A Microbe That Grows Only at the Bottom of a Tube

Question

A microbe that grows only at the bottom of a tube of thioglycollate medium is probably a(n)
A) obligate aerobe.
B) facultative anaerobe.
C) aerotolerant anaerobe.
D) microaerophile.
E) obligate anaerobe.

Accepted Answer

Microbes that grow only at the bottom of a tube of thioglycollate medium are likely to be obligate anaerobes. Thioglycollate medium is a type of differential medium used to test the oxygen requirements of microorganisms. It contains a reducing agent (thioglycollate) that removes oxygen and creates an anoxic environment at the bottom of the tube. Obligate anaerobes are microorganisms that require an oxygen-free environment to grow, as they cannot tolerate oxygen. Therefore, they will only grow at the bottom of the tube where there is no oxygen present.