Question

Large doses of antibiotics given to fight an infection are likely to destroy bacteria that produce vitamin K. In which digestive organ do we find such beneficial bacteria?

Answer 1

Vitamin K...
That's E.Coli, mainly...

Explanation:

E.Coli lives in the Gut.

It's full name is Escherichia Coli, which basically indicates that a dr. Escherich discovered it in the Colon.

There are many strains of E.Coli, each one ultimately suited/adapted to the environment it lives in.

If you pick up a strain from someone else by, primarily faecal, contamination (if they serve you food and haven't washed their hands after use of the toilet, for instance) you will suffer the consequences:

Best Case scenario: you'll have the runs for a while.
Worst case scenario: You'll end up in ICU.

In the latter it usually is not a "human" variation/strain, but more likely from a bovine, or other animal source. That is why you are always asked to wash your hands after a visit to a petting zoo (children's zoo) these days.

Back in the old days, when recombinant DNA-technology was in the early stages of development, E.Coli was (and in many cases still is) the host of choice for many experiments. But the strains had to be weakened to such an effect that they wouldn't be able to survive outside the laboratory. A scientist, at Stanford I think it was, had developed a weakened strain and wanted to test if it was fit for survival. The only way he could think of was to test it on himself...

So he drank a suspension of the newly recreated E. Coli, and every day the team monitored his stool.

He became a bit anxious when they couldn't find the strain that originally resided in his colon, they were fully replaced by the Mutant strain.

This went on for weeks, without any developments, until he ate about a kilo of black cherries (his favourite fruit).

This gave him quite a bout of diarrhoea, and to the amazement of his team, the next day the mutant strain had gone in his stool sample, but the original strain had returned!

So it hadn't been replaced,merely overshadowed, and once the mutant strain was "flushed out", they could re-establish their hegemony...

So, the answer is: in the gut, and no, it is not easy to kill them all off, even with large dose of antibiotics.....