Dear Stanley: Tips for Performing QC on ETEST® Strips

IP/IPI strip inoculated with P. aeruginosa derived from  ATCC® 27853™*

Dear Stanley,

We recently purchased your KWIK-STIK™ product to perform quality control on new lots of ETEST® strips. Do you have any tips for setting up and reading an ETEST®?

Mike from Philadelphia, PA

Dear Mike,

KWIK-STIK is the perfect product for performing QC on new lots of ETEST® strips. You made a smart first step, now follow these five tips for setting up and reading ETEST® strips to ensure a successful QC process:

1. Subculture at least once before using the growth for QC. I recommend not testing the first plate you grow from the KWIK-STIK. Subculture at least once to ensure the strain is fully resuscitated.

2. Be sure to use the correct fluid when making your 0.5 McFarland. Most ETEST® strips require 0.85% NaCI, but you should always consult the Etest product insert.

3. Remember the ETEST® generates MIC values from a continuous scale and can give results between the conventional two-fold (i.e. half dilutions). MIC results for a QC strain that fall a half dilution below the lower QC limit should be rounded up to the next two-fold value before establishing QC compliance. Similarly, MIC results that are a half dilution above the upper limit show non-QC compliance.

4. Be patient. Once inoculated with the suspension, allow the plates to fully dry before applying the ETEST® strip. Plates may take 15 to 20 minutes to dry, but it’s worth the wait. Applying strips to wet plates may result in jagged ellipse edges and uneven MIC intersections which will interfere with the reading.

5. Always keep the ETEST® reading guide that comes with the package insert handy. The manufacturer provides this information for a reason. The reading guide will help you through some of the toughest interpretation scenarios.

If you need more guidance while using a KWIK-STIK to perform QC on ETEST® strips, my colleagues are here to help. The experienced microbiologists on our Technical Support team can be reached at or 320.229.7045.


Stanley Staphylococcus

About Stanley

Stanley Staphylococcus is a Master Micro-Technologist at Microbiologics, where he is responsible for helping customers understand why microorganisms behave the way they do. You could say he’s somewhat of a psychologist. Microbiologics has been lucky to have Stanley, a graduate of Gram-Positive Cocci University, as a member of their renowned Technical Support Team for over 20 years. Stanley says his favorite type of people are microbiologists and he enjoys traveling far and wide to meet them. Amazingly, Stanley has been on every continent – even Antarctica!

How to submit inquiries: There are two ways to get Stanley’s help. You can email your questions to or you can simply submit an inquiry from our Dear Stanley page. For urgent issues, please contact our Technical Support Team at or 1.320.229.7045.

1 Comment

  1. Manuela Burtea

    Do not forget to use the right culture media when you use Etest. All Etest are validated by bioMerieux and you need them recommandation to use it.


Leave a Comment

Your email address will not be published. Required fields are marked *