Details - Public Health Image Library(PHIL)

ID#:

3909

Caption:

This photograph depicts a close-up of what is referred to as a string 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. Mixing the bacterial sample with 3% potassium hydroxide (KOH), Gram-negative bacteria will lyse, and release their contents of sticky nuclei acids, which when touched by a wire loop, will cling together forming a stringy filament as the loop is lifted away from the slide. Gram-positive bacteria have a thicker cell wall, protected by a layer of peptidoglycan, thereby, able to resist the lytic action of the KOH reagent, and thus release no sticky nuclei acids, and hence, no string is produced.

High Resolution:

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Content Provider(s):

CDC

Creation Date:

1971

Photo Credit:

Links:

Categories:

CDC Organization