The Collaborative International Dictionary of English v.0.48:

Microbacteria \Mi`cro*bac*te"ri*a\, n. pl. [NL. See Micro-,
   and Bacterium.] (Biol.)
   In the classification of Cohn, one of the four tribes of
   Bacteria.
   [1913 Webster]

   Note: In this classification bacteria are divided into four
         tribes: 1. Spherobacteria, or spherical bacteria, as
         the genus Micrococcus. 2. Microbacteria, or
         bacteria in the form of short rods, including the genus
         Bacterium. 3. Desmobacteria, or bacteria in
         straight filaments, of which the genus Bacillus is a
         type. 4. Spirobacteria, or bacteria in spiral
         filaments, as the genus Vibrio.
         [1913 Webster]