Page 233 - The Veterinary Laboratory and Field Manual 3rd Edition

202 Susan C. Cork and Roy Halliwell

Fimbriae or pili that may be located centrally, sub-terminally or
terminally. The size of the endospore may be
Fimbriae or pili are small filaments found on the sufficiently large to cause the walls of the bacte-
surface of some bacterial cells. They measure up rium to bulge (Figure 4.4). Spores are relatively
to 1.5 µm in length and 0.5–0.8 µm in width. resistant to extremes of physical and chemical
Most fimbriate bacteria have the property of environments including high temperatures, des-
adhering to red blood cells and to tissues which iccation and disinfection. Under dry conditions
may increase their pathogenicity. A mixture of or in soil, spores may remain viable for many
fimbriate bacteria and red blood cells, especially years. When conditions improve, each spore
red cells derived from the chicken or the guinea will develop into one viable bacterium. The pro-
pig results in easily visible haemagglutination duction of resistant spores allows B. anthracis
(see Chapter 6). (the cause of anthrax) to contaminate land for
Capsules, flagella and pili are antigenic (that prolonged (> 100 years) periods.
is, they stimulate an immune response) and
if inoculated into an animal will stimulate the
production of specific antibodies. This is the Morphology and classification
principle used to produce antisera for bacterial
sero-typing tests (see Chapter 6).
The original names given to bacteria often
reflected their microscopic appearance, that
Endospores is, the shape of individual organisms and their
distribution in relation to one another after divi-
When some species of bacteria (that is, sion (fission) takes place. Bacteria can be ovoid
Clostridium spp., Bacillus anthracis) are in an envi- or spheroid (coccus), rod like or cylindrical
ronment unfavourable for multiplication they (bacillus), curved (vibrio), spiral-shaped (spi-
will develop endospores. These spores are dor- rillum) or coil-shaped (spirochaete). The shape
mant forms of the organism capable of survival and the staining characteristics of bacteria can
for long periods of time under adverse condi- assist identification but experience is required
tions. Each bacterium develops one endospore
to distinguish bacteria visually and in most cases
further tests are necessary. When bacteria divide,
the daughter cell may remain attached to the
parent cell (but separates before fission occurs
again) resulting in pairs of cocci (diplococci).
If fission continues while they remain attached
they form chains (streptococci) but if the divi-
sion is not in one direction, random clumps of
cocci occur (staphylococci). Sometimes the cocci
remain in pairs for one further division and a
regular aggregate of four cocci is formed (tetra-
cocci). Most cocci are Gram-positive. The bacilli,
or rods, do not form as many groupings as the
Figure 4.4 Microscopic appearance of rod shaped cocci, but include the diplobacilli and streptoba-
bacteria as seen using an oil immersion lens (1000×). cilli (pairs and chains). After fission, rods will
Gram stain. Clostridium novyi. Gram-positive rods take different positions – the daughter cell, for
with oval subterminal spores. example, can remain attached to the parent cell

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