1/17/2016 Plotting the typical microbial death curve logarithmically(red line)results in a straight line. Microbial Exponential Death Rate: 1.000.000 TABLE 7.2 An Example 60 Time(min) Deaths per Minute Number of Survivors 0 1,000,000 3.0 600,000 1 900,000 100,000 90,000 10,.000 0,000 100.000 3 9000 1000 7 900 100 Time(min) A microbial death 5 90 10 9 3 mi he cells would 9 ance betwee 100 000 and the baseline. Several factors influence the death rate: Number of microbes:more there are the longer it takes Environmental influences: organic matter inhibits action of chemical antimicrobials biofilms -temperature fats and proteins are protective Time of exposure:longer time for more resistant microbes Time(min) Microbial characteristics:such as (b)Logarithmic plotting(red)reveals that if the rate of killing is the same,it will take longer to kill all members of a endospore or not larger population than a smaller one,whether using heat or chemical treatments. 1/17/2016 3 Plotting the typical microbial death curve logarithmically (red line) results in a straight line. r of ser of s One log decrease = 90% of population log10 of numbe r surviving cell s Arithmetic numb e surviving cell skilled Time (min) A microbial death curve plotted arithmetically (blue line) is impractical: at 3 minutes the population of 1000 cells would only be a hundredth of the graphed distance between 100,000 and the baseline. Several factors influence the death rate: • Number of microbes: more there are the longer it takes • Environmental influences: - organi tt i hibit ti f ic matter inhibits action of chemical antimicrobials - biofilms - temperature - fats and proteins are protective • Time of exposure: longer time for more resistant microbes • Microbial characteristics: such as endospore or not r of ls sterile surgical equipment log10 of numbe surviving cel l Time (min) (b) Logarithmic plotting (red) reveals that if the rate of killing is the same, it will take longer to kill all members of a larger population than a smaller one, whether using heat or chemical treatments