Which test best distinguishes Klebsiella oxytoca from K. pneumoniae?

• A. Urease
• B. Sucrose
• C. Citrate
• D. Indole

Answer: (D)

The ability to differentiate between Klebsiella oxytoca and Klebsiella pneumoniae is important in clinical microbiology, as these two species can exhibit distinct clinical behaviors and resistance patterns. The indole test is particularly effective for this purpose because it assesses the organism's ability to convert tryptophan into indole.

Klebsiella oxytoca is positive for the indole test, meaning it can produce indole from tryptophan, while Klebsiella pneumoniae is typically negative for this test. This simple biochemical test allows for easy differentiation between the two species, making it a critical tool in the laboratory setting for proper identification.

The other tests on the list do not provide such clear discrimination. For instance, urease and citrate tests may yield similar results for both species, and although they might show some variability, they are not definitive for distinguishing between Klebsiella oxytoca and Klebsiella pneumoniae. Likewise, sucrose fermentation is generally not a reliable differentiator and can vary not just between these two species but among strains within each species as well. Consequently, the indole test is the most reliable method to distinguish Klebsiella oxytoca from K. pneumoniae effectively.