Definition of bacterias:
(n) :
(US) A type, species, or strain of bacterium.
(n) :
(derogatory, slang) Lowlife, slob (could be treated as plural or singular).
(n) :
(dated, medicine) An oval bacterium, as distinguished from a spherical coccus or rod-shaped bacillus.
(n) :
(US, proscribed) Alternative form of bacterium. [(microbiology) A single-celled organism with cell walls but no nucleus or organelles.]