A 44-year-old female was rehospitalized after a gastrojejunostomy. She had increased white blood cells (21,000/mL) and was assumed to have a postsurgical infection. X-rays showed a leakage from the gastrojejunostomy site into the left upper abdomen and communication with the large cavity. Aspiration of the fluid found by radiologic examination contained small, gram-variable bacilli. Tiny, yellowish nonhemolytic colonies grew on blood agar that slightly pitted the agar. They were catalase negative and oxidase positive, but they failed to grow on MacConkey.

Questions

1. Both rapid indole and hanging drop motility tests were negative for this bacillus. What microorganisms are in the differential, and how would you approach this identification?

2. The nitrate test was negative and the organism did not ferment glucose. The oxidative-fermentation (OF) glucose test was also negative, meaning that the organism was a glucose nonoxidizer. What is the most likely identification, and how would you confirm it?

3. How is the nitrite reduction test performed when the nitrate test is negative?