[MICROPARA L] Bacterial Smear Preparation and Negative Staining

Smear

- small amount of culture spread in a drop of water on a glass slide
- first step in most bacterial staining procedures

- Kill the organism
- Preserve morphology
- Anchor the smear to the slide

3 Purpose of Fixation

Thick and Thin smears

Two Types of Smear

Thick smears

usually the result when the source of inoculum is from a solid culture media such as plated agar cultures and slant cultures

- Plated agar cultures
- Slant cultures

two types of solid culture media

Thin smear

usually result when the source of inoculum are made from broth cultures

Labelling

- this process is as important in making smears for stained slides as it is for cultures
- should be at one end of the slide

little finger of loop hand

part of hand used to remove the cap of the pure culture

Negative staining

- do not need HEAT FIXING or strong chemical
- a staining procedure where background are stained against colorless organisms

- helps study cell shape, breakage, refractable inclusion bodies and spores besides poly-hydroxy butyrate granules
- useful for bacteria which are difficult to stain
- for slender bacteria like spirochetes that are not detectable by simple staining methods

Purpose of Negative staining

Cryptococcus neoformans, Vegetative cell, Endospore,

types of organisms observed in negative staining

- drop acidic stain on slide
- add organisms and emulsify with loop
- smear using another slide
- air dry then view under microscope

the procedure to execute negative staining

Capillary action

the mechanism by which the negative staining reagent is spread along the width of another slide