Agars
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| 🇬🇧 | 🇬🇧 |
| Function of Bile Esculin agar? | Isolation of enterococci/ Group D streptococci |
| What patterns does Blood agar show? | Α : partial, green β : complete γ : none |
| Ingredients of Bile Esculin agar? | Bile esculin → inhibits growth → Hydrolyse = esculetin Ferric citrate → Combines with esculetin = black precipitate |
| Function of Chocolate agar? | Isolation of Haemophilus spp. |
| What type of agar is the Bile Esculin agar? | Selective & Differential |
| What type of agar is the Blood agar? | Enriched & Differential |
| What type of agar is the Chocolate agar? | Enrichment |
| What type of agar is the DNAse agar? | Differential |
| What is the function of the DNAse agar? | Tests the ability of an organism to produce deoxyribonuclease (DNAse) |
| What function does Methyl Green have in DNAse agar? | Indicator (cation which binds to the negatively-charged DNA) |
| What happens when Methyl Green is present? | Deoxyribonuclease = DNA into smaller fragments, which prevents the DNA from binding to the methyl green. Therefore, a clear halo will appear around the areas of growth. |
| What is the purpose of flooding the media with 10% HCL? | Becomes acidic = remaining non-degraded DNA precipitating = agar become turbid. |
| What is the function of the MacConkey agar? | Gram negative enteric bacteria & LF vs NLF |
| What type of agar is the MacConkey agar? | Selective & Differential |
| What are the ingredients of the MacConkey agar? | Bile salts → Inhibit gram + & - & prevents Proteus species from swarming. Sugar lactose → Shows fermentation RXN. Neutral red → pH indicator |
| What is the function of the Mannitol Salt agar? | Isolation of Staphylococci |
| What type of agar is the Mannitol Salt agar? | Selective & Differential |
| What are the ingredients of the Mannitol Salt agar? | High salt content → Selects for Staphylococci & other salt-tolerant like Enterococci Mannitol → Organisms which ferment the carbohydrate produce an acidic by-product Phenol red → pH indicator |
| What is the function of the Modified Thayer Martin agar? | Isolation of N. gonorrhea & meningitides |
| What type of agar is the Modified Thayer Martin agar? | Selective & Enrichment |
| What are the ingredients of the Modified Thayer Martin agar? | Colistin → Inhibits gram - organisms Vancomycin → Inhibits gram + organisms Nystatin → Inhibits fungi Trimethoprim → Inhibits gram – organisms especially swarming Proteus |
| What is the function of the New York City agar? | Isolation of Neisseria spp |
| What type of agar is the New York City agar? | Selective & Enrichment |
| What are the ingredients of the New York City agar? | Haemolyzed horse blood, dextrose & yeast dialysate → Enrichment Phosphate buffers → Prevents changes in pH due to amine production Colistin → Inhibits gram - organisms Vancomycin → Inhibits gram + organisms |
| What is the function of the Mueller Hinton agar? | Antimicrobial susceptibility testing |
| What type of agar is the Mueller Hinton agar? | Non-selective |
| What are the ingredients of the Mueller Hinton agar? | Beef Extract and Acid Hydrolysate of Casein → Nitrogen, vitamins, carbon, amino acids, sulphur and other essential nutrients. Starch → Added to absorb any toxic metabolites produced. Starch hydrolysis yields dextrose, which serves as a source of energy. Agar → Solidifying agent |
| What is the function of the SAB agar? | Isolation of Dermatophytes |
| What type of agar is the SAB agar? | Selective |
| What are the ingredients of the SAB agar? | Chloramphenicol → Eliminates bacterial contaminates Cyclohexamide → Inhibits many saprophytic, contaminating fungi Acidic pH → Inhibits growth of bacteria but permits growth of yeasts & most filamentous fungi |
| What is the function of the SS agar? | Isolation of Salmonellae & Shigellae |
| What type of agar is the SS agar? | Selective & Differential |
| What are the ingredients of the SS agar? | Brilliant green, ox bile, high thiosulfate & citrate concentrations → Inhibit normal flora Sodium thiosulphate → Used as a substrate for hydrogen sulphide production Ammonium iron (III) citrate → Reacts with hydrogen sulphide to form black, insoluble precipitate ferric sulphide Lactose → NLF vs LF (NR) |
| What is the function of the Sorbitol agar? | Isolation of E.coli 0157 |
| What type of agar is the Sorbitol agar? | Selective & Differential |
| What are the ingredients of the Sorbitol agar? | Bile salts → Inhibit gram + cocci & bile intolerant gram – bacilli Sorbitol → Carbohydrate Neutral red → pH indicator |
| What is the function of the Thio broth? | Shows growth properties |
| What type of agar is the Thio broth? | Differential & enrichment |
| What are the ingredients of the Thio broth? | Sodium thioglycolate → Reduces oxygen levels Resazurin → Redox indicator |
| What does TCBS stand for? | Thiosulphate Citrate Bile Sucrose agar |
| What is the function of the TCBS agar? | Isolation of Vibrio spp |
| What type of agar is the TCBS agar? | Selective & Differential |
| What are the ingredients of the TCBS agar? | Sodium citrate, sodium thiosulfate, oxgall, pH of 6.8 → Alkaline media → Inhibits some coliforms & Enterococci (o) Sodium chloride → Halophilic vibrio spp Sucrose → Carbohydrate → Reduces pH (Thymol Blue = indicator) |
| What is the function of the XLD agar? | Isolation of Salmonella & Shigella |
| What type of agar is the XLD agar? | Selective & Differential |
| What are the ingredients of the XLD agar? | Lactose, Sucrose, Xylose → Fermentation lowers the pH Phenol red → pH indicator → YELLOW Lysine → Second differential mechanism for Salmonella → Reverts pH back to alkaline |
| What is the function of the Tinsdale agar? | Isolation of C.diptheriae |
| What type of agar is the Tinsdale agar? | Selective & Differential |
| What are the ingredients of the Tinsdale agar? | L-Cystine & Sodium thiosulphate → Form H2S indicator system Potassium tellurite → Inhibits all gram – bacteria & most URT NF |
| Why does C.diptheriae form brown halos? | Reduces tellurite to tellurium = black colonies Produces cystinase = brown halo |