Antimicrobial Susceptibility Testing – Anaerobes

Consistent with O. Reg. 671/92 of the French Language Services Act, laboratory testing information on this page is only available in English because it is scientific or technical in nature and is for use only by qualified health care providers and not by members of the public.

This page provides antimicrobial susceptibility testing information for anaerobic bacteria at Public Health Ontario’s (PHO) laboratory. For information regarding other testing options, refer to the following PHO webpages:

Testing Indications

Acceptance/Rejection Criteria

  • Anaerobic susceptibility tests are performed on isolates from sterile sites. Specimens received from non-sterile site will be rejected.
  • Susceptibility testing will be performed on organisms commonly considered to be contaminants/commensal flora only on special request by the healthcare provider based on clinical relevance and after approval from a PHO microbiologist, e.g. Propionibacterium sppand Cutibacterium spp from a single positive blood culture1-5 or wound swab and drainage2. Contact PHO’s Laboratory Customer Service Center for these requests.
  • Primary specimens are not acceptable. Only pure cultures are accepted for testing.
  • If source of isolation of the culture is not indicated in the requisition, it will be rejected.
  • Mixed or non-viable cultures will not be tested. A written report will be issued to indicate that the test has been rejected.
  • Mislabelled or unlabelled cultures will not be tested. A report will be sent to the submitting laboratory stating “Culture received un-labelled” or “Requisition identification does not match the identification information on the culture received. Please resubmit if required.”
  • The submitting laboratory will be contacted when isolates derived from critical sites” (e.g. brain abscess) are submitted inappropriately (e.g. improper transport conditions or mislabeled/unlabeled.

Specimen Collection and Handling

Specimen Requirements

Test Requested Required Requisition(s) Specimen Type Minimum Volume Collection Kit

Antimicrobial susceptibility testing- Anaerobic bacteria

Pure viable subculture of 24 – 48 hours growth of organism on appropriate pre-reduced medium submitted in an anaerobic transport kit



Antimicrobial susceptibility testing- Anaerobic bacteria

Swab of anaerobic isolate contained in an anaerobic transport kit



Submission and Collection Notes


Complete all fields on the Reference Bacteriology Requisition, including:

  • Test(s) requested
  • Date of primary specimen collection
  • Primary source of isolation (mandatory)
  • Culture information (presumptive identification, gram morphology, catalase, oxidase)
  • Clinical/epidemiology information
  • The number of consecutive blood cultures positive for the submitted isolate when isolates are from blood cultures 
  • Contact information

Where full bacterial identification and susceptibility testing is required, e.g. for an immunocompromised patient, please clearly indicate this on the requisition.


Primary specimens are unacceptable; they should be processed in the originating lab and the isolate sent for testing. A report will be issued to indicate that the test has been rejected if primary specimen is sent.


Do not submit multiple isolates from the same specimen/site of infection – for polymicrobic infections, only submit most clinically important pathogens for testing.


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.


When the identification of bacteria from clinical specimens is unknown, it can be difficult to determine upfront if it is clinically relevant and if susceptibility testing is required for patient care.

In such cases PHO’s laboratory will perform identification. If the microorganism identified represents a common contaminant or commensal flora of the source, an antimicrobial susceptibility testing is not necessary or appropriate.

Storage and Transport

Place the sealed culture in a biohazard bag and properly seal the bag. Store at 2-8°C, maintaining anaerobic condition, while awaiting shipping.

Transport a fresh subculture to ensure viability on receipt. It should be shipped to PHO’s laboratory within 48 hours of isolation and maintained in anaerobic conditions.

All cultures must be shipped in accordance to the Transportation of Dangerous Good Act.

Requisitions and Kit Ordering

Test Frequency and Turnaround Time (TAT)

Antimicrobial susceptibility testing is performed from Monday to Saturday at PHO’s laboratory, Toronto site.

Turnaround time for test results is up to 8 days from date of receipt at the PHO’s laboratory.

Test Methods

Antimicrobial susceptibility testing for anaerobic bacteria is performed by MIC Gradient Test Strip, a quantitative assay for determining the Minimum Inhibitory Concentration (M.I.C.) of antimicrobial agents against microorganisms and for detecting the resistance mechanisms.


Antimicrobial susceptibility testing results are interpreted as per current CLSI guidelines.


Organism/antimicrobial susceptibility results’ interpretations are reported to the ordering physician or health care provider as indicated on the requisition.


  1. Institute for Quality Management in Healthcare (IQMH): Consensus Practice Recommendations – BACT-Blood Cultures. Revision date: 2017-09-28.
  2. Institute for Quality Management in Healthcare (IQMH): Consensus Practice Recommendations – BACT Superficial wound swabs. 2013-12-09.
  3. Miller JM, Binnicker MJ, Campbell S, Carroll KC, et al. A Guide to Utilization of the Microbiology Laboratory for Diagnosis of Infectious Diseases: 2018 Update by the Infectious Diseases Society of America and the American Society for Microbiology. Clinical Infectious Diseases, Volume 67, Issue 6, 31 August 2018, Pages e1–e94,
  4. Clinical and Laboratory Standards Institute (CLSI). Principles and procedures for blood culture; approved guideline. CLSI document M47-A, Vol. 27, No. 17. Wayne, Pennsylvania, USA. 2007.
  5. Baron EJ, Weinstein MP, Dunne Jr WM, Yagupsky P, Welch DF, Wilson DM. 2005. Cumitech 1C, Blood Cultures IV. Coordinating ed., EJ Baron. ASM Press, Washington DC.
contact lab

Contact Laboratory Customer Service

Laboratory Services

Updated 15 May 2024