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Neisseria gonorrh​oeae (GC) Anti​biotic Su​​​sceptibility Testing (AST) for Azithromycin, Ceftriaxone, and Cefixime​

Test ​​​​​M​​​​​​​e​t​h​o​​​​​d​​​olog​y​​​​​
​​​​N​eiss​​eria gonorrhoeae (GC) Antibiotic Susceptibility Testing (​AST) for Azithromycin, Ceftriaxone, and Cefixime

Ref​lex Testing

​bioMérieux Etest Gradient Strip (“GC Etest”)  

​Pre-Approval for isolates meeting one of following is not required: 

  • N. gonorrhoeae isolates wit​​​​h d​ecreased ​susceptibility to cefixime (MIC ≥0.25 µg/mL), ceftriaxone (MIC ≥0.125 µg/mL), or azithromycin (MIC >16.0 µg/mL).
  • N. gonorrhoeae isolates from ​​suspected treatment failures (Clinical Guidelines for Gonorrhea Treatment and Management of Suspected Treatment Failure ​PDF​) and isolated from sites, including but not limited to urethra, endocervix/vagina, rectum, pharynx, blood, synovial fluid, ​and eye.
  • N. gonorrhoeae isolat​es ​from ​disseminated gonococcal infections (DGI).
  • N. gonorrhoeae isolates ​from​ ocular inf​ections​
Pre-appro​val for other N. gonorrhoeae isolate​s is required. Please contact STD program at ​​. ​
Supp​lemental Informati​on and Required Form(s)​​​​​
​Submitters can use ​​one of the following methods to access the submittal form: MDL Lab Web Portal (LWP) (Preferred) or MDL barcode submittal form at MDL Submission Instructions and Forms

On the MDL General Submission form, select Form Antimicrobial Susceptibility Testing -AST: MDL General Electronic Submission Form (PDF)

​​The MDL General Electronic Submission Form should be downloaded and opened using a pdf viewer. To download, right-click the link and select "Save link as." If you are unable to open the Form using a pdf viewer, please contact MDL at 510-412-3700 or​.

Instructions ​on completing the form can be found at the following links:
MDL Form AST - Instructions
​​Gradient Strip (GC Etest) Neisseria gonorrhoeae Antimicrobial Susceptibility Testing Services Frequently Asked Questions (FAQ)​

Required Specimen​/ Sample Type(s)
​Pure, fresh culture of N. gonorrhoeae submitted on chocolate or modified Thayer Martin media supporting growth of N. gonorrhoeae.

Minimum Volume Required

​​​Not Applicable 

Specimen Stability
​​​Prepare culture for transportation: First, obtain fresh culture by growing a pure N. gonorrhoeae isolate at 35°C in 5% CO2 on suitable media for gonorrhea (such as chocolate agar or modified Thayer-Martin) for 24-48 hours, until obtain visible growth. Then, prepare and submit the culture fresh (24-72 hr) at time of shipping. Three options are recommended. 

  • To ship using an agar slant: Heavily inoculate a chocolate (or other suitable media for GC) slant with fresh growth. Incubate at 35°C with 5% CO2 until you see visible growth (18 – 24 hours is ideal). Then close cap tightly and ship at ambient temperature. 
  • ​​To ship using an agar plate: Heavily inoculate a chocolate (or other suitable media for GC) plate with fresh growth. Incubate at 35°C with 5% CO2 until you see visible growth (18 – 24 hours is ideal). Then seal the plate lid tightly with parafilm and place the plate in zip lock biohazard bag and ship at ambient temperature.
  • ​To ship using a frozen cryotube with TSB and 15% glycerol: Heavily inoculate a cryotube with fresh growth. Immediately place in a -60°C or lower freezer. Once the isolate is fully frozen, ship the isolate on dry ice.​
​Refer to ‘Specimen preparation for transport’ instructions in Disseminated Gonococcal Infection (DGI) Guidance for Laboratories​ for details.  

​​​Rejection Criteria

  • ​Isolate submissions with insufficient or conflicting labelling
  • ​​​Broken or leaking samples
  • Samples with insufficient quantities or growth
  • Isolates that are too old or non-viable
  • Specimen/sample types not meeting acceptance criteria (see FAQ), if no prior approval was received
  • Mixed cultures
  • Primary patient samples​
Storage/Transport Conditions 

​Culture isolates may be shipped at ambient temperature or frozen in TSB with 15% glycerol on dry ice.  ​
Transport Medium,​
if applicable

​Not Applicable
Specimen Labeling

​​Two identifiers, including patient full name, and at least one other identifier (specimen accession number, date of birth, medical record number); date and time of collection as noted for specific tests, if applicable.​

Shipping Instructions and Specimen Handling Requirements​​​​​
​​​Ship isolates grown on media that supports N. gonorrhoeae at ambient temperature or ship cultures frozen in TSB with 15% glycerol on dry ice.

Follow the appropriate DOT/IATA approved shipping procedures.

Ship to:

California Depart​ment of Public Health​
Microbial Diseases Laboratory ​
ATTN:  Bacterial Diseases Section
850 Marina Bay Parkway, Specimen Receiving Room B106
Richmond, CA  94804​​

Specimen Collection Instructions, if applicable​​

​​Only pure, live cultures of N. gonorrhoeae are acceptable for testing at MDL. Primary clinical specimens for culture isolation are not accepted by MDL at this time. Primary clinical specimens from suspected treatment failures may be tested via the ARLN regional laboratory in Washington state. Contact​​ or​ for submission instructions.

Turnaround Time

​​12 calendar days
Expedited testing may be available upon request.

Interferences & Limitations​​

​Pure culture isolates must be viable for testing.​
Reference Range

​Not Applicable
​​Additional Information
​​​Gradient Strip (GC Etest) Neisseria gonorrhoeae Antimicrobial Susceptibility Testing Services Frequently Asked Questions (FAQ)​
MDL Point of Contact
​For more information on the GC Etest and submission criteria o instructions, please email or call  MDL Bacterial Di​seases Section at (510) 412-3903​


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