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B. cereus biovar anthracis strains were identified in the early 2000s in Cameroon (strains CA) and Côte d’Ivoire (strains CI). These strains were recovered from gorillas and chimpanzees with anthrax-like disease. The organism has since been recovered from an elephant and goats in other countries of Africa.
No human infections caused by B. cereus biovar anthracis have been described at this time.
B. cereus biovar anthracis CA strains are non-hemolytic, motile, and resistant to penicillin G, while B. cereus biovar anthracis CI strains are non-hemolytic, motile, and sensitive to penicillin G. Some B. cereus biovar anthracis strains may exhibit weak beta-hemolysis upon extended incubation (48 h) and may be more hemolytic when incubated in CO2 at 48 h (see Table 1).
B. cereus bv anthracis (CA) 5% CO2
B. cereus bv anthracis (CA) ambient
B. cereus bv anthracis (CI) 5% CO2
B. cereus bv anthracis (CI) ambient
(Images courtesy of the CDC.)
Table 1. Comparison of B. anthracis, B. cereus, and B. cereus biovar anthracis characteristics
| Characteristic | B. anthracis | B. cereus | B. cereus biovar anthracis CI1 | B. cereus biovar anthracis CA2 |
|---|---|---|---|---|
| Hemolysis3 | - | + | - | - |
| Motility4 | - | + | +/- | +/- |
| Gamma phage susceptibility5 | + | - | - | - |
| Penicillin G6 | S | R | S | R |
| Capsule | + | Absent in vitro | + | + |
1. CI = Côte d’Ivoire strains, from chimpanzees
2. CA = Cameroon strains, from gorillas/chimpanzees
3. Hemolysis: + = beta hemolytic on sheep blood agar; - = non-hemolytic
4. Motility: + = motile; - = non-motile. +/- = B. cereus biovar anthracis strains are usually motile, including those recovered from gorillas, chimpanzees, and elephants; B. cereus biovar anthracis goat strains from Democratic Republic of the Congo were non-motile (3).
5. Gamma phage susceptibility: + = susceptible; - = resistant.
6. S= susceptible; R = resistant
Sentinel-level laboratories should refer to the ASM Laboratory Response Network Sentinel Level Clinical Laboratory Protocols.
Suspect Bacillus spp. isolates that are large, catalase-positive Gram-positive rods and non-hemolytic at 24-hour incubation in ambient atmosphere or 5 percent CO2 should be tested for motility. Isolates can appear weakly hemolytic upon extended incubation (48h) in ambient atmosphere and are more hemolytic in 5 percent CO2 at 48h. Semi-solid medium is recommended for motility to ensure consistent results.
Suspect isolates should be investigated to determine if the isolate is significant regardless of motility. If the isolate was recovered from a sterile site or from a wound culture, contact the patient’s attending physician to determine the likely clinical significance (e.g., does the patient have an anthrax-like clinical syndrome?). Appropriate travel history should be obtained as well.
If the isolate is deemed significant, contact the NCSLPH BTEP Unit to obtain guidance regarding the need to refer the isolate for confirmatory testing.
Updated: June 4, 2020