Correct Option: A

Typhoid fever is caused by Salmonella typhi (S. typhosa). This is fasillus type. Bacterial genus Shigella causes shigellosis or bacillary dysentry. Escherichia coli is a facultative anaerobe found in the intestine of human beings. Giardia is a flagellate protozoan, Glamblia causes giardiasis a prolonged diarroheal disease of humans.