1. Gram-Positive Bacilli Part One
MLAB 2434: Microbiology
Keri Brophy-Martinez

2. General Characteristics: Bacillus
Habitat
Thermal springs, fresh and salt water, soil, on plants
Aerobic
Spore-formers
Resistant to radiation, heat, disinfections, and desiccation
Mostly contaminants in clinical specimens
EXCEPTION: Bacillus anthracis

3. More on Spores Produced when the bacteria gets stressed
Drying
Temperature extremes
Aid in organism’s survival
Heat shock induces spores
Temperature raised to 56o
Gram stain
Appear as clear areas within the bacterial cell

5. Significant Bacillus Species
Bacillus anthracis
Agent of anthrax, a disease in livestock
Humans acquire infection by contamination of wound or ingestion or inhalation of spores
Bacillus cereus
Causes food poisoning
An opportunist
Bacillus subtilis
Common laboratory contaminant
Used in sterility testing

6. Bacillus anthracis Cutaneous anthrax Inhalation anthrax
“Malignant pustule” (also called “black escher”)
Woolsorter’s disease/ Rag-pickers disease
Organisms gain access through cuts; localized infection
Majority of cases in the world are cutaneous
Inhalation anthrax
Acquired through inhalation of spores
May result in respiratory distress and death
Gastrointestinal
Acquired by ingestion of contaminated raw meat
Usually fatal

7. Bacillus anthracis: Clinical Infections in Humans
Cutaneous anthrax

8. Laboratory Diagnosis Media Catalase positive
Most species grow well on SBA
Most species beta-hemolytic, except B. anthracis
No growth on MacConkey
Fast growers
Colony characteristics vary
Catalase positive

9. Laboratory Diagnosis
Goal in identification is to RULE OUT B. anthracis
If B. anthracis is suspect, MUST work under safety hood
Other Bacillus, identified to genus level ONLY

10. Identification of Bacillus anthracis
Microscopic morphology
Large, square-ended gram-positive rods
Bamboo appearance
Spores may be absent in patient smears

11. Identification of Bacillus anthracis
Colony Morphology
Nonhemolytic on blood agar; raised, large, grayish white, irregular, fingerlike edges
“Medusa head” or “beaten egg whites”

12. Bacillus cereus Food poisoning Diarrheal syndrome Emetic form
Associated with meat, poultry, and soups
Incubation period of 8 to16 hours
Fever uncommon
Resolves within 24 hours
Emetic form
Associated with fried rice
Abdominal cramps and vomiting
Incubation period of 1 to 5 hours
Resolves in 9 hours

13. Bacillus cereus Local infections Postsurgical/traumatic wounds Burns
Eye infections
Rare conditions
Meningitis
Bacteremia
Endocarditis
Osteomyelitis

14. Bacillus subtilis Found in the environment
Common laboratory and hospital contaminant
Used as a QC agent for sterilization procedures

15. Key Characteristics of Bacillus Species
B. Anthracis
B. Cereus
Other Bacillus
Beta-hemolysis
Negative
Positive, Large zones
variable
Motility
Positive
Pencillin
Sensitive
Resistant
Variable

16. References
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Kiser, K. M., Payne, W. C., & Taff, T. A. (2011). Clinical Laboratory Microbiology: A Practical Approach . Upper Saddle River, NJ: Pearson Education.
Mahon, C. R., Lehman, D. C., & Manuselis, G. (2011). Textbook of Diagnostic Microbiology (4th ed.). Maryland Heights, MO: Saunders.