Page 234 - The Veterinary Laboratory and Field Manual 3rd Edition

Microbiology 203

and ‘wing away’ at varying angles to give the the nature of the disease observed (clinical
appearance of Chinese lettering (Corynebacterium signs, epidemiology), list the causative agents
spp.). Sometimes a cuneiform bundle is the suspected and make a note of any previous or
characteristic form (that is, Mycobacterium spp.). current treatment. This information is impor-
Spirilla are rigid rods with a helical (corkscrew) tant because antibiotic treatment provided to
shape. They are motile by means of a tuft of fla- the animal before samples have been collected,
gella and are generally Gram-negative. Vibrios for example, may interfere with the culture of a
are short, curved, rigid rods shaped rather like pathogen even if the antibiotic therapy has not
a comma. They are motile usually by means been successful in eliminating it.
of a single flagellum and are generally Gram- Aseptic techniques should be used when
negative. Spirochaetes are also motile, and collecting and submitting specimens for micro-
possess an axial fibre around which the body is biological examination. To avoid contamination
twisted in a helical manner. Their length is usu- of samples they should be placed in suitable ster-
ally 10–20 µm and thickness 0.2–0.4 µm. The ile containers or transport media immediately
number of spirals varies with the species. Silver after collection. The skin and mucous mem-
impregnation is the staining method of choice branes of animals (and people) has a normal
for many of these organisms. flora of microbes which are usually of no clinical
Modern bacterial nomenclature (naming) is significance but which may overgrow pathogenic
based on genetic analysis of the chromosomal microbes if mixed with the sample. To reduce
material as compared with observational stud- the risk of sample contamination, sterile gloves
ies of the phenotypic characteristics. Molecular can be worn. The sample collection procedure
characterization has resulted in changes in the used will depend on the nature of the sample to
classification of some bacteria with subsequent be collected (see below). In each case use sterile
re-naming at the genus level, for example, or very clean, dry equipment. If there is going to
Pasteurella pestis, (the cause of bubonic plague or be a delay between collection and submission of
the ‘Black Death’) is now known as Yersinia pestis. samples they should be kept chilled in the refrig-
erator (4°C).

4.3 Sample collection, preparation
and submission Samples commonly collected

As outlined earlier, the type of sample submit- Prior to collecting samples the appropriate per-
ted for microbiological examination is varied. sonal protective equipment (PPE) should be
Correct collection and handling of samples worn especially in cases where zoonotic diseases
under field conditions is often difficult. As men- are suspected (see Chapter 1).
tioned earlier, to improve the chance of isolating Hair and skin samples are usually collected
the microorganism responsible for a disease for parasitology and fungal examination but
samples should be kept cool and transported may also be submitted for bacteriology. These
directly to the laboratory accompanied by a samples can be sent in a clean labelled plastic
completed sample submission form. An exam- bag, plastic pot or in a labelled paper envelope.
ple of a sample submission form is provided in Faecal samples for microbiological examina-
Appendix 2. Although different laboratories will tion should preferably be collected (with care)
have their own submission form, most of these directly from the rectum of the animal and sub-
have a space where the submitter can describe mitted in labelled plastic bags (double sealed),

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