A 20-month-old female was diagnosed with cystic fibrosis at the age of 6 months. She is taken to the hospital on her second day of respiratory difficulty and presents with cough, abundant mucus expectoration, and a temperature of 37.9°C. Because she has a history of Pseudomonas aeruginosa infections, treatment is started with ceftazidime and amikacin. Bronchial aspirates are obtained for culture; plated on blood, chocolate, and MacConkey agars; and incubated (37°C, 48 hours). A medium specific for isolation of slow-growing Burkholderia organisms also is inoculated and incubated appropriately. Abundant growth of oxidase-positive colonies that are nonmotile, catalasepositive, gram-negative rods is identified as Sphingobacterium multivorum by means of a Vitek GNI card and API 20NE. Definitive identification is provided by biochemical tests that show the following positive results: growth on MacConkey agar; urease; esculin hydrolysis; beta-D-galactosidase production; assimilation of glucose, arabinose, mannose, N-acetyl-glucosamine, and maltose; and acidification of glucose, lactose, maltose, sucrose, and xylose. Negative results are identified for the following: motility at 23°C (room temperature), 37°C, and 42°C; nitrate and nitrite reduction; indole production; arginine dihydrolase; lysine and ornithine decarboxylase; gelatin hydrolysis; hydrogen sulfide production; and assimilation of mannitol, gluconate, malate, and citrate. Antimicrobial susceptibility testing identifies susceptibility to carbenicillin, ceftazidime, ceftriaxone, cefuroxime, chloramphenicol, azlocillin, cefotaxime, ticarcillin, ciprofloxacin, imipenem, piperacillin, and amikacin. Resistance to aztreonam, mezlocillin, gentamicin, tobramycin, and cotrimoxazole also is identified. A Burkholderiaspecific medium shows no growth. The patient responds well to fluid and antimicrobial therapy and is discharged from the hospital.

Questions

1. Which microorganisms are in the differential diagnosis for this patient?

2. What tests can be done to provide differential evidence for bacterial identification?

3. What method or methods should be used to test for susceptibility of the pathogens identified in this case?