Some Common Bacteria

1. Bacillus subtilis:

Characters:

1. It is rod shaped bacterium commonly known as hay bacillus.

2. Endospore formation is very common.

3. It is commonly found in decomposing organic matters.

4. It produces an antibiotic called subtilin.

5. It is non-motile and Gram-positive.

6. It produces large quantity of extracellular hydrolytic enzyme “amylase.”

7. Bacterial amylase is used for the production of dextrins from starch.

8. Cell organization is prokaryotic type.

2. Clostridium:

Characters:

1. The members are Gram positive and rod shaped.

2. They form endospores, and the spores are more resistant to unfavourable conditions than vegetative cells.

3. Majority of the Clostridium species are non­pathogenic. However, C. perfringens causes fatal gas gangrene of wounds.

C. Botulinum, growing saprophytically in the absence of air, produces the poisonous toxin of botulinal poisoning.

5. Tetanus is caused by Clostridium tetani (Fig. 127).

6. Due to the presence of endospores, the cells are usually swollen.

3. Lactobacillus:

Characters:

1. It is widely distributed in dairy products, silage or stored green cattle food and manure.

2. Lactobacillus casei rods are generally long and slender (Fig 128A).

3. These are non-motile and Gram positive bacteria.

4. They are generally anaerobic and ferment carbohydrates to lactic acid.

5. These bacteria are non-spore producing, and divide by binary fission.

6. They are very important in cheese ripening.

7. L. acidophilus is useful in making acidophilus buttermilk. It has been associated with dental caries.

4. Rhizobium:

Characters:

1. It is found in the root nodules of clover, alfalfa, lentils, beans, peas, soybeans and several other leguminous plants.

2. It is capable of fixing the atomospheric nitrogen.

3. It actually causes the formation of nodules on the roots of legumes where it lives symbiotically.

4. Its rods are small.

5. It is motile when young (Fig. 128B).

6. It is aerobic and Gram negative.

7. Its cells utilize glucose and sometimes other sugars with little or no production of organic acids.

8. Its cells are non-spore producing.

5. Streptococcus:

Characters:

1. It is a chain shaped bacterium.

2. The cocci are round in shape.

3. These are non-motile and Gram+ve bacteria.

4. The cellular organization is prokaryotic type.

5. Species are saprophytic and pathogenic.

6. It is important in souring of milk (S. lactis).

7. S. salivaris is common in the mouth and nose of human beings.

8. Streptococcus pyogenes is pathogenic, causing wound infections, childbed fever, scarlet fever, etc.

9. S. agalactiae causes chronic mastitis in approximately 20% of the milk cows.

10. S. cremoris develops aroma and flavor in the creams.

11. S. faecalis occurs in human intenstine and helps in food poisoning.

6. Staphylococcus:

Characters:

1. Cells are arranged in plates or irregular masses.

2. Staphylococcus aureus is a common inhabitant of human skin, mucous membrane, throat and in post­nasal discharges of persons recovering from cold.

3. It causes the food poisoning in man and may also be the cause of pimples, absceses and infection of wound.

4. It is also the cause of bovine mastitis, which is an inflammatory disease of the udder.

5. The symptoms which are typical of Staphylococcus infection include nausea, vomiting, diarrhoea, acute prostration and abnormal cramps.

6. It also occurs commonly in bakeries and kitchen products, if they are not immediately refrigerated at a temperature of 4°C to 10°C.

7. Spirillum:

Characters:

1. These are the spiral shaped bacteria commonly called spirilli.

2 These are coiled and found in the soil and water.

3. They contain bacteriopurpurin and sulphur granules.

4. They are motile and move with their flagella.

5. Prokaryotic type of cell organization is present.