Modified coagglutination procedure for the serological grouping of streptococci

Serogrouping single colonies of beta-hemolytic streptococci with achromopeptidase extraction

Achromopeptidase (TBL-1; Wako Chemicals, USA, Inc., Dallas, Tex.) prepared as a 2,000-U/ml solution will extract the serogroup antigens from single colonies of groups A, B, C, F, and G streptococci in 1 min at room temperature. This enzyme extraction is not effective for the serogrouping of all group D streptococcus species. Achromopeptidase extracts can be used with latex or coagglutination reagents.

Serological grouping of streptococci: a collective evaluation in six laboratories of three rapid methods

Three serological methods for streptococci grouping: latex agglutination after pronase extraction (LAP), latex agglutination after nitrous acid extraction (LAN) and counterimmunoelectrophoresis after nitrous acid extraction (CIEN) were evaluated in six laboratories with 310 strains of streptococci. To reduce the possible influence of a particular laboratory, each serological procedure was performed in two different laboratories with identical protocols and strains. Between the three procedures, a total agreement of 81.3% with six identical results was obtained. Since only one discordant result was obtained in 12.2% (CIEN 4.8%-LAN 5.8%-LAP 1.6%) and two discordant results with two different serological methods in 2.6%, it could be concluded that agreement between the three procedures was 96%. For B (99 strains tested) and D(100 strains tested) groups, total agreements of respectively 95% and 92% were achieved. In conclusion, LAP, LAN, and CIEN gave equivalent results for streptococci grouping, but LAN was the most simple needing no heating, centrifugation, or electrophoresis equipment and lacking cross-reactivity of group C antibody.

Evaluation of Phadebact and Streptex Kits for rapid grouping of streptococci directly from blood cultures

The Phadebact Streptococcus Test and the Streptex Test kits were evaluated for grouping streptococci directly from blood cultures. Pellets of bacteria obtained from centrifuged samples of positive blood cultures were inoculated into Todd-Hewitt broth for 2- and 4-h Phadebact tests and into pronase for Streptex tests. Hemolysis was determined after pipetting a portion of each pellet into cuts made in blood agar plates incubated anaerobically for 2 to 6 h. Serological groups were also determined from colonies of the 137 strains of streptococci used in the study by the Lancefield precipitin method. Of the 126 strains tested by the 4-h Phadebact method, 120 (95.2%) agreed with Lancefield groupings, and 133 (97.1%) of the 137 strains tested by Streptex were in agreement. In contrast, only 31 of 55 strains (56.4%) were correctly identified by the 2-h Phadebact method. Misidentifications were related to multiple agglutinations and weak agglutinations in homologous antisera. Group A isolates were most frequently misidentified by all of the test methods. Hemolysis was determined within 4 h for 92.7% of the isolates and within 6 h for the remaining strains. Although the 4-h Phadebact procedure and the Streptex procedure were comparable in overall accuracy, cost, and technologist time, Streptex was the method of choice for direct groups. Results were available within 75 min for the Streptex procedure compared with 4 h for the Phadebact method. Because few cross-reactions occurred, agglutination responses were clearer and easier to interpret. Results from 2-h Phadebact tests were not satisfactory, and this method is not recommended.

Evaluation of the Phadebact Gonococcus Test in the identification of Neisseria gonorrhoeae in a routine diagnostic laboratory

The Phadebact Gonococcus Test, a coagglutination procedure for the confirmation of identity of presumptive N gonorrhoeae isolates, was evaluated under normal working conditions in a routine diagnostic laboratory and compared with an immunofluorescence technique. Of 166 isolates of N gonorrhoeae from urogenital, rectal, and pharyngeal sites, 164 gave a positive coagglutination reaction, and one of the two negative isolates gave a positive reaction on retesting after subculture. There were no cross-reactions with other organisms tested. This was in contrast with the immunofluorescence technique; with this method, three of 46 isolates of N meningitidis fluoresced brightly, and a further 17 isolates of N meningitidis gave reactions that were difficult to interpret. The coagglutination test is rapid, simple and a more specific alternative to immunofluorescence.

Serogrouping single colonies of beta-hemolytic streptococci from primary throat culture plates with nitrous acid extraction and Phadebact streptococcal reagents

The serogrouping of isolated beta-hemolytic streptococcal colonies from throat cultures by a micronitrous acid extraction method employing Phadebact Streptotoccus Test reagents was compared with results obtained with the direct-plate Phadebact procedure and the autoclave and Streptomyces albus enzyme-lysozyme extraction methods. These data were compared with those from the Lancefield grouping obtained with a capillary precipitin test. The micronitrous acid extraction method was modified to yield an uncomplicated method that provides specific coagglutination responses from one beta-hemolytic streptococcal colony that may be collected from a primary blood agar plate either on the end of an applicator stick or from a sweep of an inoculating loop from mixed growth.

Grouping of beta-haemolytic streptococci by agglutination

Streptococcal grouping sera, diluted and absorbed to remove cross-reactions, were bound to staphylococci and used to group trypsinised beta-haemolytic streptococci by coagglutination. The results compared well with those obtained using the Phadebact streptococcal grouping kit. The same sera bound to staphylococci without prior dilution and absorption could be used to group enzyme extracts of haemolytic streptococci by slide agglutination, the results again comparing favourably with those of the Phadebact kit.