String test for Vibrio cholerae

Hello everyone

Today's post is about string tests that are used for identification of Vibrio spp.

String tests are known to be around 86% sensitive tests.

What is the secret behind string test??

Well Sodium taurocholate or sodium deoxycholate specifically lyse the Vibrio cells leaking out their DNA. DNA strands tend to give the suspension a viscous mucoid texture.

For eg. If you all know there is a disease known as cystic fibrosis where the person  accumulates a lot DNA in his lungs due to killings of infectious pathogens. When these apthogens die, the DNA gets leaked into the lungs and person has a very thick mucous which is problematic for him to cough out.

Similarly here, the leaked DNA makes the suspension viscous which results in the formation of string when loop is pulled away from the slide.

So the procedure is 

1.  Pick a well isolated colony 18-24 hrs old on a clean grease free slide. 
2. Add a drop of sodium taurocholate or sodium deoxycholate on the colony. 
3. Now mix them well with the inoculating loop for good 2-3 minutes
4. Now pull the loop away, if you see a thread like formation the culture is string test positive.

Mostly Vibrio cholerae and Vibrio mimicus give a positive string test.

Hope it helps

Lots of Love

-Staph