Disease caused by micro organisms

$ The patients of cholera, vomitting and dysentary are given intravenous drip of saline solution. ! The saline solution kills the disease causing micro-organisms, after vomitting and dysentary.

The disease kala-azar is caused by a micro-organism know as :

Which of these options doesn't have a pair of diseases caused by organisms of the same genus ?

Name the bacteria whose presence in water indicates the contamination with disease-causing micro-organisms.