Antimicrobial Susceptibility Reference Testing

Antimicrobial Susceptibility Testing (AST) is done by the broth microdilution method as described by the Clinical and Laboratory Standards Institute (CLSI) guidelines.

Reference Service

Corynebacterium diphtheriae species complex

Special Bacteriology Unit

• Respiratory and cutaneous diphtheria

Pure cultures of isolates recovered from appropriate anatomical sites for patients with clinical presentation of respiratory diphtheria, or serious, non-healing cutaneous lesions.

Slants (preferred) or plates of any suitable media and swabs in transport media are all acceptable. Frozen specimens are also acceptable however, may extend turnaround times.

Store slants and swabs at room temperature until shipped for testing. Ship actively growing cultures at room temperature. Frozen specimens should be kept frozen and shipped on dry ice.

Shipping of specimens shall be done by a TDG certified individual in accordance with TDG regulations. For additional information regarding classification of specimens for the purposes of shipping, consult either Part 2 Appendix 3 of the TDG Regulations or section 3.6.2 of the IATA Dangerous Goods Regulations as applicable.

Corynebacterium diphtheriae species complex organisms that are potentially toxigenic. The patient criteria MUST be met for AST to be performed on the following organisms:

Corynebacterium diphtheriae

Corynebacterium ulcerans

Corynebacterium pseudotuberculosis

Corynebacterium rouxii

Corynebacterium belfantii

Corynebacterium silvaticum

Corynebacterium ramonii

1) Clinical presentation of respiratory and/or cutaneous diphtheria AND;

2)  Isolates must relate to a patient that is demonstrating evidence of treatment failure and/or treatment contraindication to standard treatment antimicrobials AND;

3)  Isolates must be recovered from clinically relevant sites for diphtheria, in pure culture, within the last 30 days AND/OR;

4) Confirmatory testing or other specialized testing is required – rationale must be provided, or communication with the laboratory prior to sending must occur

The most recent version of the Special Bacteriology requisition must be completed, detailing relevant patient criteria for testing. If possible, attach lab results that have already been done at local or provincial laboratories Samples accompanied by past versions of the requisition may be subject to rejection. Samples submitted without required patient criteria, will be rejected.

• Please note that duplicate bacterial isolates that have been isolated from the same patient, source, and identified as the same organism by the sender, will be rejected unless additional information is provided to warrant testing
• Acceptance and/or rejection of the additional sample(s) is at the discretion of the Special Bacteriology lab.

Please contact the Special Bacteriology laboratory for further information

• Broth microdilution using commercially available Sensititre® panels.
• Interpretations are based on the most recent CLSI guidelines.
• Interpretations for rare or undescribed taxons may not be possible.

16 calendar days. In cases where staff or resources are limited final report may be delayed and status of request will be forwarded in a preliminary report. Frozen, poor, or slow-growing isolates may require longer turnaround times.

1. Clinical and Laboratory Standards Institute. 2016. Methods for Antimicrobial Dilution and Disk Susceptibility Testing of Infrequently Isolated or Fastidious Bacteria; M45-Ed3. Volume 35, Number 17. Clinical and Laboratory Standards Institute, Wayne, Pennsylvania.
2. Clinical and Laboratory Standards Institute. 2024.  Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria That Grow Aerobically; M07-Ed12.  Clinical and Laboratory Standards Institute, Wayne, Pennsylvania
3. World Health Organization, 2021 WHO laboratory manual for the diagnosis of diphtheria and other related infections. ISBN 978-92-4-003805-9.
4. World Health Organization, Laboratory testing for diphtheria in outbreak settings: Interim guidance – January 2024. https://www.who.int/publications/i/item/who-diph-laboratory-2024.1
5. Public Health Agency of Canada.  2009.  Case description for Communicable Diseases under National Surveillance-Diphtheria. CCDR supple. Vol 35S2. Pg 63-64.
6. Badell, E., Hennart, M., Rodrigues, C., et al. 2020. Corynebacterium rouxii sp. nov., a novel member of the diphtheriae species complex. Res Microbiol. Apr-Jun;171(3-4):122-127. doi: 10.1016/j.resmic.2020.02.003. Epub 2020 Feb 28
7. Crestani, C., Arcari, G., Landier, A., et al. 2023. Corynebacterium ramonii sp. nov., a novel toxigenic member of the Corynebacterium diphtheriae species complex. Res Microbiol. Sep-Oct;174(7):104113. doi: 10.1016/j.resmic.2023.104113. Epub 2023 Aug 10.

Pathogen Safety Data Sheets: Infectious Substances – Diphtheroids

Pathogen Safety Data Sheets: Infectious Substances – Corynebacterium diphtheriae

For Health Professionals: Diphtheria

Diphtheria