Question

Would this be considered a positive or a negative for a motility test? It was left to incubate for 19 hours

Answer 1

Motility test is used to determine the motility of the living bacteria. Bacteria uses different locomotory organelles like flagella,cilia and pseudopods. Most of the bacteria are motile except cocci which are non-motile.

In the motility test, a semi-solid agar medium is used to determine the motility of bacterium. This medium is soft and allows the motile bacterium to migrate easily which causes cloudiness of the medium .The inoculum is stabbed at the center of the semi solid agar medium . The motility of bacteria is evident by a diffuse growth which extends the line of the inoculation. While the bacteria which are non motile grows in the soft agar tube and only in the area inoculated.

This explains the above test is negative for motility test - The above picture indicates sharply defined margin and the medium surrounding is transparent showing it is negative for motility test.

On contrary, diffuse growth and the surrounding medium opaqueness indicates Positive test for motility.