Bacillus spp. (gram+ve bacilli)

Babylon university
College of medicine
Microbiology dept.
Prof.Dr. Ilham Al-Saedi

Bacillus spp. (gram+ve bacilli)
? General Characteristics of Bacillus:
- 60 species; Gram-positive or Gram-variable bacilli.
- Most are saprophytic contaminants or normal flora.
- Bacillus anthracis is most important member.
- Produce endospores.
- Aerobic or facultatively anaerobic.
- Capsule is present in virulent strains.
- Can b=produce three types of toxins “exotoxin, edema toxin and lethal toxin”.
- Catalase positive (most).
- Rapidly differentiates from Clostridium, bacillus spp. are ubiquitous Soil, water, and airborne dust.
- Thermophilic (<75°C) and psychrophilic (>5-8°C).
- Can flourish at extremes of acidity & alkalinity (pH 2 to 10).

? Diseases Associated with Bacillus:


? Laboratory Characteristics of Bacillus:
- On blood agar:
- Large, spreading, gray-white colonies, with irregular margins.
- Many are beta-hemolytic (helpful in differentiating various Bacillus species from B. anthracis).
- Spores seen after several days of incubation, but not typically in fresh clinical specimens.
-
Bacillus anthracis:
Physiology and Structure:
Spore-forming Gram-Positive bacilli
Facultative anaerobe,Nonfastidious growth of nonhemolytic colonies that are adherent to the agar surface.
Polypeptide capsule consisting of poly-D-Glutamic acid observed in clinical speciemens.
Virulence:
The capsule is present in virulent strains. The virulent strains also produce three Exotoxins that combine to form edema toxin (combination of protective antigen and edema factor) and Lethal toxin (protective antigen with Lethal factor).
Spores can survive in soil for years.
? Epidemiology :
? B.anthracis primarily infects herbivores with humans as accidental hosts.
? Rarely isolated in developed countries but is prevalent in impoverished areas where vaccination of animals is not practiced.
? Individuals at risk include people in endemic areas in contact with infected animals or contaminated soil, people who work with animal materials imported from endemic areas, and military and nonmilitary people exposed to infectious aerosols.
? There is significant concern that the spores will be used in bioterrorism.
? Diseases:
? Cutaneous anthrax is the most common form.
? Inhalation anthrax is the most deadly form.
? Gastrointestinal anthrax is a rare but commonly fatal disease.
? Diagnosis:
? Isolation of the organism from clinical specimens (e.g. papule or ulcer, blood).
? Treatment, Prevention, and Control:
? Ciprofloxacin is the drug of choice; Penicillin, Doxycycline, Erythromycin, or Chloramphenicol can be used, but the bacteria are resistant to sulfonamides and Extended-spectrum cephalosporins.
? Vaccination of animal herds and people in endemic areas can control disease, but spores are difficult to eliminate from contaminated soils. Animal vaccination is effective, but human vaccines have limited usefulness.
?
? Three well-defined cycles
1. Survival of spores in the soil
2. Animal infection
3. Infection in humans
? Primarily a disease of herbivorous animals:
- Most commonly transmitted to humans by direct contact with animal products (e.g., wool and hair)
- Also acquired via inhalation & ingestion
- Increased mortality with these portals of entry
- Still poses a threat
• Importing materials contaminated with spores from these countries (e.g., bones, hides, and other materials).
• Usually encountered as an occupational disease.
• Veterinarians, agricultural workers.


? Clinical Presentation of Anthrax:
1. Cutaneous Anthrax:
- 95% human cases are cutaneous infections.
- 1 to 5 days after contact.
- Small, non-painful papule at inoculation site.
- Papule develops into hemorrhagic vesicle & ruptures.
- Slow-healing painless ulcer covered with black eschar.
- Surrounded by edema.
- Infection may spread to lymphatics w/ local adenopathy.
- Septicemia may develop.
- 20% mortality in untreated cutaneous anthrax.

2. Inhalation Anthrax:
- Virtually 100% fatal (pneumonic).
- Meningitis may complicate cutaneous and inhalation forms of disease.
- Pharyngeal anthrax.
- Fever.
- Pharyngitis.
- Nneck swelling.
3. Gastrointestinal (Ingestion) Anthrax:
- Virtually 100% fatal.
- Abdominal pain.
- Hemorrhagic ascites.
- Paracentesis fluid may reveal gram-positive rods.

? Treatment & Prophylaxis:
- Penicillin is drug of choice.
- Erythromycin, chloramphenicol acceptable alternatives.
- Doxycycline now commonly recognized as prophylactic.
? Vaccine (controversial):
- Laboratory workers
- Employees of mills handling goat hair
- Active duty military members
- Potentially entire populace of U.S. for herd immunity



? Key Characteristics to Distinguish between B. anthracis & Other Species of Bacillus.
Characteristic Bacillus anthracis Other Bacillus spp.
Hemolysis Negative Positive
Motility Negative Positive(usually)
Gelatin hydrolysis Negative Positive
Salicin fermentation Negative Positive
Growth on blood agar Negative Positive

Bacillus cereus: