Molecular characterisation of group A streptococci from invasive and non-invasive disease episodes in Belgium during 1993-1994

Five hundred clinical group A streptococcal (GAS) isolates were collected in Belgium during the period 1 Nov, 1993 to 31 Oct. 1994, Clinical and laboratory data were recorded and isolates were characterised, The presence of the genes encoding streptococcal pyrogenic exotoxin types A (speA), B (speB), C (speC), F (speF) and streptococcal superantigen (ssa) were determined by PCR to target specific sequences. These isolates were also emm-typed and analysed by pulsed-field gel electrophoresis (PFGE) of genomic macrorestriction fragments with the enzyme SmaI. In total, 136 unrelated GAS PFGE types were identified and genetic diversity was clearly demonstrated. Two GAS PFGE types predominated; a first PFGE type comprised 66 (13.2%) emm1 isolates characterised by speA(+), speB(+), speC(-), speF(+) and ssa(-); the second PFGE type comprised 44 (8.8%) emm12 isolates characterised by speA(-), speB(+), speC(+) (or speC-), speF(+) and ssa(-). Indistinguishable PFGE types were observed among both invasive and non-invasive isolates. Ten different PFGE types were found among 11 streptococcal toric shock syndrome (STSS) isolates, and five of these lacked speA, Twenty-five (34.7%) of 72 invasive isolates gave negative results for speA, speC and ssa. This retrospective study confirmed the observation that the dissemination of one specific clone cannot be associated with invasive GAS disease and posed a question regarding the role of SPE A as a major virulence factor. Other streptococcal virulence factors in conjunction with host factors may determine the outcome of invasive GAS infection.