A Comparison of the Identification of Group A Streptococci and Enterococci by Two Rapid Pyrrolidonyl Aminopeptidase Methods

Group A streptococci and enterococci can be differentiated from other streptococci by their ability to cleave L-pyrrolidonyl- β -napthylamide (PYR). The authors evaluated two pyrrolidonyl aminopeptidase (PYRase) systems—Minitek® (BBL Microbiology Systems, Cockeysville, MD) and Identicult-AE® (Scott Laboratories, Inc., Fiskeville, RI)—for the presumptive identification of Group A streptococci and enterococci. Eighty-three Group A streptococci, 77 beta-hemolytic non-Group A streptococci, 74 enterococci, 56 nonenterococcal non–beta-hemolytic streptococci, 1 Streptococcus pneumoniae , and 1 Aerococcus were tested. Compared with results obtained with reference methods (bile esculin agar and 6.5% [w/v] sodium chloride for identification of enterococci, and latex agglutination tests by Streptex® [Burroughs Wellcome, NC] for grouping of beta-hemolytic streptococci) both the Identicult-AE and Minitek systems were 100% sensitive and specific for identification of both enterococci and Group A beta-hemolytic streptococci. Advantages of the Identicult-AE system compared with Minitek were the use of a smaller inoculum for which subculture was not necessary, incubation at room temperature rather than at 37 °C, and lower cost. Both PYRase kits tested, and in particular the Identicult-AE system, were very easy to use and should be considered as rapid, reliable, and cost-effective alternative methods for the presumptive identification of Group A streptococci and enterococci in the clinical laboratory.