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Quantitative Microbiology

Q: How can you solve this question? Assume 1 out of 1.000.000 cans of paté to be contaminated with Listeria 20% of population is susceptible (old, young, pregnant, immunocompromised) Sales: 3 ·106 cans per year (all consumed evenly over population) If Listeria present and susceptible person, illness results Estimate the probability of listeriosis

V * I = 3*10^6 cans /year V*I*0.2=6*10^5 cans / year by people who get sick N(f) = 1/10^6=10^6 So Q = (1-10^6)^(6*10^5)=0.549 but this is for people that will not get sick so: 1-0.549 = 0.451 is the probability that people get sick this year.

Q: What are the different phases of the growth curve and which ones are important for food safety?

Lag phase (important) Exponential phase (important) Stationary phase

Q: What do the things in this formula stand for? log (N/N0) = -(t/δ)^β

N: concentration at certian point N0: concentration beginning δ: time for first decimal reduction β: the shape factor

5 important questions on Quantitative Microbiology

What groups are there in microbiology?

1. Pathogens
1a. Foodborne infections, bacteria that dont need to grow in order to make you sick
1b. Food poisoning, bacteria that produce toxins and need to grow in order to make you sick, because they need to produce toxins

2. Spoilage flora

Q = (1 - N(f) )^(V·I)

Q = probability that no person will get ill in one year
V(f) = size of population
I = portions per year per person
N(f) = number of pathogens in portion

if N(f) > 1 it is about the number of patogens present in one portion
if N(f) < 1 it is about the probability that a pathogen is in a portion

How can you solve this question?
Assume 1 out of 1.000.000 cans of paté to be contaminated with Listeria
20% of population is susceptible (old, young, pregnant, immunocompromised)
Sales: 3 ·106 cans per year (all consumed evenly over population)
If Listeria present and susceptible person, illness results
Estimate the probability of listeriosis

V * I = 3*10^6 cans /year
V*I*0.2=6*10^5 cans / year by people who get sick

N(f) = 1/10^6=10^6

So Q = (1-10^6)^(6*10^5)=0.549
but this is for people that will not get sick so:
1-0.549 = 0.451 is the probability that people get sick this year.