Overview

Modified Gifu Anaerobic Medium — mGAM, also written as Modified GAM — is the Japanese-pharmacopoeial-tradition broth/agar for fastidious anaerobes. Originally developed at the Department of Bacteriology, Gifu University School of Medicine for the isolation and cultivation of anaerobes from clinical specimens, and commercialised by Nissui (now Shimadzu Diagnostics), the medium has become the reference anaerobic medium across Japanese pharma, academic, and clinical microbiology, and is the recommended growth medium for Japan Collection of Microorganisms (JCM) anaerobic deposits.

The 'Modified' variant reduces glucose from 3 g/L in the original GAM to 0.5 g/L. This change minimises pH drift during long incubations, a critical requirement for slow-growing strict anaerobes. The dual-reductant system — L-cysteine 0.3 g/L plus sodium thioglycolate 0.3 g/L — gives a lower equilibrium Eh than single-reductant media and is one of the defining technical features of the medium. Hemin (10 mg/L) and vitamin K1 (5 mg/L) support haem- and menaquinone-auxotrophic Bacteroides and Prevotella, and L-arginine (1.0 g/L) supplies the arginine-dihydrolase pathway used by Eubacterium and the asaccharolytic cocci. Menadione (vitamin K3) is not in the standard formulation but can be added on request.

Which version is this? This listing is the Nissui modification of Modified GAM, prepared at 41.7 g/L to the published Nissui-lineage specification. It includes L-arginine 1.0 g/L in the dehydrated base and vitamin K1 at 5 mg/L, the latter supplied as Stock K because phylloquinone is an oil and cannot be blended into a powder. Choose this version where a published-specification match matters — for example when reproducing a literature method that cites the Nissui catalogue product, or when an arginine-dihydrolase substrate or a menaquinone precursor must be present in the base. GMExpression also supplies a richer in-house formulation, the GMExpression modification of mGAM, prepared at 49.4 g/L with proteose peptone at 10.0 g/L and digested serum at 13.5 g/L and without L-arginine or vitamin K1. The two are not interchangeable and their weigh-out figures differ; see Q9.

We also have

mGAM — GMExpression Modification · YCFA Modified Medium · YCFA Full Recipe · YCFA Base · Modified Chopped Meat Broth (ATCC 1490) · Chopped Meat with Carbohydrates · Beef Granules

Package Contents

Each GMExpression Modified GAM (Nissui Modification) kit contains:

  • Mixture A — pre-weighed Nissui-modification mGAM base (peptone, soya peptone, proteose peptone, digested serum, yeast extract, meat extract, liver extract, glucose 0.5 g/L, NaCl, soluble starch, L-cysteine·HCl, sodium thioglycollate, L-tryptophan, L-arginine, hemin, KH2PO4) for 5 L final volume.
  • Stock K — Vitamin K1 (phylloquinone) stock, 30 mg / 30 mL in 95 % ethanol = 1 mg/mL, in a transparent PET bottle vacuum-sealed inside an aluminium-plastic laminate resealable zipper bag with an oxygen absorber (30 mL covers a 5 L kit at 5 mL per litre). Supplied with every kit and required to complete the medium — vitamin K1 is an oil and cannot be blended into the dehydrated powder. The stock is deliberately dilute: at higher concentrations a significant fraction of the oil films onto the vessel wall instead of dispersing, so the liquid phase assays below nominal and the medium is under-dosed even when the calculation is correct.
  • Optional Stock H — Hemin top-up stock, 60 mg / 60 mL in 0.05 M sodium hydroxide = 1 mg/mL, for batches requiring additional hemin, in a transparent PET bottle vacuum-sealed inside an aluminium-plastic laminate resealable zipper bag (no oxygen absorber required).

Customisation options on request: agar variant at 15 g/L for plates (Modified GAM Agar, Nissui modification); semi-solid variant at 5 g/L agar for cysts/spore preservation; menadione-supplemented variant for routine clinical Bacteroides isolation; configure for Hungate-tube AAE workflows.

Composition — per 1 L equivalent unless stated otherwise

Modified GAM Broth — Nissui modification (published Nissui-lineage specification; per 1 L)

ComponentConcentrationFunction
Peptone (mixed pancreatic digest)5.0 gPeptide nitrogen source
Soya peptone3.0 gPlant-derived peptide source
Proteose peptone5.0 gHigh-quality casein digest, growth factors
Digested serum solids10.0 gComplex protein source, growth factors
Yeast extract2.5 gB-vitamins, NAD precursors
Meat extract2.2 gAmino acid mixture, peptides
Liver extract1.2 gIron, B12, folate, haem precursors
D-Glucose0.5 gReduced from 3 g/L original GAM — minimises pH drift
Sodium chloride (NaCl)3.0 gOsmotic balance
Soluble starch5.0 gTrace-toxin absorption; supports starch-fermenting organisms
L-Cysteine·HCl0.3 gReductant component 1
Sodium thioglycollate0.3 gReductant component 2 — dual-reductant system
L-Tryptophan0.2 gIndole testing substrate
L-Arginine1.0 gArginine-dihydrolase pathway substrate; supports Eubacterium and asaccharolytic cocci
Hemin10.0 mgHaem source for Bacteroides
Potassium dihydrogen phosphate (KH2PO4)2.5 gPhosphate buffer
Total, Mixture A (dehydrated powder)41.71 gVitamin K1 is added separately from Stock K — see below

Final pH: 7.3 ± 0.2 at 25 °C. Adjust with 1 M NaOH or 1 M HCl as required.

Composition per the published Nissui-lineage specification (HiMedia Technical Data M2079, 17 components summing to 41.715 g/L for the complete medium; corroborated by DSMZ MediaDive Medium 1715, which specifies 41.7 g of GAM Broth mod. powder per litre).

Supplement added from stock

ComponentFinal concentrationStock and addition
Vitamin K1 (phylloquinone, CAS 84-80-0)5.0 mg/L5 mL of 1 mg/mL stock (Stock K) per litre of base

Vitamin K1 is a viscous oil and is therefore supplied as an ethanolic stock rather than blended into Mixture A. Dry-blending an oil into a powder gives uneven distribution and a non-uniform K1 content in each weighed portion, so the stock format is what keeps the dose reproducible from batch to batch.

Modified GAM Agar variant

ComponentConcentration
Mixture A, dehydrated powder (as above)41.71 g
Agar (microbiological grade)15.0 g
Total, mGAM agar56.71 g

→Culturomics and Media Navigator

Need help matching this medium to your microorganism — or starting from a target organism and finding the medium that fits? Use the GMExpression Culturomics and Media Navigator: a curated, cross-referenced tool that lets you (i) start from a medium and view the bacterial taxa it is recommended for, or (ii) start from a target organism (genus, species, or DSMZ/ATCC strain ID) and view the panel of GMExpression media that will support it. The Navigator integrates Modified GAM Medium with the wider YCFA, Chopped Meat Broth, BHI-S, Wilkins-Chalgren, Anaerobic Columbia Blood Agar, GMM, M2GSC, BBE, KVLB, CCFA, TPY, and Egg Yolk Agar catalogue.

Use and Applications

  • Universal anaerobe enrichment in Japanese R&D and pharma workflows — broth and agar formats; the de facto standard medium in Japanese anaerobic microbiology.
  • JCM-deposit growth medium — Japan Collection of Microorganisms recommends mGAM for the majority of obligate-anaerobe deposits.
  • Cell-bank holding and working-cell-bank propagation for Clostridium, Bacteroides, Bifidobacterium, Lactobacillus (now Lactobacillus sensu stricto plus 24 further genera per Zheng et al. 2020 IJSEM 70:2782) in pharma / live biotherapeutic product manufacturing.
  • Primary isolation of intestinal anaerobes from clinical and research samples — the original Gifu use case.
  • Anaerobic AST as an alternative to Wilkins-Chalgren in laboratories that prefer Japanese-pharmacopoeial-tradition methods (CLSI M11 reference remains WCh).
  • Spore germination and outgrowth of Clostridium and related spore-formers — the dual reductant system favours rapid germination.
  • Comparative-medium studies as the Japanese-reference benchmark against YCFA, BHI-S, Wilkins-Chalgren, and Modified Chopped Meat Broth.

Compatible Microorganisms

Obligate anaerobes — organisms validated on the GAM / mGAM lineage

  • Bacteroides fragilis (ATCC 25285 = JCM 11019), B. thetaiotaomicron, B. vulgatus, B. uniformis
  • Parabacteroides distasonis, P. merdae, P. johnsonii
  • Prevotella spp., Porphyromonas spp.
  • Fusobacterium nucleatum, F. necrophorum, F. varium
  • Clostridium perfringens (ATCC 13124 = JCM 1290), C. sporogenes, C. butyricum, C. tetani, C. novyi, C. septicum
  • Clostridioides difficile (Lawson 2016 reclassification)
  • Peptostreptococcus anaerobius, Finegoldia magna, Anaerococcus spp., Peptoniphilus spp.
  • Cutibacterium acnes (Scholz & Kilian 2016 reclassification)
  • Eggerthella lenta (formerly E. lentum)
  • Veillonella parvula, V. atypica
  • Lactobacillus sensu stricto and the 24 further genera of the former genus per Zheng et al. 2020: e.g. Lactobacillus acidophilus, Lactiplantibacillus plantarum (formerly L. plantarum), Limosilactobacillus reuteri (formerly L. reuteri), Levilactobacillus brevis (formerly L. brevis), Lacticaseibacillus rhamnosus (formerly L. rhamnosus), Lacticaseibacillus paracasei
  • Bifidobacterium spp.
  • Eubacterium sensu lato (note: many reclassified to Agathobacter, Anaerobutyricum, Eubacterium sensu stricto)
  • Actinomyces spp.

Preparation

1Weigh. Use the pre-weighed Mixture A: 41.71 g per litre for mGAM broth, 56.71 g per litre for mGAM agar. Vitamin K1 is not in Mixture A — it is added from Stock K at step 4. Tare a clean autoclavable Schott bottle of at least 1.5× final volume.
2Suspend & dissolve. Add Mixture A to 950 mL of distilled or deionised water. Heat with frequent agitation to 95–100 °C until completely dissolved (typically 8–12 min — the rich peptone formulation requires extended heating).
3Adjust pH. Cool briefly to ~45 °C. Verify pH with a calibrated meter; target 7.3 ± 0.1 at 25 °C. Adjust with 1 M NaOH or 1 M HCl as required.
4Add Stock K (vitamin K1). Pipette 5 mL of Stock K (1 mg/mL vitamin K1 in 95 % ethanol) per litre, giving 5.0 mg/L. Shake the small bottle of vitamin stock well before pipetting. Add to medium that is still warm (≥ 45 °C) with rapid swirling — the ethanolic stock can crash out of solution if added to cold medium. Protect from light. The 5 mL of stock contributes 0.5 % v/v ethanol at this stage; because Stock K is added before autoclaving, the carrier is substantially driven off during the cycle and does not persist in the finished medium.
5Bring to final volume. Make up to 1000 mL with distilled water.
6Dispense. Broth: 5–10 mL per Hungate or screw-cap tube. Bulk: leave in autoclavable bottle, cap one-quarter turn loose.
7Autoclave. 115 °C × 15 min (69 kPa). The 115 °C autoclave step — rather than the standard 121 °C — is the manufacturer's specification, printed for both the Modified GAM broth and agar in the Nissui / Shimadzu Diagnostics catalogue. The lower temperature preserves thermolabile components (digest serum, liver extract) at the cost of a longer cycle. 121 °C × 15 min is acceptable as an alternative if the lower-temperature cycle is not available, but recovery of fastidious organisms is slightly reduced. For agar plates, 121 °C × 15 min is acceptable since the agar requires the higher melting temperature.
8Cool & reduce. Transfer broth to AAE for cooling and 24-h pre-reduction. For agar: cool to 48–50 °C, then pour plates inside a laminar-flow glove box maintained under an anaerobic atmosphere (AAE) — a standard laminar-flow hood has no anaerobic gas supply and blows HEPA-filtered room air across the molten agar, re-oxidising a medium that has just been pre-reduced.
9Pre-reduction QC. Verify reduction by resazurin tab indicator (if added as 1 mg/L option) or by inoculation of an Eh-sensitive QC organism (Faecalibacterium prausnitzii) into a parallel tube.

Critical control points

  • Autoclave temperature. The Nissui / Shimadzu Diagnostics catalogue specifies 115 °C × 15 min for the broth. This preserves growth factors in digest serum and liver extract. 121 °C × 15 min is acceptable but gives slightly reduced recovery of Faecalibacterium prausnitzii and related Firmicutes.
  • Dual-reductant system. The L-cysteine (0.3 g/L) plus thioglycollate (0.3 g/L) combination delivers a lower equilibrium Eh than YCFA's single-cysteine system. Verify by resazurin colour: pink/red = oxidised, colourless/pale yellow = reduced. Add 1 mg/L resazurin at the user's request for visual confirmation.
  • Pre-reduction time. Allow 24 h equilibration inside an AAE before inoculation of strict anaerobes. The dual-reductant system reaches steady-state Eh more slowly than a single-reductant medium.

Cautions

Autoclave at 115 °C if available. The manufacturer specification is 115 °C × 15 min. Use the lower temperature where possible — particularly for inoculum-grade broth used in cell-bank work or in slow-growing-organism culturomics.
Glucose excess. Do not supplement with additional glucose. The deliberately reduced glucose (0.5 g/L) is what distinguishes mGAM from original GAM. Higher glucose → pH drift → suboptimal recovery of pH-sensitive organisms (Faecalibacterium, Akkermansia muciniphila).
Liver extract and biosecurity. Liver extract is bovine-derived. The same Australian DAFF EX188M zoosanitary pipeline used for YCFA and BHI-S applies. Customs clearance documentation available for Japan, Korea, Taiwan, China, Singapore, ASEAN.
Stock K is ethanolic — flammable and light-sensitive. Stock K is vitamin K1 in 95 % ethanol: a flammable liquid and vapour. Keep away from heat, sparks and open flames, and keep the bottle closed. Phylloquinone is degraded by light, and the PET bottle is transparent — light protection comes from the aluminium-plastic laminate resealable zipper bag, so return the bottle to its bag between uses and protect the supplemented medium from light. Add to medium that is still warm (≥ 45 °C) with rapid swirling; added to cold medium the stock can crash out of solution and the K1 dose will be lost.
Thioglycolate and oxidation. Sodium thioglycolate slowly oxidises in aerobic storage. Pre-weighed Mixture A is supplied under N2; storage in original sealed packaging is essential. Once opened, use within 6 weeks.
Long-term storage of prepared broth. Even with the dual reductant, prepared mGAM stored aerobically at 4 °C will show rising Eh over 6 weeks. Anaerobic storage (vacuum-sealed + O2 absorber) extends usable life to 6 months for strict-anaerobe applications.

Storage and Expiry · Safety

  • Dehydrated Mixture A: 15–30 °C in original N2-flushed sealed packaging. Shelf life 30 months from manufacture.
  • Stock K (vitamin K1, 1 mg/mL in 95 % ethanol): 2–8 °C in the transparent PET bottle, tightly closed and returned to its aluminium-plastic laminate resealable zipper bag with the oxygen absorber, away from ignition sources. Stable 6 months unopened; once the bag is opened the bottle alone gives no light or vapour barrier, so keep it bagged between uses.
  • Stock H (hemin, 1 mg/mL in 0.05 M NaOH), optional: 4 °C, returned to its aluminium-plastic laminate resealable zipper bag between uses. Stable 8 weeks.
  • Prepared broth, aerobic 4 °C: 4 weeks routine; 6 weeks if not subject to repeated opening.
  • Prepared agar plates, aerobic 4 °C sealed: 4 weeks.
  • Prepared broth, anaerobic (vacuum-sealed + O2 absorber): 6 months for strict-anaerobe use.

Safety notes. mGAM contains bovine-derived components (meat extract, digested serum, liver extract). Handle in a Class II BSC when culturing BSL-2 pathogens. L-cysteine and thioglycolate are mild eye irritants — wear nitrile gloves and safety glasses during weighing. Hemin in alkaline NaOH is corrosive. SDS available on request.

References

  1. HiMedia Laboratories, Technical Data M2079, Gifu Anaerobic Broth, Modified (GAM) — Directions: “Suspend 41.7 grams in 1000 mL”.
  2. DSMZ MediaDive Medium 1715, GAM Broth, mod. — 41.7 g GAM Broth mod. powder (HyServe) per 1000 mL. https://mediadive.dsmz.de/medium/1715
  3. Ninomiya K., Suzuki K., Koosaka S., Ueno K., Suzuki S. (1970). Phenylethyl alcohol agar medium for isolation of anaerobic bacteria. Japanese Journal of Medical Science and Biology 23(6): 403–411. doi: 10.7883/yoken1952.23.403. Department of Bacteriology, Gifu University School of Medicine — prints the GAM agar formula and states that "Commercial GAM agar (Nissui) was made according to our formula with minor modifications".
  4. Mitsuoka T., Sega T., Yamamoto S. (1965). Eine verbesserte Methodik der qualitativen und quantitativen Analyse der Darmflora von Menschen und Tieren. Zentralblatt für Bakteriologie, Parasitenkunde, Infektionskrankheiten und Hygiene, Abt. I, Originale 195: 455–469 (in German; PMID 5860078). An intestinal-flora analysis method, not a description of GAM. Zentralblatt für Bakteriologie Abt. I Orig. 195: 455.
  5. Shimadzu Diagnostics (formerly Nissui Pharmaceutical) dehydrated media catalogue: GAM Broth 05422 (59.0 g/L); Modified GAM Broth 05433 (41.7 g/L); Modified GAM Agar 05426 (56.7 g/L). The catalogue states that Modified GAM is "a modified medium of GAM Agar that is developed by Medical School of Gifu University, Japan".
  6. Mitsuoka T. (2014). Establishment of intestinal bacteriology. Bioscience of Microbiota, Food and Health 33(3): 99–116. doi: 10.12938/bmfh.33.99.
  7. Goodman AL et al. (2011). Extensive personal human gut microbiota culture collections characterized and manipulated in gnotobiotic mice. PNAS 108(15): 6252–6257.
  8. Zheng J et al. (2020). A taxonomic note on the genus Lactobacillus: Description of 23 novel genera. IJSEM 70: 2782–2858.
  9. JCM (Japan Collection of Microorganisms) catalogue, RIKEN BRC. https://jcm.brc.riken.jp.
  10. Sasaki H et al. (2019). Comparative analyses of human gut microbiota using cultivation-based and culture-independent methods. Frontiers in Microbiology 10: 1839.

Frequently Asked Questions

Q1. What is the difference between GAM and Modified GAM (mGAM)?
Original GAM, the Gifu University formula commercialised by Nissui as 05422 at 59.0 g/L, contains 3 g/L glucose. Modified GAM (mGAM; Shimadzu Diagnostics / Nissui 05433 broth, 05426 agar) reduces glucose to 0.5 g/L. The lower glucose minimises pH drift during long anaerobe incubations and improves recovery of pH-sensitive organisms (Faecalibacterium, Akkermansia). For most modern anaerobic-microbiology applications mGAM is preferred. For specific spore-germination protocols or for direct comparison with historical original-GAM data, unmodified GAM (59.0 g/L) may be requested as a custom order.
Q2. Why is the autoclave temperature 115 °C instead of 121 °C?
The 115 °C cycle preserves thermolabile components in digest serum and liver extract that contribute to recovery of fastidious organisms. 121 °C × 15 min is acceptable but gives slightly reduced recovery of Faecalibacterium prausnitzii and related Firmicutes. For agar plates, 121 °C is recommended for adequate agar melting; for broth, 115 °C × 15 min is preferred.
Q3. What is the difference between mGAM and YCFA Modified Medium?
Both are fastidious-anaerobe media but with different design rationales. YCFA (Duncan, Hold, Stewart, Flint 2002) is engineered for SCFA-utilising butyrate-producing Firmicutes — it includes acetate, propionate, isovalerate, valerate, isobutyrate in the formulation. mGAM (Gifu University formula + the Nissui modification) is a richer general-purpose broth — it includes liver extract and digested serum but no exogenous SCFA. For gut-microbiome culturomics with butyrate-producer focus → YCFA. For general anaerobic enrichment, Japanese-pharmacopoeial alignment, or richer growth of Bacteroides/Prevotella → mGAM.
Q4. Is mGAM compatible with CLSI M11 AST?
mGAM is not the CLSI M11 reference (Wilkins-Chalgren is). However, mGAM is widely used in Japanese clinical microbiology as an AST broth and gives generally comparable MICs to WCh for most antibiotic / anaerobe combinations. For CLSI-conformant AST reporting use WCh; for in-house or Japanese-tradition AST, mGAM is acceptable with appropriate QC.
Q5. Can mGAM be used for Bifidobacterium isolation from infant stool / probiotic products?
Yes, but TPY (Trypticase-Phytone-Yeast extract; Scardovi 1986) is the more selective and reproducible Bifidobacterium medium. mGAM supports Bifidobacterium growth but does not differentiate from other anaerobes. For Bifidobacterium-targeted work (probiotic QC, infant gut studies) use TPY (GMNB-TPY01). For general gut-anaerobe enrichment with Bifidobacterium as one of many target genera, mGAM is appropriate.
Q6. Why does my mGAM broth appear darker after autoclaving?
Mild Maillard browning is expected from the rich peptone + reducing-sugar combination at 115–121 °C. The medium should be straw-yellow to light-amber. Dark amber → brown indicates excessive autoclaving (> 20 min or > 121 °C). Limit autoclave time to 15 min at the specified temperature.
Q7. Is the medium compatible with the Anaerobic Preparation Kit (APK)?
Yes. The APK vacuum-deoxygenation workflow applies identically to mGAM in Hungate-tube format. Pre-reduction inside the AAE for 24 h before inoculation is the recommended protocol. Resazurin can be added at 1 mg/L (custom order) for visual reduction confirmation.
Q8. Are taxonomic name changes (Lactobacillus reclassification, Clostridium → Clostridioides difficile) reflected in the QC organism list?
Yes. The instruction manual provides both the historical name (familiar to long-time mGAM users) and the current valid name per IJSEM. The Zheng et al. 2020 IJSEM 70:2782 reclassification splits the historical genus Lactobacillus into 25 genera, of which 23 were newly described; the Lawson et al. 2016 paper reclassifies Clostridium difficile as Clostridioides difficile; the Scholz & Kilian 2016 paper reclassifies Propionibacterium acnes as Cutibacterium acnes. All three changes are reflected in the QC organism list.
Q9. What is the difference between the Nissui modification and the GMExpression modification of mGAM?
Both are Modified GAM in the Gifu University lineage, and both carry the defining mGAM change — glucose reduced to 0.5 g/L. They are different formulations and are prepared at different weigh-outs, so they are not interchangeable.

mGAM — Nissui modification (this page): prepared at 41.7 g/L for broth, 56.7 g/L for agar. Proteose peptone 5.0 g/L, digested serum 10.0 g/L, L-cysteine·HCl 0.3 g/L, hemin 10 mg/L, plus L-arginine 1.0 g/L in the powder and vitamin K1 5 mg/L added from Stock K — neither of which the GMExpression modification contains. Mixture A itself weighs 41.71 g/L; vitamin K1 is an oil and ships as a separate ethanolic stock.

mGAM — GMExpression modification (listed separately): prepared at 49.4 g/L for broth, 64.4 g/L for agar. Proteose peptone 10.0 g/L, digested serum 13.5 g/L, L-cysteine·HCl·H2O 0.5 g/L, hemin 5 mg/L. No L-arginine and no vitamin K1 in the base — a richer peptone and serum load than the Nissui modification.

Which to choose. This Nissui modification is the one to order for reproducing a published method that specifies the Nissui catalogue product, and wherever an arginine-dihydrolase substrate or a menaquinone precursor must be present in the dehydrated base. For general fastidious-anaerobe enrichment, cell-bank work and richer growth of Bacteroides and Prevotella, the GMExpression modification is the richer medium. Weigh-out figures are not transferable between the two — always use the figure printed on the kit you have received.