Mediums
Medium | Type | Selective/Differential Agents | Main Purpose / Notes | Indicators / Results |
TSA / NA | General Purpose | None | Supports growth of most organisms except fastidious ones (e.g., Haemophilus, Neisseria, Mycobacterium) | None |
CBA | Differential and Enriched | 5% Sheep Blood | Supports most organisms; enriched for general use | Hemolysis types: α (partial), β (complete), γ (none); Haemophilusand Neisseria need S. aureus as satellite |
CNA | Differential and Selective | Colistin & Nalidixic Acid (selective for Gram+), Blood (differential) | Selective for Gram-positive cocci; inhibits Gram-negatives | Hemolysis can be observed |
CHOC | Enriched (Heated Blood Agar) | Provides X (hemin) & V (NAD+) factors | Supports fastidious organisms (Haemophilus, Neisseria); produces larger colonies than on CBA | No hemolysis indicator due to lysed RBCs |
SDA | Selective | Low pH, Chloramphenicol | Selective for fungi | Fungal growth observed, bacterial growth inhibited |
MSA | Differential and Selective | 7.5% NaCl (selective), Mannitol (differential) | Selective for Staphylococcusspp.; mostly S. aureus | S. aureus: yellow colonies, yellow agar (acidic); other Staph: pink colonies, no color change |
MAC | Differential and Selective | Bile salts & Crystal violet (selective), Lactose (differential) | For enteric Gram-negative rods (Enterobacteriaceae) | Lactose fermenters: bright pink (e.g., E. coli); Non-fermenters: clear (e.g., Salmonella, Shigella) |
HE | Differential and Selective | Bile salts (selective), Lac/Suc/Salicin (differential), Sodium thiosulfate | For enterics, especially Salmonella/Shigella | Fermenters: pink/orange (E. coli); Non-fermenters: clear; H₂S producers: black-centered colonies |
TSI Slant | Differential (Confirmatory) | Glucose/Lactose/Sucrose, Sodium thiosulfate | Confirmatory test for enterics based on sugar fermentation and H₂S production | Yellow butt: glucose fermentation; yellow slant: lactose/sucrose fermentation; black: H₂S; red: no fermentation |