Bacterial Smear & Simple Staining

What is the purpose of making a bacterial smear?

To prepare bacteria on a slide so they can be stained and observed under a microscope

what should you always do before beginning a bacterial smear?

Obtain a clean slide and label it with an “X” on the sside that will hold the bacteria

Why might you add a drop of sterile water when making a smear from solid media? 

To help spread the sample evenly on the slide surface 

What is aseptic technique used for when making a smear?

To prevent contamination of the bacterial sample and the work area

Why should the smear be thin and even? 

Thick smears make it difficult to observe individual bacteria under the microscope 

what are the two main purposes of heat - fixing a bacterial smear?

1. to kill the bacteria

2. to make the cells stick to the slide so they don’t wash off during staining

What happens if a slide is overheated during heat- fixing?

the cells can rupture or the slide may crack

what is a chromophore? 

The color- bearing part of a stain that gives it its color 

Why do most bacterial stains use a positively. charged chromophore?

Because bacterial cell surfaces are negatively charged and attract the positively charged stain (resulting on a positive stain)

what is a positive stain?

A stain where the bacterial cells take up the color, making them visible against a clear background

what is a negative stain? 

A stain where the background is colored and the cells remain clear because the negatively charged dye is repelled by the negatively charged cell surface 

What kind of information can be learned from a simple stain?

bacterial shape, size, and arrangement

What are three bacterial species commonly used for simple staining practice?

Bacillus subtilis, Escherichia coli, and staphylococcus epidermidis