1) The unknown tested positive (A/G) for lactose fermentation (both MOs should read negative).
2) The unknown tested negative for hydrogen sulfide (true for S. flexneri only).
3) The unknown tested positive for lipase (true for P. vulgaris only).
4) The unknown did not grow on MSA (true for P. vulgaris only).
The growth on the EMB plate was a purple color/not very iridescent which indicates a non-lactose fermentation, correct?. If so, then why would I get a positive lactose test for reasons other than contaminated sample or different strains?
For your edification the other test results which lead me to these two choices out of 30 possible MOs include:
light gray on TSA,
growth at 37 degrees,
I am leaning towards P. vulgaris but I am not sure how to justify my final decision given the contradiction in the test. Any thoughts on my choice or how to justify this? Thanks for any help.
Edited by mpoper, 25 April 2010 - 06:28 AM.