The relationship between the number of bacteria in a population at a given time (Nt), the original number of bacterial cells in the population (No), and the number of divisions those bacteria have undergone during that time (n) can be expressed by the following equation:
For example, Escherichia coli, under optimum conditions, has a generation time of 20 minutes. If one started with only 10 E. coli (No = 10) and allowed them to grow for 12 hours (n = 36; with a generation time of 20 minutes they would divide 3 times in one hour and 36 times in 12 hours), then plugging the numbers in the formula, the number of bacteria after 12 hours (Nt) would be
10×236=Nt=687,194,767,360 E. coli
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E. coli generation time = 20 minutes
My. tuberculosis generation time = 20 hours
Cl. perfringens generation time = 7 minutes
1) How many microbes on one hamburger – the story of how Hilda became sick
Hilda bought a pound of hamburger from the local grocery store. The hamburger happened to have one E. coli on it. The hamburger is sealed in an air-tight container. Hilda has to run a few (okay, several) errands after grocery shopping, so her groceries sit in her nice warm car for a while….
a) How many E. coli after 1 hour?
b) How many E. coli after 5 hours?
2) A ruined day(s) because of one patient’s inconsiderate sneezing!
Patient Harry has tuberculosis. Harry happened to sneeze right in your face. Allowing one Mycobacterium tuberculosis to enter into your nasal passages and into your lungs. You have been under a lot of stress lately both at work and at home, and have not had much sleep lately, so this incident did not sit well with you at all.
a) How may My. tuberculosis after 20 hours?
b) How may My. tuberculosis after one week?
3) The case of cold feet and an irritated cut
Lorraine has diabetes mellitus, and doesn’t really follow dietary recommendations nor does she regularly check her blood sugar levels. Lorraine often complains of cold feet, and was working in the garden and cut her big toe. A perfect entry point for a Clostridium perfringens endospore. The endospore becomes a vegetative cell.
a) How many Cl. perfringens after 1 hour?
b) How many Cl. perfringens after 5 hours?