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General Microbiology. Group 1 Chimi Seldon Dorji Sangay Wangmo Tek Bahadur Powdel Sang Dorji Tamang Hem Raj Subba Norbu ( 14/04/2010). Definition Study of living organism of microscopic size

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general microbiology

General Microbiology

Group 1

Chimi Seldon Dorji

Sangay Wangmo

Tek Bahadur Powdel

Sang Dorji Tamang

Hem Raj Subba

Norbu ( 14/04/2010)



  • Study of living organism of microscopic size

Eg.:Bacteria, fungi, algae, protozoa, and the infectious agents called viruses.

  • Concerned with their form, structure, reproduction, physiology, metabolism and classification
  • Study of their distribution in nature, relationship to each other and to other living organisms, effects on human beings, animals and plants


  • Some are beneficial while others are detrimental

Example: Some micro-organisms are involved in making of yogurt, cheese and wine, in production of penicillin, interferon and alcohol, processing of domestic and industrial wastes

  • On the other hand they can cause disease, spoil food and deteriorate materials like iron pipes, glass lenses and wood pilings.
  • Unicellular and multi cellular
  • Single cell performs all the life processes
  • higher organisms are composed of many cells arranged in tissues and organs that perform specific functions

Branches of Microbiology

  • Bacteria
  • Virus
  • Fungi: Molds
  • Fungi: Yeasts
  • Protozoa
  • Algae

(1) Bacteria

(2) Viruses


(3) Fungi: Molds

  • (4) Fungi: Yeasts

(5) Protozoa

  • (6) Algae

Microbial Classification


  • bringing order to the bewildering variety of organism in nature.
  • Pure culture- a population of micro-organism
  • a culture consist of single kind of micro organism(one living species), regardless of the number of individuals, in an environment free of other living organism is called pure culture.


  • (1) Virus
  • The Baltimore classification
  • Classification of virus into families depending on their type of genome (DNA, RNA, single-stranded (ss), double-stranded (ds) etc.) and their method of replication.
  • (2)Bacteria
  • shape, either gram positive or gram negative, based on whether they take up the gram stain that is commonly used to make them easier to see under the microscope. live in the presence of oxygen (aerobic) or require the absence of oxygen (anaerobic).

Gram Positive Bacteria (e.g., Staphylococcus aureus)

The walls of gram positive bacteria have more peptidoglycans (the large molecular network of repeating disaccharides attached to chains of four or five amino acids) than do gram-negative bacteria. Thus, gram-positive bacteria retain the original violet dye and cannot be counterstained.

  • Gram Negative Bacteria(e.g., Escherichia coli )
  • have thinner walls, containing an outer layer of lipopolysaccharide, which is disrupted by the alcohol wash. This permits the original dye to escape, allowing the cell to take up the second dye, or counterstain. Thus, gram-positive bacteria stain violet, and gram-negative bacteria stain pink.

Main Requirements for bacterial culture

  • Moisture
  • Warmth and Temperature
  • Time
  • pH level
  • Oxygen
  • Competition
  • How to grow/culture bacteria?
  • Things required
  • Agar
  • Cooking thermometer
  • Small cooking pot
  • Petri dishes
  • Sterile cotton swabs
  • Warm dark cupboard
  • Book on bacteria cultures

Step 1

Mix the agar according to the manufacturer's instructions. Agar is a bit like Jell-o and the ingredients will need to be heated to precise temperatures. Make certain that you have a clean cooking thermometer handy.

Step 2

Open a petri dish and pour just enough agar into the dish to cover the bottom completely. Put the lid back on immediately and set the dish aside until the agar firms. Fill each dish the same way, never leaving the top of the dish off any longer than absolutely necessary. Once the agar hardens you may store the dishes in the refrigerator upside down to avoid the possibility of any airborne bacteria getting into the dishes.

  • Step 3
  • Remove the petri dishes from the refrigerator only when you are ready to use them. Open your sterile cotton swab package and rub the cotton swab on a surface you wish to test for bacteria, such as a countertop. Open a petri dish and rub your swab gently across the surface of the agar in an "S" pattern. Close the lid on the petri dish.

Step 4

  • Set the dish in a warm dark cupboard for three to four days Step 5

Remove the dish from the cupboard. There is no need to open the dish. Observe the bacteria colonies through the top of the dish. Record their color, shape and anything else distinguishing. Look in a bacteria book or on the Internet for illustrations that match the bacteria you have cultured.

Step 6

Destroy your cultured bacteria once you have identified it. Pour 1 tbsp. of bleach into the petri dish and then seal the dish closed with packing tape, put the dish in a baggie, seal it and throw away.


Scope of Microbiology

1.Medical biology

Causative agents of disease; diagnostic procedures; diagnostic procedures for identification of causative agents, preventive measures

2.Aquatic Microbiology

Water purification, microbiological examination, biological degradation of waste,ecology


Contamination and soilage; dissemination of diseases

4.Food microbiology

Food preservation and preparation; foodborne diseases and their prevention


5.Agricultural microbiology

Soil fertility, plant and animal diseases

6.Industrial microbiology

Producton of medicinal products such as antibodies and vaccines; fermented beverages; industrial chemicals, production of proteins and hormones by genetically engineered microorganisms.


Exploration for life in the outer space

8.Geochemical microbiology

Coal, mineral and gas formation; prospecting for deposits of coal, oil, and gas; recovery of minerals from low-grade ores