Bacitracin and coagglutination for grouping of beta-hemolytic streptococci.

Bacitracin may be used for presumptive differentiation of group A from other beta-hemolytic streptococci. Whatever criteria are used for the test, a small number of erroneous results will be obtained. With the 1,161 strains studied in this laboratory, using a zone of 10 mm or greater as indicative of group A was better than using Maxted's original criterion of any zone of inhibition for group A. Co-agglutination is a preferable alternative to bacitracin testing, providing a grouping result as quickly as the bacitracin test but with the advantage of giving a definite grouping result. With the 247 strains studied so far, coagglutination results have correlated exactly with results of conventional grouping by a precipitin method.     

Serological grouping of streptococci by a slide coagglutination method.

A new method for the serological grouping of streptococci by coagglutination with specific antibodies absorbed to protein A-containing staphylococci has been assessed. A total of 242 strains of streptococci, including beta-haemolytic streptococci of groups A, B, C, F, and G, Streptococcus pneumoniae and Strep. faecalis were studied. All streptococci of groups A, B, C, and G, groupable by standard methods, were correctly grouped by coagglutination, although 7-3% showed varying degrees of cross-agglutination. Two beta-haemolytic strains of Strep. faecalis produced coagglutination with group C streptococcal reagent. The method appears to be quick, accurate, reproducible, and simple to perform.     

Modified method for serological identification of group B streptococci.

Extracts from 10- and 40-ml cultures compared favorably for serological identification of group B streptococci. Typing by gel diffusion proved reliable and efficient. These modifications save time, media, and antisera.     

Novel coagglutination method for serotyping group B streptococci.

A group G streptococcal strain was coated with antibody against six different serotypes (Ia, Ib, II, III, IV, and V) of group B streptococci. The coagglutination patterns of 114 strains of group B streptococci were compared with the serotypes determined after immunoprecipitation. The specificity of the method was 100% and the sensitivity 97%. It was used for the typing of 89 invasive and 101 colonizing isolates. The new method is swift, specific, and highly sensitive. It consumes only minute amounts of antibody.     

The reliability and rapidity of the coagglutination technic and its comparison with precipitin technic in the grouping of streptococci.

Three methods of the grouping of 170 strains of beta-hemolytic streptococci belonging to Groups A, B, C, F, and G by capillary and agar-gel precipitation using Lancefield extract and by coagglutination of antibody-coated protein A-containing staphylococci were compared. Capillary and agar-gel precipitin technics correctly grouped all 170 strains, with no cross-reaction. One hundred sixty-nine out of the 170 strains were also correctly grouped by the coagglutination technic, and the one strain with a cross-reaction was correctly grouped after blood--agar subculture. Although 20 of the 170 strains showed minor cross-reactions by the coagglutination technic, the specific groups were easily and unquestionably detected, and the minor cross-reactions were easily overcome. A rapid method of grouping by coagglutination technic using 4--6-hour broth culture, done on 75 strains, showed that 73 strains could be correctly grouped by the rapid method and two after overnight incubation. Thus, the coagglutination technic of grouping was found to be easy, reliable, and economical, and could be adopted in any routine diagnostic laboratory as a rapid grouping procedure.     

Use of the Streptosec test for grouping beta-haemolytic streptococci.

The Streptosec test, which embodies the coagglutination principle for grouping beta-haemolytic streptococci, was used against 72 streptococci previously grouped by precipitin methods. Only two of the 72 strains failed to react. The test is easy to manipulate, represents a considerable saving in time and effort, and produces results with an acceptable degree of accuracy.     

Rapid slide coagglutination test for identifying and typing group B streptococci.

A Cowan I strain of Staphylococcus aureus was labeled with either group B streptococcal grouping or typing antiserum. These antibody-labeled reagent cells (ARC) were used in a slide coagglutination test to identify and type group B streptococci from blood agar plates. All streptococci were also identified by the standard Lancefield capillary precipitin test. In a blind study, all 141 group B streptococci were correctly identified by the coagglutination grouping test. None of the 148 non-group B streptococci caused agglutination of ARC. The coagglutination grouping test required an acid extract prepared from only four colonies and could be completed less than 30 min after colonies were removed from plates. The coagglutination typing test correctly identified 98.6% of the types of the 141 group B streptococcal strains tested. At least 88.6% of these streptococci could be typed directly from blood agar plates within 5 min by the coagglutination typing test. The remaining 11.4% of the group B streptococci were acid extracted (less than a 30-min procedure), and the extract was used for coagglutination typing. Coagglutination typing can be performed with only four colonies. The coagglutination grouping and typing tests are inexpensive, rapid, reliable, and easy to perform.     

Rapid slide agglutination test for Lancefield grouping of streptococci.

A rapid slide agglutination test (the Phadebact [PB] Streptococcus test) was compared with the standard autoclave extraction method of Lancefield and presumptive clinical laboratory tests for grouping of streptococci (bacitracin disk sensitivity for group A and sodium hippurate hydrolysis for group B). Identification of group A streptococci by the PB kit was statistically as accurate as by the Lancefield method, whereas bacitracin grouping was significantly less accurate than the Lancefield method (P = less than .02). With regard to group B, there was no statistically significant difference between the PB test and the sodium hippurate test. The PB test correctly identified all group C and G streptococci. The PB kit provides a rapid and reliable method for Lancefield grouping of streptococci.     

Evaluation of commercial latex agglutination reagents for grouping streptococci.

A total of 155 strains of beta-hemolytic streptococci were serologically grouped by conventional techniques (Lancefield extraction and capillary precipitin testing) and by latex agglutination (LA). Agreement between conventional and LA techniques was 97% when the instructions of the manufacturer for the LA technique were followed. Agreement of 99% was obtained when modified autoclave extracts were used as antigens in the LA procedure. A total of 82 strains of non-beta-hemolytic streptococci were also tested by conventional, prescribed LA, and modified autoclave procedures. The agreement between conventional techniques and both LA procedures was 76%. However, when serological cross-reactions in the conventional grouping procedures were considered as errors, the accuracy of identification of both LA procedures was 88% among the non-beta-hemolytic strains. Of 13 strains of Streptococcus bovis, 10 did not react with the LA group D reagent but were serogroup D by conventional techniques. More S. bovis strains were grouped by the LA technique when extracts of 20 ml of broth cultures were used as antigens; however, cross-reactions were observed with non-group D strains when this technique was applied to them.     

Serological grouping of streptococci by slide agglutination.

Streptococcal grouping sera for groups A, B, C, and G prepared for conventional testing by precipitation were made specific by absorption and used to identify streptococci by slide agglutination with and without staphyloccocal coagglutination. Trypsinised suspensions of 1055 strains, identified by precipitation as belonging to group A, B, C, or G, were tested by slide agglutination. Of these, 998 were correctly identified using a streptococcal suspension and antisera alone and a further 65 were identified when a loopful of protein A-positive staphylococci was added. Suspensions of 88 strains not of groups A, B, C, or G gave no reaction in the agglutination test with or without the addition of staphylococci. Group polysaccharide extracted by conventional methods also caused agglutination of staphylococci on a slide when specific antiserum was added. Growth from primary or secondary cultures digested in streptomyces enzyme for only 15-30 minutes provided an excellent antigen for a quick and simple method of streptococcal grouping using non-sensitised staphylococcal suspension and specific antisera for coagglutination.     

Multicentre evaluation of a direct coagglutination test for group A streptococci

A coagglutination test for detection of group A streptococci in throat samples was evaluated in a multicentre study and found to be about 95 % sensitive when applied to swabs taken from symptomatic patients which yielded more than 100 colonies per plate on culture. The sensitivity of the test dropped significantly when it was applied to swabs giving fewer than 100 colonies on culture. The specificity of the test was high regardless of colony count on conventional media.     

Rapid grouping of beta-hemolytic streptococci by latex agglutination.

Latex agglutination was compared with fluorescent-antibody staining with group A conjugate and Lancefield precipitation for grouping of beta-hemolytic streptococci. Latex agglutination correctly grouped 98.8% of 82 group A streptococci and more than 95% of 187 group B, C, or G streptococci. Occasional cross-reactions occurred between groups A and C and groups B and G.     

Rapid grouping of streptococci by immunoelectroosmophoresis

Immunoelectroosmophoresis (IEOP) or countercurrent immunoelectrophoresis has been used to develop a rapid procedure for grouping group A, B, C, D, G and H streptococci. The group-specific carbohydrates were extracted by conventional methods such as treatment with acid or formamide and compared with extraction by autoclaving and pronase treatment for evaluation of the convenience with which many samples from clinical isolates can be handled. Grouping was then performed with commercial antisera for these 6 groups and the specificity and sensitivity of the test was compared with those of gel-immunodiffusion (ID) experiments. Immunoprecipitates developed in IEOP after 15 to 30 min (15 V/cm, 4 C). IEOP was up to 20 times more sensitive than ID or capillary precipitin tests, which makes it a rapid and convenient method. Clinical isolates could be typed the same day by IEOP. The IEOP method was also suitable for handling many samples at one time, which makes it a useful method for a diagnostic laboratory.     

Rapid coagglutination test for the direct detection of group A streptococci from throat swabs

A one-minute antigen detection test was compared with a conventional culture method for detecting group A -hemolytic streptococci. The test detects coagglutination between protein A and streptococcal antigen extracted directly from throat swabs. Of the 307 specimens tested, 66 (21.5%) were positive for group A streptococci by culture and 16 specimens (5.2%) were positive for other -hemolytic streptococci. The direct test agreed with the culture in 274 of 307 specimens (accuracy 89.3 %). The sensitivity of the test was 86.4 % (57/66), the specificity 90 % (217/241), the positive predictive value 70.4 % and the negative predictive value 96 %. If only throat cultures with more than 100 colonies of group A streptococci per plate, were considered, the sensitivity of the direct test rose to 96 %. If only a strong agglutination was considered positive, the specificity of the direct test rose to 98 %. Further studies are needed to determine whether this test could be used alone or in addition to culture.     

Evaluation of an improved Streptex kit for the grouping of beta-haemolytic streptococci by agglutination.

A modified Streptex kit in which the extraction procedure had been simplified was used to group 200 streptococcal strains. Positive reactions could be obtained with live colonies and over 90% of isolates were correctly grouped from primary isolation plates. Some minor cross-reactions were seen with Streptex, but these were not strong enough to cause any confusion and no isolates were incorrectly grouped. The extraction enzyme in the Streptex kit was relatively poor at extracting the group-specific teichoic acid of group D strains but worked well with groups A, B, C, F and G.     

Lim group B Strep Broth and coagglutination for rapid identification of group B streptococci in preterm pregnant women.

A total of 147 preterm pregnant women at Orlando Regional Medical Center were screened for group B streptococci by using Lim Group B Strep Broth (GIBCO Laboratories, Madison, Wis.) and the Phadebact Strep B Test (Pharmacia Diagnostics, Piscataway, N.J.). Test results were available within 20 h of culture and, in the case of heavily colonized women, within 5 h. This procedure is useful in rapid diagnosis of preterm pregnant women for group B streptococcal colonization.     

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.