Direct-Plate Serological Grouping of Beta-Hemolytic Streptococci from Primary Isolation Plates with the Phadebact Streptococcus Test

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Abstract
The grouping of .beta.-hemolytic streptococcal isolates by a new direct-plate procedure employing Phadebact Streptococcus Test reagents was compared with the results obtained with the 4- and 24-h Phadebact grouping procedure and with the Lancefield grouping obtained with a capillary precipitin test. The new procedure employed a modification of the Phadebact procedure that permitted the grouping of streptococci on glass slides with a minimum of 5 primary isolated colonies. When only 5-8 colonies were available for direct testing with each Phadebact reagent, coagglutination was better manifested when the colonies were disaggregated on a glass slide in a loopful of Tween 80 solution. Further enhancement of the coagglutination reaction was effect when the respective Phadebact reagents were employed in relatively small volumes. The direct-plate procedure permitted the correct identification of 127 out of 129 .beta.-hemolytic isolates. The 4-h method correctly identified 192 of the 200 streptococci tested. All of the 200 isolates tested by the 24-h procedure and the Lancefield grouping were correctly identified. The direct-plate Phadebact procedure affords the clinical microbiologist a rapid and reliable means of identifying groups A, B, C and G .beta.-hemolytic streptococci. When sufficient numbers of primary colonies are not available for the direct procedure, the 4- or 24 h procedures may be employed.