Molecular Epidemiological Research Of Group A Streptococci From Children In Chongqing

Objective: (1) To analyze the distribution of macrolide-resistance genes (ermB, ermTR and mefA) between GAS infective and asymptomatic children. (2) To analyze the distribution of eight superantigen genes(ssa, smeZ, speA, speC, speG, speH, speI and speJ) in children's GAS infective isolates. (3) To analyze emm type, macrolide-resistance genes and superantigen gene profile among children's pharyngitis of GAS isolatesMethods: The macrolide-resistant genotype (ermB, ermTR and mefA) and superantigen gene of group A streptococcal isolates(ssa,smeZ,speA,speC,speG,speH,speI,speJ)were detected by PCR. Emm types were applied by PCR and sequencing. According to the CDC (http://www.cdc.gov/ncidod/biotech/strep/doc.htm) guidelines, a sequence was considered to belong to a specific emm gene.Results: (1) Among 217 isolates of GAS, 212 isolates were detected ermB gene(97.1%), 136 isolates were detected ermTR gene(62.7%), and 12 isolates were detected mefA gene(5.5%); The frequency carried ermTR gene in GAS asymptomatic children(71.8%) was significantly higher in GAS infective children(50.5%) (P=0.001<0.05); The frequency carried ermTR gene in GAS infective isolates apparently decreased from 66.0% in 2007 to 30.0% in 2008(P=0.001<0.05). (2) Amoung 93 isolates from GAS infective children, 93 isolates were detected ssa and speA(100.0%), 90 iolates were detected smeZ(96.8%), 83 isolates were detected speC(89.2%), 74 isolates were detected speG(79.6%), 55 isolates were detected speI(59.1%), 37 isolates were detected speA(39.8%), and 15 isolates were detected speJ(16.1%). SpeA was detected by 50.9% in 2007, and 25.0% in 2008. The incidence of speA gene decreased significantly over the two years (p=0.011<0.05). Amoung 93 isolates from GAS infective children, it had 18 superantigen gene profiles. Profile A was the common superantigen gene profile of 31 isolates(33.3%).(3) Emm12 was the most common emm types with 26 isolates among children's pharyngitis of GAS isolates in 2007(59.1%). Emm1 was the second with 7 isolates (15.9%). Emm22 had 2 isolates, emm6 had 2 isolates, emm3 had 2 isolates, emm80, emm63, emm102, stG485 and st1815 had 1 isolate respectively. 6 in 7 isolates of emm1 type were detected speA gene (85.7%), and 7 in 26 isolates of emm12 type were detected speA gene (26.9%). The distribution of speA in emm1 and emm12 was a statistically significant difference (P=0.008, <0.05). ProfileA was the common superantigen gene profile of 11 isolates in emm12 (42.3%). The distribution of macrolide-resistant genotype was random, and had no correlation with emm types.Conclusion : (1) The macrolide-resistant mechanism was most determined by the change of target site in the 23SrRNA methylase encoded by erythromycin resistance methylase B (ermB) genes, and most had the constitutive macrolide-lincosamide-streptogramin B (MLSB) resistance phenotype. Because inducible resistance was possiblely transformed to constitutive resistance, the frequency carried ermTR gene was higher in GAS asymptomatic children than GAS infective children, and the frequency carried ermTR gene in GAS infective isolates decreased in two years. (2) SpeC was associated with non-invasive GAS infection especially with pharyngeal infection. The incidence of speA decreased over the two years because of the possible decrease of severe GAS infection. Profile A was the common superantigen gene profile in children's non-invasive GAS infection especially in tonsillitis of Chongqing. (3) Most prevalent emm types in pharyngeal isolates were emm12 and emm1. Emm type was not apparantly related to macrolide-resistance genes. The distribution of speA was mainly related to emm1. Profile A was the common superantigen gene profile in emm12.