You are screening for antibiotic resistant bacteria in the gut of a cow whose di

Question

You are screening for antibiotic resistant bacteria in the gut of a cow whose diet is supplimented with antibiotics (a common practice in the USA). You take 1 ml of gut content and add it to 9 ml of sterile buffer. You then serially dilute this sample 7 more times (by transferring 1 ml to 9ml sterile buffer for a total of 8 ten fold dilutions). You plate 1 ml from each dilution onto two plates of complex media, one which contains vancomycin and one that does not. After allowing colonies to form you observe 50 colonies on the 8th plate that lacked antibiotic and 150 colonies on the 3rd plate that contained vancomycin. What is the frequency of vancomycin resistant bacteria in the gut of the cow? 3 times 10^5 50 times 10^-3 150 times 10^3 30 times 10^8 3 times 10^-5

Explanation / Answer

The eighth plate that didn't have vancomycin cannot be used to calculate the frequency of vancomycin resistance bacteria in the cow gut.

we got 150 colines in the third plate which have vancomycin.

1ml of the gut contain is diluted 10*10*10 times in the third plate.

so the frequency of vancomycin-resistant bacteria in cow gut is 150*103

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