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Bacteriology is a field of microbiology which deals with the study of bacteria. This field also includes the study of the structure, specific functions and the corresponding actions of the bacteria on living organisms. There are specific characteristics that classify microorganisms into bacteria.

Bacteria have the following characteristics:

1.They are subdivided into 3 phenotypic categories namely:

1.1.Gram-positive with cell walls. These are bacteria that are colored violet when stained because they absorb the initial stain.

1.2.Gram-negative with cell walls. These are bacteria that do not absorb the initial stain but the secondary stain instead and are colored pink.

1.3. Without cell walls. These are the bacteria that do not have protective out covering.

2. Bacteria could also be classified through their cell morphology. They have 3 basic types:

2.1. Spherical or round which are called cocci.

They usually stain gram-positive (take up the initial stain- crystal violet) and may occur in pairs (diplococci), or in chains (streptococci), or in clusters (staphylococci). There are exceptions to the rule with regards to the staining methods; like the Neisseria species, which are pink because they are gram-negative.

2.2. Rectangular or rod-shaped which are called bacilli

They may occur singly, in pairs or in chains. They usually stain gram-negative (take up the counter stain safranin). There are exceptions to the rule too; one is Bacillus anthracis which is gram positive.

Short rounded rods are called coccobacilli. The family Enterobacteriaceae is examples of bacilli

2.3.Spiral or curved shaped which are called spirilla. Examples of these are the Vibrio species. The spiral shaped microorganisms are called spirochetes. One example is the causative agent of syphilis, Treponema pallidum, which is coiled tightly.

2.4.There are certain species which could not be classified through grams staining because their waxy cell wall could not take up the gram stain, but only through the Acid fast stain (Uses carbol fuchsin and heat). Examples of these are the Mycobacterium species like Mycobacterium tuberculosis, the causative agent of tuberculosis.

3.Bacteria could also be classified by their motility:

3.1.Motile they could move through the use of flagella

(whip like projections), pseudopods (blunt projections), cilia (hair like projections)

3.2.Non-motile they stay immobile and stationary because they lack the means of locomotion.

4.Bacteria could be classified according to their pathogenicity

4.1.Pathogenic

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