Q1. What are bacteria? List down some characteristics of bacteria.
Bacteria are prokaryotic microorganisms, typically a few micrometers in length. Bacterias have a number of shapes, ranging from spheres to rod to spirals. Bacteria were among the early few life forms to appear on Earth and present in most habitats, soil, water, acidic areas and even radioactive waste.

Q2. How can bacteria be identified?

1. Gram Staining
This technique is named after a pioneering Danish micro-biologist and works as follows:

  1. The bacteria are stained with a 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 is known as Gram Positive bacteria. Those that lose the dye is known as Gram Negative bacteria
  4. The bacteria are further stained with a pink dye(Safranin). Gram Negative bacteria will turn pink after dyeing, whereas Gram Positive bacteria will remain purple, from the original purple dye.

2. Ziehl-Neelsen Staining
This technique is also known as acid-fast staining. This technique is necessary because some bacteria, notably all Mycobacteria, have waxy coats around their cells that prevent them from taking in the dye from the Gram Staining procedure. As part of the acid-fast staining process, detergents are applied to remove the waxy coat.

  1. The bacteria are stained with hot Carbon-Fuchsin, a red dye that contains detergent. All bacteria are then stained red. 
  2. The bacteria are then 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 retains the red dye from the original dye from the original stain are acid-fast bacteria, the others turn blue.

Note: All Mycobacteria test positive using the Ziehl-Neelsen acid-fast stain test, i.e. all species of Mycobacteria stain red using this procedure. Thus, this procedure cannot be used to differentiate between species of Mycobacteria.

3. Genetic Testing
Staining techniques, such as described above, are useful for identifying the genus of a bacterium, but not for identifying the species of a bacterium, within a genus. To identify the bacterium, it's DNA is "multiplied" using the Polymerase chain reaction. This technique creates large numbers of copies of the DNA to be tested for the presence of target genetic sequence.

4. The IS900 insertion sequence
Recently discovered mycobacterial "insertion sequences" that are important in the IS900 and IS902 sequences. The IS900 sequence is unique to Mycobacterium paratuberculosis. The IS902 sequence is unique to Mycobacterium avium subspecies silvaticum. Even though Mycobacterium paratuberculosis and Mycobacterium avium* are very closely related, IS900 will test positive with Mycobacterium paratuberculosis but will test negative with Mycobacterium avium. 

Q3. Name three common bacteria and places where they are commonly found.
-Salmonella(Raw food)
-E. Coli(intestines)
-Norovirus(stool or vomit of infected person)

Q4. Are all bacteria harmful? If not, name some bacteria beneficial to humans.
No, not all bacteria are harmful.

Some bacteria that are beneficial to humans:
Probiotics- are live, lactic-acid producing microorganisms, and are found in the human digestive tract. It is widely used in clinical nutrition and complementary alternative medicine.
Lactobacillus Acidophilus- frequently used in yoghurt cultures.
Bifidobacterium Animalis- famed for it's ability to improve digestive regularity.

*Mycobacterium avium-complex group of genetically related bacteria belonging to the genus Mycobacterium


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