AM - Practical Images

Flashcards covering bacterial staining procedures (Gram, Ziehl-Neelsen, Capsule), colony morphology, haemolysis types, and biochemical identification tests like Catalase, Coagulase, and Oxidase.

Fixed Smear Preparation

The process of placing a small loopful of sterile water on a slide, emulsifying an isolated colony to create a thin suspension, air drying, and heat fixing.

Heat Fix

Passing a dry slide smear side up through a Bunsen flame three times to adhere cells without damaging their structure.

Gram-positive

A bacterial Gram reaction result characterized by a purple color.

Gram-negative

A bacterial Gram reaction result characterized by a pink/red color.

Crystal violet

The primary stain in a Gram stain, applied for $30$ seconds.

Lugol's iodine

The mordant in a Gram stain, applied for $30$ seconds.

Alcohol-acetone

The decolouriser used in Gram staining for $2-5$ seconds until the slide runs clear.

Safranin

The counterstain in a Gram stain, applied for $30$ seconds.

Colony

A visible mass of identical cells on agar arising from a single bacterial cell representing a pure culture.

Colony Elevation Types

Categories of vertical growth including Flat or Effuse, Low Convex, Umbonate, Draughts-Man Shaped, Raised, Convex or Domed, and Convex with Papillate.

Carbol fuchsin

The stain used in Ziehl-Neelsen staining, heated for $5$ minutes on a heating block; releases toxic phenol vapour.

Acid alcohol ($3\%$)

The decolouriser used in Ziehl-Neelsen staining for $2-3$ minutes or until washings run clear.

Methylene blue ($0.3\%$)

The counterstain used in Ziehl-Neelsen staining, applied for $2$ minutes.

Capsule Stain

A specialized staining method that is not heat-fixed, using Nigrosin and crystal violet.

Nigrosin

An acidic dye used in capsule staining to create a thin film with a bacterial colony, air dried for $5-7$ minutes.

Haemolysis

The breakdown of red blood cells in agar caused by bacterial enzymes.

Beta ($\beta$) haemolysis

Complete clearing around colonies on blood agar due to complete lysis of red blood cells.

Alpha ($\alpha$) haemolysis

Partial haemolysis on blood agar producing a green or brown discolouration.

Gamma ($\gamma$) haemolysis

No haemolysis, resulting in no visible change in the blood agar.

Oxidase Test

A test where a colony is smeared onto filter paper with oxidase reagent; a positive result is a dark purple/blue colour change within $10-30$ seconds.

API CIT (Citrate)

An API strip test that is positive only if the colour is distinctly green/blue.

API Carbohydrate tests

Tests where yellow indicates acid production (positive) and green/blue indicates a negative result.

Catalase Test

A test using hydrogen peroxide ($H_2O_2$) where immediate bubbling indicates the production of oxygen gas (positive).

Coagulase Test

A test using rabbit plasma to observe for clumping (coagulation), used to differentiate Staphylococcus species.

Staphylococcus aureus

A Gram-positive coccus that is both catalase-positive and coagulase-positive.

Staphylococcus epidermidis

A Gram-positive coccus that is catalase-positive but coagulase-negative.