A bacitracin-resistant, hippurate hydrolysis positive, bile esculin positive, beta-hemolytic Streptococcus that grows in 6.5% NaCl is probably a(an)?

The organism described in the question exhibits several significant characteristics that point toward it being an enterococcus. Enterococci are known to be bacitracin-resistant, which aligns with the traits of this isolate. Additionally, they are capable of hydrolyzing hippurate and can grow in a bile esculin medium, allowing them to survive in the presence of bile salts and utilize esculin as a carbon source.

The ability to grow in a 6.5% NaCl environment is another defining feature of enterococci, as they can tolerate high salt concentrations. This characteristic is distinct within the streptococci family, which helps differentiate enterococci from other groups such as Streptococcus pneumoniae or group D streptococci, which do not share all the same traits.

While group D streptococci can also be bile esculin positive, they typically do not share the same salt tolerance as enterococci. Diphtheroids, on the other hand, are not members of the Streptococcus genus and do not exhibit the hemolytic properties or other biochemical characteristics mentioned in the description. This combination of biochemical reactions and growth conditions strongly supports the conclusion that the isolate in question is indeed an enterococcus.