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.
However, they differ from anthrax bacilli in many ways as follows:
|1.||Known as||Bacillus anthracis||B. anthracis similis, B. pseudo-anthracis or “anthrax-like” bacilli and Pseudoanthrax.|
|2.||Shape (Chain Length)||In long chains||In short chains|
|3.||Position of spores||Central, do not bulge the bacilli.||Central, subterminal or terminal, may bulge the bacilli.|
|6.||Under lower power microscope||Medusa head colony seen||Not seen|
|7.||Oxygen requirement||Strict aerobe||Aerobic or facultative anaerobic|
|8.||Growth at 45°C||No Growth||Growth usually seen|
|9.||Blood Agar||No hemolysis (or weak)||Hemolytic colonies(usually well marked)|
|10.||Turbidity||No Turbidity in broth||Turbidity seen usually|
|11.||Solid medium with penicillin||String of pearls appearance||No growth|
|12.||Gelatin stab agar||Inverted fir tree appearance||Absent|
|13.||In nutrient broth||Fluffy Cotton wool without pellicle||Turbidity and pellicle formation but no fluffy Cotton wool|
|14.||Salicin Fermentation||Negative||Usually Positive|
|15.||Rate of gelatin liquefaction||Slow||Rapid|
|16.||Lecithinase activity on egg yolk agar||— weak||+ marked|
|17.||Reduction of methylene blue in milk||Reduce methylene blue slowly||Rapidly reduce methylene blue|
|18.||Chloral Hydrate||Growth inhibited by Chloral Hydrate||Not Inhibited|
|19.||Susceptibility to Gamma Phage||Susceptible||Not susceptible|
|20.||Penicillin sensitivity 10 unit disc||Susceptible||Resistant|
|21.||Pathogens||Pathogenic||Except B. cereus, most of them are non-pathogenic or opportunistic pathogens with low virulence.|
|22.||Diseases caused||■ Cutaneous anthrax
■ Gastrointestinal anthrax
■ Inhalational anthrax
■ Anthrax meningitis.
|■ Bacillus cereus is the most important pathogen causing GI infection, ocular infections, and catheter-related infections.
■ Bacillus subtilis may act as an opportunistic pathogen, causing eye infections and septicemia.
■ Bacillus licheniformis has also been incriminated in patients with food poisoning.
|23.||Pathogenicity for mice or guinea pigs||Pathogenic (death in 24 – 48 hours)||No death|
|24.||Contaminants||Not a common contaminant.||Common contaminants in laboratory cultures.|
|25.||Organism(s)||Bacillus anthracis||B. cereus, B. subtilis, B. licheniformis, B. stearothermophilus etc.|
- 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.