The Collaborative International Dictionary of English v.0.48:

mycobacteria \mycobacteria\ n. pl.
   A group of rod-shaped bacteria, some saprophytic or causing
   diseases.

   Syn: mycobacterium.
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

mycobacterium \mycobacterium\ n.; pl. mycobacteria.
   Any of various rod-shaped bacteria, some saprophytic or
   causing diseases.
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

mycobacteria
    n 1: rod-shaped bacteria some saprophytic or causing diseases
         [syn: mycobacteria, mycobacterium]