A genus of common Gram-negative, facultatively-anaerobic,
rod-shaped bacteria of the family Enterobacteriaceae.
Several strains of the these bacteria are pathogenic and
cause opportunistic infections in immunocompromised (usually
hospitalized) hosts and in those who are on mechanical
ventilation. The urinary and respiratory tract are the most
common sites of infection. It is also a fecal coliform,
along with Escherichia. Two clinically-important species
from this genus are E. aerogenes and E. cloacae.