Which characteristic differentiates Enterococcus faecalis from Group D streptococci?

• A. Ability to ferment lactose
• B. Tolerance to 6.5% NaCl
• C. Growth in bile
• D. Production of catalase

Answer: (B)

High-salt tolerance is the distinguishing feature. Enterococcus faecalis can grow in 6.5% NaCl, whereas Group D streptococci do not tolerate that level of salt. This property is routinely used in the lab to separate Enterococcus from other Group D species. Other options aren’t as reliable: lactose fermentation varies among species and isn’t a definitive marker; growth in bile isn’t unique to Enterococcus since many Group D streptococci tolerate bile; catalase production isn’t helpful here because both Enterococcus and Group D streptococci are catalase negative. So, the best discriminator is the ability to grow in 6.5% NaCl.