Bacillus anthracis – Confirmation

Conformément au Règlement de l’Ontario 671/92 de la Loi sur les services en français, les renseignements d’analyses de laboratoire liés à la présente page ne sont offerts qu’en anglais parce qu’ils sont de nature scientifique ou technique et destinés uniquement à l’usage des fournisseurs de soins de santé qualifiés et non aux membres du public.

Background
This page provides details on the identification of Bacillus anthracis at Public Health Ontario (PHO). The diseases caused by Bacillus anthracis are collectively referred to as anthrax which are of several forms according to the route of infection- cutaneous, inhalation, gastrointestinal, injection.¹

For information regarding other testing options, refer to the following PHO webpages:

Aerobic bacteria identification : Bacterial cultures – Aerobic – Reference ID/Confirmation
Anaerobic bacteria identification: Bacterial cultures – Anaerobic – Reference Identification/Confirmation
Aerobic bacteria susceptibility testing: Antimicrobial Susceptibility Testing – Aerobic Bacteria
Anaerobic bacteria susceptibility testing: Antimicrobial Susceptibility Testing – Anaerobes

Updates

The turnaround time for Bacillus anthracis confirmatory testing at National Microbiology Laboratory (NML) has been updated to align with their published turnaround time.
A table of possible results and corresponding interpretation has been added.

* Copie d'impression non contrôlée. Valide uniquement le jour de l'impression : 18 sept. 2025.

Testing Indications

Submitting laboratories must contact Public Health Ontario laboratory Customer Service Centre by telephone prior to submission of the isolate.

An isolate may be considered likely or suspected Bacillus anthracis based on the following:

Clinical and epidemiological indicators
- The patient presents with a clinically compatible illness, such as cutaneous lesions with black eschar, severe respiratory symptoms, gastrointestinal symptoms following consumption of contaminated meat and soft tissue injection at injection sites.²
- There is relevant exposure history, including- contact with animal products like hides, wool, bone meat; exposure to environments where anthrax is endemic; occupational risks like veterinarians, farmers, lab workers; known or suspected bioterrorism-related exposure.³

Laboratory indicators
- Microscopic and cultural characteristics: Gram-positive, rod-shaped bacteria occurring singly or in chains; non-motile, spore-forming colonies with “medusa head” appearance on agar.²
- Environmental or epidemiological linkage: Isolate obtained from a site or patient linked to a known anthrax outbreak or contaminated material.³

Acceptance/Rejection Criteria

Acceptable specimens include:

Pure cultures only: Mixed cultures or primary specimens (e.g. direct swabs, tissue or fluids) are not accepted
Properly labeled cultures: The patient and specimen identification on the requisition form must match the label information on the culture container
Source of isolation indicated: The requisition must clearly state the source of the isolate (e.g. skin lesion swabs, blood cultures, respiratory secretions, stool)

Rejected specimens include:

Swabs: Specimens received on dry or gel-based swabs will be rejected
Primary specimens: Direct human patient samples (e.g. skin lesion swabs, blood cultures, respiratory secretions, stool and others) and direct animal samples will be rejected
Missing source information: Cultures without a clearly indicated source of the isolate on the requisition will be rejected.
Mixed or non-viable cultures: These will not be tested. The submitting laboratory will be contacted and a written report will be issued stating the rejection.
Mislabeled or unlabeled cultures are not tested.

Specimen Collection and Handling

Specimen Requirements

Test Requested	Required Requisition(s)	Specimen Type	Minimum Volume	Collection Kit
Bacillus anthracis – confirmation	Reference Bacteriology Requisition	Pure viable subculture of organism on appropriate media that supports the growth (e.g. Blood Agar)	N/A	Columbia sheep blood agar plate or slant

Submission and Collection Notes

Complete all fields of the requisition form, including:

Test(s) Requested: Select confirmation and identification
Culture Information: Indicate the presumptive identification (if available) and Gram morphology; provide oxygen requirement for growth; oxidase test result; catalase test result; indicate presence or absence of growth on MacConkey
Clinical diagnosis: Indicate if patient is immunocompromised
Date of Collection of primary specimen from which isolate was recovered:
Source of isolate (Mandatory):
- The number of consecutive blood cultures positive for the submitted isolate when isolates are from blood cultures
- Type of urine specimen(s) (e.g. midstream, indwelling catheter, cystoscopy etc.)
- The site and type of wound swab; be as specific as possible (e.g. animal bite, surgical wound, decubitus ulcer, etc.
- If the source was collected for surveillance or screening, write the source or body part
- The type of specimen if other than blood culture, urine or wound swab, provide as much detail as possible

Label the culture container(s) with the patient’s first and last name, date of collection, and one other unique identifier such as the patient’s date of birth or Health Card Number. For additional information see: Criteria for Acceptance of Patient Specimens. Failure to provide this information may result in rejection or testing delay.

If the bacterial culture submitted for identification confirmation is provided on a swab in Amies charcoal transport media or broth media (instead of on a plate) the turnaround time will be delayed by at least 24 hours.

If susceptibility testing is required, the submitter must call within 5 days of receiving final results and provide necessary information and justification for susceptibility testing request.

Do not submit multiple isolates from the same specimen or site of infection.

Primary specimens are unacceptable as they must be processed at the originating laboratory.

If full bacterial identification and susceptibility testing is clinically indicated-such as in cases involving immunocompromised patients, it must be clearly indicated on the requisition.

Limitations

Culture must be viable. Use a fresh subculture and ship in conditions to ensure viability on receipt.

Storage and Transport

Place the sealed culture in a biohazard bag and properly seal. Store at 2-8°C while waiting for shipping. The requisition form must be placed in the outer pouch of the biohazard bag, separate from the culture container. Transport a fresh subculture to ensure viability on receipt. It should be shipped to PHO’s laboratory within 48 hours of isolation. All cultures must be shipped in accordance to the Transportation of Dangerous Good Act.

Special Instructions

Bacillus anthracis must be handled in accordance with the Canadian Biosafety Standards and shipped in accordance with the Transportation of Dangerous Goods Regulations.

The sender must contact the PHOL by calling the Customer Service Centre at 416-235-6556 or 1-877-604-4567 before submitting the isolate.

Requisitions and Kit Ordering

Test Frequency and Turnaround Time (TAT)

Testing is performed daily (Monday to Friday) as received at Public Health Ontario’s laboratory-Toronto. Turnaround time for test results is up to 3 days from receiving by PHO laboratory-Toronto.

Isolates that are positive for Bacillus anthracis are forwarded to the National Microbiology Laboratory (NML) for confirmatory testing. Turnaround time for test results from NML is up to 4 calendar days for a preliminary result: 14 calendar days for a final result.

STAT and Critical Samples Testing

Urgent testing is available upon request by calling the Customer Service Centre 416-235-6556 or 1-877-604-4567.

Test Methods

Bacillus anthracis identification is performed using a real-time polymerase chain reaction test - Canadian Laboratory Response Network (CLRN) Real Time-PCR.

Algorithm

Any isolate that is positive by the CLRN real-time PCR assay is considered as presumptive Bacillus anthracis and is forwarded to the National Microbiology Laboratory (NML) for confirmatory testing.

Interpretation

Result	Interpretation
Not Detected	Bacillus anthracis DNA NOT detected by real-time PCR
Presumptive Detected	Presumptive Bacillus anthracis DNA (virulent strain) DETECTED by Real-time PCR.
Inconclusive	Bacillus anthracis real-time PCR result is inconclusive due to specimen quality. If Bacillus anthracis is still suspected, submit additional specimens for testing.
Invalid	Bacillus anthracis real-time PCR result is invalid. Sample is unsuitable for PCR testing.

Reporting

Results are reported to the ordering physician or health care provider as indicated on the requisition.

Specimens that are positive for Bacillus anthracis are to be reported to the Medical Officer of Health as per the Health Protection and Promotion Act.

References

World Health Organization. Anthrax: implementation guidance for clinicians. Available from: https://www.who.int/publications [Accessed 8 Sep 2025]
Public Health Agency of Canada. Pathogen Safety Data Sheets-Bacillus anthracis. Available from: https://www.canada.ca/en/public-health/services/laboratory-biosafety-biosecurity/pathogen-safety-data-sheets-risk-assessment.html [Accessed 8 Sep 2025)
Center for Disease Control. Emerging Infectious Diseases- Volume 8, Number 10- October 2002. Investigation of Bioterrorism-Related Anthrax, United States, 2001: Epidemiologic Findings. Available from: https://wwwnc.cdc.gov/eid/ [Accessed 8 Sep 2025]