Exercise 2: Bacterial Smear Preparation

properly prepared bacterial smear

one that withstands one or more washings during staining without loss of organisms, is not too thick, and does not result in excessive distortion due to cell shrinkage

good quality stain

___________ is directly related to the quality of the smear

Use clean, unscratched microscope slides.

use a clean, unscratched microscope slide because:

dirt, dust and other debris

________ can be mistaken for microorganisms after the staining process.

scratches

_____________ on a slide can be confused with microorganisms after the staining process.

microorganisms

can be washed off a greasy slide during the staining process.

soap
water
scouring powder

Grease or oil from the fingers on slides must be removed by washing the slides with ___________

label the slides

proper ________ of the slide is essential. write the organism’s initials on either end of the slide with glassware making pencil on the surface on which the smear is to be made.

avoid making smears that are too thick

this will result in uneven staining and/or decolorization

avoid making smears that are too thin

this smear will not provide enough cells for a thorough examination of the specimen

thin whitish layer or film

characteristic of a good smear

broth cultures

Resuspend the culture by tapping the tube with your finger. Depending on the size of the loop and the amount of culture growth, apply one or two loopfuls to the center of the slide with a sterile inoculating loop and spread evenly over an area about a dime's size. Set the smears on the laboratory table and allow to air-dry.

 

cultures from a solid medium

Organisms cultured in a solid medium produce thick, dense surface growth and are not amenable to direct transfer to the glass slide. these cultures must be diluted.

heat fixation
methanol fixation

two methods for fixing a smear

heat fixation

______ should only be used for biosafety level 1 organisms because aerosols can be generated

methanol fixation

______ the preferred method, as it does not create aerosols and has fewer cellular morphology changes