In this video, we're going to talk about the second consideration when selecting a method for microbial growth control, which is the number of microbes that are present. When a microbial population is treated with either a physical or a chemical process, usually the microbes within that population die at a constant rate, rather than all at once. This means that the larger the initial population of microbes is, the longer it will take for the entire population to be destroyed. Washing and scrubbing can help to remove microbes and biofilms, ultimately reducing the time to sterilize or disinfect an item if you're able to remove some of the microbes present just by physical disruption.
Below, we are showing you these two plots, this one and this one over here. These are known as microbial death curves, which are plots of the death of a microbial population over time due to either a physical or a chemical microbial control treatment method. On these plots, you will find a value known as the decimal reduction time or just the D-value for short. The decimal reduction time or D-value refers to the specific amount of time required to kill 90% of a microbial population under set conditions. It's important to note that the greater the D-value is, the more resistant the microbial population is to the specific treatment method.
Take a look at our image below; we are showing you a microbial death curve along with the D-value. Notice on the y-axis we have the number of living microbial cells, and on the x-axis, we have the amount of time in minutes. At time 0, we're starting with a population of 10,000 microbes. When applying this particular microbial growth control method, the population starts to decrease over time. When 90% of the population is gone, going from 10,000 cells down to 1,000 cells, this is a 90% drop-off. This is on a logarithmic scale y-axis. This population after one D-value shows that the D-val
