Microbial Isolation Techniques: An Overview of Culture Media

Table of Contents

• What is Culture Media?
• How to prepare culture media?
• Types of culture media based on consistency/ physical state
• 1. Solid media
• 2. Semi-solid media
• 3. Liquid media
• Types of culture media based on chemical composition/application
• 1. Basal media
• 2. Enriched media
• 3. Selective media
• 4. Enrichment media
• 5. Indicator or differential media
• 6. Transport media
• 7. Storage media
• Types of culture media based on oxygen requirement
• 1. Aerobic media
• 2. Anaerobic media
• Types of special purpose culture media
• 1. Assay media
• 2. Minimal media
• 3. Fermentation media
• Resuscitation culture media
• Application of culture media
• Limitations of culture media
• List of Culture media used in Microbiology with their uses

What is Culture Media?

Culture media serve as a nutrient source that supports the in-vitro growth of microorganisms. It plays a crucial role in promoting microbial growth, enabling microbial cell counting, selecting specific microorganisms, and ensuring their survival. Culture media can be in liquid form or as a gel.

Common components of culture media include:

• Peptone: Provides carbon and nitrogen.
• Beef extract: Supplies amino acids, vitamins, and minerals.
• Yeast extract: Acts as a source of vitamins, carbon, and nitrogen.
• Distilled water
• Agar: Used as a solidifying agent.

How to prepare culture media?

1. Weigh the Ingredients: Accurately measure the required amount of powdered ingredients using a weighing machine.
2. Dissolve the Ingredients: Add the measured ingredients to distilled water and dissolve thoroughly.
3. Adjust the pH: If necessary, adjust the pH of the medium to the desired level.
4. Add Agar (if solid media is needed): Add agar and bring the mixture to a boil to dissolve it completely.
5. Pour the Media: Transfer the prepared media into a flask.
6. Autoclave the Media: Sterilize the media using an autoclave at 121ºC for 15 minutes under 15 lbs of pressure to prevent contamination.
7. Prepare for Sterile Work: After autoclaving, place the media flask in a laminar airflow cabinet, which has been sterilized with 70% alcohol.
8. Cool the Media: Allow the media to cool slightly before pouring it into sterile Petri plates for solidification.
9. Inoculate the Sample: Once solidified, the medium is ready for inoculation. Spread or streak the sample using a spreader or inoculation loop for microbial identification or isolation.
10. Seal and Label: Seal the Petri plates with paraffin and label them appropriately.
11. Incubate the Plates: Store the plates in an inverted position in an incubator at 37ºC for 24 hours.
12. Observe Results: The next day, observe the formation of microbial colonies on the media.

What is a Defined Medium?

A defined medium contains precise, known quantities of all its components, such as a carbon source (like glucose or glycerol) and a nitrogen source (such as ammonium salts or nitrate). Defined media are often used in experiments requiring strict control over metabolic, nutritional, and physiological conditions, such as Czapek Dox Medium.

What is an Undefined Medium?

An undefined medium contains complex ingredients in unknown quantities, such as yeast extract, beef extract, various salts, or enzymatic protein digests. Examples include Potato Dextrose Agar and MacConkey Agar.

What is Complex Media?

Complex media go beyond basal media by including additional ingredients to meet the unique nutritional requirements of certain microorganisms. These specialized components help in bringing out distinct characteristics of the microorganisms.

Types of culture media

1. Solid Medium
2. Semi-Solid Medium
3. Liquid Medium

1. Solid Media

Principle of Solid Media:

Solid media are primarily used for isolating bacteria into pure cultures. Robert Koch pioneered the use of solid media for this purpose. Agar is added at a concentration of 1.5–2.0% to solidify the medium. This allows bacteria to grow as distinct colonies when streaked on the surface, with the medium solidifying at 37°C. Agar, an unbranched polysaccharide derived from red algae such as Gelidium, provides the medium's solid consistency, enabling colony identification.

Examples of Solid Media:

• Nutrient agar
• MacConkey agar
• Blood agar
• Chocolate agar

Bacteria on solid media can appear in various forms, such as smooth, rough, mucoid, round, irregular, filamentous, or punctiform colonies.

2. Semi-Solid Media

Principle of Semi-Solid Media:

Semi-solid media are useful for determining bacterial motility and for cultivating microaerophilic bacteria. Agar is used at a concentration of 0.5% or less, giving the medium a jelly-like consistency.

Examples of Semi-Solid Media:

• Stuart's and Amies transport media.
• Hugh and Leifson’s oxidation-fermentation medium.
• Mannitol motility media.

Bacterial growth in semi-solid media appears as a thick line along the inoculation site.

3. Liquid Media

Principle of Liquid Media:

Liquid media, also known as broth, are used for the cultivation of large numbers of bacteria. Unlike solid media, liquid media do not contain agar and allow bacteria to grow uniformly, resulting in turbidity. Growth typically occurs in an incubator at 37°C over a period of 24 hours. Liquid media are often employed in fermentation studies.

Examples of Liquid Media:

• Nutrient broth
• Tryptic soy broth
• MR-VP broth
• Phenol red carbohydrate broth

Bacterial growth in liquid media is observed as turbidity throughout the broth.

Types of culture media based on chemical composition/application

Seven Types of Routine Laboratory Media

1. Basal Media

Basal media are simple formulations that support the growth of a wide range of microorganisms. Commonly used in laboratories, this non-selective medium provides carbon and nitrogen sources and supports the growth of non-fastidious bacteria. It is frequently used for sub-culturing bacteria.

Examples of Basal Media:

Nutrient Agar, Peptone Water.

Organisms:

Supports the growth of Staphylococcus and Enterobacteriaceae.

2. Enriched Media

Enriched media are basal media supplemented with additional nutrients such as blood, egg, or serum. These added components support the growth of fastidious microorganisms, which require specific nutrients like vitamins and growth-promoting factors.

Examples of Enriched Media:

Blood Agar, Chocolate Agar, Lowenstein-Jensen Media, LSS, Monsor’s Taurocholate.

• Blood agar is used to identify hemolytic bacteria, while chocolate agar is suitable for growing Neisseria gonorrhea.

3. Selective Media

Selective media promote the growth of specific microorganisms while inhibiting others. The inhibition is achieved through the addition of bile salts, antibiotics, dyes, or pH adjustments. These media are often agar-based and can be modified into selective types by adding inhibitory agents.

Examples of Selective Media:

• Mannitol Salt Agar: Selective for Staphylococcus aureus. It contains 7% sodium chloride and phenol red dye, which changes color based on acid production.
• Salmonella-Shigella Agar: Selective for Salmonella and Shigella.
• MacConkey Agar: Selective for Enterobacteriaceae by inhibiting gram-positive bacteria with bile salts.
• TCBS Agar: Selective for Vibrio cholerae; yellow colonies appear due to sucrose fermentation.
• Lowenstein-Jensen Media: Selective for Mycobacterium tuberculosis with the addition of malachite green.

4. Enrichment Media

Enrichment media are liquid media that support the growth of specific bacteria, particularly when present in low concentrations. It creates conditions similar to selective media, promoting the growth of desired bacteria while suppressing unwanted microorganisms. It is especially useful for isolating soil and fecal microorganisms.

Examples of Enrichment Media:

• Selenite F-broth, used for the isolation of Salmonella typhi from fecal samples.

5. Indicator or Differential Media

Indicator or differential media contain chemical indicators that produce visible changes, allowing for the differentiation of bacterial species based on colony color and biochemical characteristics. The media often include indicators like neutral red, phenol red, and methylene blue.

Examples of Indicator or Differential Media:

• Mannitol Salt Agar: Differentiates based on mannitol fermentation (yellow colonies).
• Blood Agar: Distinguishes between hemolytic and non-hemolytic bacteria.
• MacConkey Agar: Lactose fermenters appear as pink colonies, while non-lactose fermenters produce pale colonies.

6. Transport Media

Transport media are used to preserve and transport specimens, maintaining the viability of microorganisms while preventing overgrowth or drying out. It acts as a temporary storage medium until further cultivation is possible.

Examples of Transport Media:

Stuart’s Transport Medium (lacks carbon and nitrogen sources), Cary Blair’s Transport Medium, VR Medium for transporting fecal samples from cholera patients, Pike’s Medium for transporting streptococci from throat swabs.

7. Storage Media

Storage media are designed to maintain the viability of bacterial cultures over extended periods, ensuring their longevity.

Examples of Storage Media:

Cooked Meat Broth, Nutrient Agar, Egg Saline Medium.

Types of culture media based on oxygen requirement

1. Aerobic Media

Aerobic media are designed to cultivate microbes that require oxygen for growth. On solid media, these microorganisms grow easily when cultures are placed in an incubator. These media support the growth of non-fastidious organisms, which do not need special nutritional requirements.

Examples of Aerobic Media:

• Liquid media
• Solid media

Formulations:

• Peptone Water: 1% peptone, 0.5% NaCl, and 100ml water.
• Nutrient Agar: Nutrient broth with 2% agar.

2. Anaerobic Media

Anaerobic media are used to grow bacteria that thrive in low-oxygen environments. These media reduce the oxidation-reduction potential, enabling the growth of anaerobes. They are enriched with additional nutrients like vitamin K and hemin, and oxygen is reduced through physical or chemical processes. Ingredients such as glucose (1%), thioglycolate (0.1%), ascorbic acid (0.1%), cysteine (0.05%), or iron filings are added to lower oxygen levels. The medium is boiled in a water bath to remove dissolved oxygen and sealed with sterile paraffin.

Examples of Anaerobic Media:

• RCM (Robertson's Cooked Meat): Commonly used for the isolation of Clostridium species.
• Thioglycolate Broth: Contains sodium thioglycolate, which helps maintain low oxygen levels.

Types of special purpose culture media

1. Assay Media

Assay media are used to test for the presence of vitamins, amino acids, and antibiotics. For example, the Muller-Hinton agar is commonly used in antibiotic sensitivity tests. It contains 1.7% agar, which allows better diffusion of antibiotics, and also includes starch, which absorbs toxins released by bacteria. In this test, a zone of inhibition forms around the antibiotics, indicating their effectiveness.

2. Minimal Media

Principle of Minimal Media:

Minimal media is a defined medium with specific compositions depending on the microorganism being cultured. It typically contains a carbon source like sugar or succinate, and inorganic salts like magnesium, nitrogen, sulfur, and phosphorus. Carbon acts as the energy source, while magnesium and ammonium salts provide essential ions for metabolism. Phosphate serves as a buffering agent.

Minimal media is used to compare the growth of microbial cultures and their mutant forms. Supplementing minimal media allows differentiation between wild-type and mutant cells.

Uses:

• Selection of recombinants.
• Growth of wild-type microorganisms.

3. Fermentation Media

Fermentation media are designed to optimize microorganism growth and produce high yields of specific products. These media provide essential energy and nutrients for growth, and substrates for synthesizing products during fermentation.

Composition:

• Major components: Carbon and nitrogen, essential for energy.
• Minor components: Inorganic salts, growth factors, vitamins, buffers, anti-foaming agents, dissolved gases, growth inhibitors, and enzymes.

The nutrients required in fermentation media depend on the organism and fermentation process.

Two Types of Fermentation Media:

• Growth Media: Low in nutrients, used as raw material for further fermentation.
• Fermentation Media: Rich in nutrients, used to produce end products.

Example:

Yeast typically requires 1% carbon for growth, but during alcohol fermentation, it needs 12-13% carbon in the medium.

Role of Fermentation Media:

The media provides high nutrient levels, allowing microorganisms to undergo metabolism during incubation under optimal conditions. Fermentation causes hyperactivity in microorganisms, resulting in nutrient consumption and partial degradation of the medium. However, if the substrate concentration becomes too high, it can inhibit vital enzymes, increase osmotic pressure, and disrupt enzymatic activity in cells. In response, microbes release excess substrate as partially digested fermentation media or convert it into an inert compound, serving as reserve food.

Examples:

Yeast extract, beef extract, YPD, BMGY.

4. Resuscitation Culture Media

Resuscitation media are specialized media used for the recovery of stressed bacteria that have lost the ability to grow due to environmental stress. These media provide necessary nutrients to restore bacterial metabolism.

Example:

If a bacterium requires histamine for growth and is placed in a medium lacking this component, it will not grow. However, when transferred to a medium containing histamine, growth resumes. This medium acts as a resuscitation medium.

Example of Resuscitation Media:

Tryptic Soy Agar.

Application of culture media

• Cultivation of microorganisms.
• Identification of infectious agents.
• Characterization of microbial properties.
• Isolation of pure cultures.
• Preservation of culture stocks.
• Observation of biochemical reactions.
• Detection of microbial contamination in samples.
• Evaluation of the effects of antimicrobial agents and preservatives.
• Examination of microbial colony characteristics, including color, shape, and morphology.
• Differentiation between various microbial colonies.
• Production of antigens for laboratory purposes.
• Estimation of viable microbial counts.
• Testing antibiotic sensitivity.

Limitations of culture media

• Risk of cross-contamination.
• Requires a high level of skill for optimal results.
• Increased likelihood of media drying out.

List of Culture media used in Microbiology with their uses

• A7 and A8 agars: Selective and differential media used for the cultivation, identification, and differentiation of Ureaplasma species and Mycoplasma hominis.
• Alkaline peptone water: An enrichment broth designed for isolating small numbers of Vibrio and Aeromonas organisms from stool samples.
• American Trudeau Society medium: A nonselective enriched medium utilized for the isolation and cultivation of mycobacteria.
• Amies transport medium with and without charcoal: A modification of Stuart’s medium, with the charcoal variant being preferred for isolating Neisseria species.
• Anaerobic blood agar (CDC formulation): A general-purpose medium from the Centers for Disease Control and Prevention (CDC) used to isolate and cultivate anaerobic bacteria.
• 10B arginine broth (Shepard’s broth): A medium employed for the transport and growth of Mycoplasma hominis and Ureaplasma urealyticum.
• Ashdown agar: A selective and differential medium designed for isolating Pseudomonas pseudomallei.
• Bacillus cereus medium: An enriched medium specifically used for isolating Bacillus cereus.
• BACTEC 12B radiometric medium: A liquid, nonselective medium used in conjunction with the BACTEC system to isolate and identify Mycobacterium species.
• Bacteroides bile esculin agar: An enriched, selective, and differential medium used for isolating and presumptively identifying members of the Bacteroides fragilis group and Bilophila wadsworthia.
• Baird-Parker agar base: An enriched, selective, and differential agar designed for detecting coagulase-positive staphylococci (S. aureus) in food and other non-clinical samples.
• Barbour-Stoenner-Kelly medium: A complex medium used for the isolation of Borrelia burgdorferi.
• Bile esculin agar: A selective and differential medium for isolating and differentiating Enterococcus and Streptococcus bovis (group D streptococci) from non-group D streptococci.
• Bile esculin agar with vancomycin (6 μg/ml): A selective and differential medium used to identify vancomycin-resistant streptococci and enterococci.
• Bile esculin azide agar and broth (Enterococcosel): A selective and differential medium for the identification of Streptococcus bovis (group D streptococci) and enterococci.
• Bismuth sulfite agar: A highly selective and differential medium used to isolate Salmonella enterica serovar Typhi and other enteric bacteria.
• Blood agar: Similar to Columbia agar, with 5% sheep blood for the growth of fastidious organisms.
• Blood culture media: Composed of nutrient peptone broth, with variations depending on the hydrolysis or digestion of the protein source.
• Bordet-Gengou medium: An enriched medium used for isolating and cultivating Bordetella pertussis from clinical samples.
• Brain heart infusion agar: A general-purpose medium used for isolating a wide variety of pathogens, including yeasts, molds, and bacteria.
• Brain heart infusion agar with 7% horse blood and 1% serum: Enriched media used for the isolation of Helicobacter species.
• Brain heart infusion broth: A general-purpose clear liquid medium for cultivating a wide range of organisms. Variants with 6.5% NaCl are used to isolate salt-tolerant streptococci, 0.1% agar formulations lower oxygen tension and favor anaerobes, while Fildes enrichment is added for isolating fastidious organisms like Haemophilus and Neisseria.
• Brain heart infusion-vancomycin agar: A selective medium used to isolate vancomycin-resistant enterococci, with vancomycin (6 μg/ml) added to the base brain heart infusion agar.
• Brilliant green agar: A highly selective and differential medium for isolating Salmonella species, excluding S. Typhi.
• Brucella agar: A medium originally developed to isolate Brucella species from dairy products.
• Brucella agar with cefoxitin and cycloserine: A selective and differential medium with sheep blood used for isolating Clostridium difficile. The nutritive base is brucella agar.
• Brucella agar with hemin and vitamin K: A nonselective, enriched medium for the isolation and cultivation of anaerobic bacteria.
• Brucella agar with 5% horse blood: Horse blood enriches brucella agar, providing hemin (factor X) and NAD (factor V), supporting the growth of fastidious organisms like Helicobacter pylori.
• Brucella broth: A liquid medium used to cultivate Campylobacter species and to identify them at the species level.
• Buffered charcoal yeast extract (BCYE): A specialized enriched agar medium used for the isolation and cultivation of Legionella species from environmental and clinical specimens.
• Buffered glycerol saline: A versatile transport medium used for isolating bacteria such as Aeromonas and certain viruses, as well as for the long-term storage of isolates and biopsy specimens.
• Burkholderia cepacia selective agar: An enriched and selective medium designed for isolating B. cepacia.
• Campylobacter blood agar: An enriched selective medium with blood, used for isolating Campylobacter species.
• Campylobacter charcoal differential (CCD) agar: A blood-free selective medium used for isolating Campylobacter from stool samples.
• Campylobacter thioglycolate medium: A selective holding medium for isolating Campylobacter species.
• Cary-Blair transport medium: A transport medium specifically designed to preserve the viability of enteric bacterial pathogens.
• Cefoperazone-vancomycin-amphotericin B (CVA) medium: A selective and enriched blood agar medium used for isolating Campylobacter species.
• Cefsulodin-Irgasan-novobiocin (CIN) medium (Yersinia selective agar): A selective and differential medium for isolating and differentiating Yersinia enterocolitica from clinical samples and food sources.
• Cetrimide agar: A selective and differential medium used to identify Pseudomonas aeruginosa.
• Charcoal selective medium: An enriched selective medium used for isolating Campylobacter species.
• Chocolate agar: A general-purpose medium for isolating and detecting a wide range of microorganisms, including fastidious species like Neisseria and Haemophilus.
• Chopped meat glucose broth: An enriched medium that supports the growth of most anaerobes, commonly used to isolate Clostridium botulinum from mixed bacterial growth.
• CHROMagar (Rambach Agar): CHROMagar is a specialized chromogenic culture medium designed for the isolation and identification of various microorganisms. Developed by Alain Rambach, the original formulations were monochromogenic for detecting E. coli and Salmonella species. The newer, second-generation agars are multicolor, allowing for differential and selective identification. The agar base contains peptone and glucose, with various additives, proprietary chromogenic mixtures, and antibiotics creating media specific to organisms such as Listeria, Staphylococcus aureus (including MRSA), E. coli O157, yeasts, and more.
• Columbia Agar with 5% Sheep Blood: Columbia agar supplemented with 5% sheep blood serves as a general-purpose medium for isolating a range of microorganisms, including fastidious species. The addition of 20 g of ampicillin per ml aids in isolating Aeromonas.
• Columbia Broth: Columbia broth is a clear liquid medium primarily used for blood cultures, supporting the growth of a wide variety of microorganisms.
• Columbia-Colistin-Nalidixic Acid Agar with 5% Sheep Blood: This selective and differential medium is commonly used for isolating both aerobic and anaerobic gram-positive organisms from mixed clinical specimens.
• Cycloserine-Cefoxitin-Fructose Agar: This selective and differential agar medium is specifically used for isolating Clostridium difficile.
• Cysteine-Albumin Broth with 20% Glycerol: This medium is used for the transport and storage of gastric biopsy specimens for the recovery of Helicobacter pylori.
• Cystine Glucose Blood Agar: Cystine glucose blood agar is an enriched medium suitable for isolating Francisella species.
• Cystine-Tellurite Blood Agar: A modification of Tinsdale agar, this selective and differential medium is utilized for detecting Corynebacterium diphtheriae.
• Cystine Tryptic Agar: This pancreatic digest of casein-enriched medium is primarily used for cultivating and maintaining fastidious organisms. The addition of 1% carbohydrates and phenol red facilitates fermentation reaction differentiation in Neisseria species.
• Diagnostic Sensitivity Agar: This medium is used for cultivating organisms to conduct susceptibility testing.
• DNA-Toluidine Blue Agar: This differential medium is most commonly utilized for detecting and differentiating Staphylococcus species.
• Dubos Tween-Albumin Broth: This nonselective medium is intended for isolating and cultivating mycobacteria.
• Egg Yolk Agar (Modified McClung-Toabe Agar): This selective and differential medium is designed for isolating and differentiating Clostridium species.
• Ellinghausen-McCullough/Johnson-Harris Medium: This enriched semisolid medium is used for isolating and cultivating Leptospira.
• Enterococcosel Agar: Similar to Bile Esculin Azide Agar and broth, this medium is used for the isolation of enterococci.
• Eosin-Methylene Blue (EMB) Agar: EMB agar is a selective and differential medium for isolating and differentiating enteric pathogens from clinical specimens.
• ESP Culture System II: The ESP Myco medium is utilized with the ESP Culture System II (TREK Diagnostic Systems) for detecting mycobacterial growth.
• Egg-Tellurite-Glycine-Pyruvate-Agar (ETGPA): This medium is similar to the Baird-Parker agar base.
• Fastidious Anaerobic Agar (Fusobacterium Selective Agar): This enriched sheep blood medium is used for isolating and cultivating anaerobic organisms.
• Fletcher’s Medium: An enriched semisolid medium, Fletcher’s medium is used for isolating and growing Leptospira.
• FlexTrans Viral and Chlamydia Transport Medium: This transport medium (Trinity Biotech) is designed for viruses and/or chlamydiae.
• GC Agar Base: A chocolate agar base that is utilized with various additives to isolate Neisseria gonorrhoeae and other fastidious organisms, including Haemophilus species, for susceptibility testing.
• GN Broth: GN broth is an enriched selective broth medium effective for isolating gram-negative rods, particularly Salmonella and Shigella.
• Haemophilus Test Medium (HTM) and Broth: HTM is an enriched medium used for susceptibility testing of Haemophilus species.
• Heart Infusion Agar and Broth: These general-purpose media are used for isolating a variety of microorganisms. The incorporation of 5% rabbit blood enhances the detection of fastidious Actinomyces.
• Hektoen Enteric Agar: This selective and differential medium is designed for isolating and differentiating enteric pathogens from contaminated clinical specimens. Fermenters like E. coli yield yellow-pink colonies, while Shigella species appear green or transparent, and Salmonella species are green or transparent with black centers.
• Hemin-Supplemented Egg Yolk Agar: This medium is comparable to Neomycin egg yolk agar.
• Isolator or Lysis-Centrifugation Tube (Wampole Laboratories): The Isolator is a unique system for recovering organisms from blood through a simultaneous lysis and centrifugation process. It is particularly effective for recovering dimorphic fungi, yeasts, mycobacteria, and Bartonella species, although recovery of anaerobes, Haemophilus species, and pneumococci may be less efficient.
• Iso-Sensitest Agar and Broth: These media are used for susceptibility testing in countries outside the United States.
• John E. Martin Biological Enrichment Chamber (JEMBEC) (BBL) and InTray GC System Transport Medium (Biotest): The JEMBEC and InTray GC systems serve as transport and inoculation media designed for the direct plating of specimens to detect Neisseria gonorrhoeae.
• Kanamycin-Vancomycin Laked Sheep Blood Agar: This enriched, selective, and differential medium is utilized for isolating and cultivating anaerobic bacteria, particularly slow-growing and fastidious anaerobes like Bacteroides spp. and Prevotella spp. from clinical specimens.
• Lactobacillus MRS Broth: Lactobacillus MRS (deMan, Rogosa, and Sharpe) broth is a nonselective liquid medium employed for the isolation and cultivation of lactobacilli from clinical specimens, dairy, and food products.
• Levinthal Agar with Bacitracin and H. influenzae Antiserum: This medium is similar to Chocolate agar in its composition and use.
• Lim Broth: A modification of Todd-Hewitt broth, Lim broth is an enriched selective liquid medium used for isolating and cultivating Streptococcus agalactiae.
• Lithium Chloride-Phenylethanol-Moxalactam Agar: This enriched and selective agar medium is specifically designed for isolating and cultivating Listeria monocytogenes.
• Loeffler’s Medium: An enriched nonselective medium, Loeffler’s medium is used for cultivating corynebacteria, particularly Corynebacterium diphtheriae.
• Lombard-Dowell Egg Yolk Agar: This medium resembles Neomycin egg yolk agar in its formulation.
• Lowenstein-Jensen Medium: An enriched nonselective medium, Lowenstein-Jensen medium is used for isolating and cultivating mycobacteria. Its composition is akin to that of the American Trudeau Society medium.
• Lowenstein-Jensen Medium (Gruft Modification): The Gruft modification is an enriched selective medium for isolating mycobacteria, enhanced with penicillin and nalidixic acid to inhibit gram-positive and gram-negative organisms, respectively. RNA is included as a growth stimulant.
• Lowenstein-Jensen Medium (Mycobactosel Modification): This modification is an enriched selective medium used for isolating mycobacteria, with cycloheximide, lincomycin, and nalidixic acid added to inhibit saprophytic fungi and various bacteria. No RNA is included.
• Lowenstein-Jensen Medium with 1% Ferric Ammonium Citrate: This enriched and selective egg-based medium supports the recovery of Mycobacterium haemophilum, with ferric ammonium citrate as the key additive.
• Lowenstein-Jensen Medium with 5% NaCl: This enriched selective medium differentiates sodium chloride-tolerant strains of mycobacteria, allowing rapid growers like Mycobacterium fortuitum and slower-growing organisms like Mycobacterium triviale to thrive.
• Lysis-Centrifugation Tube: Similar in function to the Isolator system, this tube is designed for recovering organisms through a lysis and centrifugation process.
• MacConkey Agar: A selective and differential medium for isolating gram-negative organisms, MacConkey agar contains a nutritive base of various peptones. Its selectivity is enhanced by bile salts and crystal violet, which inhibit gram-positive organisms, especially enterococci and staphylococci.
• MacConkey Agar with Sorbitol (SMAC): SMAC is a selective and differential medium for isolating and differentiating sorbitol-negative E. coli.
• MacConkey Broth: This differential medium, containing bromcresol purple, is used to detect coliform organisms in contaminated food, water, or stool samples.
• Mannitol-Egg Yolk-Polymyxin B Agar: This enriched, selective, and differential medium facilitates the isolation of Bacillus cereus from mixed clinical specimens.
• Mannitol Salt Agar: A selective and differential medium, Mannitol salt agar is primarily used for isolating Staphylococcus aureus.
• Martin-Lewis Agar: An enriched selective medium for isolating Neisseria gonorrhoeae, Martin-Lewis agar is specifically designed for this purpose.
• MB/BacT ALERT (bioMèrieux): MB/BacT ALERT contains a modified Middlebrook 7H9 medium supplemented with casein, bovine serum albumin, and catalase, used with the MB/BacT ALERT 3D system for the cultivation and detection of mycobacterial growth.
• MGIT (Mycobacteria Growth Indicator Tube) (BD Diagnostic Systems): The MGIT system utilizes a Middlebrook 7H9-based broth that features a fluorescence indicator to detect mycobacterial growth.
• Middlebrook 7H10 Agar: This enriched nonselective agar-based medium is used for isolating and cultivating mycobacterial species.
• Middlebrook 7H11 Agar: A nonselective agar-based medium, Middlebrook 7H11 agar is also used for the isolation and cultivation of mycobacterial species.
• Middlebrook 7H9 Broth with Glycerol: Middlebrook 7H9 broth supplemented with glycerol is a nutrient-rich, non-selective medium designed for the isolation of Mycobacterium species.
• Mitchison 7H11 Selective Agar: Mitchison 7H11 selective agar is an enriched, selective agar medium used specifically for isolating Mycobacterium species.
• Modified Irgasan-Ticarcillin-Potassium Chromate Broth: Modified Irgasan-ticarcillin-potassium chromate broth serves as a selective medium for isolating Yersinia enterocolitica.
• Modified Thayer-Martin Agar: Modified Thayer-Martin agar is both enriched and selective, designed for the isolation of pathogenic Neisseria species from clinical specimens containing mixed flora.
• Mueller-Hinton Agar with and without 5% Sheep Blood: Mueller-Hinton agar with 5% sheep blood is utilized for susceptibility testing of Streptococcus pneumoniae. In contrast, Mueller-Hinton agar enriched with 5% chocolate blood, 1% IsoVitaleX, and 3 g of vancomycin per ml is specifically used for isolating Haemophilus ducreyi.
• Mueller-Hinton Agar with 2% NaCl: Mueller-Hinton agar containing 2% NaCl is a selective medium for assessing the susceptibility of Staphylococcus to penicillinase-resistant penicillins, such as methicillin, nafcillin, and oxacillin, using either agar dilution or gradient-based methods (E test).
• Mueller-Hinton Agar with 4% NaCl and 6 g of Oxacillin per ml: Mueller-Hinton agar with 4% NaCl and 6 g of oxacillin per ml is a selective, differential medium for screening Staphylococcus aureus (excluding coagulase-negative staphylococci) for resistance to penicillinase-resistant penicillins, including nafcillin, methicillin, and oxacillin.
• Mueller-Hinton Broth: Mueller-Hinton broth is a liquid medium adjusted for magnesium and calcium cations, employed in susceptibility testing procedures for both aerobic gram-positive and gram-negative organisms using macro dilution and microdilution techniques.
• Multiprobe Media (M4-3, M5, and M4-RT) (Remel): M4-3 contains vancomycin, amphotericin B, and colistin, making it suitable for transporting viruses, chlamydiae, Mycoplasma, and Ureaplasma. M5 is similar to M4-3 but omits gelatin, and is also suitable for the transport of viruses, chlamydiae, Mycoplasma, and Ureaplasma.
• Mycobactosel Agar: Mycobactosel is a BBL trademark for an enriched selective agar medium designed for the isolation of Mycobacterium species.
• MycoTrim GU and MycoTrim RS (Irvine Scientific): The MycoTrim GU and MycoTrim RS culture systems are innovative triphasic flask systems specifically created for the isolation and identification of Mycoplasma hominis, Ureaplasma urealyticum (GU), and Mycoplasma pneumoniae (RS).
• NAG Medium: NAG medium is an enriched, selective medium utilized for the isolation and cultivation of Haemophilus species from clinical specimens containing mixed flora.
• Neomycin Egg Yolk Agar: Neomycin egg yolk agar serves as a selective and differential medium for distinguishing anaerobic organisms that are lipase-positive, including Clostridium species, Prevotella intermedia, Fusobacterium necrophorum, and certain strains of Prevotella loescheii.
• Neomycin-Vancomycin Agar: Neomycin-vancomycin agar is an enriched selective medium particularly effective for isolating and cultivating Fusobacterium from clinical samples.
• New York City Medium: New York City medium is an enriched and selective medium for the isolation of pathogenic Neisseria from clinical specimens.
• Nucleic Acid Transport (NAT) (Medical Packaging Corporation): NAT is a nucleic acid transport device that has been FDA cleared for use with various amplification and hybridization testing formats.
• Oxford Agar: Oxford agar is an enriched selective medium designed for the isolation of Listeria monocytogenes.
• Oxidative-Fermentative Polymyxin B-Bacitracin-Lactose Agar: Oxidative-fermentative polymyxin B-bacitracin-lactose medium is a selective and differential medium used for isolating Burkholderia cepacia from respiratory specimens of patients with cystic fibrosis.
• P Agar: P agar is an enriched medium employed for the cultivation and isolation of staphylococci.
• Peptone Yeast Extract Broth: Peptone yeast extract broth is utilized in the analysis of metabolic products via gas-liquid chromatography, as it exhibits minimal acid volatility.
• Petragnani Medium: Petragnani medium is an egg-based medium also employed for the cultivation and maintenance of Mycobacterium smegmatis.
• Phenylethyl Alcohol Agar: Phenylethyl alcohol agar is an enriched, selective blood agar medium used for detecting and isolating anaerobic organisms, particularly fastidious and slowly growing bacteria, from clinical specimens with mixed flora.
• PLM-5 TM: PLM-5 TM is a proprietary medium formulation from Intergen Co. (Purchase, N.Y.) that is similar to Ellinghausen-McCullough/Johnson-Harris medium and is used for the isolation and cultivation of Leptospira.
• Polymyxin B-Acriflavine-Lithium Chloride-Ceftazidime-Esculin-Mannitol (PALCAM) Agar: PALCAM agar is an enriched, differential, and selective agar medium utilized for the isolation of Listeria monocytogenes.
• Polymyxin B-Lysozyme-EDTA-Thallous Acetate Agar: This selective agar is designed for the isolation of Bacillus anthracis from environmental specimens.
• Polymyxin B-Pyruvate-Egg Yolk-Mannitol-Bromthymol Blue Agar: This enriched, selective, and differential medium is used for the isolation of Bacillus cereus.
• Polysorbate 80 Medium: This medium is similar to Ellinghausen-McCullough/Johnson-Harris medium.
• PRAS Media: Prereduced anaerobically sterilized (PRAS) media, manufactured by Anaerobe Systems, are specifically packaged to eliminate oxygen, thereby enhancing the growth of anaerobic organisms.
• Pseudomonas Cepacia (PC) Agar: PC agar is a selective medium for isolating Burkholderia cepacia (formerly Pseudomonas cepacia) from respiratory specimens of cystic fibrosis patients.
• Rambach Agar: This medium is comparable to CHROMagar.
• Rappaport-Vassiliadis Enrichment Broth: Rappaport-Vassiliadis enrichment broth is a selective, enriched broth used for isolating and cultivating Salmonella species from food and environmental samples.
• Regan-Lowe Medium: Regan-Lowe medium is an enriched selective medium for isolating Bordetella pertussis, containing beef extract pancreatic digest, horse blood, and niacin as its nutritional base.
• Salmonella-Shigella Agar: Salmonella-shigella agar is a selective and differential medium for the isolation and differentiation of Salmonella and Shigella from clinical and other specimens.
• Schaedler’s Agar: Schaedler’s agar is a general-purpose medium for the isolation and cultivation of anaerobic bacteria.
• Schleifer-Kramer Agar: This selective medium is used for isolating Staphylococcus from heavily contaminated specimens, such as fecal samples.
• Selenite Broth: Selenite broth is an enrichment broth medium designed for isolating Salmonella and Shigella species.
• Sensitest Agar: Sensitest agar is utilized for susceptibility testing outside the United States.
• Septic-Chek Biphasic Mycobacterial Media: The Septic-Chek system, developed by Becton Dickinson Microbiology Systems, is a mycobacterial culture system containing modified 7H9 broth and three types of solid media: modified Lowenstein-Jensen, Middlebrook 7H11, and chocolate agars, along with various supplements.
• Skirrow Medium: Skirrow medium is an enriched selective blood agar medium for isolating Campylobacter species from specimens containing mixed flora.
• STGG: STGG medium (skim milk, tryptone, glucose, and glycerin) serves as a transport medium for collecting nasopharyngeal swabs aimed at isolating and preserving Streptococcus pneumoniae.
• StrepB Carrot Broth Kit (Hardy Diagnostics) and GBS Broth (Northeast Laboratory Services): Carrot broth and GBS broth are media that facilitate the detection of red, red-orange, or orange pigment production by beta-hemolytic Streptococcus agalactiae (GBS) through hemolytic reactions with substrates such as starch, protease, peptone, and serum.
• Streptococcus Selective Agar: Streptococcus selective agar is a specialized medium designed for the detection of streptococci. Its base consists of Columbia agar.
• Stuart’s Transport Media (with and without Charcoal): Stuart’s transport medium, introduced in 1948, is an early transport medium formulated with glycerol phosphate to preserve specimens and maintain pH levels. It also contains agar, methylene blue as a redox indicator, and sodium thioglycolate, which supports the survival of anaerobic organisms.
• Sucrose-Phosphate-Glutamate Transport Medium: This medium is specifically used for the maintenance and transport of Chlamydia species and viruses.
• 2-Sucrose-Phosphate Transport Medium: This variant is utilized for transporting specimens intended for culturing Chlamydia trachomatis and Mycoplasma species.
• Tetrathionate Broth Base: Tetrathionate broth base is an enriched liquid medium that facilitates the isolation of Salmonella species from contaminated clinical specimens and various products.
• Thayer-Martin Agar: Thayer-Martin agar serves as an enriched and selective medium for isolating Neisseria from clinical specimens with mixed flora.
• Thioglycolate with Hemin and Vitamin K: Thioglycolate broth containing hemin and vitamin K is an enriched liquid medium that supports the growth of microaerophilic and anaerobic organisms, including those that are fastidious.
• Thiosulfate Citrate Bile Salt Sucrose (TCBS): TCBS is a highly selective and differential medium designed for the recovery of Vibrio species, with the exception of Vibrio hollisae and Vibrio cincinnatiensis.
• Tinsdale Agar: Tinsdale agar is comparable to Cystine-tellurite blood agar.
• Todd-Hewitt Broth with Gentamicin and Nalidixic Acid: Todd-Hewitt broth is utilized for isolating beta-hemolytic streptococci from mixed flora, particularly from vaginal specimens to identify Group B Streptococcus (GBS).
• Tryptic or Trypticase Soy Agar Base with 5% Sheep Blood: This general-purpose medium is employed for isolating a wide variety of organisms. The addition of sheep blood aids in interpreting hemolytic reactions, especially those related to Streptococcus species.
• Tryptic or Trypticase Soy Broth: Tryptic or Trypticase soy broth is a clear liquid medium suitable for cultivating a broad range of organisms. The CLSI recommends it for preparing inoculums for Kirby-Bauer disk diffusion susceptibility testing and as a sterility testing medium. Variants with 6.5% NaCl are available to differentiate enterococcal species or salt-tolerant streptococci, and Fildes enrichment is added to cultivate fastidious organisms such as Haemophilus species.
• Trypticase Soy Agar with Horse or Rabbit Blood: This medium is utilized for the isolation of Haemophilus species.
• University of Vermont Modified Listeria Enrichment Broth: This enriched and selective liquid medium is intended for isolating L. monocytogenes.
• V Agar: V agar is an enriched and selective medium designed for the isolation of G. vaginalis from clinical specimens.
• VMGA III Medium: VMGA III (Viability Medium, Goteborg, Anaerobic) is a transport and collection medium specifically created to maintain the viability of mixed anaerobes from periodontal and endodontic sites.
• Wadowsky-Yee Medium: This medium is similar to Buffered Charcoal Yeast Extract (BCYE).
• Wilkins-Chalgren Broth and Agar: Wilkins-Chalgren medium is recommended for susceptibility testing of anaerobic organisms. It contains specific nutrients, including yeast extract, vitamin K, hemin, and arginine, to support the growth of anaerobes.
• Xylose-Lysine-Desoxycholate (XLD) Agar: XLD agar is a selective and differential medium for isolating and differentiating enteric pathogens from clinical specimens. It is more supportive of fastidious enteric organisms like Shigella. For Salmonella, which possesses the lysine enzyme, this reaction shifts the pH back to an alkaline state, causing the colonies to appear transparent or red with a black center. Various other media exist for isolating enteric pathogens, including xylose-galactosidase medium, which is more specific for Aeromonas species.
• Yersinia Selective Agar: This agar is similar to Cefsulodin-Irgasan-novobiocin medium.