Clinical Characterization of Group A Streptococcal Bacteremia and Restriction-Fragment Length Polymorphism of emm Gene and Pulsed-field Gel Electrophoresis

Koh, Eun Ha; Kim, Sunjoo; Kim, Eui Chong

Abstract

BACKGROUND
M protein is the major virulence factor of group A streptococci (GAS). As the emm gene, which encodes the M protein, has a variable sequence at 5'-terminus by each M type, it can be classified into several restriction-fragment length polymorphisms (RFLP) by restriction enzymes. Pulsed-field gel electrophoresis (PFGE) is useful for investigating clonal outbreaks or bacterial transmission. Molecular epidemiological analysis using emm-RFLP and PFGE was performed on GAS isolated from bacteremia. METHODS: Twenty-eight strains of GAS isolated from patients with bacteremia were included. Medical records of 27 cases were reviewed retrospectively to see the prognosis of GAS bacteremia. The restriction patterns of emm gene digested with HaeIII enzyme were compared by each emm genotype. Macrorestriction patterns were produced by PFGE after digestion of chromosomal DNA with SmaI and ApaI enzymes. RESULTS: All but 2 cases with toxic streptococcal syndrome survived. The DNA fragments of emm-HaeIII restriction showed 3 to 4 bands. Each emm genotype showed a different emm-HaeIII restriction pattern, except emm49 and SP2346, of which the restriction pattern was similar to that of emm1. Thirteen different PFGE patterns were observed by SmaI, and emm6, emm12, and emm75 were not cut with SmaI. All 28 strains were cut with ApaI, which yielded 17 different PFGE patterns. All but emm13 showed a high concordance between the PFGE patterns and the emm genotypes. CONCLUSIONS: The patients with GAS bacteremia showed a relatively good prognosis. We found that the restriction enzyme analysis of emm gene was rapid, simple and inexpensive to perform, and that PFGE was useful for classifying GAS strains because it generally discriminated well between each emm genotype. Although the number of strains studied was small, GAS bacteremia was not due to a single clone.