Page 230 - The Veterinary Laboratory and Field Manual 3rd Edition

Microbiology 199

sections for bacteriology, virology and mycol- one of the first people to describe cells, bacte-
ogy. There is also a supplementary section on ria, yeasts and a range of parasites. During the
molecular techniques used in the microbiology latter part of the 19th century the French sci-
laboratory. The emphasis is on the practical entist Louis Pasteur (1822–1895) demonstrated
aspects of sample handling, testing methods the role that microorganisms played in the pro-
commonly used in the district laboratory and the cesses of disease, fermentation and putrefaction
preliminary interpretation of results. (rotting). Numerous outstanding scientists have
added to our knowledge since then.
The majority of bacteria vary in size between
4.2 Introduction to bacteriology 0.003 mm and 0.005 mm (most viruses are
much smaller, Figure 4.1). To observe bacteria
Two hundred years ago factual knowledge of it is necessary to use a microscope with a mag-
microorganisms and their importance in dis- nification of 500× or 1000× (we usually use an
ease was limited. The smallest living organisms oil immersion lens with a 100×10× magnifica-
known were those that could be seen by the tion). Bacteria are single-celled organisms which
naked eye (lice, fleas, maggots and so forth). multiply by binary fission and, under optimum
In the 17th century, a Dutch merchant called growth conditions, are capable of dividing
Leuwenhoek (1632–1723) was the first to get an approximately every 20 min. Theoretically that
insight into the ‘invisible’ world of microorgan- means, after 24 h, one cell can produce a mass
isms. Leuwenhoek’s hobby was to grind down equal to many millions of times its original
and produce lenses from glass and by placing weight. This rarely occurs naturally but it can
one on top of another he produced a primitive happen under ideal laboratory conditions.
microscope. Leuwenhoek, with his insatiable The majority of bacteria isolated from ani-
scientific curiosity, used this microscope to mals are harmless or even beneficial. These
examine things around him, such as oil, drops are referred to as normal flora or commensal
of water, yeast, plants and body fluids and was bacteria. It is important to be familiar with the

Figure 4.1 The relative size of a red cell, a streptococcal bacterium,
a chlamydial agent and an adenovirus.

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