microbial

from WordNet (r) 3.0 (2006)

microbial
    adj 1: of or involving or caused by or being microbes;
           "microbial warfare" [syn: {microbial}, {microbic}]

from The Collaborative International Dictionary of English v.0.48

microbial \mi*cro"bi*al\, microbian \mi*cro"bi*an\, a. (Biol.)
   Of, pertaining to, or caused by, microbes; as, microbial
   growth; the microbian theory; a microbian disease.
   [1913 Webster +PJC]