Page 255 - The Veterinary Laboratory and Field Manual 3rd Edition

224 Susan C. Cork and Roy Halliwell

brial antigens (K88, K99, F41, 987Por F165)
is usually required and/or the enterotoxin of
enterotoxigenic strains.
• Specific Salmonellae (calf, poultry patho-
gens). Various subgroups (I, II, IIIa, IIIb, IV,
V and VI).
• Specific Clostridium sp. Numerous strains with
different toxins identified, that is, Clostridium
perfringens types A, B, C, D and E (rare).
• Streptococci (Lance field grouping of haemo-
Figure 4.11d API strip card used to illustrate the lytic streptococci). Streptococci of groups A,
typical biochemical reactions of ‘type’ cultures rep- B and C are the most regularly encountered
resentative of bacterial species obtained from the in veterinary medicine.
American Type Culture Collection. See also Plate 10.
Some panels of antisera are available commer-
cially but larger laboratories may prepare their
bacteriology laboratory if there is ready access own. It is quite common practice for veterinary
to true type cultures and access to required typ- laboratories to send Salmonellae and E. coli iso-
ing sera. The latter can be done by generating lates to human health laboratories to further
type-specific antibodies in laboratory rabbits characterization and to check whether or not
but this requires appropriate training and facili- animal strains are also found in humans.
ties. Commercial antisera are also available. In
most cases strains of bacteria that require sero-
typing are sent to specialist reference centres quantitative tests –counting bacteria
where strains can be compared with archived
type cultures. Strain identification is some- In some situations, it is necessary to assess the
times necessary because some bacteria such number as well as the type of bacteria present
as Escherichia coli have a range of serotypes and in a sample; this is particularly important in
only some are pathogenic. Strain characteriza- water and milk samples as part of quality con-
tion can also be important for survey work and trol programmes. It is accepted that in some
for epidemiological studies. Sero-typing tests are water samples there will be some bacterial
usually performed by mixing a specific antise- contaminants but in most cases there will be
rum (containing antibody) with a pure sample of guidelines for what is acceptable, for example,
the isolate under test (antigen) on a microscope coliform count in town water supplies. There are
slide. If the antigen and antibody are specific to a range of methods and some kit tests available
one another ‘agglutination’ (clumping) will take to estimate the number of bacteria present in a
place. A more detailed description of the agglu- given amount of sample, one simple method is
tination test is given in Chapter 6. outlined in Figure 4.12. In this method, serial
The serological typing capability in a larger dilutions are made of a sample. Samples are
regional laboratory may include confirmation of plated out using a plate flooding technique.
specific serotypes of the following organisms. A plate with 30–100 colonies is usually chosen for
counting and the number of bacteria in the initial
• Specific E. coli (pig, calf pathogens) various samples can then be calculated by multiplying
serotypes. Demonstration of significant fim- by the dilution used for the plate counted. Other

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