1. Aerobic Gram-Positive Bacilli
Bacillus
Aerobic Gram-Positive Bacilli

2. Bacillus Large, G(+) rods, square cut ends
Saprophyte in nature; soil, dust
Aerobic, facultative anaerobic
Spore former, survive in environment
Lab presumptive ID by spore stain
Most motile
B. anthracis = non-motile

3. Bacillus: Genera
B. anthracis - “charcoal” carbuncle; major pathogen, anthrax disease
B. cereus – “waxen”, gastroenteritis (rice, meat, vegetable), opportunistic infections
B. subtilis – isolated as contaminant in clinical specimens, opportunistic infections (catheter, prosthesis)

4. Bacillus: Lab Culture Grows well on ordinary lab media, CBA
Large granular colonies, irregular edge; coarse, dull or frosted-glass texture
B. cereus = hemolytic
B. anthracis = non-hemolytic

5. Bacillus anthracis: Virulence Factors
Capsule ­ resist phagocytosis; lab presumptive ID by stain or DFA (direct fluorescent antibody) test
Exotoxins ­ complex, coded by plasmid; three genes (three proteins, each alone not toxic)
Protective antigen (PA) - bind
Lethal factor (LF) - active
Edema factor (EF) - active
PA combine with LF or EF, binds to host cell receptor, entry into host cell; LF & EF toxic

6. Bacillus anthracis: Two Toxins
Lethal toxin: PA + LF; protease, causes cell death
Edema toxin: PA + EF; increase in cAMP, results in edema
Both toxins:
increase vascular permeability
interferes with phagocytosis

7. Bacillus anthracis: Anthrax
Mainly disease of animals - acquire MO by ingestion or inhalation of spores
Spores extremely resistant, source of infection in soil 2-3 years
Humans acquire anthrax:
Contact animal products (hides, fur, wool, hair)
Less commonly, work in agricultural setting with infected animals
Disease depends on mode of transmission
Skin (cut, abrasion, wound)
Ingestion
Inhalation

8. Cutaneous Anthrax Most common (95% infections)
Spores enter exposed skin, germinate, multiply
Exotoxin released, rapid development of pustule
Occasionally, MO disseminate - septicemia, death in few days
Vascular injury - edema, hemorrhage, thrombosis
Death - respiratory failure, anoxia by toxin on CNS
Mortality ~20% if untreated

9. Gastrointestinal Anthrax
Ingest spores, inoculated into lesions of mucosa
Ulcers in mouth, esophagus, intestine
GI tract symptoms – nausea, vomiting, malaise
Lead to lymphadenopathy, edema, sepsis
Rapidly progress to systemic disease
High mortality, as anthrax not suspected

10. Inhalation Anthrax (Woolsorter‘s Disease)
Inhale spores by aerosols into RT
Germinate in lungs, multiply, spread to cause fatal septicemia or meningitis
Most serious form of disease
High mortality, as anthrax not suspected
Use as biologic weapon – need to break up spore clumping, aerosolize, so can reach airway
CDC category A Select Biological Agent
Weaponized spores inhaled, easily disseminated
Inhalation anthrax fatal unless treated immediately

11. Bacillus anthracis: Treatment and Prevention
Sensitive to penicillin, but some strains now showing resistance
Ciprofloxacin drug of choice,
Control infection in animals:
Vaccine useful to prevent infection
Bury diseased animals
Short-term PA vaccine available for at high risk individuals, less useful

12. Bacillus cerus: Opportunistic Infections
Ubiquitous, infecton via contaminated soil
Gastroenteritis – two different enterotoxins (emetic, diarrheal)
Cytotoxin - cerolysin, phospholipase)
Eye infection – traumatic injury
Endocarditis – commonly IV drug abuser
Pneumonitis, bacteremia, meningitis - immunocompromised patient, neonate, IV-catheter, surgery patient
Resistant to penicillin – combination treatment of clindamycin + gentamycin

13. Food Poisoning: Emetic Form
Contaminated fried or boiled rice, spores survive cooking
Rice not refrigerated, spores germinate, MO release enterotoxin
Intoxication – ingest toxin in rice; toxin not destroyed by reheating rice
Short incubation <6 hr.- vomiting, nausea, abdominal cramps, ±diarrhea (33%)
Last <24 hr.

14. Food Poisoning: Diarrheal Form
Infection – ingest contaminated soup, meat, vegetable, sauce, pudding
Longer incubation >6 hr., MO multiplies, release toxin; diarrhea, nausea, abdominal pain, ±vomiting (25%)
Last >24 hr.
Both forms of food poisoning short, uncomplicated
Symptomatic treatment adequate
Prevent by proper food handling

15. Class Assignment
Textbook Reading: Chapter 16 Aerobic Gram-Positive Bacilli
Bacillus
Key Terms
Learning Assessment Questions

16. Case Study 6 - Bacillus
A 56-year-old female postal worker sought medical care for fever, diarrhea, and vomiting.
She was offered symptomatic treatment and discharged from the community hospital emergency department.
Five days later she returned to the hospital with complaints of chills, dry cough, and pleuritic chest pain.
A chest radiograph showed a small right infiltrate and bilateral effusions but no evidence of a widened mediastinum.

17. Case Study 6 - Bacillus
She was admitted to the hospital, and the next day her respiratory status and pleural effusions worsened.
A computerized tomographic (CT) scan of her chest revealed enlarged mediastinial and cervical lymph nodes.
Pleural fluid and blood was collected for culture and was positive within 10 hours for gram-positive rods in long chains.

18. Case Study - Questions
1. The clinical impression is that this woman has inhalation anthrax. What tests should be performed to confirm the identification of the isolate?
2. What are the three primary virulence factors found in B. anthracis?
3. Describe the mechanisms of action of the toxins produced by B. anthracis.
4. Describe the two forms of B. cereus food poisoning. What toxin is responsible for each form? Why is the clinical presentation of these two diseases different?