Butyrate Esterase Disk Guide
A bench reference for rapid spot-test identification of Moraxella catarrhalis based on butyrate esterase activity.
Bench card visual
Butyrate spot tests A-B
Read first
Read the color shift on the bromo-chloro-indolyl butyrate disk within 5 minutes of incubation.
A
PositiveMoraxella catarrhalisDevelopment of a distinct blue-violet/indigo color from indoxyl release.
B
NegativeNeisseria gonorrhoeaeNo color change; disk remains white/grey with rubbed colony smear.
PositiveMoraxella catarrhalis
Development of a distinct blue-violet/indigo color from indoxyl release.
NegativeNeisseria gonorrhoeae
No color change; disk remains white/grey with rubbed colony smear.
What to look for
| Visual clue | Meaning | Student shorthand |
|---|---|---|
| Blue-Violet Color | Butyrate esterase hydrolyzes substrate, releasing indoxyl which oxidizes to indigo | Shorthand: Positive (+) |
| No Color Change | Substrate remains unhydrolyzed; no indoxyl release | Shorthand: Negative (-) |
| Rubbed Inoculum | Heavy smear of fresh colonies applied to a moistened disk | Must read within 5 minutes |
Butyrate study readout
| Pattern | What to call it | How to think about it |
|---|---|---|
| Positive | Development of blue-violet color within 5 mins | Presumptive Moraxella catarrhalis (highly useful in respiratory isolates). |
| Negative | No color change within 5 mins | Presumptive Neisseria species (e.g. N. gonorrhoeae, N. meningitidis). |
| Differential logic | Separates Moraxella from Neisseria | M. catarrhalis is butyrate (+), DNase (+), and carbohydrate fermenter negative (asaccharolytic). |
Key takeaways
- Rapidly separates M. catarrhalis from fastidious Neisseria species.
- Moraxella catarrhalis is routinely isolated in otitis media, sinusitis, and COPD exacerbations.
- Always confirm diplococci morphology on Gram stain before reporting.
Remember
M. catarrhalis shows a hockey-puck colony behavior, sliding intact across the agar surface.