CLINICAL LAB SCIENEC

CHAPTER 15: MICROBIOLOGY 391
In the Lab
BASIC MICROBIOLOGY PROCEDURES
MANUAL MICROBIOLOGY PROCEDURE #1
Specimen Setup for Isolation and Identification
Principles
Bacterial infections may be contracted from many sources, including
food, water, sexual practices, contact with dirty surfaces or equipment,
and directly from another human or animal. Coughing and
sneezing (which generate droplets and aerosols containing bacteria)
onto surfaces and contact between the hands and mucus membranes
are convenient routes for passing bacteria and other microorganisms
to others.
Typically, bacterial specimens are collected by physicians or
nurses and transported to the laboratory. Following collection of a
specimen with microbiological organisms, the first step in processing
it is to provide an environment (media) on which the organisms will
grow to numbers sufficient for identification and other testing, such
as antibiotic sensitivity procedures. Many bacteria will not survive
extreme heat or cold and should be inoculated on a nutrient media as
soon as possible. During collection of the sample, the sterile tube or
plated media may be inoculated directly with a bacterial specimen.
Unfortunately, it is easy to contaminate a specimen through careless
handling. Media that are designed to grow bacteria and fungi are
easily contaminated even by the air and the organisms in suspension
there.
The source of the culture and the type of organism suspected will
dictate the type of media on which the bacterial specimen is placed.
Growth of the organisms on the nutrient media is enhanced by conditions
close to those encountered in the human body. This is achieved
by using an incubator. A sufficient number of organisms must be
grown to make possible morphological studies and staining, the first
steps in organism identification.
A variety of solid and liquid media are available for meeting
the nutritive needs of bacteria and for growing them in numbers
that allow for their identification (Figure 15-3). Appropriate media
must be chosen for inoculating and streaking plates for isolation of
bacterial colonies. Specimens screening is based in part on the site from which
organisms were obtained, as certain organisms are more likely to be found in certain
anatomic regions of the body.
Safety Alert
The laboratory student or professional
must always be aware of and practice
personal safety when performing
microbiological procedures. Such
procedures require the handling of
viable organisms as part of the process
of accurately identifying and ensuring
the growth and survival of those
organisms. Some of the equipment
used in microbiological procedures is
also inherently dangerous, such as the
heated incinerator that sterilizes the
loops and needles used to inoculate
slides and agar plates.
Most laboratory-acquired infections
are acquired via the respiratory route
when treating patients and handling
specimens. To prevent this, it is
incumbent upon lab personnel to avoid
producing aerosols when incinerating,
centrifuging, or otherwise working
with samples. A variety of shields and
biological safety cabinets are designed
to minimize and help prevent the
production of aerosols. In addition to
respiratory precautions, disinfectants
should be used on a continuous basis
to prevent the hands from becoming
contaminated and then placed near a
mucus membrane such as the nose or
mouth.
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