EXTENSIVE GENETIC DIVERSITY AMONG CLINICAL ISOLATES OF STREPTOCOCCUS-PYOGENES SEROTYPE M5

The genetic diversity of clinical isolates of Streptococcus pyogenes s erotype M5 has been characterized. Strain genotypes were defined by ma crorestriction profile, 165 ribotype, emm gene subtype, insertion elem ent IS1239 profile, and exotoxin gene determinant. By these criteria, clinical isolates of M5 constituted a multiplicity of strain clusters rather than a homogeneous population as found for certain serotypes. D istance matrices and an unrooted tree were constructed from macrorestr iction data with three rarely cutting endonucleases, determined by PFG E. A single IS1239 profile was common to 85% of isolates but there was great diversity of both ribotype and macrorestriction profile, and 18 different emm gene subtypes were detected by PCR-RFLP. DNA sequence a nalysis of the antigen-coding 5' (hypervariable) region of emm gene am plicons (about 240 bp) showed that 14/18 exhibited up to 6% divergence . Four amplicons had highly divergent sequences - corresponding to tho se previously determined for emm 6, emm 11, emm 18 and emm 77. Further serological and hybridization studies were used to analyse the discre pancy between the Lancefield serotype of these strains (Ms) and their emm genotype, Overall, this study shows a high degree of genetic diver sity in serotype M5, with implications for the Lancefield scheme itsel f, for the epidemiology of group A streptococci, and for recombinant D NA strategies for M protein-based vaccine development.