![Listeria monocytogenes colony morphology listeria monocytogenes morphology on blood agar](colonies-of-listeria-monocytogenes.jpg)
Listeria monocytogenes on Columbia sheep blood agar with colistin and aztreonam (CAP).
Cultivation 48 hours, aerobic atmosphere, 37°C.
Colonies on blood agar are whitish gray and can be confused with streptococci, enterococci or diphtheroids (particularly after 24 hours of cultivation when beta-hemolysis is often quite weak).