Lecture 3:- Bacterial requirement , Growth curve
- 1. Microbiology Lecture 3:- Bacterial requirement , Growth curve Dr. Raghda Saad Mohammed
- 2. Nutritional Requirement of Bacteria • Bacteria may require adequate nutrition of optimum pH , temperature and oxygen for multiplication and growth .Bacteria can be classified into following types on the basis of nutritional requirement . • 1- On the basis of energy sources . • A- Photrophics which get energy from photochemical reactions . • B- Chemotrophic gets energy from chemical reactions . • 2- On the basis of their ability to synthesize essential metabolites . • A- Autotrophic :- These are the organisms in which all essential metabolites are synthesized from inorganic sources . They use carbon dioxide as the main source of carbon and simple inorganic salts . e.g. : nitrates , niters , ammonium sulphate , phosphates . • B-Heterotrophic :- Here some of the essential metapolites are not synthesized . Organic compounds e.g. protein , peptones , amino acids , vitamins and growth factor are supplied from outside . Most of the bacteria producing disease in man are heterophic.
- 3. Nutritional Requirement of Bacteria • The other nutritional requirement are as under : • 1-Minerals :- These are sodium , potassium ,magnesium , calcium ,iron , chlorine, zinc , copper , iodine and traces . These are essential for physiological activities of bacteria. • 2-Gas requirements : • A-Oxygen :- The capacity of bacteria to grow in the presence of oxygen and to utilize it depends on possession of a cytochrome oxidase systems . • 1. Aerobes :- The aerobe organisms grow only in the presence of oxygen .e.g. Pseudomodaceae , bacillus , nitrobacter sarcina etc • 2. Facultative anaerobes :- They are the organisms that can live with or without Oxygen .e.g. vibrio , E.coli , salmonella and staphylococcus. The micro – Aerophilic organism grow well with relatively small quantites of oxygen .e.g. Haemophilus . • 3. Obligate anaerobes :- The strict anaerobes multiply only in the absence of oxygen .e.g. bacteroides ,clostridium
- 4. Nutritional Requirement of Bacteria • .B. Carbon dioxide : The metabolic activator of some organisms like Neisseria , Brucella abortus are greatly enhanced by the presence of extra amount of carbon dioxide in atmospheric air . • 3- Moisture :- Bacteria require water for their growth . Desiccation may kill most of bacteria like Neisseria gonorrhoeae . • 4- Necessary nutritional requirement :- Most often the necessary growth factors are vitamins . The requirement of growth factors differ widely in various bacteria . • e.g. : Neisseria gonorrhoeae ............... Glutathione . • Staphylococcus aureus ................However 0.5% sodium .
- 5. Growth Curve When organism are cultured in appropriate fluid media there would be increase in the size of bacteria without any multiplication for some time . This is followed by multiplication and increase in numbers of bacteria to the extent that media look turbid to the naked eye (log phase ) . After some time growth rate becomes stationary and later on declines . Counting of bacteria at different periods after inoculation and then events of sequences are represented on a graph which is called growth curve .
- 6. Growth Curve
- 7. Growth Curve • A-Lag phase :- During this phase there occurs • 1- Increase in size of cell . • 2-Increase in metabolic rate . • 3-Adaptation to new environment and necessary enzymes and intermediate metabolites are built up for multiplication proceed. • The length of lag phase depends upon : • a-Type of bacteria . • b-Better the medium , shorter the lag phase. • c-The phase of culture from which inoculation in taken • d-Size of inoculum. • e-Environmental factors like temperature .
- 8. Growth Curve • B-Log phase :- Following lag phase . The cells start dividing and their number increase by geometric progress on with time . Logarithms of viable count plotting against time gives straight line , during this periods . • i. Bacteria have high rate of metabolism . • ii. Bacteria are more sensitive to antibiotics .Control of log phase is brought about by : • a-Nature of bacteria . • b-Temperature . • c-Rate of penetration of the medium . It depends on the concentration of material in the medium. • C-Stationary phase :-After some time a stage comes when rate of multiplication and death becomes almost equal. It may be due to : • a-Depletion of nutrient . • b-Accumulation of toxic products . Sporulation may occur during this stage. • D- Decline phase :-During this phase population decrease due to death of cells .Factors responsible for the phase are : • a-Nutritional exhaustion • b-Toxic accumulation . • c-Autolytic enzymes . Involution is common in phase of decline.
- 9. • Survival phase :-When most organisms have died , a few survive for several months or years . Factors influencing growth: • 1-Temperature:The temperature range at which an organism grows best is called optimum temperature . It human , parasitic organisms , optimum temperature ranges between 30c and 37c. • There are three groups of bacteria as regards the temperature of growth : • a-Psychrophilic:- These are the organisms growing between 0c to 25c . They are mostly soil and water bacteria. • b-Mesophilic:- They grow between 20c and 45c . This group includes bacteria producing disease . • c-Thermophilic:- Some organisms grow between 50c and 60c . e.g. bacillus and algae. • 2-Hydrogen ion concentration :- Most of pathogenic bacteria grow best at pH( 7.2-7.6) .However lactobacilli grow at acidic ph while Vibrio cholera grows at alkaline pH . • 3-Moisture:- Water in quite essential for the growth of bacteria . Organism like Neisseria gonorrhea and Treponema pallidum die almost at once on drying .However mycobacterium tuberculosis and staphylococcus aureus survive for quite along time even on drying .
- 10. Growth Curve • 4-Osmotic pressure :-Bacteria are usually resistant to changes of osmotic pressure. However 0.5% sodium chloride is added to almost all culture media to make environment isotonic. • 5- Light :-Darkness usually favorable for the growth and viability of all the organisms . Direct light exposure shorten the survival of bacteria Photochromogenic mycobacteria form pigment on exposure to light . Organism are sensitive to ultraviolet and other radiations • 6- Mechanical and sonic stress :-Bacteria tough cell wall . Vigorous shaking and exposure to ultra sonic vibration may cause rupture or disintegration of cell wall .
- 11. • Bacteria divide by simple binary fission .The cell grows in size , almost double its size . the process of cell division is initialed .The sequence of cell division include :- Reproduction in bacteria 1. Formation of initial of chromosome replication . 2. Chromosome duplication 3. Separation of chromosomes. 4. Formation of septa and cell division