Mueller Hinton Agar (MHA)
Mueller Hinton Agar (MHA)
International Reference Medium for Antimicrobial Susceptibility Testing
Catalog Number: AS-1299
Overview
Mueller Hinton Agar (MHA) is the universally accepted reference solid medium for standardized antimicrobial susceptibility testing by disk diffusion (Kirby–Bauer) and for MIC determination of non-fastidious aerobic and facultatively anaerobic bacteria.
It is the official medium specified in CLSI M02 and M07, EUCAST guidelines, ISO 20776-1, FDA, and WHO recommendations, and is used globally as the benchmark agar for susceptibility testing.
Applications
• Disk diffusion susceptibility testing (CLSI M02, EUCAST)
• Base medium for MIC testing when used with Mueller Hinton Broth
• Etest and gradient diffusion strip methods
• Routine testing of Staphylococcus, Enterobacteriaceae, Pseudomonas, Acinetobacter
• Testing of Enterococcus (with supplements)
• Testing of Haemophilus spp. (MH-F) and streptococci (MHA with blood)
Key Features & Benefits
• Low thymidine and thymine content for accurate sulfonamide and trimethoprim results
• Controlled calcium and magnesium levels for reproducible aminoglycoside and tetracycline activity
• Starch absorbs bacterial toxins and produces sharp, well-defined inhibition zones
• Standardised agar depth ensures consistent diffusion rates
• Fully compliant with CLSI, EUCAST, ISO, FDA, and WHO standards
Principle of the Medium
Mueller Hinton Agar provides a nutritionally adequate yet controlled environment for antibiotic diffusion and bacterial growth. Precise cation adjustment is essential for reproducible susceptibility results, particularly for aminoglycosides and tetracyclines. Low thymidine and thymine prevent false resistance to folate pathway inhibitors, while starch neutralises bacterial toxins that may interfere with antimicrobial activity.
Typical Composition (per litre)
Beef Infusion Solids – 2.0 g
Acid Hydrolysate of Casein – 17.5 g
Starch – 1.5 g
Agar – 17.0 g
Final pH: 7.3 ± 0.1 at 25 °C
Final cation content (after sterilisation):
Calcium (Ca²⁺): 20–25 mg/L
Magnesium (Mg²⁺): 10–12.5 mg/L
Preparation
Suspend 38.0 g of dehydrated medium in 1 L of purified water.
Heat with frequent agitation and boil for 1 minute to dissolve completely.
Sterilise by autoclaving at 121 °C for 15 minutes.
Cool to 45–50 °C.
Pour exactly 25–30 mL into 90–100 mm flat-bottom Petri dishes to obtain a final depth of 4.0 ± 0.5 mm (critical).
Dry plates with lids ajar at 35 °C for 15–20 minutes before use.
Special Versions
Mueller Hinton Agar + 5% defibrinated horse or sheep blood: for Streptococcus and Enterococcus
MH-F (Mueller Hinton Agar with supplements): for Haemophilus spp.
Mueller Hinton Agar + 2% NaCl: oxacillin or methicillin screening for MRSA
Incubation
Incubate at 35 ± 1 °C in ambient air unless CO₂ is specifically required.
Standard incubation time: 16–20 hours (18 hours typical).
Storage & Stability
Prepared plates: Store at 2–8 °C in sealed plastic bags.
Use within 7 days for routine testing.
May be used up to 4 weeks if performance is quality controlled.
Intended Use
For antimicrobial susceptibility testing only.
Not for human, veterinary, pharmaceutical, or therapeutic use.
Quality & Compliance
Manufactured under controlled conditions for batch-to-batch consistency.
Meets performance criteria of CLSI M02/M07, EUCAST, and ISO 20776-1.
Performance comparable to leading international reference media suppliers.
Customs & Trade Information
HS / AHECC Code: 3821.00.00
Prepared culture media for the development or maintenance of microorganisms