Survey of the bp/tee genes from clinical Group A Streptococcus isolates in New Zealand - implications for vaccine development.
[acute rheumatic fever]
Group A Streptococcus (GAS) is responsible for a wide range of diseases ranging from superficial infections, such as pharyngitis and impetigo to life-threatening diseases like toxic shock syndrome and acute rheumatic fever (ARF). GAS pili are hair-like extensions protruding from the cell surface and consist of highly immunogenic structural proteins; the backbone pilin (BP) and one or two accessory pilins (AP1 and AP2). The protease-resistant BP builds the pilus shaft and has been recognised as the T-antigen, which forms the basis of a major serological typing scheme that is often used as a supplement to M-typing. A previous sequence analysis of the bp gene (tee gene) in 39 GAS isolates revealed 15 different bp/tee types. In this study, we sequenced the bp/tee gene from 101 GAS isolates obtained from patients with pharyngitis, ARF or invasive disease in New Zealand. We found 20 new bp/tee alleles and 4 new bp/tee types/subtypes. No association between bp/tee type and clinical outcome was observed. We confirmed earlier reports that emm-type and tee-type are strongly associated, but we also found exceptions, where multiple tee-type can be found in certain M/emm type strains, such as M/emm89. We also report, for the first time, the existence of a chimeric bp/tee allele, which was assigned into a new subclade (bp/tee 5.1). A strong sequence conservation of the bp/tee gene was observed within the individual bp/tee types/subtypes (>97% sequence identity), as well as between historical and contemporary New Zealand, and international GAS strains. This temporal and geographical sequence stability provides further evidence for the potential use of the BP/T-antigen as a vaccine target.
