D. LIBERTUCCI, B. M. WILLEY, A. BERNSTON, G. TYRRELL, M. LOVGREN, S. PONG-PORTER, D. E. LOW, The Group A Streptococcal Study Group, A. MCGEER. Mount Sinai and Princess Margaret Hospitals, University of Toronto, Ontario; and The National Center for Streptococcus (NCS), Edmonton, Alberta.

Objective: To determine the association between PFGE and M-protein typing (performed by the NCS) of GAS.

Methods: A total of 887 sterile site isolates were available from population based surveillance for invasive disease in Ontario between 1992-96. Of these 145 M1/T1, 90 M3/T3, 8 M4/T4, 74 M12/T12, 16 M28/T28, and 27 M-variable/T11 were selected for SmaI PFGE. These were compared to 101 M-non-typeable (NT)/T-variable strains, which included 46 M-NT/T11. PFGE parameters were as follows: 5-60s, 200V, 12° C, for 20h.

Results: PFGE found all strains of the same M-type to be clonally related, with only occasional band shifts. Clonality was also established among typeable and NT GAS. Within the 90 M3/T3 strains, 54 strains exhibited the single most pattern, which differed by one band. This one band shift was associated both with the presence of the speA gene, and with a significant increase in the incidence of toxic shock and mortality. Of the 46 MNT/T11 isolates, 32 had a single PFGE pattern, which was indistinguishable from that of MPT4245/T11 strains identified in 1997/8 (MPT4245 antiserum was not available for typing until 1997). Several individual M-NT and/or T-NT strains had PFGE patterns indistinguishable from M-typeable strains.

Conclusion: PFGE patterns are highly conserved within GAS of the same M-type. In most situations, PFGE yields the same information as M-typing. However, PFGE adds information when strains cannot be serotyped. Differences in genotype within strains of a single M-serotype may be associated with important differences in severity of illness.

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