| 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 |
