Tuesday, 3 June 2014


• What are bacteria? List down some characteristics of bacteria.

Bacteria are members of a large group of unicellular micro-organisms which have cell walls but lack organelles and an organised nucleus, including some which can cause disease.

Bacteria have three typical shapes- rod (bacillus), round (coccus), and spiral (sprillum). The cytoplasm and plasma membranes of most bacteria are surrounded by cellulose cell wall. Most bacteria, chiefly the bacillus and spirillum forms, are motile. They swim around with whip-like movements of the flagella. Other bacteria have rigid and rod like protuberances names pili that serve as tethers.

•How can bacteria be identified?

Gram Staining.

Bacteria is mostly identified by Gram Staining. This technique, is named after pioneering Danish micro-biologist. The procedure is as it follows:

1. The bacteria are stained with purple dye (Crystal Violet). Most bacteria are then stained red.

2. The bacteria are stained again with Potassium Iodine.

3. The bacteria are then washed with alcohol. Those bacteria that retain the dye after washing are known as Gram Positive bacteria. Those that loose the dye are named Gram Negative bacteria.

4. The bacteria are further stained with a pink dye (Safranin). Gram Negative bacteria will go pink after this dyeing, whereas Gram Positive bacteria will remain purple, from the original purple dye.

Zhiel-Neelsen Staining.

This technique is also referred to as acid-fast staining. This technique is necessary because some bacteria, notably all Mycobacteria, have waxy coats on their cell walls that prevent them taking in the dye from the Gram Staining procedure. As a part of the acid-fast staining process, detergents are applied to remove this waxy coat.

1. The bacteria are stained with hot Carbol-Fuschin, a red dye which contains detergents. All bacteria are then stained red.

2. The bacteria are washed with acid alcohol. Those bacteria that retain the red dye are known as acid-fast bacteria.

3. The bacteria are then stained with Methylene Blue, a blue dye. Those bacteria that retain the red dye from the original stain are known as acid-fast bacteria, all others go blue.

•Name three common bacteria and places where they are commonly found.

Three common bacteria are:


Bacilli are rod shaped bacteria that look like cylinders, arranges singly or in chains. Bacillus, areobic or anaerbic, are  widely found in soil and water.


Spirilla are a subgroup of bacteria with a more rigid spiral shape. These bacteria are generally found in water bodies that contain stagnant water. Therefore they are found in ponds and lakes as they contain unmoving and still water, allowing fro growth of spirillum.


Cocci are round, spherical shaped bacteria. They can occur as single bacterium or be arranged in a pair, chain or cluster of bacteria depending on which type of coccus it is. Cocci are found mostly in numerous different places with neutral alkalinity such as the mouth, nose and throat.

•Are all bacteria harmful? If not, name some bacteria beneficial to humans.

No, not all bacteria are harmful. Beneficial bacteria include probiotics, which are micro-organisms that some have claimed provide health benefits when consumed. The term probiotic is currently used to name ingested micro-organisms associated with beneficial effects to humans and animals. 

Another bacteria that is beneficial is Lactobacilli, a genus of Gram Positive facultative anaerobic rod-shaped bacteria. They are a major part of the lactic acid bacteria group, named such as because most of its members convert lactose and other sugars to lactic acid.

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