The saprophytic organisms which simulate the anthrax bacillus closely, both in their morphological and cultural characters within the group of Gram-positive aerobic sporing bacilli are termed as Anthracoid bacilli.
They have a general resemblance to anthrax bacilli such as producing dry wrinkled colonies and in the smear, appearing as chains of spore-bearing gram-positive bacilli.
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However, they differ from anthrax bacilli in many ways as follows:
S.N. |
Character |
Anthrax bacilli |
Anthracoid bacilli |
1.ย ย ย ย ย | Known as | Bacillus anthracis | B. anthracis similis, B. pseudo-anthracis or “anthrax-like” bacilli and Pseudoanthrax. |
2.ย ย ย ย ย | Shape (Chain Length) | In long chains | In short chains |
3.ย ย ย ย ย | Position of spores | Central, do not bulge the bacilli. | Central, subterminal or terminal, may bulge the bacilli. |
4.ย ย ย ย ย | Capsule | Present | Absent |
5.ย ย ย ย ย | Motility | Non-motile | Motile |
6.ย ย ย ย ย | Under lower power microscope | Medusa head colony seen | Not seen |
7.ย ย ย ย ย | Oxygen requirement | Strict aerobe | Aerobic or facultative anaerobic |
8.ย ย ย ย ย | Growth at 45ยฐC | No Growth | Growth usually seen |
9.ย ย ย ย ย | Blood Agar | No hemolysis (or weak) | Hemolytic colonies(usually well marked) |
10.ย ย | Turbidity | No Turbidity in broth | Turbidity seen usually |
11.ย ย | Solid medium with penicillin | String of pearls appearance | No growth |
12.ย ย | Gelatin stab agar | Inverted fir tree appearance | Absent |
13.ย ย | In nutrient broth | Fluffy Cotton wool without pellicle | Turbidity and pellicle formation but no fluffy Cotton wool |
14.ย ย | Salicin Fermentation | Negative | Usually Positive |
15.ย ย | Rate of gelatin liquefaction | Slow | Rapid |
16.ย ย | Lecithinase activity on egg yolk agar | — weak | + marked |
17.ย ย | Reduction of methylene blue in milk | Reduce methylene blue slowly | Rapidly reduce methylene blue |
18.ย ย | Chloral Hydrate | Growth inhibited byย Chloral Hydrate | Not Inhibited |
19.ย ย | Susceptibility to Gamma Phage | Susceptible | Not susceptible |
20.ย ย | Penicillin sensitivity 10 unit disc | Susceptible | Resistant |
21.ย ย | Pathogens | Pathogenic | Except B. cereus, most of them are non-pathogenic or opportunistic pathogens with low virulence. |
22.ย ย | Diseases caused | โ Cutaneous anthrax
ย โ Gastrointestinal anthrax ย โ Inhalational anthrax ย โ Anthrax meningitis. |
โ ย Bacillus cereus is the most important pathogen causing GI infection, ocular infections, and catheter-related infections.
โ Bacillus subtilis may act as an opportunistic pathogen, causingย eye infections and septicemia. โ Bacillus licheniformis has also been incriminated in patients with food poisoning. |
23.ย ย | Pathogenicityย for mice or guinea pigs | Pathogenic (death in 24 โ 48 hours) | No death |
24.ย ย | Contaminants | Not a common contaminant. | Common contaminants in laboratory cultures. |
25.ย ย | Organism(s) | Bacillus anthracis | B. cereus, B. subtilis, B. licheniformis, B. stearothermophilus etc. |
References
- http://ecoursesonline.iasri.res.in/mod/page/view.php?id=66763
- https://microbiologyinfo.com/difference-between-anthrax-bacilli-and-anthracoid-bacilli/
- http://fac.ksu.edu.sa/sites/default/files/medical_bacteriology_section_4_0.pdf
- Parija S.C. (2012). Textbook of Microbiology & Immunology.(2 ed.). India: Elsevier India.
- Sastry A.S. & Bhat S.K. (2016). Essentials of Medical Microbiology. New Delhi : Jaypee Brothers Medical Publishers.