Question

5. A student is testing for lysine deaminase by stabbing Lysine Iron Agar slant several times with the test organisms and a control. After 24 hours of incubation in a regular incubator, the butt of the tubes turned yellow, but there was no sign of red or purple color. Even the control, which was a positive deamination organism, produced these same results. What might have gone wrong? RESULTS / INTERPRETATION F5 F4 F6 F8 F9 F10 og * 90

Answer 1

The LIA agar should have been stabbed with bacterial cells as well as streaked on the slanted surface. The streaking step was not performed. Lysine deamination is an aerobic process which occurs on the slant of the media. If bacteria is not present on the surface, then the deamination reaction cannot take place (thus no red or purple color). This is a result of incorrect methodology followed during the experiment.

Lysine decarboxylation is an anaerobic process which occurs in the butt of the media. If the decarboxylase is not produced, the butt remains acidic yellow. Both the test organism and the control did not produce lysine decarboxylase.