Microbiology Lecture Notes Review

Flashcards for reviewing key microbiology concepts and tests.

Gram Stain

Differentiates bacteria based on cell wall structure (Gram-positive vs. Gram-negative).

Gram Stain - Key Ingredients

Crystal violet, iodine, alcohol, safranin.

Gram Stain - Interpretation

Purple cells = Gram-positive (thick cell wall). Pink/red cells = Gram-negative (thin cell wall).

Catalase Test - Metabolic Activity

Tests for the presence of the enzyme catalase, which breaks down hydrogen peroxide into water and oxygen.

Catalase Test - Interpretation

Bubbles form = Catalase positive (enzyme present). No bubbles = Catalase negative (enzyme absent).

Oxidase Test - Metabolic Activity

Tests for the presence of cytochrome c oxidase, involved in the electron transport chain.

Oxidase Test - Interpretation

Purple color = Oxidase positive. No color change = Oxidase negative.

Dextrose (Glucose) Fermentation - Metabolic Activity

Tests for the ability to ferment glucose, producing acid and/or gas.

Dextrose (Glucose) Fermentation - Interpretation

Yellow broth with gas = Glucose fermented (acid and gas). Yellow broth, no gas = Glucose fermented (only acid). Red broth = No fermentation (neutral pH). Pink broth = No fermentation (alkaline).

Lactose Fermentation - Metabolic Activity

Tests for the ability to ferment lactose, producing acid and/or gas.

Lactose Fermentation - Interpretation

Yellow broth with gas = Lactose fermented (acid and gas). Yellow broth, no gas = Lactose fermented (only acid). Red broth = No fermentation (neutral). Pink broth = No fermentation (alkaline).

Mannitol Fermentation - Metabolic Activity

Tests for the ability to ferment mannitol, producing acid and/or gas.

Mannitol Fermentation - Interpretation

Yellow broth with gas = Mannitol fermented (acid and gas). Yellow broth, no gas = Mannitol fermented (only acid). Red broth = No fermentation (neutral). Pink broth = No fermentation (alkaline).

Methyl Red Test - Metabolic Activity

Tests for mixed acid fermentation (producing stable acids like lactic acid).

Methyl Red Test - Interpretation

Red color = Positive (acidic pH, mixed acid fermentation). Yellow color = Negative (no acid production).

Voges-Proskauer Test - Metabolic Activity

Tests for the production of acetoin from fermentation (a neutral product).

Voges-Proskauer Test - Interpretation

Red color = Positive (acetoin produced). No color change = Negative (acetoin not produced).

Hydrogen Sulfide Production - Metabolic Activity

Tests for the ability to reduce sulfur (to produce H2S gas).

Hydrogen Sulfide Production - Interpretation

Black precipitate = H2S production (positive). No color change = No H2S production (negative).

Citrate Utilization - Metabolic Activity

Tests for the ability to use citrate as the sole carbon source, which produces an alkaline pH.

Citrate Utilization - Interpretation

Blue color = Positive (citrate utilized). Green color = Negative (citrate not utilized).

Litmus Milk Test - Metabolic Activity

Tests for the fermentation of lactose, reduction of litmus, and production of acid or gas.

Litmus Milk Test - Interpretation

Pink (acid) = Lactose fermentation (acid production). Blue (alkaline) = No lactose fermentation (alkaline production). White (reduction) = Litmus reduction. Curdling = Coagulation of proteins (acid production). Gas bubble = Gas production.

Starch Hydrolysis - Metabolic Activity

Tests for the ability to break down starch using the enzyme amylase.

Starch Hydrolysis - Interpretation

Clear zone around growth = Starch hydrolyzed (positive). No clear zone = Starch not hydrolyzed (negative).

Phenylethyl Alcohol (PEA) Agar - Metabolic Activity

Selective medium to inhibit the growth of Gram-negative bacteria.

Phenylethyl Alcohol (PEA) Agar - Interpretation

Growth = Gram-positive bacteria. No growth = Gram-negative bacteria.

Mannitol Salt Agar (MSA) - Metabolic Activity

Selective and differential; tests for the ability to ferment mannitol and tolerate high salt concentrations.

Mannitol Salt Agar (MSA) - Interpretation

Yellow agar around growth = Mannitol fermentation (acid production). Red or no change in color = No fermentation. Growth = Salt tolerance (positive for salt tolerance). No growth = Inability to tolerate salt (negative).

MacConkey's Agar - Metabolic Activity

Selective and differential; tests for the ability to ferment lactose and tolerate bile salts.

MacConkey's Agar - Interpretation

Pink colonies = Lactose fermentation (acid production). Colorless colonies = No lactose fermentation. Growth = Tolerance to bile salts. No growth = Inability to tolerate bile salts.

ELISA - Sample

The sample contains the substance you're testing for (e.g., a virus, bacteria, or antigen).

ELISA - Primary Antibody

This antibody is designed to specifically bind to the target molecule in your sample.

ELISA - Secondary Antibody

This antibody binds to the primary antibody and is linked to an enzyme that will help with detecting the target.

ELISA - Enzyme Substrate

The substrate reacts with the enzyme linked to the secondary antibody, producing a color change or signal.

ELISA - Wash Buffer

This is used to wash away any unbound antibodies or proteins that are not specifically attached to the target.

ELISA - Positive Result

If the sample contains the target antigen (or antibody), a color change (or other detectable signal) will occur after the enzyme substrate is added.

ELISA - Negative Result

If the sample doesn’t contain the target antigen (or antibody), there will be no color change, meaning the test is negative.