Page 239 - The Veterinary Laboratory and Field Manual 3rd Edition

208 Susan C. Cork and Roy Halliwell

4 De-colourize with acetic acid for 30 s. turnaround times for the different diagnostic
5 Wash the slide in water. tests provided by the laboratory.
6 Counter-stain with methylene blue (leave for
30 s).
7 Wash the slide again in water and leave to dry. Media and special requirements

When dry, the slide can be examined under Oxygen requirements
the microscope using the oil immersion lens Most bacteria grow well under ordinary condi-
(10×100×). Acid-fast bacteria will stain pink to tions of oxygen tension (aerobes). However,
red, the background will be blue.
some bacteria grow better without oxygen
(anaerobes). Organisms that can grow in reduced
oxygen tension are classified as microaerophilic.
4.4 Culture and identification of This is usually achieved in the laboratory by
bacteria
replacing oxygen in the incubating atmosphere
with carbon dioxide.
The successful culture of microorganisms on Anaerobic conditions can be achieved in a
artificial culture media (see Figure 4.5) is depen- number of ways including the following:
dent upon a number of very important factors
including the following:
1 adding an oxygen reducing substance to the
medium
1 the condition (and degree of contamination) 2 inoculating the specimen into the deeper
of the specimen before attempting culture layers of solid media or under a layer of oil
2 the nutritive elements available in the culture which covers a liquid media
medium 3 incubation in an atmosphere devoid of free
3 level of available oxygen oxygen, for example, anaerobic jars.
4 the degree of moisture present
5 the pH of the medium For anaerobic culture, it is common practice
6 the incubation temperature to use an anaerobic jar along with the ‘GasPak’
7 the sterility of the medium.
system (Figure 4.6). To achieve anaerobic con-
ditions the GasPak system comes with a foil
2
Laboratory animals have been used for the iso- packet containing a mixture of chemicals to
lation of bacteria but better techniques that do which water is added. The packet of chemicals
not use laboratory animals are now preferred for is then placed in the anaerobic jar along with an
diagnostic testing. Although laboratory animals anaerobic indicator to check that true anaerobic
may still be used in research and for the pro- conditions have developed. Full instructions and
duction of biological products this will not be information are given with the GasPaks. GasPaks
discussed further here. to provide an enhanced carbon dioxide level are
A point to consider when performing micro- also available commercially.
biological procedures is that they can be time The addition of a catalyst (for example, pal-
consuming and that ‘turnaround’ and reporting ladiumized alumina) may also be required to
times for culture results are often longer than initiate the reaction. The resulting reactions are
for tests in other sections of the laboratory. as follows:
Before, or at the time of, sample submission the
submitter should be made aware of the likely

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