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Many
characteristic features are used in classifying
and identifying microorganisms. In general, these
characteristic features have been divided into
two major categories such as classical and molecular
characteristics. |
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Classical
characteristics |
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The classical
type of approaches such as morphological, physiological,
biochemical, ecological and genetic characteristics
have been widely employed to study microbial taxonomy
and it also provide phylogenetic information of
microorganisms. |
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Morphological
characteristics:- Morphological features
are important in microbial taxonomy for many reasons.
Morphology is easy to study and analyze both eucaryotic
and procaryotic microorganisms. Many different
morphological features are used in the classification
and identification of microorganisms. Some of
these features are cell size, cell shape, colonial
morphology, ultrastructural characteristics, staining
behavior, cilia and flagella, mechanism of motility,
color etc. |
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Physiological
and Metabolic characteristics:- |
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Physiological
and metabolic characteristics are very useful
because they are directly related to the nature
and activity of microbial enzymes and transport
proteins. Because proteins are gene products,
analysis of these characteristics provides an
indirect comparison of microbial genomes. Some
of the physiological and metabolic characteristic
features are carbon and nitrogen sources, cell
structure, energy sources, fermentation product,
nutritional type, growth temperature optimum and
range, luminescence, motility, osmotic tolerance,
oxygen requirements, pH optimum and growth range,
photosynthetic pigments, salt tolerance, sensitivity
to metabolic and antibiotics etc. |
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Ecological characteristics:- |
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Microorganisms
are well associated and growing in terrestrial
fresh water and marine environments. The taxonomically
important ecological properties are life cycle
patterns, the nature of symbiotic relationship,
the ability to cause decease in particular host
and habitat preference such as the temperature,
pH, oxygen and osmotic concentration. |
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Genetic
characteristics:- |
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Most eucaryotes are able to reproduce sexually,
hence genetic analysis has been of considerable
usefulness in the classification of these type
of microorganisms. However, procaryotic do not
produce sexually and chromosomal gene exchange
(through transformation and conjugation) is sometimes
useful in the classification of procaryotes. |
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Molecular
characteristics |
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The recent molecular
approaches such as comparison of protein, nucleic
acid base composition, and nucleic acid hybridization
and sequencing are the most powerful molecular
tools have been employed to study the taxonomy
of some microbial groups, especially important
for the procaryotic taxonomy. |
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Further, they are classified based on
their risk categories, |
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Harmless microorganisms (EFB class 1) |
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Micro-organisms
that have never been identified as causative agents
of disease in man and that offer no threat to
the environment. |
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| Low-risk
microorganisms (EFB class 2) |
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Micro-organisms that may
cause disease in man and might, therefore, offer
a hazard to laboratory workers. They are unlikely
to spread in the environment. Prophylactics are
available and treatment is effective. |
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Medium-risk
microorganisms (EFB class 3) |
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Micro-organisms that offer
a severe threat to the health of laboratory workers
but a comparatively small risk to the population
at large. Prophylactics are available and treatment
is effective. |
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High-risk
microorganisms (EFB class 4) |
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Micro-organisms that cause
severe illness in man and offer a serious hazard
to laboratory workers and people at large. In
general effective prophylactics are not available
and no effective treatment is known. |
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Environmental-risk
microorganisms |
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Micro-organisms that offer
a more severe threat to the environment than to
man. They may be responsible for heavy economic
losses. This group includes several classes, Ep
1, Ep 2, Ep 3, to accomodate plant pathogens.
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