Spot Indole Reagent PL.391-10 — IFU summary + QC organism guide
Below is the procedural summary, QC organism panel, and chemistry note for Pro-Lab Spot Indole Reagent (PL.391-10). PL.391-10 uses DMACA chemistry — documented in peer-reviewed literature as more sensitive and easier to interpret than the Kovacs (DMAB) reagents many labs still use.
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Procedure (per IFU Rev. 2021-03)
- Pick a well-isolated colony from a fresh (18–24 h) pure culture growing on non-selective media (blood agar, MacConkey, or chocolate).
- Smear the colony onto filter paper or a paper disc.
- Apply 1 drop of PL.391-10 directly to the smear.
- Read within 3 minutes: blue = indole-positive (e.g., E. coli, P. vulgaris); pink/colourless = indole-negative (e.g., P. mirabilis, K. pneumoniae).
- Discard test material per your lab’s biohazard protocol.
Storage: 15–25°C in original container, protected from light. Stable until labelled expiry. No refrigeration required.
QC organism panel
| Organism | ATCC | Expected result |
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| Escherichia coli | 25922 | Positive (blue) |
| Proteus vulgaris | 13315 | Positive (blue) |
| Klebsiella pneumoniae | 13883 | Negative (pink/colourless) |
| Proteus mirabilis | 25933 | Negative (pink/colourless) |
QC frequency: each new lot, each new shipment, and per your IQCP plan thereafter (typically weekly or monthly).
Why DMACA over Kovacs (DMAB)?
Miller & Wright (J Clin Microbiol 1982, PMID 7040458) compared four indole reagents across 359 gram-negative rod strains. DMACA was “the most sensitive of those tested and provided results that were easiest to interpret.” The blue positive on PL.391-10 is unambiguous — no pink-to-red fade that catches new techs out.
Two clinically validated workflows
Presumptive E. coli ID from urine: Peterson et al., Am J Clin Pathol 1982 (PMID 6753569) — spot indole + morphological criteria across 191 lactose-fermenting GNRs achieved 99.1% accuracy for E. coli ID vs. full biochemical panel. Saves a panel on your highest-volume organism.
Proteus speciation: Bale et al., Am J Clin Pathol 1985 (PMID 3966445) — on 172 swarming Proteus isolates, spot indole yielded >99% predictive value for P. mirabilis vs. P. vulgaris. Drives empiric antibiotic selection (P. mirabilis is typically ampicillin-susceptible; P. vulgaris is typically resistant).
Specifications
- SKU: PL.391-10 — 10 mL dropper bottle
- Chemistry: p-dimethylaminocinnamaldehyde (DMACA) in hydrochloric acid
- Storage: 15–25°C ambient, protect from light — no cold chain
- Direct list: $43.37 · Fisher 22-286-249 · VWR 18973677
- Regulatory: CE Marked under IVD Directive; CLIA Moderate Complexity
- Same-day shipping from Round Rock, TX
Want the full IFU PDF or a printable QC log template? Reply and we will send same business day.
View this document online: https://www.pro-lab-direct.com/indole/deliverables/ifu-qc-guide.html
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