood or chocolate agar at 25°C–37°C (77°F–98.6°F)
- Motile, have flagellae
- Produce 2 types of enterotoxins:
- Diarrheal toxin (heat labile)
- Emetic toxin (heat table)
- Virulence factors:
- Phospholipase C regulator (PlcR)
- Controls expression of hemolysins, enterotoxins, phospholipases, and proteases
- Primarily affects animals (herbivores)
- Sheep, cattle, goats, and horses act as a natural reservoir.
- Humans usually become infected accidentally through contact with animals or their products.
- Spores are used as a bioterrorism agent.
- Some cases were reported secondary to laboratory accidents.
- Infected animals
- Animal products
- Ingestion: undercooked meat from animals infected with anthrax
- Spore inhalation
- Direct, parenteral injection: rare
- Does NOT occur person to person
- Named so because PA serves as the target for the anthrax vaccine
- Attaches to host surface proteins
- Allows toxin entrance into the cytosol
- Mimics cyclic adenosine monophosphate (cAMP)
- Causes characteristic edematous, black eschar in cutaneous anthrax
- Induces multiorgan hemorrhage
- Exotoxin that acts as a protease
- Cleaves mitogen-activated protein (MAP) kinase
- Causes tissue necrosis
- Polypeptide capsule: aids aversion of phagocytosis
In the United States, 3 clinical manifestations occur.
- Cutaneous anthrax:
- Painless papule surrounded by vesicles
- Black eschar at the site of contact
- Most common manifestation, self-limited course
- Rarely, can progress to bacteremia and death
- Gastrointestinal anthrax:
- Ulcerative lesion that produces abdominal pain, vomiting, and diarrhea
- Lesion may then perforate.
- Rare and lethal
- Pulmonary anthrax (wool-sorter’s disease):
- Flu-like symptoms
- Long incubation initially, up to 60 days
- Rapid progression to fever, pulmonary hemorrhage, mediastinitis, and shock
- Chest X-ray: widened mediastinum or pleural effusion
- Approximately 50% of patients will develop hemorrhagic meningitis.
- Cultures showing encapsulated bacilli:
- Pleural fluid
- Cerebrospinal fluid
- Serologic testing during the convalescent period
- Antimicrobials (fluoroquinolones and doxycycline)
- Antitoxin (raxibacumab or anthrax immunoglobulin)
- Drainage of pleural effusions
- Supportive care, glucocorticoids
- Primarily through animal vaccination
- Human anthrax vaccine is available for:
- Certain veterinary, laboratory, or military personnel
- Post-exposure prophylaxis
- Abundant in soil, fresh and marine water
- Frequent food contaminant
- Normally transiently present in the human gastrointestinal tract (up to 43%)
- B. cereus bacteremia can occur in injection drug users, neonates, immunosuppressed patients, and patients with prosthetic devices.
- Reheated rice/grains
- Can survive cooking temperatures
- As food cools, spores germinate and produce toxins.
- Direct parenteral injection: IV drug users
- Food poisoning when ingested:
- Symptoms are related to toxin production.
- Diarrheal toxin is produced by ingested bacteria in vegetative or spore forms.
- Emetic toxin is produced in the food and ingested directly.
- Bacteremia (bloodstream infection) causes various organ seeding.
- Soft-tissue infections can occur in traumatic wounds on direct contact.
- Diarrheal food poisoning:
- Occurs 6–14 hours after ingestion
- Associated with meats and vegetables
- Symptoms secondary to heat-labile enterotoxin
- Watery diarrhea and abdominal cramps for a median of 24 hours
- Emetic food poisoning:
- Rapid onset, occurs 2–3 hours after ingestion
- Associated with reheated rice and grains
- Symptoms secondary to heat-stable enterotoxin
- Nausea and vomiting for a median of 9 hours
- Remember to differentiate from Staphylococcus aureus (S. aureus) food poisoning
- Rare manifestations:
- Necrotizing soft tissue infections
- Keratitis: associated with post-cataract surgery or contact lens usage
- Stool (for cases of diarrheal poisoning)
- Blood (if systemic infection suspected)
- Assays to detect diarrheal toxin
- Noonan L., & Freeman J. (2020). Bacillus cereus and other non-anthracis Bacillus species. UpToDate. Retrieved December 30, 2020, from https://www.uptodate.com/contents/bacillus-cereus-and-other-non-anthracis-bacillus-species
- Wilson, K. (2020). Clinical manifestations and diagnosis of anthrax. UpToDate. Retrieved December 30, 2020, from https://www.uptodate.com/contents/clinical-manifestations-and-diagnosis-of-anthrax
- Wilson, K. (2020). Microbiology, pathogenesis, and epidemiology of anthrax. UpToDate. Retrieved December 30, 2020, from https://www.uptodate.com/contents/microbiology-pathogenesis-and-epidemiology-of-anthrax
- Bacillus anthracis. https://microbewiki.kenyon.edu/index.php/Bacillus_anthracis
- Tankeshwar, A. (2020). Bacillus anthracis: Properties, Pathogenesis and Laboratory Diagnosis. Retrieved 30 December 2020, from https://microbeonline.com/bacillus-anthracis-properties-pathogenesis-diagnosis/
- Grace Ucar. (2011). Bacillus cereus. https://www.sciencedirect.com/topics/medicine-and-dentistry/bacillus-cereus