Negative Staining of Bacterial Capsules

Vocabulary flashcards covering the concepts, reagents, functions, and laboratory steps of the negative staining technique for bacterial capsules.

Bacterial capsule

A non-ionic, uncharged polysaccharide structure surrounding certain bacteria that provides anti-phagocytic protection and promotes adherence to host tissues.

Anti-phagocytic function

The role of a bacterial capsule in limiting the ability of host phagocytes to engulf the bacterial cell.

Attachment to host tissue

A capsule function that facilitates bacterial adherence to host cells, thereby promoting infection.

Negative stain technique

An indirect staining method used to visualize bacterial capsules by darkening the background and staining the cell, leaving the capsule unstained.

Indirect staining

A staining approach where the target structure itself is not dyed, but is instead revealed by staining the surrounding background and cellular body.

Capsule appearance in negative stain

A clear, unstained "halo" surrounding the cell, resulting from non-ionic polysaccharides being unable to bind charged dyes.

India Ink

A non-ionic chemical reagent that does not bind to bacterial capsules, creating a dark background on the slide.

Crystal violet (capsule staining)

A positively charged dye chromophore applied for $60\,\text{seconds}$ that binds to the negatively charged peptidoglycan cell wall, staining the bacterium purple.

Confirmation of a true capsule

The direct microscopic visualization of a stained bacterial cell located inside the clear, unstained halo.

"Pushing" slide method

The procedure of placing a second glass slide at an angle against the India ink and specimen mixture to push and spread it evenly across the first slide.

Air drying (capsule stain)

The smear preparation step where the slide is dried without heat fixation to avoid damaging or shrinking the capsule.

Oil immersion lens

The $100\times$ objective lens used to examine the final stained capsule slide under the microscope.

Descriptive Chart data

The three recording criteria evaluated for the Gram stain: Gram reaction, cell shape, and arrangement.

Pure culture techniques

Laboratory methods used for microbial isolation and culture, specifically quadrant streak, fishtail streak, and stab inoculation.