The Collaborative International Dictionary of English v.0.48:

bacilli \bacilli\ n.
   plural of bacillus; usually designating aerobic rod-shaped
   spore-producing bacteria; they often occur in chainlike
   formations.

   Syn: bacillus
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

Bacillus \Ba*cil"lus\, n.; pl. Bacilli. [NL., for L. bacillum.
   See Bacillari[ae].] (Biol.)
   A variety of bacterium; a microscopic, rod-shaped vegetable
   organism.
   [1913 Webster]