Med. Mico. Lab Final_2.Preparation of Bacterial Smear

Why is it essential that smears be air-dried? Why can't they be gently heated over the flame to speed up the drying process?

1. Overheat will denature and rupture the cell wall. 2. excess water on the slides will boil during fixation destroying the overall shape of the bacteria

Why should you be careful not to overheat the smear during the heat-fixing process?

Overheating will distort the morphology through plasmolysis of the cell wall

*Why do you think the presence of grease or dirt on a glass slide will result in a poor smear preparations?

1. Bacteria will attach to the grease or dirt and wash away when staining. 2. It can also diminish the microscopic light making it hard to see the cells.

Why are thick or dense smears less likely to provide a good smear preparation for microscopic evaluation?

It will diminish the amount of light that can pass through making it difficult to visualize the morphology of single cells under the microscope.

Some times the stain can't penetrate all of the bacteria.

What is a basic stain (simple stain)?

In simple staining, the bacterial smear is

stained with a single reagent, which produces

a distinctive contrast between the organism

and its background.

Why are basic dyes more effective for bacterial staining than acidic dyes?

Basic stains with a positively charged chromogen are preferred be-

cause bacterial nucleic acids and certain cell

wall components carry a negative charge that

strongly attracts and binds to the cationic

chromogen.

Can simple staining techniques be used to identify more than the morphological characteristics of microorganisms?

The purpose of simple staining is to make  the morphology and arrangement of bacterial cells easier to observe so yes it does provide information about cellular components and biochemical properties

During the performance of the simple staining procedure, you failed to heat fix your E. coli smear preparation.  Upon microscopic examination, how would you expect this slide to differ from the correctly prepared slides?

There will be less bacteria in the smear because it would have been washed away during the staining process. The bacterial proteins won’t be “coagulated and fixed to the glass surface” like the other correctly prepared slides.