Identification of Enterococcus Species From Clinical Cultures

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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.