Clinical microbiology – indole production among Klebsiella Which Klebsiella species/subspecies is characteristically indole-positive on biochemical testing?

Introduction / Context:
Biochemical identification in the Enterobacterales relies on a panel of tests. Indole production differentiates species within Klebsiella and related genera—an essential bench skill for accurate reporting.

Given Data / Assumptions:

• Indole test detects the organism’s ability to split tryptophan to indole.
• Most K. pneumoniae strains are indole-negative.
• Klebsiella oxytoca is typically indole-positive.

Concept / Approach:
Historically, “K. pneumoniae subsp. aerogenes” corresponds to what is now Enterobacter aerogenes (currently Klebsiella aerogenes), not an indole-positive Klebsiella. K. oxytoca’s consistent indole positivity makes it the classic correct answer in exam settings. K. granulomatis (formerly Calymmatobacterium granulomatis) is not commonly assessed by routine stool or urine biochemical panels.

Step-by-Step Solution:
Recall the rule: K. oxytoca is indole-positive; K. pneumoniae sensu stricto is indole-negative.Evaluate each option’s typical biochemical profile.Select “Klebsiella oxytoca.”

Verification / Alternative check:
Laboratory manuals and identification databases (e.g., API, VITEK) list K. oxytoca as indole-positive, aiding differentiation from K. pneumoniae in urinary and respiratory isolates.

Why Other Options Are Wrong:

• K. pneumoniae subsp. pneumoniae/rhinoscleromatis: classically indole-negative.
• “Subsp. aerogenes”: taxonomically reclassified and not the indole-positive Klebsiella tested here.
• K. granulomatis: etiologic agent of donovanosis; not identified by standard indole testing workflows.

Common Pitfalls:
Confusing older taxonomic names; relying on outdated subspecies designations can mislead identification.

Final Answer:
Klebsiella oxytoca.