MCB Staining

Acid Fast Stain

Some bacteria have waxy cell walls that contain large amts of lipid materials → hydrophobic → repel water → impermeable to stains & other chemicals (dyes) in aqueous solution.

To stain these bacteria, needs special staining reagents (eg Carbol Fuschin) is soluble in lipoidal material

A+ STAIN = PINK/ RED

A- STAIN = BLUE

Capsular Stain

Combination of negative and simple staining

Often employed in diagnosis of pneumonia and other when causative agent might encapsulated

Capsule / slime layer (glycocalyx) is the mucous like secretion (polysaccharides, glycoprotein, / polypeptides) of some bacteria that surrounds the cell wall

Slime layer = Thin Glycocalyx

Capsule layer = Thick Glycocalyx

Capsular Stain Info

Capsules NOT absolutely essential cellular structures but often important in terms of survival

Capsule allows bacterium to evade the body’s phagocytic defense mechanism to greater extent than non encapsulated cell

Presence of large capsule is generally indication of virulent form of organism capable of causing disease.

Functions of Capsule

Protects cell from being phagocytized by host WBCs

Retardation against drying

Attraction & retention of nutrients

Adhesion to sites with favorable environments

Spore Stain

Malachi need to be vaporized — can be carcinogenic

Resistant to UV, detergents, radiation, heat

Can cause anthrax in lungs (deadly)

Allows to differentiate bacterial endoscopes (green) from their vegetative cells (pink)

Some bacteria can produce round structures called spores

Endoscopes found inside cells

Spores released due to disintegration of cell wall are called free spores.

Flagella Stain

Length: 10-20 UM

Diameter: 20 nm → outside visibility range of reg microscope

To make flagella visible, necessary to increase flagellar thickness by precipitating coating of dye over entire length of flagella via flagella stain.

Bacterial Flagella Arrangement

For QUIZ/ Lecture EXAM

Negative stain

Method of choice for observing bacteria that are difficult to stain

Also good for fragile bacteria because the preparation does NOT subject cell to strong chem agents/ phys treatment —> bacteria is NOT heat fixed → there is little chance of distortion of cell morphology (eg shape , size)