Rapid method for identification of group B streptococci in neonatal blood cultures

Abstract

A rapid technique used for the identification of Streptococcus agalactiae, Lancefield group B, from the blood cultures of two neonatal infants is reported. The method utilized the Phadebact Streptococcus Test System (Pharmacia Diagnostics, Piscataway, N.J.) and the supernatant from 13-and 14-h blood cultures. Additional studies with simulated neonatal blood cultures revealed that this method was reproducible. Additional studies also revealed that some nonspecific agglutination did occur, which could not be eliminated with dithiothreitol, but was visibly reduced by treatment with soluble staphylococcal protein A.

Direct Testing of Blood Cultures for Detection of Streptococcal Antigens

“…For this reason, rapid identification of organisms has been a major area of research in the microbiology laboratory over the past few years. This is evidenced by the numerous studies which have attempted to solve this problem by testing the reliability of different methods of bacterial identification (e.g., latex agglutination, coagglutination, enzyme-linked immunosorbent assay, counterimmunoelectrophoresis) directly on body fluids and blood cultures (1,5,8,11,12).…”

“…In our study the coagglutination test was chosen because it has been shown to be a very rapid, accurate, and easy test to perform for identifying streptococci (3,7,9). We wanted to expand on previously reported studies (8,11,12) to directly test for streptococcal antigens in blood cultures other than just group B and to include patients of all age groups rather than just infants. We developed a method for direct coagglutination testing for streptococcal groups A, B, C, D, and G by using simulated blood cultures and subsequently used this method to test clinical cultures.…”

“…Blood cultures and other body fluids are some of the most important specimen types processed in the laboratory, since results can significantly influence the therapy and final outcome of the patient. Therefore, many investigators have focused their attention on improving reporting time with these specimens (1,5,8,11,12). Direct testing of fluids by counterimmunoelectrophoresis and coagglutination has proven to be a valuable asset in the early detection of organisms (1,5,8,12).…”

“…Thus far, the coagglutination method has only been used to directly test for group B streptococcal antigen in a very limited number of clinical blood cultures (8). Hence, by expanding on this concept, the objective of this study was to develop a method in which coagglutination could be used to directly test blood cultures for streptococcal groups A, B, C, D, and G.…”