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level: Level 1

Questions and Answers List

level questions: Level 1

QuestionAnswer
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