Now, let us look at the last section of the course in basics in medical microbiology and that is microbial growth and nutrition. We will begin with studying the microbial growth curve, then, the physical and chemical factors involved in microbial growth, the culture media and we will end the study with the streak plate method of bacterial isolation. When microorganisms are cultivated in liquid medium, they usually grow in a batch culture that is, their incubated in a closed vessel with a single batch of medium. Since during the time of incubation, no fresh medium is provided, then you can concentration declines and the waste products increase the growth of microorganisms reproducing by binary fission can then be plotted as the log of the number of cells versus the incubation time. The resulting curve has four distinct phases, the lag phase, the law phase, which is short for a logarithmic phase and is also known as exponential phase, the stationary phase are and the death phase or the decline phase.
Let us look at each one of these phases in detail. The lag phase is the first portion of the microbial growth curve. At this stage there is neither cell division or cell death. The microorganisms that were just added to the medium are adapting to the new environment. It is time for the cells to grow storage nutrients and synthesize essential enzymes, the cells are getting prepared for division by binary fission. The log or logarithmic phase is the phase of exponential growth of cells by binary fission.
It is the doubling time or the generation time. That is the time it takes for a bacterium to undergo binary efficient, having just gone through efficient itself. Usually, the doubling time is of 20 minutes, but it can take hours or several days depending on each growth rate and ideal growth conditions. If there is infection, the symptoms of the disease start surfacing. If there is a toxin release, there will be tissue destruction. If it is in growth media, the media will become more cloudy 50s that the microorganisms are in a solid medium, there will be visible colonies from the growth.
This is a time that the bacteria are susceptible to antibiotics. stationary phase occurs after a few days of infection or a few hours in a culture to at this point, the number of cells reproducing equals the number of cells dying and the cell population enters the plateau. In the tube, the nutrients tend to be scarce and waste products begin to accumulate. In the decline phase, as the name suggests, the number of cells dying exceeds the number of cells being formed. At this stage, capsules help prevent the bacteria from Getting desiccated or dehydrated. The flagella helps the bacteria move to a more nutrient environment within the media.
And then the spores can be formed in these harsh conditions, as it is the case of soil bacteria, which allows the cells to escape so that in summary, the microbial growth curve is typical for bacterial growth. In a batch culture, the four phases of growth are the lag phase, the exponential or the logarithmic phase, the stationary and decline order that phase