Growth Curve of Bacteria PDF

GROWTH CURVE vnm 1  What is Bacterial Growth? Bacterial Growth - an increase in bacterial numbers - does not refer to an increase in size of the individual cells vnm 2 How to determine Microbial Numbers? directly – through counti...

GROWTH CURVE vnm 1  What is Bacterial Growth? Bacterial Growth - an increase in bacterial numbers - does not refer to an increase in size of the individual cells vnm 2 How to determine Microbial Numbers? directly – through counting indirectly – through measuring their metabolic activity vnm 3 Bacterial Division Binary Fission - most common method of reproduction, asexual reproduction, splitting of parent cell into two daughter cells Budding - another form of bacterial division, also asexual reproduction, it forms from outgrowths (buds) of mature organisms, it is a form of mitotic cell division, when the bud reaches the size of the parent cell, it separates vnm 4 vnm 5 vnm 6 vnm 7  Filamentous bacteria (some actinomycetes) reproduce by producing chains of conidiospores carried externally at the tips of the filaments. Other filamentous bacteria simply fragment and the fragments initiate the growth of new cells vnm 8 Generation Time In binary fission, one cell’s division produces two cells, two cells’ divisions produces four cells and so on. When the arithmetic number of cells in each generation is expressed as a power of 2 (2x), where x is the exponent that tells the number of doubling (generations) that have occurred. vnm 9  Generation time is the time required for a cell to divide (and its population to double). The generation time among organisms vary according to environmental conditions such as temperature or pH level. Most bacteria have a generation time of 1 – 3 hours while other species can require up to 24 hours per generation vnm 10 vnm 11 PHASES OF GROWTH Bacterial growth is regulated by nutritional environment. When suitable environment is there that time bacterium is incubated, its growth leads to increase in number of cells which allow definite course. The growth curve has got four phases: Lag phase Log phase(logarithmic) or exponential phase Stationary phase Decline phase vnm 12 vnm 13 The Lag Phase After inoculation there is normally a brief period of adaptation by the cells to the new conditions. Bacteria are producing the enzymes necessary to digest the nutrients. The rate of growth begins to increase towards the end of this phase. vnm 14 The Log (Logarithmic / Exponential) phase There is a rapid period of growth during this phase due to the fact that: Bacteria have developed the necessary enzymes and there are plenty of nutrients. There are few waste products being produced. The rate of cell division is currently at its maximum with the number of bacteria doubling as often as every 20 minutes. vnm 15 Limitation of log or exponential phase Exhaustion of nutrition Accumulation of toxic metabolites end products Rise in cell density Change in PH [Log phase is the time when cells are most active metabolically and is preferred for industrial purpose] vnm 16 The Stationary Phase The rate of growth levels stop during this period. This is because: The nutrients are becoming used up. The amount of waste produced by the bacteria themselves is increasing. The rate at which new cells are produced is equal to the rate at which other cells are dying. vnm 17 The Death (Decline) Phase During this phase more bacteria are dying than are being produced. This is because: Very few nutrients are left. Many bacteria are poisoned by the waste produced by such large numbers Finally, after certain time period all the cells die and culture becomes sterile. vnm 18 Association of Growth and Cell Changes Lag Phase- maximum cell size towards end of phage Log Phase- cells are smaller and stain uniformly Stationary Phase- cells are Gram variable and irregular staining due to presence of intracellular granules, Sporulation occurs Decline Phase- involution forms are common vnm 19 Plate Counts Measures the number of viable cells It takes about 24 hours or more for visible colonies to form Reported as colony-forming units (CFU) Only a limited number of colonies must be developed in the plate because when too many colonies are present, some cells are overcrowded and do not develop. The original inoculum is diluted several times in a process called serial dilution to ensure that colony counts will be within 25 – 250 colonies. vnm 20 vnm 21  Serial Dilutions Example: A milk sample has 10,000 bacteria per milliliter. If 1 ml of this sample were plated out, there would theoretically be 10,000 colonies formed in the Petri plate of the medium. Obviously, this would not produce a countable plate. If 1 ml of this sample were transferred to a tube containing 9 ml of sterile water, each milliliter of fluid in this tube would now contain 1000 bacteria. If 1 ml of this sample were inoculated into a Petri plate, there would still be too many potential colonies to count on a plate. Therefore, another serial dilution could be made. vnm 22  One milliliter containing 1000 bacteria would be transferred to a second tube of 9 ml of water. Each milliliter of this tube would now contain only 100 bacteria, and if 1 ml of the contents of this tube were plated out, potentially 100 colonies would be formed– an easily countable number vnm 23 vnm 24 Pour Plates and Spread Plates A plate count is done by either the pour plate method or the spread plate method vnm 25 vnm 26 vnm 27 vnm 28 Pour Plates: Disadvantages Some relatively heat-sensitive microorganisms may be damaged by the melted agar and will then be unable to form colonies When certain differential media are used, the distinctive appearance of the colony on the surface is essential for diagnostic purposes. Colonies that form beneath the surface of a pour plate are not satisfactory for such tests. To avoid these problems, the spread plate method is used instead vnm 29 Filtration Used when the quantity of bacteria is very small vnm 30 PHYSICAL REQUIREMENTS Temperature Psychrophiles - cold-loving microbes about -10˚C to 20˚C optimum growth 15˚C not grow in 25˚C Mesophiles - moderate-temperature- loving microbes about 10˚C to 50˚C optimum growth 25˚C to 40˚C Thermophiles - heat-loving microbes about 40˚C to 70˚C optimum growth 50˚C to 60˚C vnm 31  Psychrotrophs - microorganisms responsible for spoilage of refrigerated food about 0˚C to 30˚C Hyperthermophiles/Extreme Thermophiles about 65˚C to 110˚C optimum growth 80˚C *usually has 30˚C between maximum and minimum growth vnm 32 pH Acidity or alkalinity of a solution Most bacteria grow best at pH 6.5-7.5 Very few bacteria grow below pH 4 Acidophiles - chemoautotrophic bacteria that are remarkably tolerant of acidity vnm 33 Osmotic Pressure High osmotic pressures have the effect of removing necessary water from a cell Plasmolysis - shrinkage of cell’s plasma membrane caused by osmotic loss of water vnm 34 Extreme Halophiles - adapted well to high salt concentrations Obligate Halophiles - require high salt concentrations for growth Facultative Halophiles - do not require high salt concentrations but are able to grow at salt concentrations up to 2%, some can tolerate at 15% salt vnm 35 vnm 36 vnm 37