Microbiology Lab Review

Comprehensive vocabulary flashcards covering microbiology laboratory principles, staining techniques, media types, and biochemical tests as outlined in the lecture notes.

Negative stain

A method where the background is stained with Nigrosin (negatively charged) and bacteria remain colorless; it is used to determine size and shape without heat fixing to prevent shrinkage.

Gram stain

A differential stain identifying Gram positive (purple) and Gram negative (pink) bacteria using Primary stain (Crystal violet), Mordant (Gram’s iodine), Decolorizer (alcohol), and Counter stain (Safranin).

Decolorizer (Gram stain)

Alcohol; the most critical step in the Gram stain process.

Acid Fast Stain

Used to stain bacteria with thick, waxy cell walls like the Mycobacterium genus (leprosy and TB); uses Carbol fuchsin, acid alcohol, and Methylene blue.

Spore Stain

A procedure to identify spore producing bacteria; uses Malachite green with heat as the primary stain and Safranin as the counterstain; spores appear green.

Capsule stain

Identifies capsules as a white halo around purple bacteria using Crystal violet and Copper sulfate; heat fixing is avoided to prevent cell shrinkage.

Selective media

Media that selects for only some groups of bacteria to grow using inhibitors.

Differential media

Media that allows the differentiation of closely related groups of bacteria based on biochemical characteristics.

Mannitol Salt Agar (MSA)

Identifies Staphylococcus; uses $7.5\%$ NaCl as an inhibitor and Phenol red as an indicator; Staphylococcus aureus ferment mannitol and turn yellow.

MacConkey Agar

Grows enteric bacteria and inhibits gram ($+$) using Crystal violet and bile salts; differentiates lactose fermenters (pink) from non-lactose fermenters (white).

Eosin Methylene Blue (EMB) Agar

Used to find food contamination by enterics; E. coli shows a green metallic sheen due to lactose fermentation.

Gelatinase

An enzyme secreted by bacteria; if present, the gelatin tube becomes liquid (hydrolyzed); confirmed by placing on ice for $5\,min$.

Amylase

An exoenzyme that breaks down starch; a positive Starch Plate test shows a clear zone or halo after adding Iodine indicator.

Phenol Red Broth

Determines carbohydrate fermentation; uses a Durham tube to trap gas; positive result is yellow and negative is red.

Citrate permease

The enzyme needed to use Citrate as a carbon source; a positive Citrate Agar test is Blue and a negative is Green.

Methyl Red (MR)

A test to determine if glucose is fermented to mixed acids; uses Methyl red indicator which turns red in a positive test.

Acetoin

The neutral end product from glucose fermentation detected by the Voges-Proskauer (VP) test using reagents VP-A and VP-B.

SIM Media

Tests for Sulfur reduction (Black color), Indole production (Red ring with Kovac’s reagent), and Motility (Growth away from stab).

Tryptophanase

The enzyme tested for in the Indole portion of the SIM test; utilizes the substrate Tryptophan.

Nitrate Reduction Test

Determines if nitrate is used as a final electron acceptor; uses Nit A, Nit B, and Zinc powder (Nit C) for confirmation of negative results.

Oxidase Test

Determines oxidase activity and aerobic respiration; a positive test result is a blue color after adding Oxidase reagent to bacteria on TSA plates.

Catalase Test

Determines if bacteria break down peroxide; a positive result produces bubbles when $H_2O_2$ is added.

Beta Hemolysis

Complete lysis of RBCs on Blood Agar Plate resulting in a clear zone, such as in Streptococcus pyogenes.

Alpha Hemolysis

Incomplete lysis of RBCs resulting in a greenish halo on Blood Agar Plate.

Kirby-Bauer Method

A method to determine antibiotic sensitivity using a Mueller-Hinton plate and antibiotic discs.

Zone of inhibition

A clear area created around an antibiotic or chemical disc where bacterial growth is inhibited.