SELECTIVE CULTURE MEDIA: FOUNDATION, SOLID AND LIQUID - BIOLOGY - 2025

The selective culture media are broths and agars those which serve for isolation of a defined group of microorganisms, while inhibiting the development of others. They are ideal for sowing polymicrobial samples, allowing the pathogen to be recovered from the accompanying microbiota.

There is a great variety of selective media, between solids and liquids. Some are intended for the isolation of Gram positive bacteria, such as coagulase positive Staphylococcus, Lactobacillus, Bifidobacteria, etc.

Selective culture media. Source: Air1404

Others for the recovery of Gram negative pathogens, such as species of the genera Salmonella, Shigella, Vibrio, Bordetella, Brucella, Pseudomonas, among others.

As well as there are also them to favor the growth of fungi and yeasts, such as Candida species, Histoplasma, Cryptococcus, dermatophytes, among others.

It should be noted that some non-selective enriched media can become selective with the addition of antibiotics. Likewise, some culture media can be selective and differential at the same time.

On the other hand, there are selective liquid culture media; some can serve as enrichment media, favoring the exacerbation of a selective group of bacteria, while suppressing that of others.

Selective culture media are widely used in microbiology laboratories for the analysis of various types of samples; as well as for the isolation of a great variety of microorganisms of clinical, industrial, environmental and food interest.

Basis

Selective culture media are based on containing nutritive substances that favor the growth of a specific bacterium or fungus or of a certain group of these, and at the same time they must contain inhibitory substances that do not allow the development of other undesirable microorganisms.

Among the nutritional substances they may contain are: pancreatic digest of casein, yeast extract, polypeptones, among others.

Inhibitors include: antibiotics, bile salts, bright green, crystal violet, basic fuchsin, eosin, methylene blue, sodium deoxycholate, sodium sulfite, sorbitan monoleate, ammonium citrate, cetrimide, lithium chloride, potassium tellurite, malachite green, among others.

Sometimes the media can be both selective and differential. Likewise, the degree of selectivity varies from one medium to another.

Some are highly selective, characterized by having extreme hostility conditions for most microorganisms and where only a small number of species are able to withstand the conditions present in the environment and therefore grow satisfactorily. For example, TCBS agar and MRS agar, among others.

While others are moderately selective, that is, those that inhibit a specific group of microorganisms, such as Gram positive bacteria. On the other hand, they favor the growth of a great variety of Gram negative bacteria; for example, Mac Conkey agar.

Finally, there are culture media with a low selective power, that is, they are those that allow the growth of a great variety of bacteria between Gram positive and Gram negative, as well as some yeasts, while inhibiting only a small group of microorganisms. Example: EMB agar.

Selective Solid Culture Media

Baird-Parker agar

Medium designed for the detection of coagulase positive staphylococci (Staphylococcus aureus). Contains as inhibitory substances lithium chloride and potassium tellurite.

BCYE Agar or Yeast Charcoal Extract Buffered Agar

It is a highly enriched culture medium, especially for the isolation of Legionella and Nocardia species. This medium becomes selective with the addition of antimicrobials such as polymyxin B, vancomycin, and anisomycin.

BHI agar with antibiotics

BHI agar is originally an enriched medium, but if chloramphenicol and cycloheximide are added, it is ideal for the selective isolation of fungi of clinical interest.

BIGGY agar

Selective and differential medium for the isolation of Candida species. It contains ammonium citrate, bismuth and sodium sulfite, which act as inhibitors of bacterial growth.

Bordet Gengou Agar

Enriched and selective culture medium, especially for the isolation of B ordetella pertussis and Bordetella parapertussis. It contains cephalexin to inhibit the accompanying flora.

Campy agar with blood

Medium used for the isolation of the genus Campylobacter. Contains cefoperazone, vancomycin, and amphotericin B to inhibit the growth of Gram negative, Gram positive bacteria, and fungi.

Campylobacter Butzler Agar

Special medium for the isolation of species of the genus Campylobacter. It is supplemented with horse blood, among other nutrients. It also contains various inhibitory substances, such as novobiocin, colistin, cefazolin, bacitracin, and cycloheximide.

Campylobacter Skirrow Agar

Selective medium for the isolation of Campylobacter species. Contains horse blood and other nutrients. As inhibitory substances it contains vancomycin, polymyxin B and trimethoprim.

CCF agar or fructose agar, cycloserine, cefoxitin

As its name implies, it contains cycloserine and cefoxitin as inhibitory substances and is used for the isolation of Clostridium diffcile in stool samples, among other intestinal samples.

Cetrimide agar

Selective medium, designed for the isolation of Pseudomonas aeruginosa, favoring the production of pigments. Cetrimide (cetyl trimethyl ammonium bromide) is the substance that inhibits the growth of bacteria other than P. aeruginosa.

Chocolate agar with isovitalex and vancomycin

This medium is originally very enriched. The addition of vancomycin is useful for the selective isolation of Neisseria gonorrhoeae and N. meningitidis strains.

CIN agar or cefsulodine agar, irgasan, novobiocin

It is a moderately selective culture medium for the isolation of Yersinia species.

CNA agar (colistin, nalidixic acid)

It is a special selective medium for the isolation of Gram positive bacteria such as Staphylococcus, Enterococcus, Streptococcus and yeasts, but it inhibits the development of Gram negative bacteria such as Pseudomonas and species of the Enterobacteriaceae family.

Czapek agar

Medium designed for the cultivation of saprophytic bacteria and fungi. This medium contains inorganic nitrogen. For this reason, this medium is considered selective, since only microorganisms capable of using inorganic compounds as the sole source of nitrogen can develop.

EMB agar

Slightly selective and differential medium, used for the isolation of Enterobacteriaceae. Escherichia coli is especially detected on this medium by the glossy greenish-black color of its colonies. The degree of selectivity that it possesses is due to the presence of aniline dyes (eosin and methylene blue).

Endo agar

Minimally selective and differential medium, used for the isolation and differentiation of lactose fermenting and non-fermenting Gram negative bacilli belonging to the Enterobacteriaceae family and to other families.

Sodium sulfite and basic fuchsin inhibit most Gram positive bacteria. Escherichia coli on this medium produces characteristic dark red colonies with an iridescent greenish metallic sheen.

Hektoen agar

Selective and differential medium for the isolation of enteropathogenic bacteria of the Shigella and Salmonella genera. As an inhibitory substance it contains bile salts, suppressing the development of Gram positive and some Gram negative bacteria.

Löwenstein-Jensen agar

Medium specially designed for the isolation and development of bacteria of the genus Mycobacterium, especially the tuberculosis species, among others.

The medium contains malachite green; This substance inhibits the accompanying Gram positive and Gram negative flora that have been able to resist the previous disinfection of the sample. It also contains glycerin that stimulates the growth of M. tuberculosis, but inhibits the growth of M. bovis and other microorganisms.

Mac Conkey agar

It is a selective and differential medium. It is used for the isolation of lactose non-fastidious, fermenting and non-fermenting Gram negative rods.

Its selective character is provided by the presence of bile salts and crystal violet. These substances inhibit the growth of Gram positive bacteria and some fastidious Gram negative rods.

Salty mannitol agar

Selective and differential agar for the isolation of Staphylococcus aureus. This medium has a high concentration of sodium chloride that inhibits the growth of most bacteria.

SS agar

Moderately selective and differential medium for the isolation of the genera Salmonella and Shigella. The medium contains inhibitory substances, such as bile salts, sodium citrate, and bright green. These substances suppress the growth of Gram positive bacteria, certain Gram negative bacteria, and some coliforms.

Regan Lowe Agar

Selective agar for the isolation of Bordetella pertussis. The medium contains charcoal, cephalexin and amphotericin B as inhibitory substances.

SABHI agar

Selective medium for the isolation of pathogenic fungi, such as dermatophytes, Blastomyces dermatitidis and Histoplasma capsulatum. Contains chloramphenicol.

Horse blood agar with bacitracin

Special medium for the isolation of Haemophilus influenzae. Bacitracin inhibits the accompanying flora.

Horse blood charcoal agar

Selective medium useful for recovering Bordetella pertussis and B. parapertussis strains from clinical samples. It contains cephalexin to inhibit the accompanying flora.

Kanamycin-Vancomycin (KV) Blood Agar

Selective medium, special for the isolation of anaerobic bacteria, such as Bacteroides, Prevotella, Fusobacterium and Veillonella.

Bismuth Sulfite Agar

Selective medium for the isolation of Salmonella enterica subgroup enterica serotype Typhi. This medium contains bright green bismuth sulfite to inhibit the growth of Gram positive microorganisms and certain Gram negative bacteria.

TCBS agar (thiosulfate, citrate, bile salts)

Highly selective medium for the isolation of species of the genus Vibrio. It contains sodium citrate, ox bile and an alkaline pH that inhibits the accompanying flora.

Thayer-Martin agar

Highly nutritious and selective medium for the isolation of Neisseria meningitidis and Neisseria gonorrhoeae. The accompanying flora is inhibited by the presence of vancomycin, colistin, and nystatin.

Bright green agar

Selective medium for the isolation of strains of the genus Salmonella. As the name suggests, it contains bright green as an inhibiting substance. This prevents the growth of Gram positive bacteria and a large number of Gram negative microorganisms.

Vogel-Johnson agar

It is a selective and differential culture medium, formulated for the isolation of Staphylococcus aureus and inhibits the growth of Gram negative bacteria and even some Gram positive ones. The inhibiting substances are potassium tellurite, lithium chloride, and glycine.

XLD agar

It is a selective and differential medium for the isolation of Salmonella and Shigella enteropathogens. Sodium deoxycholate gives the selective character to the medium.

CHROMagar (Candida Medium)

It is a selective and differential medium to aid in the isolation and identification of Candida species. The medium contains chloramphenicol to inhibit the growth of bacteria.

Middle Ellinghausen McCulough Johnson and Harris (EMJH)

Selective medium for the cultivation of Leptospiras. It contains polysorbate 80, which inhibits the growth of most bacteria.

Selective liquid culture media

BHI Broth NaCL 6.5%

Selective broth for recovery of Enterococcus. The high concentration of sodium chloride inhibits the growth of the accompanying microbiota.

EC broth

Selective broth for the recovery of total and fecal coliforms. Contains bile salts that inhibit the growth of other microorganisms.

GN broth

Selective broth for the recovery of Salmonella and Shigella. Contains sodium citrate and sodium deoxycholate, which inhibit Gram positive bacteria and coliforms.

Rappaport-Vassiliadis Broth

It is a selective enrichment medium for Salmonella species. Contains malachite green as an inhibiting substance.

Selenite broth

It is a selective culture medium, useful for the enrichment of samples where the presence of enteropathogenic bacteria of the genus Salmonella is suspected.

As its name suggests, it contains sodium selenite as an inhibitory substance, suppressing the growth of Gram positive bacteria and most bacteria in the gastrointestinal tract.

Tetrathionate broth

Selective broth for the enrichment and recovery of strains of the genus Salmonella.

The tetrathionate formed by the reaction generated between sodium thiosulfate and the iodinated solution present in the medium inhibits the growth of coliforms and favors the development of bacteria that contain the enzyme tetrathionate reductase (Salmonella).

It also contains bile salts and some varieties include bright green; both substances inhibit most Gram positive and some Gram negative bacteria (coliforms).

Campy Thioglycollate Broth

Special broth to promote the development of C. jejuni subsp jejuni. Contains amphotericin B, cephalothin, polymyxin B, trimethropim, and vancomycin.

Todd-Hewitt broth with blood and antibiotics

It serves to enrich the samples and promote the development of Streptococcus agalactiae from vaginal secretions. As inhibitory substances it contains nalidixic acid and gentamicin or colistin.

References

1. Clinical microbiology culture media (academic year 2012-2013). Available at: asignatura.us.es
2. BD Laboratories. Campylobacter Skirrow Agar and Campylobacter Butzler Agar. 2013.Available at: bd.com
3. IVD Laboratories. Löwenstein-Jensen. 2011.Available at: bio-rad.com
4. Neogen Laboratories. GN broth (Hajna). Available at: foodsafety.neogen.com
5. BD Laboratories. CHROMagar. Candida Medium 2014.Available at: bd.com
6. BD Laboratories. Rappaport Vassiliadis Broth. 2003.Available at: bd.com
7. Lifeder.com Web Portal. Available at: Lifeder.com
8. BD Laboratories. Leptospira Medium Base EMJH2011 Available at:
9. Koneman E, Allen S, Janda W, Schreckenberger P, Winn W. (2004). Microbiological Diagnosis. 5th ed. Editorial Panamericana SA Argentina.
10. Forbes B, Sahm D, Weissfeld A. (2009). Bailey & Scott Microbiological Diagnosis. 12 ed. Editorial Panamericana SA Argentina.