A stool culture reveals an oxidase-positive, non-lactose fermenting colony

A suspension of the organism was made in sterile distilled water and used to inoculate a commercial identification strip that did not demonstrate any positive reactions after incubation. The microbiologist then set up traditional biochemical tube tests and the results were still negative. What is the next step in the identification process?
A) Perform halotolerance testing
B) Perform serologic testing using O1 and O139 antisera
C) Reincubate the identification tubes in CO2
D) Perform a string test

A