Use of a serotype-specific DNA microarray for identification of group B Streptococcus (Streptococcus agalactiae)

Abstract

Group B Streptococcus (GBS; Streptococcus agalactiae) is an important cause of sepsis and meningitis. Nine GBS serotypes, based on capsular polysaccharide (CPS) antigens, have been described. Their distribution varies worldwide and needs to be monitored to understand the epidemiology of GBS disease and inform the development of vaccines. In this study, we sequenced cpsH of GBS serotype II (cpsHII) and compared it with that of the other eight serotypes to identify serotype-specific regions. We then developed a DNA microarray based on the cpsH gene and used it to test 88 GBS isolates-9 serotype reference strains and 79 clinical isolates-and 7 other bacterial and fungal species which are commonly present in the vagina flora. The microarray was shown to be specific and reproducible. This is the first report of a microarray which can identify the nine GBS serotypes. The use of a microarray has advantages over traditional serotyping methods and will be of practical value in both reference and diagnostic laboratories.

FIG. 1.

Schematic diagram of the microarray, showing positions of immobilized probes spotted within a single well of the four-well glass slides. Each array contains 150 spots arranged in 15 columns. Cy3 is a fluorescent dye. Sequences of probes immobilized at each location are shown in Table 3.

FIG. 2.

A phylogenetic tree generated based on cpsH of all nine GBS serotypes by the neighbor-joining method.

FIG. 3.

Representative hybridization results of GBS strains of nine serotypes. The number under each array shows the serotype of GBS tested. Three lines of dots located in the middle of the array are positive controls based on cfb of GBS.