THE NATURE OF BACTERIA BY DR. SHNYAR HAMID BACTERIAL STRUCTURE Bacteria are the smallest and most versatile independently living cells known. They are the first and
smallest organism capable of independent existence. In the wider microbial world, their prokaryotic cell plan is still considered to provide the minimum possible size for an independently reproducing organism Individuals of different bacterial species that colonize or infect humans range from 0.1 to 10 m
(1 m 106m) in their largest dimension. Most spherical bacteria have diameters of 0.5 to 2 m, and rod-shaped cells are generally 0.2 to 2 m wide and 1 to 10 m long The small size and nearly colorless nature of bacteria require the use of stains for visualization with a light
microscope or the use of electron microscopy. The major morphologic forms are spheres, rods, bent or curved rods, and spirals. Spherical or oval bacteria are called cocci (singular: coccus) and are typically arranged in clusters or chains. Rods are called bacilli (singular: bacillus) and may be straight or curved. Bacilli that are small and pleomorphic to
the point of resembling cocci are often called coccobacilli. Whatever the overall shape of the cell, the 1-m size could not accommodate eukaryotic mitochondria, nucleus, Golgi apparatus, lysosomes, and endoplasmic reticulum in a cell that is itself only as large as an average mitochondrion.
The solution is the unique design of the prokaryotic bacterial cell. The major structures of the cell belong either to the multilayered envelope its appendages
to the interior core consisting of the nucleoid (or nuclear body) and the cytosol. The cytosol is analogous to the cytoplasm of eukaryotic cells, but because there is no nucleus it is not separated from the genetic material.
The general chemical nature of the bacterial design includes the familiar macromolecules of life (DNA, RNA, protein, carbohydrate, phospholipid) plus some unique to bacteria such as the peptidoglycan and lipopolysaccharide of bacterial cell walls. The smallness and simplicity of the bacterial design contribute to the ability of the cytosol to grow at least an order of
magnitude faster than eukaryotic cells, a significant feature in producing disease. Microbiological techniques are different in many ways when compared with other laboratory disciplines. Although results are not obtained in a short time, the time required to perform the test is very short.
Most of the techniques are simple, yet requires a great deal of theoretical background to be correctly interpreted. For this reason, each laboratory exercise was supplemented with the theory behind it. GENERAL VIEW ON THE PARAMETERS USED IN THE PROCESS OF
MICROORGANISM IDENTIFICATION A. CULTURAL CHARACTERISTICS In clinical terms, it is the shape, size, color, elevation and other characteristics of the colony formed on the culture plate. In taxonomy, it includes the nutrient requirements for the growth of the organism
and the physical factors such as temperature, pH and the incubation period. These factors are used to identify certain pathogenic species but less commonly used in routine procedures. The cultural characteristics of a microorganism usually vary depending on the media used and many other factors. B. MORPHOLOGY AND STAINING
This includes the microscopic appearance of a stained preparation of the organism. Useful information to be taken into account, are the size of the individual cells, cell shape and arrangement and staining reaction if differential staining procedures is used.
EXAMPLE: A gram stained film prepared from a pure culture of certain microorganism shows the following: -Small spherical cells "Cocci" -Arranged in clusters -Gram-positive = violet in color Some laboratories which have a little facility could give the report of a microbiological examination of a clinical specimen just by
stating their morphological characteristics and the sensitivity testing results. C. BIOCHEMICAL CHARACTERISTICS Frequently, the identity of a species requires detailed knowledge of its biochemical activities, since other characteristics are not sufficiently distinctive or differential.
For example, the bacterium Escherichia coli, a normal inhabitant of our intestinal tract, is indistinguishable microscopically from Salmonella typhi, the bacterium that causes typhoid fever. However, if these two bacteria are examined for their metabolic (or biochemical) characteristics, they are found to be very different and distinguishable on this basis. Numerous laboratory techniques are available for
the characterization of microorganisms. In general, the microorganism is grown in the presence of a specific substrate, after which the culture is examined to determine what chemical changes have taken place. This subject will be discussed in details.
D. SEROLOGICAL CHRACTERISTICS Sometimes, to identify a species as E. coli is insufficient, for the reason that some strains of this organism are non-pathogenic and others are highly associated with diseases. Serological testing in such case will identify the exact strain number based on testing against prepared specific antisera. In-Vivo serological tests (skin tests) are of great value in the diagnosis of
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