The different Lancefield T-serotypes correlate with the sequence of the pilus backbone protein (Pbp) in Streptococcus pyogenes (GAS). We have sequenced Pbp for over 50 GAS strains, representing the major disease associated serotypes, and have identified 15 Pbp variants. These 15 variants have been shown to determine the specificity of the T-serotyping, such that sequencing of the Pbp from a given GAS strain reliably predicts that strain's T-serotype. Thus the invention permits the T-serotype of a GAS strain to be determined based on genotype.
