Bacterial Classification, Staining

Bacterial classification, staining Dr. Mejbah Uddin Ahmed

Classification • Bacteria can be classified on the basis of: A) Shape; Cocci, Bacilli, Cocco bacilli, pleomorphic. B) Staining character: Gram-positive, Gram-negative, Acid-fast. C) Motility; Motile, non-motile. D) Growth requirement. E) Structures: Capsule, spore etc. F) Clinically.

Types of stain Simple stain: A single basic dye such as: methylene blue or basic fuchsin is used as simple stain. Differential staining: They impart different colours to different bacteria (Gram’s stain and acid -fast stain.)

Types of stain • Impregnation stain: Demonstration of spirochetes and bacterial flagella e.g.,Silver impregnation stain for Treponema pallidum. • Negative stain: This technique is useful for the demonstration of bacterial capsule e. g.,- India ink.

Types of stain • Fluorescence stain: When fluorescence dye is used. It needs special microscope. • detection of antigen & antibody by use of fluorescence labeled antibodies. • Staining Of Nucleoid: Feulgen stain for DNA.

Types of stain • Spore stain: Spores are commonly stained with melachite green & carbolfuchsin.

Simple staining • A single staining agent is used such as methylene blue, carbol fuchsin, crystal violet or safranin. • It highlights the entire microorganism. • Cellular shapes and basic structures are visible.

Gram stain • Developed by the Danish bacteriologist Christian Gram in 1884. • Classifies bacteria into two groups based on differences in cell wall structureGram – positive & Gram- negative • The gram stain is a very important early step in some medical situations to select an antibiotic.

StepsStain of Gram stain Steps Steps of of Gram Gram Stain

Ziehl-Neelsen stain 1. Primary Stain by heated carbol fuchsin. 2. Decolorize with 20% sulfuric acid and alcohol separately or with acid alcohol (which contains hydrochloric acid and ethanol). 3. Wash the slide in water. 4. Counterstain usually with methylene blue or malachite green.