Close-up of what is referred to as a string test (KOH test), which was being performed on a droplet of sample that was harvested from a Petri dish growing suspected colonies of Vibrio cholerae bacteria. Note the mucoid string still clinging to the wire inoculating loop, indicating a positive string test result (image by Centers for Disease Control and Prevention, USA; Public Health Image Library, image ID #3909); image modified by MIC. The cover is published under the Creative Commons Attribution (CC BY) license.