Media/Agar Exam 1 Flashcards Preview

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Flashcards in Media/Agar Exam 1 Deck (25)
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Describe the elements of the Gram Stain

Crystal Violet- Initial Stain-stains all organisms present.
Gram's Iodine-Mordant- fixes initial stain in all gram positive organisms.
Decolorizer- ETOH, acetone mixer- washes away CV
Safranin-secondary (counter) stain-takes up by Gram neg organisms


When do you use Acid Fast Stain?

For bacteria that don't stain well with the gram stain. High amount of teichoic acid


Why are they called acid fast bacteria?

Fast refers to the quality or state of being fixed and/or the resistance to the action of a specific stain or de-staining agent.


What is a pure culture?

Only one bacterial sp. is represented on a culture plate


What are the 4 media classifications?

Supportive, Enrichment, Selective, and Differential


Describe enrichment media

Contains specific nutrients to promote growth of a particular type of organism.


What are some additives that can be added to selective media?

Dyes, bile salts, alcohols, acids, and antibiotics.


How does differential media work?

Contains additives allowing organisms to be differentiated by metabolic characteristics as evidenced by distinct colonial appearances on the media. Usually contains an indicator and a fermentable carbohydrate.


What is Sheep Blood Agar?

Enriched and Differential


What is Chocolate Agar?

Enriched; has X and V factors (supports the growth of Neisseria gonorrhoeae, Haemophilus spp. Neither grows well on SBAP).


What is Phenylethyl Alcohol Agar?

Selective for gram + cocci
PEA inhibits growth of g- bacilli
*Inhibits swarming of Proteus*
Good for anaerobic work


What is MacConkey Agar?

Selective and Differential for Gram - bacilli, both lactose fermenting (pink) and non-lactose fermenting (clear).


What is Modified Thayer-Martin Media?

Highly enriched (chocolate agar + hemoglobin) and selective (antibiotics) for Neisseria gonorrhoeae and Neisseria meningitidis.


What are the antibiotics added to Modified Thayer-Martin Media and what do they inhibit?

Colistin- inhibits gram -
Vancomycin- inhibits gram +
Nystatin- Inhibits yeast
Trimethoprim- Inhibits spreading of Proteus


What is New York City Agar?

Selective media for Neisseria gonorrhaeae, Ureaplasma urealyticum, and Mycoplasma spp.


What is Xylose-Lysine Desoxychoolate (XLD) Media?

Selective and differential for Salmonella spp. and Shigella spp. (both are gnr and enteric pathogens). They stay red on the media. Salmonella produces hydrogen sulfide and has black centers.


What does XLD media contain?

Contains sodium desoxycholate which inhibits growth gram - bacilli that aren't enteric pathogens and also inhibits gram + cocci. Contains xylose, lactose, and sucrose sugars.


What is Thioglycollate broth enriched with?

Casein, yeast and beef extracts, and vitamins.


What is LIM broth selective for?

Promotes growth of Group B strep especially from specimens from the female genital tract.


What 3 tests should you do for Gram + organisms?

Catalase, Coagulase, and PYR


What 3 tests should you do for Gram - organisms?

Indole, oxidase, and urease


What is spot indole test presumptive ID for?

E. coli


What is urease test presumptive ID for?

Proteus spp.


Sensitivity means?

The % of people in whom the organism is present actually test positive.


Specificity means?

The % of people without disease that test negative for the organism.