A 71-year-old female with acute myeloid leukemia was being treated with immunosuppressive therapy and was neutropenic with 100 white blood cells per microliter. She had a low-grade fever and was not responding to treatment with a thirdgeneration cephalosporin. Severe periodontal disease was noted. Her blood cultures became positive after 48 hours with a gram-negative fusiform rod that did not grow on MacConkey and was neither oxidase nor catalase positive. On blood agar, the organism was nonhemolytic but spread out from the initial colony, producing a haze on the agar. The laboratory reported that the organism was resistant to beta-lactam drugs. The patient’s therapy was changed to ciprofloxacin, and she became afebrile within 24 hours.

Questions

1. What is the likely organism isolated from the blood culture, and what is the likely source of the organism?

2. Which tests will confirm the identification?

3. The patient was not responding to cephalosporin antimicrobial agents. What rapid testing can the laboratory perform to aid in the appropriate treatment of this organism?