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 cell covering.
2. Bacteria could also be classified through their cell morphology. They have 3 basic types:
2.1. Spherical or round shaped 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 regard 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 an example 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 gram 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
these are diseases causing because they have capsules, pili and enterotoxins, like Bacillus anthracis- causes anthrax
Clostridium botulinum causes botulism, and many others.
4.2.Non-pathogenic these do not cause any disease. Examples are
Lactobacillus in the stomach, Staphylococcus in the skin, etc.
5.Bacteria could be classified according to their oxygen requirement into:
5.1.Obligate aerobe those that need oxygen to survive.
5.2.Microaerophile those that could survive with little amount of oxygen.
5.3.Facultative anaerobe those that could survive in non-oxygenated and oxygenated environment.
5.4.Aerotolerant anaerobe those that are facultative anaerobe but could grow in the presence of oxygen.
5.5.Obligate anaerobe those that are incapable of surviving in the presence of oxygen.
5.6.Capnophiles they need elevated concentrations of carbon dioxide.
6.They could be cultured in agar media to form colonies (clumps of bacteria) and stained through differential stains and examined for their morphological characteristics. This will help clinicians identify the bacteria, and consequently the disease present in the patient.
7.Culture and sensitivity could also be performed to determine what drug could cure the disease.
The bacteria are made to multiply by culturing them and then are testing them against antibiotics, whether they are resistant or sensitive to the drugs.
8.In order to survive, bacteria also need these vital substances like carbon, nitrogen, hydrogen, oxygen, sulfur, phosphorus, potassium, calcium.
Bacteriology is a dynamic and rapidly growing science. As long as the world continues to exist, bacteria would also continue to proliferate and contribute - positively or negatively - towards the eco-system and our human existence.
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