BACTERIA by vijay sir

 

             Bacteria are free living, microscopic, unicellular organisms. These are capable of performing all essential functions of life,e.g. growth, metabolism, and reproduction.

Size of Bacteria :-

Bacteria are very small in size. The unit of measurement of bacteria is called micrometer (um).Bacteria generally measure 0.2 – 1.5 um in diameter and 3-5 um in length.The study of morphology of bacteria requires the use of microscopes.

Classification of bacteriology

Bacteria are classified as under :-

1. Cocci

2.Bacilli

3.Spirilla

4. Vibrio

5. Spirochaetes

6. Mycoplasmas

 Cocci –

          They are round or oval in shape.They exist in various patterns. Some cocci are gram positive and some are gram negative.

Types of coci –

1.Diplococci –

              They occur in pairs , e.g., pneumo cocci.

2.Streptococci –

                They occur in chain.

3. Staphylococci –

                  They occur in clusters.

4. Tetrads –

            They occur in four.

Bacilli -

          They are of rod or stick shape . In some of the bacilli the length may be equal to the width . Some bacilli are gram positive and some are  gram negative, some are acid fast bacilli.

Types of bacilli

1. Gram positive bacilli :

 A . Spore forming anaerobic bacilli ,e.g . clostridium .

 B. Spore forming aerobic bacilli ,e.g. salmonella.

2. Acid fast bacilli , e.g. Mycobacterium.

Spirilla - 

          They are non – flexible spiral forms . They have one to three fixed curves in their body.

Vibrio -

        They are curved or comma shaped rods. They are actively motile . They are gram negative , e.g. vibrio cholera. Most of them are non – pathogenic but some are pathogenic.

Spirochates –

             They are slender spiral filaments. They are flexible. They live in soil and stagnant pools , e.g. Treponema Pllidum .

Mycoplasmas –

             They do not possess cell wall. Therefore they do not have stable morphology. They occur as round or oval bodies or as filaments .

MORPHOLOGY OF BACTERIA

Bacteria Cell Wall :

                    It is a complex rigid structure. It  is a complex rigid structure. It  gives bacteria its definite shape . It  is semi – permeable. The cell wall of gram-positive bacteria is thicker than the gram-negative bacteria. In many bacteria cell wall is enclosed by protective covering called capsule.

Cytoplasmic  Membrane :

                      It is also called cell membrane . It is thin and elastic . It is semi –premeable . This membrane posses many enzyme and pigments .

Cytoplasm :

           It is a viscous watery solution. It contains varity of organic and inorganic solutes and ribosomes.

Ribosomes –

            They  are composed of ribosomal RNA and ribosomal  proteins. They measure 10 -20  nm in diameter. Each cell contain thousand of ribosomes. They synthesize proteins.

Nucleus :

         The bacterial nucleus does not divided by mitosis.The genetic information is contained in a single ,circular , double strand molecule of DNA . It occur tightly coiled.

Capsule or Slim layer –

                       It is a protective covering around the bacterial cell wall. If it is thick it is a called capsule.    

Bacterial  growth Curve 

                         A typical growth curve contains four major phases .

1. Lag phase :

               When bacteria are  seeded into fresh medium , then the multiplication takes some time. The period  between inoculation and beginning of multiplication is called lag phase.

2. Log phase:

              It is also known as growth phase. In this phase bacteria multiply at their maximum rate. The time required  for one bacterial division is called generation time.

3. Stationary Phase –

                     The growth of bacterial slow down and becomes stationary. There is balance between  the bacterial  reproduction and bacterial death.

4. Phase of decline –

                     In this phase rate of death of bacteria is more than rate of growth . Thu the number of living cell  decline. After a variable period , all the cells die and culture become sterilize.

Factor of Influencing Growth of Bacteria

1.Nutriton –

            The growth of micro – organisms depend on adequate supply of suitable nutrients . They require elements present in their chemical composition . All bacteria have three major nutritional needs for growth.

A) A source of carbon -

B) A source of nitrogen

C) A source of energy

2) Moisture -  

              Bacteria requires specific temperature range of their growth . The temperature for growth of most of the pathogenic bacteria is 30’ C with upper limits of 40’ – 50’ C and lower limit of 15’ – 20’ C .  Bacteria can be killed by very high temperature and very low temp.

3)Ph -

      This denotes the acidity or alkalinity of the medium in which bacteria can be grown. Some bacteria grow in neutral medium , some  grow in alkaline media and some grow in acidic media.

4)Light and other Radiations -

                             Bacteria grow in dark places. Bacteria can be destroyed or killed by ultraviolet rays, ionizing radiations, infrared red rays and other radiations.

5)Osmotic Pressure -

                    Osmotic Pressure changes can effect the growth of bacteria.Sudden change in osmotic pressure can cause destruction of bacteria .

                                 Thanks for read this blog. 

                                          Jeena Seekho