Sigma-Aldrich NutriSelect® Plus Middlebrook 7H11 Agar Base, suitable for microbiology

Middlebrook 7H11 Agar Base is an agar-based culture medium designed specifically for the isolation, cultivation, and antimicrobial sensitivity testing of Mycobacterium species, including Mycobacterium tuberculosis. Its formulation provides essential nutrients, inorganic salts, and energy sources required for the growth of fastidious Mycobacteria. The addition of Middlebrook OADC Supplement further enhances the medium, providing essential growth factors like oleic acid, albumin, dextrose, sodium chloride, and catalase.

Key Features

1. Agar-Based Formulation
   • More stable than egg-based media (e.g., Lowenstein-Jensen) and does not liquefy in the presence of proteolytic contaminants.
2. Enhanced Drug Stability
   • Lacks egg components, minimizing inactivation of added antimicrobial agents for sensitivity testing.
3. Nutrient-Rich Composition
   • Contains glycerol, L-glutamic acid, and inorganic salts for carbon and energy metabolism of Mycobacteria.
4. Selective Inhibition
   • Malachite green suppresses the growth of contaminating bacteria while allowing the growth of Mycobacteria.
5. Middlebrook OADC Supplement Compatibility
   • Addition of Middlebrook OADC Supplement provides essential long-chain fatty acids, protective albumin, and energy sources like dextrose to support robust growth.

Specifications

Composition (per liter)

Preparation Instructions

1. Suspend 10.25 g of Middlebrook 7H11 Agar Base in 450 mL of distilled water.
2. Add 2.5 mL of glycerol (Cat. No. 49767).
3. Boil the solution to dissolve the medium completely.
4. Sterilize by autoclaving at 121°C for 15 minutes at 15 lbs. pressure.
5. Cool the medium to approximately 50°C.
6. Add 1 vial of Middlebrook OADC Supplement (M0678) aseptically.
7. Mix thoroughly and dispense into sterile Petri dishes or tubes.

Applications

1. Primary Isolation of Mycobacterium Species
   • Suitable for recovering slow-growing and fastidious Mycobacterium tuberculosis and other Mycobacteria from clinical and environmental specimens.
2. Drug Susceptibility Testing
   • Middlebrook 7H11 Agar Base is ideal for antimicrobial sensitivity testing of Mycobacterium species due to its stability and lack of inhibitory egg components.
3. Microbial Cultivation
   • Used in research and diagnostics to cultivate and maintain Mycobacterium tuberculosis, M. avium, M. bovis, and other Mycobacterium species.
4. Environmental and Veterinary Microbiology
   • Detects Mycobacteria from environmental samples, including soil and water, as well as veterinary specimens.

Advantages

1. Greater Stability
   • Unlike egg-based media, it does not liquefy when contaminated with proteolytic organisms.
2. Improved Drug Sensitivity Testing
   • Minimal risk of inactivating antibiotics due to the absence of egg ingredients.
3. Enhanced Growth Support
   • Inorganic salts, glycerol, and amino acids ensure consistent and reproducible growth of Mycobacterium species.
4. Selective Action
   • Malachite green partially inhibits non-mycobacterial contaminants while allowing the growth of Mycobacteria.
5. Wide Applicability
   • Can be used in clinical diagnostics, research laboratories, and veterinary microbiology.

Comparative Advantages Over Egg-Based Media

Quality Control

Comparison Table: Middlebrook 7H11 vs. 7H9 vs. 7H10

Summary

1. Middlebrook 7H11 Agar
   • Solid medium designed for isolation, cultivation, and drug susceptibility testing.
   • Contains malachite green for selective inhibition of contaminants.
   • Ideal for slow-growing Mycobacteria in clinical and research diagnostics.
2. Middlebrook 7H9 Broth
   • Liquid medium ideal for bulk cultivation and propagation of Mycobacterium species.
   • Used in research, vaccine production, and metabolic studies.
   • Supports rapid growth but is prone to contamination without strict aseptic techniques.
3. Middlebrook 7H10 Agar
   • Solid medium for the isolation, quantification, and primary culture of Mycobacterium spp.
   • Lacks malachite green, making it less selective but excellent for colony enumeration.

This table provides a clear distinction between the 7H11 Agar, 7H9 Broth, and 7H10 Agar in terms of composition, applications, and advantages. 

Storage and Shelf Life

• Powdered Medium: Store at 2–8°C in a dry environment.
• Prepared Plates: Store at 2–8°C away from light.
• Shelf life depends on proper storage; refer to the expiry date on the product label.

The Sigma-Aldrich NutriSelect® Plus Middlebrook 7H11 Agar Base offers a robust, reliable, and selective medium for the isolation, cultivation, and sensitivity testing of Mycobacterium species, addressing challenges posed by egg-based alternatives.