When the microorganism growing in a rich medium is inoculated into nutritionally poor medium, the organism will take more time to adapt with the new environment. The length of the lag phase depends directly on the previous growth condition of the organism. This phase is termed as Lag phase, in which cellular metabolism is accelerated, cells are increasing in size, but the bacteria are not able to replicate and therefore no increase in cell mass. When a microorganism is introduced into the fresh medium, it takes some time to adjust with the new environment. The growth curve has four distinct phases (Fig 2) The amount of transmitted light through turbid broth decreases with subsequent increase in the absorbance value.įig 1: Absorbance reading of bacterial suspension Thus the increasing the turbidity of the broth medium indicates increase of the microbial cell mass (Fig 1). The degree of turbidity in the broth culture is directly related to the number of microorganism present, either viable or dead cells, and is a convenient and rapid method of measuring cell growth rate of an organism. The Spectrophotometer measures the turbidity or Optical density which is the measure of the amount of light absorbed by a bacterial suspension. The increase in the cell mass of the organism is measured by using the Spectrophotometer. The curve thus obtained is a sigmoid curve and is known as a standard growth curve. The dynamics of the bacterial growth can be studied by plotting the cell growth (absorbance) versus the incubation time or log of cell number versus time. The bacterium starts utilising the components of the media and it will increase in its size and cellular mass. To study the bacterial growth population, the viable cells of the bacterium should be inoculated on to the sterile broth and incubated under optimal growth conditions. The bacterium is then known to be in an actively growing phase. When the bacteria reach a certain size, they divide by binary fission, in which the one cell divides into two, two into four and continue the process in a geometric fashion. Bacteria are unicellular (single cell) organisms. The nutritional factors include the amount of Carbon, nitrogen, Sulphur, phosphorous, and other trace elements provided in the growth medium. The physical factors include the pH, temperature, Osmotic pressure, Hydrostatic pressure, and Moisture content of the medium in which the organism is growing. The growth of the organism is affected by both physical and Nutritional factors. The organism must require certain basic parameters for their energy generation and cellular biosynthesis. It is the unique characteristics of all organisms. The increase in the cell size and cell mass during the development of an organism is termed as growth. To determine the generation time of given bacteria. To plot standard growth curve of Staphylococcus aureus.To study the different phases of bacterial growth.
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