Microbiology Lab Media Overview

This set of flashcards is designed to cover key vocabulary and concepts from microbiology lab media, emphasizing the types of media used, their ingredients, and applications in culture studies.

Basic media

Promote the growth of just about any bacterium.

Enriched media

Used for fastidious organisms.

Selective media

Take advantage of the growth requirements of specific bacteria.

Differential media

Use color changes to distinguish among groups of organisms.

Tryptic Soy Agar (TSA)

Basic media used for observing colony morphology and developing pure cultures.

Blood Agar

Basic, Enriched, and differential media

Hemolysis

The destruction of red blood cells.

Alpha hemolysis

Incomplete hemolysis producing a green color.

Beta

hemolysis

Complete hemolysis producing a clear zone.

Gamma hemolysis

No hemolysis observed.

Phenylethyl Alcohol Agar (PEA)

Selective media for isolating gram-positive organisms.

Mannitol Salt Agar (MSA)

Selective and differential media that supports halophiles and differentiates Staphylococcus species.

Staphylococcus aureus

Appears as yellow colonies on MSA due to mannitol fermentation.

Non-mannitol fermenters

Appear clear or pink with no yellow color change in MSA.

MacConkey Agar

Selective and differential media for gram-negative bacteria; differentiates lactose fermenters.

Coliforms

Lactose-fermenting bacteria that appear pink to red on MacConkey Agar.

GI Tract Pathogens

Non-lactose fermenters that appear transparent on MacConkey Agar.

Hektoen Enteric Agar

Selective and differential media for gram-negative bacteria; used to differentiate GI tract pathogens.

Simmons’s Citrate

Differential media indicating citrate utilization through color change.

Bile Esculin Agar

Selective and differential media for Enterococcus; turns black with esculin hydrolysis.

Carbohydrate Fermentation Tubes

Used to identify fermenting bacteria based on acid and gas production.

Eosin Methylene Blue Agar (EMB)

Selective media for gram-negatives; differentiates lactose fermenters.

Triple Sugar Iron Agar (TSI)

Differential media indicating carbohydrate fermentation and hydrogen sulfide production.

Sulfur Indole Motility (SIM)

Differential media for testing sulfur reduction, indole production, and motility.

Indole positive

Production of a pink liquid in SIM with Kovac's Reagent.

Indole negative

Kovac's Reagent shows a golden liquid in SIM.

Methyl Red Test

Determines acid production from glucose fermentation.

Voges-Proskauer Test

Detects acetoin production from glucose fermentation.

Urea Broth

Differential media testing for urease production leading to ammonia production.

Colony morphology

The visible characteristics of bacterial colonies, including color and shape.

Fastidious organisms

Organisms that require specific nutrients or growth conditions.

Crystal Violet in MacConkey

Selectively inhibits Gram-positive bacteria in MacConkey agar.

Bile Salts in Enteric Media

Selective agents in MacConkey and Hektoen agars that inhibit non-enteric bacteria.

Eosin Y and Methylene Blue

Dyes in EMB agar that inhibit Gram-positives and serve as pH indicators for lactose fermentation.

Sodium Chloride (7.5%) in MSA

Creates a selective osmotic environment for halophilic organisms like Staphylococcus.

Phenol Red pH Indicator

Turns yellow below pH 6.8 (acidic) and magenta above pH 7.4 (alkaline), used in MSA and fermentation broths.

Durham Tube

Small inverted tube in fermentation broths to visually trap and detect gas production.

Methyl Red Indicator (pH)

Turns red at pH 4.4 or below (acidic) in the Methyl Red test.

Voges-Proskauer Reagents

Alpha-naphthol and KOH; detect acetoin in the VP test, resulting in a red color.

Kovac's Reagent

Used in SIM test; detects indole by reacting with it to form a red upper layer.

Ferric Ammonium Citrate

Indicator for H_2S production in Hektoen and TSI, forming a black precipitate with sulfide.

Sodium Thiosulfate

Source of oxidizable sulfur for H_2S production in media like Hektoen and TSI.

Bromthymol Blue Indicator

Used in Simmons's Citrate, green at neutral, blue at alkaline pH ( > 7.6).

Tryptone

Defined peptone from enzymatic digestion of casein, rich in tryptophan, used for indole test.

Lactose

Disaccharide sugar frequently used in differential media to identify fermenting bacteria.

Catalase Positive Test

Rapid bubbling upon addition of hydrogen peroxide due to oxygen gas release.

Oxidase Enzyme

Cytochrome c oxidase, a component of the electron transport chain, reduces oxygen.

Oxidase Positive Test

Reagent turns dark purple/blue within seconds, indicating presence of cytochrome c oxidase.

Coagulase Positive Result

Clumping of plasma or formation of a clot, indicative of S. aureus.

Urease Enzyme

Hydrolyzes urea into ammonia and carbon dioxide.

Urease Positive Result

Urea broth turns pink/red due to ammonia production increasing the pH.

Tryptophanase Enzyme

Cleaves tryptophan into indole, pyruvic acid, and ammonia.

Citrate Permease

Enzyme allowing bacteria to use citrate as a sole carbon source.

TSI Slant

Aerobic portion of Triple Sugar Iron Agar; reaction indicates carbohydrate fermentation and gas production.

TSI Butt

Anaerobic portion of Triple Sugar Iron Agar; reaction indicates carbohydrate fermentation and gas production.

TSI K/A

Alkaline slant/Acid butt: Glucose fermented, no lactose/sucrose fermentation.

TSI A/A

Acid slant/Acid butt: Glucose and lactose and/or sucrose fermented.

TSI K/NC

Alkaline slant/No change butt: No carbohydrate fermentation (non-fermenter).

Black Precipitate in TSI

Indicates hydrogen sulfide (H_2S) production, typically obscuring butt color.

Gas in TSI

Cracks or bubbles in the agar butt, indicating gas production from fermentation.

Mixed Acid Fermentation

Glucose fermentation pathway yielding stable acidic end products, detected by Methyl Red test.

Butanediol Fermentation

Glucose fermentation pathway producing acetoin as an intermediate, detected by Voges-Proskauer test.

Motility Test in SIM

Diffuse growth away from the stab line in semi-solid agar indicates motility.

Lactose Fermenter on EMB

Colonies appearing dark purple to black, often with a metallic green sheen (e.g., E. coli).

Salmonella spp. on Hektoen

Appear blue-green with black centers (H_2S production), non-lactose fermenters.

Shigella spp. on Hektoen

Appear blue-green without black centers (no H_2S), non-lactose fermenters.

E.col on EMB

Forms dark colonies with a distinctive metallic green sheen due to rapid lactose fermentation.

Blood Agar

Contains Blood for enrichment, 5% Sheep blood

Mannitol Salt Agar (MSA)

Contains Mannitol (fermentable sugar), 7.5% Sodium Chloride (selective agent), and Phenol Red (pH indicator).

MacConkey Agar

Contains Lactose (fermentable sugar), Crystal Violet (selective inhibitor), and Bile Salts (selective inhibitor), neutral red pH indicator.

Hektoen Enteric Agar

Contains Lactose, Sucrose, Salicin (carbohydrate sources), Bile Salts (selective agent), Ferric Ammonium Citrate (H_2S indicator), and Bromthymol Blue (pH indicator).

Simmons's Citrate

Contains Citrate (sole carbon source) and Bromthymol Blue (pH indicator).

Bile Esculin Agar

Contains Esculin (for hydrolysis), Ferric Ammonium Citrate (indicator for black color), and bile salts (selective agent).

Carbohydrate Fermentation

Contain specific carbohydrates (e.g., Glucose, Sucrose, Lactose), peptone (nutrient base), Phenol Red (pH indicator), and a Durham tube (for gas detection).

Eosin Methylene Blue Agar (EMB)

Contains Lactose (fermentable sugar), Eosin Y (dye, pH indicator, selective agent), and Methylene Blue (dye, pH indicator, selective agent).

Triple Sugar Iron Agar

Contains Glucose, Lactose, Sucrose (fermentable carbohydrates), ferrous sulfate indicator H2S formation, and Phenol Red (pH indicator).

Sulfur Indole Motility (SIM)

Contains peptonized iron, Sodium Thiosulfate (sulfur source), peptone, beef extract

Urea Broth

Contains Urea (source of carbon) and Phenol Red (pH indicator).

Nitrate Broth

Contains Potassium Nitrate (NO_3^- source), beef extract, and peptone (nutrient base).

Tryptic Soy Agar (TSA)

digests of casein and soybean meal

Phenylethyl Alcohol Agar (PEA)

Phenylethyl alcohol, sheep blood

digest of soybean meal, digest of casein

Methyl Red / Voges-Proskauer

simple broth that contains peptone and glucose