Why is this downvoted? I'm not asking for an upvote and I'm aware this post can bring in more downvotes, just want to know the reason.
Presumably those who downvoted it thought what it says in the tool-tip
“This question does not show any research effort: it is not clear or not useful.”
There is no obligation for down-voters to explain their actions, and although this can help the poster, people may be reluctant to do so to avoid getting into a vituperative exchange (aka ‘flame war’).
Personally, I would say that your question is a series of naïve and general questions that could be answered by the “research effort” of reading generally about bacteria and disease, or by internet searches for the specific questions you pose.