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Identification of Enterococcus Species From Clinical Cultures

Gram stain: Gram-positive cocci in singles, pairs, or chains; cells can be ovoid to coccobacillary
Colony morphology: On blood agar after 24 hours of incubation, colonies are nonhemolytic or alpha hemolytic (rare strains may be beta hemolytic), and approximately 1 to 2 mm in diameter.
Catalase: Negative
Presumptive identification: Growth on bile esculin agar and in 6.5% salt broth are two characteristics that have commonly been used to identify Enterococcus species to the genus level. A positive esculin in combination with a positive PYR reaction is another approach to presumptive identification.
Species identification: E. faecalis and E. faecium are usually easily identified by most commercial systems. Successful identification of the other species on these systems may vary. With respect to vancomycin intermediate or resistant strains, two key characteristics are motility and pigment. E. casseliflavus is both motile and possesses a yellow pigment; E. gallinarum is also motile but non-pigmented. E. faecalis and E. faecium demonstrate neither characteristic.