[Microbiology] phenol red fermentation tests

[Lisa Moore]

I teach a basic microbiology lab class and have included the phenol red
fermentation test in the lab after the students do the
oxidation-fermentation glucose test.  I am trained as a phytoplankton
ecophysiologist, so I am not familiar with this test outside of teaching
this lab.  From the various lab books and websites that I have looked
at, the test is done in test tubes under aerobic conditions.  My
question is whether a non-fermenter can oxidize the sugars (such as
lactose and sucrose) and turn the medium yellow (indicative of acid
production), thus giving a false positive?  It seems to me that this is
possible, making the test rather limited.  Of course, I could be missing
something in understanding the protocol or chemistry behind the test.  

If someone has a quick answer or a good reference, I would appreciate
the help.

Thank you, 
Lisa

Lisa R. Moore
Assistant Professor
Department of Biological Sciences
University of Southern Maine
96 Falmouth Street
Portland, ME  04103
email:  lmoore from usm.maine.edu
phone:  (207) 780-4261 
fax:  (207) 228-8116