The genus Enterococcus consists of gram-positive, facultatively anaerobic organisms that are ovoid in shape and may appear on smear in short chains, in pairs, or as single cells. These organisms do not have cytochrome enzymes and are thus catalase negative, although some strains do produce pseudocatalase. Most react with group D antisera and some react also with group Q antisera. Hydrolysis of L-pyrrolidonyl-β-naphthylamide (PYR) is a characteristic feature that is seen also with group A streptococci but not other streptococci. Most strains in the newly defined Enterococcus genus possess the characteristics summarized by Sherman in 1937 such as the ability to grow in 6.5% NaCl and at pH 9.6, to grow at 10 and usually 45°C, and, for the most part, to survive at 60°C for 30 min, although E. avium grows poorly if at all at 10°C. In clinical laboratories, enterococci have been presumptively identified for years by their appearance on smear and culture plus the demonstration of their ability to hydrolyze esculin in the presence of bile and to grow in the presence of 6.5% NaCl. However, because some enterococci may require up to 48 h of incubation for the correct reaction to occur, more rapid screening procedures have been sought. One such system is a 2-h test that uses 0.2% esculin in a buffered 5% NaCl solution which was reported to be positive for all of 239 enterococci after 2 h. Although the test itself is rapid, the heavy inoculum used would likely require 24 h of growth of the organism following its isolation. Several other screening systems use the ability of enterococci to hydrolyze PYR. Bosley et al. found that all 78 enterococci were positive at 4 h in PYR broth. The inoculum consisted of a loopful of colonies from an overnight growth. Since group A streptococci also hydrolyze PYR, this system included serologic testing with group D antisera. A number of different PYR preparations have been used, including one which yields results in 10 min. PYR has also been used to identify successfully 24 of 25 enterococci from real or simulated positive blood cultures; this method required using bacterial pellets following centrifugation. Group D serologic testing was not reliable in this system, but excellent results were obtained with antisera for group A streptococci, the only streptococci that are PYR positive. Thus, a combination of Gram stain, positive PYR test, and negative groupThe genus Enterococcus consists of gram-positive, facultatively anaerobic organisms that are ovoid in shape and may appear on smear in short chains, in pairs, or as single cells. These organisms do not have cytochrome enzymes and are thus catalase negative, although some strains do produce pseudocatalase. Most react with group D antisera and some react also with group Q antisera. Hydrolysis of L-pyrrolidonyl-β-naphthylamide (PYR) is a characteristic feature that is seen also with group A streptococci but not other streptococci. Most strains in the newly defined Enterococcus genus possess the characteristics summarized by Sherman in 1937 such as the ability to grow in 6.5% NaCl and at pH 9.6, to grow at 10 and usually 45°C, and, for the most part, to survive at 60°C for 30 min, although E. avium grows poorly if at all at 10°C. In clinical laboratories, enterococci have been presumptively identified for years by their appearance on smear and culture plus the demonstration of their ability to hydrolyze esculin in the presence of bile and to grow in the presence of 6.5% NaCl. However, because some enterococci may require up to 48 h of incubation for the correct reaction to occur, more rapid screening procedures have been sought. One such system is a 2-h test that uses 0.2% esculin in a buffered 5% NaCl solution which was reported to be positive for all of 239 enterococci after 2 h. Although the test itself is rapid, the heavy inoculum used would likely require 24 h of growth of the organism following its isolation. Several other screening systems use the ability of enterococci to hydrolyze PYR. Bosley et al. found that all 78 enterococci were positive at 4 h in PYR broth. The inoculum consisted of a loopful of colonies from an overnight growth. Since group A streptococci also hydrolyze PYR, this system included serologic testing with group D antisera. A number of different PYR preparations have been used, including one which yields results in 10 min. PYR has also been used to identify successfully 24 of 25 enterococci from real or simulated positive blood cultures; this method required using bacterial pellets following centrifugation. Group D serologic testing was not reliable in this system, but excellent results were obtained with antisera for group A streptococci, the only streptococci that are PYR positive. Thus, a combination of Gram stain, positive PYR test, and negative group