Media Flashcards
Use: Enrichment of Vibrio species, particularly Vibrio cholerae.
Principle: The alkaline pH inhibits the growth of most other bacteria while promoting the growth of Vibrio species.
Positive: Turbid
Alkaline Peptone Water
Use: Isolation and identification of Staphylococcus aureus.
Principle: Selective agents like lithium chloride and tellurite inhibit the growth of most other bacteria. S. aureus colonies appear black with a clear zone around them.
P: black, shiny, and convex colonies
Baird-Parker (BP) Agar
Use: General-purpose medium for the cultivation of a wide range of fastidious and non-fastidious bacteria.
Principle: Provides a rich nutrient source for the growth of various microorganisms
P: Growth
Brain-Heart Infusion (BHI) Broth
Use: Isolation of Salmonella species, especially Salmonella typhi.
Principle: Bismuth sulfite inhibits the growth of most other bacteria. Salmonella colonies appear black with a metallic sheen.
P: Black Metallic Sheen
Bismuth Sulfite Agar
Use: Identification of bacteria based on their ability to ferment specific carbohydrates.
Principle: Bacteria that ferment a carbohydrate produce acid, which can be detected by a pH indicator.
P
Phenol red - Yellow
Bromocresol blue - (A)Yellow (N)Green (B)Blue
Carbohydrate Fermentation Media
Use: Isolation and differentiation of enteric pathogens, particularly Salmonella and Shigella species.
Principle: Selective agents like bile salts and dyes inhibit the growth of most Gram-positive bacteria. Differential agents like lactose, sucrose, and ferric ammonium citrate allow for the differentiation of lactose fermenters and non-fermenters, as well as H2S producers.
P: (Sal)Blue-green colonies (Shi)Green (Lac)Yellow
Hektoen Enteric (HE) Agar
Use: Identification of enteric bacteria based on their ability to ferment glucose, produce H2S, and decarboxylate lysine.
Principle: The medium contains glucose, lysine, and ferrous sulfate. Color changes and gas production indicate different biochemical reactions.
P: Purple Slant/Purple Butt (K/K): Indicates lysine decarboxylation.
Purple Slant/Yellow Butt (K/A): Indicates glucose fermentation without lysine decarboxylation.
Red Slant/Yellow Butt (R/A): Indicates lysine deamination.
Blackening in Butt: Indicates H₂S production.
Lysine Iron Agar (LIA) Slants
Use: Isolation and identification of Staphylococcus aureus.
Principle: High salt concentration inhibits the growth of most bacteria except halophiles like Staphylococcus. Mannitol fermentation by S. aureus produces acid, which changes the pH indicator to yellow.
P: Yellow Colonies
Mannitol Salt Agar (MSA)
Use: Differentiation of enteric bacteria based on their fermentation pathways.
Principle: The medium is used to test for mixed acid fermentation (MR test) and butanediol fermentation (VP test).
P: (MR)Red (VP)Red
Methyl Red-Voges-Proskauer (MRVP) Medium
Use: Simultaneous testing for motility, indole production, and ornithine decarboxylation.
Principle: The medium contains the necessary substrates for these tests, and color changes and gas production indicate positive results.
P: (M) Growth away from stab line
(I) Red ring (O)Purple
Motility-Indole-Ornithine (MIO) Medium
Use: Determination of a bacterium’s ability to reduce nitrate to nitrite or nitrogen gas.
Principle: The addition of reagents to the medium after incubation reveals nitrate reduction.
P: (Nitrite)Red
Nitrate Reduction (NR) Test Medium
Use: Differentiation of bacteria based on their metabolic pathways.
Principle: The medium contains a carbohydrate and a pH indicator. Oxidative metabolism produces acid only in the open tube, while fermentative metabolism produces acid in both open and closed tubes.
P: (OM)Open Tube - Yellow
(FM)Open and Closed - Yellow
Oxidative-Fermentative (OF) Medium
Use: Selective enrichment of Salmonella species from food and clinical samples.
Principle: The high pH and selective agents inhibit the growth of most other bacteria.
P:Turbidity
Rappaport-Vassiliadis (R-10) Broth
Use: Selective enrichment of Salmonella species from fecal samples.
Principle: Selenite inhibits the growth of most other bacteria.
P:Turbidity
Selenite F (SF) Broth
Use: Determination of a bacterium’s ability to utilize citrate as a sole carbon source.
Principle: A pH indicator changes color when citrate is utilized.
P: Blue from bromothymoll blue
Simmon’s Citrate Agar
Use: Differentiation of E. coli O157:H7 from other E. coli strains.
Principle: E. coli O157:H7 does not ferment sorbitol, resulting in colorless colonies on the medium.
P: Colorless colonies
Sorbitol-MacConkey (SMac) Agar
Use: Quantitation of viable bacteria in a sample.
Principle: A general-purpose medium used for counting bacteria.
P:Growth
Standard Plate Count (SPC) Agar
Use: Selective enrichment of Salmonella species from fecal samples.
Principle: Tetrathionate inhibits the growth of most other bacteria.
P:Turbidity
Tetrathionate Broth
Use: Isolation of Vibrio cholerae and other Vibrio species.
Principle: Selective agents like bile salts and sodium thiosulfate inhibit the growth of most other bacteria. Sucrose fermentation by V. cholerae produces yellow colonies.
P: Yellow colonies
Thiosulfate Citrate Bile Salts Sucrose (TCBS) Agar
Use: Differentiation of enteric bacteria based on their ability to ferment glucose, lactose, sucrose, and produce H2S.
Principle: The medium contains these sugars and a pH indicator. Color changes and gas production indicate different fermentation patterns.
P: (GF)B-Yellow (LF)SB-Yellow (H2S)B-Black
Triple Sugar Iron (TSI) Agar Slants
Use: General-purpose medium for the cultivation of a wide range of bacteria.
Principle: Provides a rich nutrient source for bacterial growth.
P:Turbidity
Tryptic Soy Broth (TSB)
Use: Used for the indole test to identify bacteria that produce indole from tryptophan.
Principle: Tryptophan is hydrolyzed to indole, which can be detected by adding Kovac’s reagent.
P:Red or red-violet color
Tryptone Broth (TRB)
Use: Isolation and enumeration of coliform bacteria in water and food.
Principle: Bile salts inhibit the growth of most non-coliform bacteria. Lactose fermentation by coliforms produces red colonies.
Violet Red Bile (VRB) Agar
Use: Isolation and differentiation of Salmonella and Shigella species.
Principle: Selective agents like desoxycholate inhibit the growth of most Gram-positive bacteria and some Gram-negative bacteria. Differential agents like xylose, lysine, and ferric ammonium citrate allow for the differentiation of lactose fermenters and non-fermenters, as well as H2S producers.
P: (Sal)Red with Black Center (Shi)Red (Lac)Yellow
Xylose Lysine Desoxycholate (XLD) Agar
Use: Identification of Staphylococcus aureus.
Principle: S. aureus produces coagulase, an enzyme that clots plasma.
Whole Rabbit Plasma for Coagulase Test
Use: Identification of bacteria that produce cytochrome c oxidase.
Principle: The oxidase reagent oxidizes the cytochrome c, resulting in a color change.
P: Dark blue or purple
Oxidase Test Strips
