a. General Structures.
(1) Cell wall. A cell wall is a layer of lipid and protein that encloses the
protoplasm of the cell giving rigidity to the bacterial shape.
(2) Cytoplasmic membrane. A cytoplasmic membrane is a thin semi
permeable membrane located directly beneath the cell wall, governing osmotic activity.
(3) Cytoplasm. The cytoplasm is the protoplasmic or vital colloidal material
of a cell; the site of metabolic activities.
(4) Genetic material. Genetic material is a circular, single-stranded DNA
diffused throughout the cytoplasm. It carries the genetic code of heritable traits and is
responsible for directing metabolism and replication of the cell. The bacterial cell does
not have a nuclear membrane or a well-defined nucleus.
b. Special Structures.
(1) Capsule. A capsule is relatively thick layer of mucoid polysaccharides
(slime layer) around a bacterium. A capsule serves as a defense mechanism.
(2) Flagellum. A flagellum is a protoplasmic strand of elastic protein
originating in the cytoplasmic membrane, and extending from the body of the cell. A
flagellum serves as an organ of locomotion. The arrangement of flagella (plural) is
peculiar to the species.
(3) Spore. A spore is a metabolically resistant body formed by a vegetative
bacterium, which is in a dormant state, to withstand an unfavorable environment. Only
bacilli form spores. The position and size of a spore within a bacillus is peculiar to the
species. Bacteria that are actively reproducing by fission do not produce spores
(4) Inclusion bodies. Inclusion bodies are vacuoles of reserve or waste
materials contained within the cytoplasm.
Ribosomes. Ribosomes is a site of protein production.
IDENTIFICATION OF BACTERIA
Since there are several thousand species of bacteria, it would be impossible to
identify them on the basis of appearance alone. Therefore, the bacteriologist employs a
wide variety of techniques, based upon known characteristics of specific bacteria, to
arrive at the identity of a given specimen. The following characteristics, which are used
frequently as terms of reference, assist the microbiologist in the positive identification of
bacteria as well as in eliminating them from consideration.