36. Genus Bacillus. Bacillus anthracis. Morphology, biology, pathogenic factors. Pathogenecity, disease and immunity. Microbiological diagnosis. Specific prophylaxis and therapy. Bacillus cereus. General characteristics and disease.
Topic 36 of 50 in the MU Plovdiv syllabus for Microbiology (Medicine, Years 2 and 3). The free AceMed note covers it in 12 sections, about 470 words (4 min of reading), with 16 flashcards.
In this note
Genus Bacillus – Bacillus anthracis
General Characteristics
Microscopy & Staining
Cultural Characteristics
Resistance
Virulence Factors
Pathogenesis
Clinical Forms of Anthrax
Laboratory Diagnosis
Treatment
Prevention
Anthrax vs. Anthracoid Bacilli (Pseudoanthrax)
General Characteristics
Gram-positive, large, rod-shaped bacilli
Spore-forming – spores are oval, central, non-bulging
Non-motile (unlike most other Bacillus species)
Arranged singly, in pairs, or in long chains ("bamboo stick appearance")
Aerobic or facultative anaerobe
Forms polypeptide capsule (unique – made of D-glutamic acid)
Capsule visible only in the presence of CO₂ or bicarbonate
Grows on simple media (not fastidious)
Microscopy & Staining
Gram stain: Large G⁺ rods in chains
Capsule: Detected using India ink or McFadyean’s stain (shows pink capsule on blue bacilli)
Spore stains: Peshkov, Sudan Black B
In culture, gives the “bamboo stick” appearance
No spores seen in clinical samples — only in culture
Cultural Characteristics
Growth at 37°C on blood or meat-peptone agar
Colonies:
Large, irregular, grey-white
“Medusa head” appearance (interlacing chains at colony edges)
Non-hemolytic (important feature)
Gelatin stab culture: Shows “Inverted fir tree” pattern
String of Pearls reaction
Selective media:
PLET medium (Polymyxin, Lysozyme, EDTA, Thallous acetate) — used to isolate B. anthracis
Continue reading free
The whole note, all 12 sections, is free with an AceMed account, with its 16 flashcards. Premium adds flashcard recall, highlights and Ask AI.
