bacterium
bac·te·ri·um
 /bækˈtirijəm/  noun  ,  pl   -te·ria /-ˈtirijə/ [  count  ]
  : any one of a group of very small living things that often cause disease
  — usually plural
   Keep the wound clean and dry to prevent the growth of bacteria.
  bac·te·ri·al /bækˈtirijəl/  adj