Expert: Florence M Rollwagen - 8/13/2008

Question
Dear Rollwagen,
Please ignore the previous questions because i forgot to say they were about oxidase test.

Question regarding oxidase test
"why do we have to set a strict time limit (10 seconds)for observing the color change?
Why is the oxidase paper stored at 5 degree Celcius and in a dry state? (Why not other temp?)
Do oxidase negative organism lack an electron transport chain?
Is a strict anaerobe an oxidase negative and why?"

Answer
Hi again:

In the oxidase test, we are making the determination whether bacteria have cytochrome oxidases in their respiratory chain.  The reason the test is so short is that the paper can be oxidised by air as well as bacterial enzymes.  So if you want to test the bacteria alone, the test has to be virtually immediate.  Any longer, and you will get positives for all your organisms.

We store these materials cold and dry to preserve the reagent [N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) or N,N-Dimethyl-p-phenylenediamine (DMPD)]. 5C is refrigerator temperature for convenience.

Organisms can be oxidase negative but still be aerobic because they use different enzymes in the ETC.  Check this website:
http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed.section.406

A strict (obligate) anaerobe will be oxidase negative because they do not use the ETC and do not use oxygen as the final electron acceptor.   

I hope this answer has helped you.  Please write back if you have more questions.

FM Rollwagen, PhD