INTRODUCTION TO MICROBIOLOGY
THE CHARACTERIZATION, CLASSIFICATION AND
IDENTIFICATION OF MICROORGANISMS
(Study Guide)
INDEX: 1. Major Characteristics of Microorganisms
•Morphological Characteristics •Chemical Characteristics •Cultural
Characteristics • Metabolic Characteristics •Antigenic Characteristics
•Genetic Characteristics •Pathogenicity •Ecological Characteristics
2. Microbial Classification, Nomenclature, and Identification
•Classification •Nomenclature •Identification •The Past and Present
State of Bacterial Taxonomy
Major Characteristics of Microorganisms:
The major characteristics of microorganisms fall into the following categories:
1. Morphological characteristics- Cell shape, size, and structure; cell arrangement
occurrence of special structures and developmental forms; staining reactions; and
motility and flagellar arrangement.
2. Chemical composition- The various chemical constituents of the cells.
3. Cultural characteristics- Nutritional requirements and physical conditions re
quired for growth, and the manner in which growth occurs.
4. Metabolic characteristics- The way in which cells obtain and use their energy,
carry out chemical reactions and regulate these reactions.
5.Antigenic characteristics- Special large chemical components (antigens) of the
cell, distinctive for certain kinds of microorganisms.
6. Genetic characteristics- Characteristics of the hereditary material of the cell
(deoxyribonucleic acid, or DNA); and occurrence and function of other kinds of
DNA that may be present, such as plasmids.
7. Pathogenicity- The ability to cause disease in various plants or animals or even
other microorganisms.
, 8. Ecological characteristics- Habitat and the distribution of the organism in nature
and the interactions between and among species in natural environments.
Morphological characteristics
Unlike other kinds of microbial characteristics, determination of morphology
features usually requires studying individual cells of a pure culture. Microorganisms
are very small and their size is usually expressed in micrometres (One μm is
equivalent to 0.001 millimetre (mm) or about 0.00004 in; consequently, routine
examination of microbial cells requires the use of a high-power microscope, usually
at a magnification of about 1,000 diameters.
The use of electron microscopy provides magnification of thousands of diameters
and makes it possible to see fine details of cell structure.
Chemical composition
Microbial cells consist of a wide variety of organic compounds. When cells an
broken apart and their components subjected to chemical analysis, each kind of
microorganism is found to have a characteristic chemical composition. Both
qualitative and quantitative differences in composition occur among various
species. For example, the occurrence of lipopolysaccharide in cell walls is
characteristic of Gram-negative bacteria but not Gram-positive bacteria; on the
other hand, many Gram-positive bacteria have cell walls that contain teichoic acids,
compounds not found in Gram-negative bacteria. Fungal and algal cell walls are
very different in composition from those of bacteria. A major distinction among
viruses is made on the basis of the kind of nucleic acid they possess namely
ribonucleic acid (RNA) or deoxyribonucleic acid (DNA).
Cultural characteristics
Each kind of microorganism has specific growth requirements. Many
microorganisms can be grown in or on a culture medium (a mixture of nutrients
used in the laboratory to support growth and multiplication of microorganisms)
Some microorganisms can grow in a medium containing only inorganic com
pounds, whereas others require a medium containing organic compounds (amino
acids, sugars, purines or pyrimidines, vitamins, or coenzymes). Some require
complex natural substances (peptone, yeast autolysate, blood cells, or blood serum),
and some cannot as yet be grown in an artificial laboratory medium and can be
THE CHARACTERIZATION, CLASSIFICATION AND
IDENTIFICATION OF MICROORGANISMS
(Study Guide)
INDEX: 1. Major Characteristics of Microorganisms
•Morphological Characteristics •Chemical Characteristics •Cultural
Characteristics • Metabolic Characteristics •Antigenic Characteristics
•Genetic Characteristics •Pathogenicity •Ecological Characteristics
2. Microbial Classification, Nomenclature, and Identification
•Classification •Nomenclature •Identification •The Past and Present
State of Bacterial Taxonomy
Major Characteristics of Microorganisms:
The major characteristics of microorganisms fall into the following categories:
1. Morphological characteristics- Cell shape, size, and structure; cell arrangement
occurrence of special structures and developmental forms; staining reactions; and
motility and flagellar arrangement.
2. Chemical composition- The various chemical constituents of the cells.
3. Cultural characteristics- Nutritional requirements and physical conditions re
quired for growth, and the manner in which growth occurs.
4. Metabolic characteristics- The way in which cells obtain and use their energy,
carry out chemical reactions and regulate these reactions.
5.Antigenic characteristics- Special large chemical components (antigens) of the
cell, distinctive for certain kinds of microorganisms.
6. Genetic characteristics- Characteristics of the hereditary material of the cell
(deoxyribonucleic acid, or DNA); and occurrence and function of other kinds of
DNA that may be present, such as plasmids.
7. Pathogenicity- The ability to cause disease in various plants or animals or even
other microorganisms.
, 8. Ecological characteristics- Habitat and the distribution of the organism in nature
and the interactions between and among species in natural environments.
Morphological characteristics
Unlike other kinds of microbial characteristics, determination of morphology
features usually requires studying individual cells of a pure culture. Microorganisms
are very small and their size is usually expressed in micrometres (One μm is
equivalent to 0.001 millimetre (mm) or about 0.00004 in; consequently, routine
examination of microbial cells requires the use of a high-power microscope, usually
at a magnification of about 1,000 diameters.
The use of electron microscopy provides magnification of thousands of diameters
and makes it possible to see fine details of cell structure.
Chemical composition
Microbial cells consist of a wide variety of organic compounds. When cells an
broken apart and their components subjected to chemical analysis, each kind of
microorganism is found to have a characteristic chemical composition. Both
qualitative and quantitative differences in composition occur among various
species. For example, the occurrence of lipopolysaccharide in cell walls is
characteristic of Gram-negative bacteria but not Gram-positive bacteria; on the
other hand, many Gram-positive bacteria have cell walls that contain teichoic acids,
compounds not found in Gram-negative bacteria. Fungal and algal cell walls are
very different in composition from those of bacteria. A major distinction among
viruses is made on the basis of the kind of nucleic acid they possess namely
ribonucleic acid (RNA) or deoxyribonucleic acid (DNA).
Cultural characteristics
Each kind of microorganism has specific growth requirements. Many
microorganisms can be grown in or on a culture medium (a mixture of nutrients
used in the laboratory to support growth and multiplication of microorganisms)
Some microorganisms can grow in a medium containing only inorganic com
pounds, whereas others require a medium containing organic compounds (amino
acids, sugars, purines or pyrimidines, vitamins, or coenzymes). Some require
complex natural substances (peptone, yeast autolysate, blood cells, or blood serum),
and some cannot as yet be grown in an artificial laboratory medium and can be
