Molecular epidemiological research of superantigen genes of group A Streptococci isolated from children in Chaoyang district, Beijing, 2011

Objective To describe the molecular epidemiological characteristics of superantigens of group A Streptococcus (GAS) in Chaoyang district, Beijing, 2011, and to analyze the relationship between superantigen genes, emm types and the diseases caused by GAS. Methods The 71 GASs were isolated from the throat swabs of hospita-lized children with scarlet fever, pharyngitis or tonsillitis.The presence of 8 known superantigens were determined in all the strains by PCR, including the speA, speI, ssa, speC, speJ, speG, speH and SMEZ.The emm genes were amplified from each strain and sequenced to determine the emm types using PCR.Based on the chi-square test, the relationships between superantigen genes, emm types and the diseases caused by GAS were analyzed. Results Eight superantigen genes, including speC, SMEZ, ssa, speG, speH, speI, speA and speJ were found in 100.0%(71/71 cases), 100.0%(71/71 cases), 97.2%(69/71 cases), 95.8%(68/71 cases), 80.3%(57/71 cases), 80.3%(57/71 cases), 15.5%(11/71 cases)and 12.7%(9/71 cases)of all GAS isolates.The most prevalent emm type was emm12.0 (62 isolates), followed by emm1.0 (7 isolates), emm22.0 (1 isolate) and emm75.0 (1 isolate). The speA and speJ gene were detected primarily in emm1.0 strains(all P<0.05), while speI and speH genes were in emm12.0 strains(all P<0.05). The distribution of speH and speI was correlated with the diseases caused by the GAS(all P<0.05). The distribution of diseases caused by the GAS in the emm12.0 and emm1.0 strains had no significant difference. Conclusions The detection rates of the superantigen genes are associated with the region where the GAS are isolated.Conserved superantigen profiles for different emm types, especially the presence or absence of bacteriophage encoded superantigens, support the contention that surface M proteins selectively influence the entry of bacteriophages, including those encoding superantigens.The research also indicates that the presence of superantigen genes is more important for the disease caused by the GAS than emm types. Key words: Group A Streptococcus; Superantigen gene; Emm type