Question

Please answer all questions

A 73-year-old man with an endotracheal tube has been in the intensive care unit on mechanical ventilation for 7 days. Sputum was suctioned and sent for culture. The colonies on the MacConkey plate were clear and those on the blood agar plate were a grayish-green and non- beta hemolytic. An oxidase test was done; it was negative. The laboratory has a Vitek that it uses for identification and susceptibility testing. Identification and susceptibility cards were set up on this organism. The next day, the Vitek identification was Stenotrophomonas maltophilia with only a few drugs listed from the susceptibility panel.

Questions

1. Why was testing for so many antimicrobials suppressed?
2. Care should be exercised in interpreting this results given the patients history. Why?

3. What is the drug of choice?

Answer 1

1. Drug susceptibility testing for so many antimicrobials was suppressed because Strenotrophomonas maltohilia is resistant to many of the broad spectrum antibiotics. S.maltophilia is resistant to the penicillins, cephalosporins and aminoglycosides.

2. Strenotrophomonas maltophilia is an opportunistic pathogen and is being recognized as an important nosochomial pathogen. It is frequently isolated from respiratory specimens from patients who are on mechanical ventilation. Therefore the clinician needs to determine whether this is a colonization or an infection, as the patient is also on mechanical ventilation.

3. The drug of choice for S.maltophilia is trimethoprim-sufamethoxazole.