Diptheria, leprosy and plague are the bacterial diseases of humans. Diptheria is a serious airborne contagious disease. It is caused by Cornybacterium diptheriae which is a Grampositive bacterium. It is inhaled through droplets and reaches to respiratory tract and infects it. Leprosy or Hansen?? disease is a contact disease, caused by bacterium Mycobacterium leprae. It degenerates the tissues and deforms the body organs. Plague is a disease caused by bacterium Yersinia pestis or Pasteurella pestis.