I would use a comma to delineate the two (dependent and independent) clauses in that sentence.
If possible, say a bit more about the infection. Although some species of bacteria are very dangerous, and some have become resistant to antibiotics, a mere infection is unlikely to cause the loss of a foot.
That's certainly possible. He may have had a compromised immune system or perhaps had gangrene or complications from diabetes. However, my comment still stands.
I just want to say that I posted the above sentence to see if I have used the preposition correctly, because I was in doubt whether to use the preposition "to" or from", but of course, I could have added the reason why the infection of his foot led to an amputation.
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