bacteriocin

[băk-tîrē-ə-sĭn′]
n.
  1. An antibacterial substance, such as colicin, produced by a strain of bacteria and harmful to another strain within the same family.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.