Page 247 - The Veterinary Laboratory and Field Manual 3rd Edition

216 Susan C. Cork and Roy Halliwell

bacterial isolates of interest. Next, preliminary the purity plate(s) a suspension of bacteria can
biochemical tests will need to be performed. be prepared for inoculation of secondary media
Further biochemical tests and specialist media and biochemical reagents. Detailed biochemical
are usually necessary to identify the organisms tests should not be performed on mixed cultures
to family and genus level. Before this can take as the results will be impossible to interpret.
place, a sub-culture is made of each colony of Broths made from purity plates can be used
interest to produce a ‘purity’ plate (see Figure for a wide range of biochemical tests and can
4.8). These plates are incubated further until a also be used to determine the antibiotic sen-
good pure growth of bacteria is present. From sitivity of the suspect pathogen(s). Table 4.2b

Figure 4.9 Classification chart according to staining reaction and cellular morphology of common bacteria
of veterinary importance.
Note: *The Enterobacteriaceae include Escherichia coli, Salmonellae, Yersinae and other bacteria that are frequently
isolated from the intestinal tract of healthy and sick animals. The staining characteristics and appearance under the
microscope are similar for most bacteria in this group so it is usually necessary to perform a range of biochemical tests
to identify the bacteria present in a sample.

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