CHARACTERIZATION OF GROUP-A STREPTOCOCCAL ISOLATES FROM TROPICAL AUSTRALIA WITH HIGH PREVALENCE OF RHEUMATIC-FEVER - PROBING FOR SIGNATURE SEQUENCES TO IDENTIFY MEMBERS OF THE FAMILY OF SEROTYPE-5

The prevalence of rheumatic heart disease (RHD) in Northern Territory Aboriginal communities is high, but there is a low isolation rate of h istorically rheumatic fever associated M types (such as M5) of group A streptococci (GAS). Many isolates are M non-typable (MNT). Serology s uggests that the population is exposed to M5-like isolates; some RHD p atients having high IgM or IgG titres to two M5 B-repeat region peptid e epitopes, B1 (KQQESK) and B4 (EQKSKQ). To identify relatives of M5 i n our collection of GAS, oligonucleotide probes to the B1 and B4-repea t regions shared by M5 and a local M5-like isolate, were used to scree n 101 isolates for the presence of signature sequences. In all, 28% of the tropical Australian isolates contained the signature sequences, i dentifying members of the M5 family. The 5' region of the genes for M proteins from th ree members of the M5 family fell into two sequence t ypes. Hybridisation to probes based on these sequences suggested that among tropical Australian isolates there are at least three distinct s equence types that contained the M5 signature sequences. These results suggest that a considerable number of M5 family GAS are circulating i n tropical Australia.