Types of Agar: Portage Microbiology Module 4.2

Lysogeny Broth (LB) Agar

Trypticase Soy Agar (TSA)

non-selective and non-differential

BUT

Blood Agar is a type of this agar that is - non-selective, differential, and enriched

Blood Agar

(a type of TSA)

Columbia CNA Agar

Chocolate Agar

MacConkey Agar

Sorbitol-MacConkey Agar (SMAC)

Eosin Methylene Blue Agar (EMB)

Mannitol Salt Agar (MSA)

S/D?

Lysogeny Broth Agar (LB)

Non-selective

Non-differential

S/D?

Trypticase Soy Agar (TSA or TSAYE with yeast)

Non-selective

Non-differential

S/D?

Blood Agar

Non-selective

Differential

Enriched

S/D?

Columbia CNA Agar

Selective

Differential

Enriched

S/D?

Chocolate Agar

Non-selective

Non-differential

Enriched

S/D?

MacConkey Agar

Selective

Differential

S/D?

Sorbitol-MacConkey Agar

Selective

Differential

S/D?

Eosin Methylene Blue Agar

Selective

Differential

S/D?

Mannitol Salt Agar (MSA)

Selective

Differential

Explain: Lysogeny Broth Agar (LB)

• grows wide array of microbes

• used to grow E. coli a lot

Explain: Trypticase Soy Agar

• can be incorporated with yeast

• multi-purpose medium

• similar color to LB agar

Explain: Blood Agar

• a type of TSA agar

• grows fastidious microbes (complex growth reqs)

• differentiates between streptococcus strains

• mixed with 5-10% sheep’s blood

• differentiates alpha, beta, and gamma hemolysis

Alpha hemolysis

• appears greenish brown due to incomplete/partial lysis of RBCs (Blood agar plates)

Beta hemolysis

• appears clear-ish due to the capacity of a microbe to completely lyse RBCs (Blood agar plates)

Gamma hemolysis

• appears white/tan due to the absence or lack of hemolytic activity (Blood agar plates)

Explain: Columbia CNA Agar

• cultures/sustains gram-POSITIVE microbes

• antimicrobial agents incorporated in the media inhibit gram NEGATIVE bacteria growth

• Blood in the media provides differentiation based on hemolysis

Explain: Chocolate Agar

• derivative of blood agar

• used for fastidious (complex growth req) and pathogenic microbes

• medium made of already lysed RBS (lysed via heat)

  • these RBS release growth nutrients in the media

• since RBCs are already lysed, we can’t observe hemolytic differences

Explain: MacConkey Agar

• promotes growth of gram NEGATIVE microbes

• Crystal violet and bile salts inhibit growth of gram positive bacteria

• if a microbe does ferment lactose, it will become acidic making the medium display a pink/red color

• if a microbe does NOT ferment lactose, it will become alkaline (basic?) and the medium will display a yellow culture

Explain: Sorbitol-MacConkey Agar

• detects pathogenic strain of E-Coli (which is E. coli 0157:H7)

• agar contains sorbitol that pathogenic e. coli cannot ferment, but nonpathogenic can

  • Pathogenic E. coli colonies are colorless

  • Nonpathogenic E. coli colonies are pink/red (indicating fermentation IS occurring)

Explain: Eosin methylene Blue Agar

• Main two ingredients inhibit gram positive microbes (selective)

• Stratified by lactose fermentation

  • Microbes that CAN ferment lactose look dark purple/black

  • Microbes that CANNOT ferment lactose look white/tan

  • ***E. coli produce metallic green colonies because cells are absorbing some of the dyes present in the agar

Explain: Mannitol Salt Agar (MSA)

• detects gram POSITIVE microbes

  • differentiates Staphylococci family

• plate has sodium chloride and mannitol sugars incorporated

• Pathogenic microbes that can ferment mannitol sugar appear yellow (due to pH)

• Nonpathogenic microbes that cannot ferment mannitol sugar appear red (due to pH)

  • (Plate has a reddish background to begin with)