Diagnostic Media Flashcards for Test 3

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1

General (Complex) Medium

Contains necessary nutrients, vitamins, minerals, etc. Most types of non-fastidious organisms, but not all, are able to grow on this type of media.

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Enriched Medium

Contains added ingredients such as blood, serum, vitamins, growth factors, etc.

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Differential Medium

Contains an indicator designed to cause certain organisms to develop a different appearance from other microbes growing on the same medium. The colonies of one particular bacteria might be a different color than those of another bacterial species growing on the same medium.

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Selective Medium

Permits or encourages the growth of certain organisms while preventing or inhibiting the growth of others.

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Selective/Differential Medium

Many of the media commonly used in the lab possess both selective and differential qualities.

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Eosin Methylene Blue Agar

Red plate
Selective for Gram -
Differential for lactose fermenters and coliforms
Positive for lactose fermentation -- pink/dark purple colonies, organism produces B-galactosidase
Positive for coliforms -- green metallic sheen, denotes vigorous lactose fermentation
Pink -- Enterobacter
Green -- E. coli
24 hours

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MacConkey Agar

Clearish plate
Selective for Gram -
(Bile salts and crystal violet dye inhibit G+)
+ lactose fermentation -- pink/lavender colonies
Pink/lavender -- E. coli, Enterobacter
24 hours

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Starch Agar

Clear plate with iodine added after growth
+ starch fermentation -- clear area around culture
Positive organisms -- Bacillus
Negative organisms -- E. coli

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Mannitol Salt Agar

Red plate
Selective for Staph (7.5% salt)
+ mannitol fermentation -- yellow culture (yellow halo means pathogenic)
Positive -- Staph. aureus
Negative -- Staph epidemidis

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Colistin-nalidixic acid

Opaque red plate
Selective for Gram +, inhibits Gram -
Differential for hemolysis
Enriched by addition of blood

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Blood Agar

Red plate
TSA enriched with 5-10% sheep blood
Gamma - Negative no change(Staph. epidermidis)
Alpha - Partial destruction, greenish agar (S. salivarius)
Beta - Total destruction, clear zone (Strep. pyogenes)

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Blood Agar- Alpha hemolysis

Partial destruction, greenish agar (S. salivarius)

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Blood Agar- Beta hemolysis

Total destruction, clear zone (Strep. pyogenes)

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Blood Agar- Gamma hemolysis

Negative no change(Staph. epidermidis)

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Hektoen Enteric Agar

Dark Blue Plate
Differential for Salmonella and Shigella Gram -
Differential for lactose fermentation and H2S
+ lactose fermentation -- yellow/salmon pink colonies (E. coli)
- lactose fermentation -- blue/green colonies (Shigella)
+ H production -- black colonies (Salmonella)

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Phenol Red Carbohydrate Fermentation Broth

Red Tube with durham tube
Differential for carbohydrate fermentation (any sugar: sucrose, lactose, mannitol)
+ carbohydrate fermentation -- broth turns yellow (E. coli, Staph. aureus)
- carbohydrate fermentation -- broth stays red (Salmonella)
Bubble positive for gas production during fermentation (E. coli)

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Triple Sugar Iron Agar

Red slant tube, contains glucose, lactose, sucrose.
Differential for fermentation, H2S.
Distiguish Gram - enteric
+ glucose fermentation -- red slant, yellow butt
+ glucose and/or lactose, sucrose -- yellow all
+ H2S -- blackening
+ gas -- lifted or cracked agar

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Triple Sugar Iron Agar (positive fermentation of only glucose)

red slant, yellow butt

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Triple Sugar Iron Agar (positive fermentation of glucose, lactose, and/or sucrose plus positive gas formation.)

all yellow
lifted or cracked agar

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Citrate Agar Slants

Green slant tube
Differential for citrate utilization
+ citrate - slant turns blue (Citrobacter)
- citrate -- B. cereus

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Urea Broth

Orange-ish slant
Differential for urease production
+ Urease -- dark pink (Proteus)
- Urease -- orange (Salmonella, Shigella)

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Phenylalanine Agar

Clear to yellowish slant
Differential for phenylalanine deaminease
Add ferric chloride after incubation
+ phenylalanine - green (Proteus)
- phenylalanine - no change (Salmonella)

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SIM Medium (Semisolid)With positive Hydrogen Sulfide

Sulfur Reduction
Clear to yellow semisolid tube
Three tests: H production, motility, Indole Production
+ H2S -- blackened (Proteus)
+ motility -- growth diffuses away from stab line (Enterobacter)
+ indole (after adding Kovac's reagent) -- pink or red ring

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SIM Medium (Semisolid)With positive motility

+ motility -- growth diffuses away from stab line (Enterobacter)

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SIM Medium (Semisolid) with positive indole production

+ indole (after adding Kovac's reagent) -- pink or red ring

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Motility GI Medium/ TTC (MOT) with positive motility

Clear tube
+ motility - diffuse red thru out (E. coli)
- motility - red stab line (Shigella)

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Optichin Disk Test

Red plate painted with white circle (optichin)
Presumptive for Strep. pneumoniae
+ optichin sensitivity - 14+mm zone of inhibition
- optichn sensitivity - <14mm zone, requires more test

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Coagulase Test

Clear tube
Differential for Staph. species
+ coagulase - plasma thickens to semisolid (S. aureus)
- coagulase - plasma remains liquid (S. epidermidis)

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Oxidase Test

Test strips
+ oxidase - strip turns purple or black (Pseudomonas or Neisseria)
- oxidase - no color change (Enterobacteriaceae)

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Catalase Test

H2O2
+ Catalase - Bubbles (Staph)
- Catalase - no bubbles (Strep)