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Lab 2 Objectives
Microscopic
Measurements
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Background and Purpose:
Although microbes in general are extremely small, they
exhibit a relatively broad range of sizes or dimensions. Knowing the exact
size of a microbe can be an important physical feature used for identification.
Measurements of microbes are accomplished through the use of an ocular
micrometer. When properly calibrated with a special slide called a
stage micrometer, this measuring device can easily determine the dimensions
of an organism as it is being viewed with the microscope.
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General Procedure:
Using a stage micrometer, an ocular micrometer is mathematically calibrated for
each objective lens on the microscope.
After calibration, the ocular micrometer is used to measure the dimensions of
different microbial specimens.
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Materials:
Ocular micrometer, stage micrometer, microscope
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Ubiquity of
Bacteria
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Background and Purpose:
The term ubiquitous can be defined as "the state or capacity of
being, or seeming to be, everywhere at the same time." This term largely
describes the bacteria. No other groups of organisms are as widely
distributed in nature as the bacteria are. To demonstrate this, you and
your classmates will be sampling a variety of environmental surfaces, humans,
and the air for the presence of bacteria. Because of this ubiquity, this
exercise should help emphasize the need to properly execute aseptic techniques
and standard microbiological practices to help reduce contamination and maintain
a high degree of laboratory safety.
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General Procedure:
Using a sterile cotton swab moistened with sterile nutrient
broth, rub the surface of some object or a part of your body and return the
swab to a nutrient broth tube. Using a trypticase soy agar plate,
gently press an object against the medium or expose it to the air for a
specified time. Incubate both the nutrient broth tube and trypticase soy
agar plate at 37º C for 48 hours and then examine
these media for bacterial growth.
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Materials:
1 tube of nutrient broth, 1 sterile cotton swab, 1 petri plate of trypticase soy
agar
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Aseptic Technique:
Much of the work in a microbiology lab routinely involves transferring microbes
from one culture medium to another or from a culture to a microscope slide.
To reduce the risks of contamination, as well as preventing exposure of lab
workers to potential pathogens, it is necessary to perform aseptic techniques.
These techniques allow workers to safely handle microbes and perform the general
lab procedures known as the 5 I's: inoculation, incubation,
isolation, inspection, and identification.
Throughout this semester you will be utilizing and perfecting all these
techniques.
Smear Preparation:
Aseptic techniques are used when preparing smears for various staining
procedures. Starting with a liquid suspension of microbes, a smear
is prepared by spreading a thin film of this suspension onto the surface of a
microscope slide. After allowing this film to air-dry, the smear is
heat-fixed by gently heating the slide with the flame of a Bunsen burner.
After heat-fixing, the smear is ready for staining.
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