Media To Know

Question 1

MacConkey

Answer 1

MacConkey- peptone base with lactose

Key characteristics

Lactose fermenting organism will have pink colonies

Non-lactose fermenters will have colorless colonies

Inhibit: gram positive (crystal violet, bile salts)

Indicator: natural red

Isolation and Differentiation: lactose fermenting and non-lactose fermenting enteric bacilli

Escherichia coli: pink colonies

Klebsiella pneumonia: pink colonies; mucoid colonies

Citrobacter freuundii: pink colonies

Proteus mirabilis: colorless

Shigella sonnei: colorless colonies: flat with jagged edges

Salmonella enteritidis: colorless colonies

Pseudomonas aeruginosa: colorless (mucoid)

Yersinia enterocolitica: colorless to peach (variable lactose fementation)

Question 2

Hectoen enteric agar

Answer 2

Hectoen enteric agar- peptone base with bile salts, lactose, sucrose, salicin, and ferric ammonium citrate

Key Characteristics:

Enterics that ferment one or more of the carbohydrates will produce yellow to salmon colored colonies

Escherichia coli

Non-fermenters will produce blue-green colonies

H2S organisms will produce black or blue-green colonies

Indicators: bromthymol blue and acid fuchsin

Differential and Selective: Salmonella and Shigella from other gram negative enteric baccili

Escherichia coli: yellow colonies

Klebsiella pneumonia: yellow/orange colonies

Citrobacter freundii: colorless colonies

Proteus mirabilis: colorless

Shigella sonnei: blue-green colonies

Salmonella enteritidis: blue-green colonies w/ black centers

Question 3

Xylose Lysine Desoxycholate (XLD)

Answer 3

Xylose lysine desoxycholate (XLD) agar- Yeast extracts with lysine, xylose, lactose, sucrose, and ferric ammonium citrate

Key Characteristics

Enterics that ferment lactose/sucrose produce yellow colonies

Salmonella produces red colonies, some with black centers (H2S positive)

Shigella produces colorless colonies

Inhibits: gram positive (sodium desoxycholate)c

Indicator: phenol red

Isolation and Differentiation: Salmonella and Shigella from other gram-negative enteric bacilli

Escherichia coli: yellow colonies

Klebsiella pneumonia: yellow colonies

Citrobacter freundii: red, yellow, or colorless w/ or w/o black centers

Proteus mirabilis: yellow/ colorless w/ or w/o black centers

Shigella sonnei: colorless colonies

Salmonella enteritidis: red colonies with black centers

Question 4

MacConkey Sorbitol

Answer 4

MacConkey Sorbitol- MacConkey agar but with sorbitol instead of lacose

Selective and Differentiation: E.coli 0157:H7 in stool

Organisms:

Escherichia coli: only 0157:H7 will grow

Question 5

Thiosulfate citrate-bile salts agar (TCBS)

Answer 5

Thiosulfate citrate-bile salts agar (TCBS)- peptone base with bile salts, yeast extract, citrate, sucrose, ferric acid, and thiosulfate.

Key Characteristics:

Non-Vibro H2S Organism produce small black colonies

Sucrose fermenting Vibros produce blue colonies

Other Vibros produce various colors of yellow, green, and blue

Indicator: bromythymol blue

Selective and Differential: Vibro spp.

Vibro cholerae

Question 6

Cefsulodin-irgasen-novobiocin agar (CIN)

Answer 6

Cefsulodin-irgasan-novobiocin agar (CIN)- Peptone base with yeast extract, mannitol, and bile salts, supplemented with cefsulodin, irgasan, and novobiocin.

Key Characteristics:

No Growth of non-Yersinia organisms

Yesrsinia organism appear colorless to pink (may have zone of precipitate bile)

Inhibits: select organisms

Indicators: natural red and crystal violet

Selective: Yersinia spp (may be useful for isolation of Aeromonas)

Yersinia enterocolitica: dark red culls-eye colonies

Question 7

Pyocyanin agar

Answer 7

Selective agar for pseudomonas

Question 8

Salmonella-Shigella agar (SS agar)

Answer 8

Selective agar for Salmonella and Shigella

Question 9

Tetrathionate broth

Answer 9

Tetrathionate broth- peptone base broth with enzyme tertethionate

Key Characteristics

Tetrathionate positive organisms will grow (Salmonella, Shigella, Proteus)

Tetrathionate negative organisms are inhibited (E. coli)

Inhibit: gram positive and Enterobacteria (iodine, potassium iodide, bile salts, sodium thiosulfate)

Selective: Salmonella and Shigella (except S. typi)

Proteus mirabilis: growth

Shigella sonnei: growth

Salmonella entertidis: growth

Question 10

Selenite broth

Answer 10

Selective for Salmonella and Shigella

Question 11

Centrimide agar

Answer 11

Selective for Pseudomonas

Question 12

PC and OFPBL agar

Answer 12

selective for B. cepacia

Question 13

Pyocyanin agar

Answer 13

Selective for pseudomonas