M-Protein Genotyping and Exotoxin A Production of Group A Streptococci Isolated from Blood

Kim, Seon Ju; Kim, Eui Chong

Abstract

BACKGROUND
S: While M protein is the most important virulence factor of group A -hemolytic streptococci (GAS), the routine laboratories have difficulty to maintain more than 80 kinds of antibodies. emm gene encoding M protein has variable sequence at 5'-terminus according to each M type and is an appropriate target for molecular typing of GAS. Molecular epidemiologic analysis using emm gene sequencing and serological typing were conducted for GAS isolated from bacteremic patients. Also production of streptococcal pyrogenic exotoxin A (SPE A), a well known virulence factor in toxic streptococcal syndrome, and the frequency of speA and speB gene for the strains were observed.
METHODS
Twenty-eight strains of GAS isolated from blood specimens were analyzed with serological or molecular typing. Serological typing including T antigen and serum opacity reaction was processed by standard methods. 5' region of emm PCR products was analyzed by automatic DNA sequencer. The obtained DNA sequences were matched with GenBank. Production of SPE A was confirmed by Western blot and the frequencies of spe genes were analyzed by PCR.
RESULTS
All GAS strains were well classified into 13 kinds of different emm genotypes. emm13 (18%) was most common and emm1 and emm3 were three and two strains respectively. Discrepancy between T typing and emm genotyping was observed in two strains. speA gene and SPE A toxin were positive in six over 28 strains, of which emm types were emm1, emm3 and SP2346.
CONCLUSION
In the distribution of emm genotypes of GAS isolated from blood, emm13 was the most common genotype, of which finding is quite different from the results of foreign countries. Virulent types such as emm1 (11%) and emm3 (7%) genotypes were not uncommon, which were positive in speA gene and SPE A toxin.