identifier: METPO:1005013
label: methyl red test
definition: An assay that tests the ability of an organism to produce and maintain
  stable acid end products from glucose fermentation.
trait_category: OTHER
term_kind: CLASS
mapping_status: SEEDED
parent_traits:
- METPO:1000059
curation_history:
- timestamp: '2026-09-12T20:14:22Z'
  curator: seed_from_metpo
  action: SEEDED_FROM_METPO
  changes: imported from data/raw/metpo.owl (CLASS)
- timestamp: '2026-09-12T20:15:55Z'
  curator: codex
  action: ENRICHED_FROM_LITERATURE
  changes: Added the METPO methyl-red-test assay parent with stable-URL methyl-red
    readout evidence after a repository-wide duplicate review covering ignored and
    hidden files.
  llm_assisted: true
- timestamp: '2026-09-12T20:35:11Z'
  curator: codex
  action: CURATION_REVIEW_REVISION
  changes: Added parent-level ASM evidence for high-acid mixed fermentation after
    PR 866 review issue 867 noted that the parent reused child assay-readout quotes.
  llm_assisted: true
- timestamp: '2026-09-12T21:00:37Z'
  curator: codex
  action: CURATION_REVIEW_REVISION
  changes: Expanded the ASM mixed-acid evidence quote through its butanediol contrast
    and narrowed its note after PR 866 review issue 871.
  llm_assisted: true
definition_source: https://asm.org/getmedia/40946f85-9357-4563-aa8a-994427efa825/Methyl-Red-and-Voges-Proskauer-Test-Protocols.pdf
evidence:
- reference: https://asm.org/getmedia/40946f85-9357-4563-aa8a-994427efa825/Methyl-Red-and-Voges-Proskauer-Test-Protocols.pdf
  snippet: Escherichia coli and other members of the low-ratio organisms described
    by Clark and Lubs ferment sugars by the mixed acid pathway resulting in a low
    ratio of CO2 to H2 gas produced by fermentation. The mixed acid pathway gives
    4 mol of acidic products (mainly lactic and acetic acid), 1 mol of neutral fermentation
    product (ethanol), 1 mol of CO2, and 1 mol of H2 per mol of glucose fermented
    (9). The large quantity of acids produced causes a significant decrease in the
    pH of the culture medium. In contrast, Enterobacter aerogenes and other members
    of the high-ratio organisms (those that produce a high ratio of CO2 to H2 from
    the fermentation of glucose) ferment sugars via the butanediol fermentation pathway,
    producing only 1 mol of acid per mol of glucose. This pathway results in a lower
    degree of acidification of the culture medium.
  notes: The ASM protocol contrasts mixed-acid fermentation's 4 mol acidic products
    per mol glucose with the butanediol pathway's 1 mol acid per mol glucose and lower
    medium acidification.
- reference: https://asm.org/getmedia/40946f85-9357-4563-aa8a-994427efa825/Methyl-Red-and-Voges-Proskauer-Test-Protocols.pdf
  snippet: When the culture medium turns red after addition of methyl red, because
    of a pH at or below 4.4 from the fermentation of glucose, the culture has a positive
    result for the MR test (Fig.1A).
  notes: The ASM protocol PDF defines the methyl-red-test positive readout as acidification
    to pH 4.4 or below after glucose fermentation.
- reference: https://asm.org/getmedia/40946f85-9357-4563-aa8a-994427efa825/Methyl-Red-and-Voges-Proskauer-Test-Protocols.pdf
  snippet: A negative MR test is indicated by a yellow color in the culture medium
    (Fig. 1B), which occurs when less acid is produced (pH is higher) from the fermentation
    of glucose.
  notes: The same protocol defines the negative readout as a yellow culture reflecting
    less glucose-derived acid production.