Enterococcus is a bacterium, of the phylum Firmicutes. They are round gram-positive cells which occur in pairs and are difficult to distinguish from Streptococcus. Two species are common commensal organisms in the intestines of humans: E. faecalis and E. faecium . They are anaerobic, not requiring oxygen to live but can survive in the presence of oxygen. Important clinical infections caused by Enterococcus are urinary tract infection, bacteremia, bacterial endocarditis , diverticulitis, wound infections and rarely meningitis. This bacterium is usually sensitive to ampicillin and vancomycin. During the last decade, a particularly virulent strain of Enterococcus has plagued hospitalized patients., which is resistant to both ampicillin and vancomycin.