Distribution of Streptococcal Groups in Clinical Specimens with Evaluation of Bacitracin Screening

In a clinical trial, Strep-A-Chek (a 10-min chromogenic test) was compared with the bacitracin disk susceptibility test for accuracy and turnaround time in the presumptive identification of Streptococcus pyogenes. Among 461 isolates of beta-hemolytic streptococci (344 throat isolates and 117 isolates from other sites), 303 group A S. pyogenes isolates were found. The sensitivities of the Strep-A-Chek and bacitracin tests were high (96.4 and 100%, respectively), but the bacitracin test had a lower specificity (84.2%) than the Strep-A-Chek test (98.7%). The predictive values for positive and negative test results were 99.3 and 93.4%, respectively, for Strep-A-Chek and 92.4 and 100%, respectively, for bacitracin. Strep-A-Chek correctly identified all isolates upon repeat testing. All bacitracin tests were performed on subcultures of isolates from the primary plate. Strep-A-Chek testing was performed on colonies from the primary plate when isolated colonies were available. This shortened the turnaround time for Strep-A-Chek compared with bacitracin by at least 24 h on nearly one-half (45%) of the isolates. A peripheral finding of this study was that sulfamethoxazoletrimethoprim blood agar offered no advantage over conventional blood agar with regard to the number of false-positive bacitracin tests obtained from each medium.

Section: Discussionsupporting

confidence: 83%

mentioning

confidence: 46%

Clinical trial comparing bacitracin with Strep-A-Chek for accuracy and turnaround time in the presumptive identification of Streptococcus pyogenes

Yajko¹,

Lawrence²,

Nassos³

et al. 1986

“…In lieu of serogrouping, susceptibility to bacitracin has thus been used to distinguish group A and non-group A beta-streptococci in many laboratories. This method has the advantage of simplicity, but its limitations (including false-positive and false-negative results) are well known (14,16). Immunofluorescent antibody techniques have also been used, but their effective application to streptococci, especially non-group A streptococci, requires frequent testing and standardization of the antisera and a detailed knowledge of the patterns of crossreactions that occur (20).…”

Section: Resultsmentioning

confidence: 99%

Identification of streptococci: use of lysozyme and Streptomyces albus filtrate in the preparation of extracts for Lancefield grouping

Watson¹,

Moellering²,

Kunz³

1975

A combination of lysozyme and Streptomyces albus filtrate has been shown effective in extracting group-specific antigen for all commonly occurring serologically groupable streptococci. A prospective comparison of this method with that of Rantz and Randall (1955) for grouping 761 clinical isolates has confirmed its accuracy, which in our hands exceeded that of the latter more complicated method of serogrouping. Its rapidity and simplicity and the relatively low cost of the reagents involved make it practical for routine use in clinical bacteriology laboratories.

“…and others (3,4) have demonstrated that L-pyrrolidonyl-pnaphthylamide (PYR) hydrolysis is a reliable test for the identification of GAS and ENT. Whereas earlier tests required incubation for 4 h to overnight to obtain results, recent modifications allow detection of PYR hydrolysis in 10 to 15 min (1,4,5).…”

mentioning

confidence: 99%

Rapid, cost-effective identification of group A streptococci and enterococci by pyrrolidonyl-beta-naphthylamide hydrolysis

Wellstood

1987

Group A streptococci and enterococci were identified by two L-pyrrolidonyl-f0-naphthylamide (PYR) hydrolysis tests. One uses Minitek PYR disks (BBL Microbiology Systems, Cockeysville, Md.); the other uses a swab impregnated with PYR reagent. Both tests and Strep-A-Chek (EY Laboratories, San Mateo, Calif.), a commercially available PYR test, were compared with conventional methods. The PYR methods correctly identified all strains of group A streptococci and enterococci tested. Presumptive tests for identification of group A streptoçocci (GAS) and enterococci (ENT) include bacitracin susceptibility testing, bile-esculin hydrolysis, and salt tolerance (2, 3). Although inexpensive and easy to perform, traditional methods require overnight incubation and results are not always reliable. Latex and coagglutination tests provide rapid, accurate group identifications (2) but are expensive. ENT must be differentiated from other group D streptococci by a salt tolerance test that adds to the total cost and time to obtain results.