Group A Streptococcus Gene Expression in Humans with Pharyngitis Using a Microarray

This study represents the first in vivo genome wide analysis of gene epxression of Group A Streptococcus (GAS) in humans with pharyngitis. The micorarray used is a custom microarray that relies on an electrochemical reaction as the measured signal rather than flourescence. Distinct clusters of gene expression were discovered and analyzed. A functional analysis examining differences and similarities between the clusters was performed. Samples were taken from pediatric patients who had received a throat swab as part of their clinical care for evaluating pharyngitis. Eleven samples that were culture postive for GAS were used along with 3 samples from subjects who were GAS culture negative. The microarray was a composite comprised of 12,000 probes, representing 2724 GAS open reading frames belonging to serotypes M1, M3, M4, M12, and M28. There were 1671 probe sets that were homologous for the M1 serotype and represented over 95% of the total predicted coding region. Probe sets were 30-40mers in length and were selected using a Combimatrix probe selection algorithm taking into account gene (>90% BLAST score) and serotype specificity, Tm, hairpins and GC content. In addition, 70 Combimatrix built in probes were used as negative controls for background subtraction.