儿童耐甲氧西林金黄色葡萄球菌感染分离株毒力特征研究

Comparative analysis of the virulence characteristics of epidemic methicillin-resistant Staphylococcus aureus strains isolated from Chinese children

目的 探讨儿童耐甲氧西林金黄色葡萄球菌（MRSA）感染分离株的毒力特征.方法 收集2004年6月至2012年7月4家儿童医院分离的243株MRSA,采用PCR法对MRSA进行多位点序列分型（MLST）;按随机分层抽样法对136株菌进行42种毒力基因及4种重要毒力基因hla、psmα、RNAⅢ和pvl的表达水平检测.结果 MRSA分离株大多数来源于肺炎和皮肤软组织感染（SSTIs）,占88.1％（214/243株）.243株菌检测到22种MLST,6种主要流行克隆是ST59、ST239、ST1、ST910、ST88和ST338.131株菌（96.3％）至少含有1种超抗原基因.所有菌株均携带黏附基因中的fnbA、clfA和spa.所有菌株均携带hla,psmα和RNAⅢ,pvl的携带率为39％.pvl在ST59、ST910、ST338分离株中的携带率较ST239、ST1、ST88高（P均＜0.05）.hla、smα、RNAⅢ在ST59中的表达水平较其他分型高（P均＜0.05）.社区获得性MRSA （CA-MRSA）分离株pvl的携带率高于医院获得性MRSA（HA-MRSA）分离株（48.8％比24.1％,x2 =8.356,P=0.004）,但pvl表达水平比较差异无统计学意义（t=-0.777,P=0.441）.CA-MRSA分离株hla、smα和RNAⅢ的表达水平较HA-MRSA分离株高（P均＜0.05）.肺炎分离株fnbB的携带率明显高于SSTIs分离株（27.5％比12.7％,x2 =4.050,P=0.044）,而SSTIs分离株pvl的携带率明显高于肺炎分离株（52.7％比27.5％,x22=8.186,P=0.004）.侵袭性感染分离株的hla表达水平较非侵袭性感染高（=2.433,P=0.0163）.结论 儿童MRSA感染分离株的主要流行克隆间部分毒力基因携带存在差异.CA-MRSA较HA-MRSA高表达hla、psmα、RNAⅢ,尤其是ST59型,提示该型菌株可能具有较强的致病性.fnbB与肺炎、pvl与SSTIs可能有关.菌株高表达hla可能与侵袭性感染有关.

Obgective To investigate the virulence characteristics of methicillin-resistant Staphylococcus aureus（MRSA） isolates from Chinese children.Methods A total of 243 MRSA isolates were collected from 4 hospitals from June of 2004 to July of 2012.Multilocus sequence typing was analyzed by PCR.A total of 136 strains were selected from 6 major STs of 243 isolates based on stratified sampling.The carriages of 42 virulence genes were tested.Expression levels of hla,psmα and RNA Ⅲ genes were also detected,as well as pvl.Results Most of MRSA isolates were from pneumonia and skin and soft tissue infections （SSTIs）,accounting for 88.1% （214/243 strains）.Twenty-two sequence types were obtained,and 6 epidemic clones were ST59,ST239,ST1,ST910,ST88 and ST338.It was found that 96.3% strains（131/136 strains） contained at least one superantigen gene.All isolates were presented with fnbA,clfA and spa genes.All these 136 isolates all had hla,psmα and RNAⅢ.The percentage ofpvlgene was 39%.The pvl gene was more frequent in ST59,ST910,ST338 than in ST239,ST1,ST88（all P 〈0.05）.The expression levels of hla,psmα and RNA Ⅲ were higher in ST59 than in other STs（all P 〈0.05）.Thepvl gene was more associated with community acquired MRSA（CA-MRSA） than with hospital acquired MRSA（HA-MRSA） （48.8% vs 24.1%,x2 =8.356,P =0.004）,but there was no statistically significant difference in their expression levels （t =-0.777,P =0.441）.CA MRSA expressed hla,psma,and RNA Ⅲ in much higher levels （P 〈 0.05）.The fnbB gene was more associated with pneumonia than with SSTIs （27.5% vs 12.7%,x2 =4.050,P =0.044）,while the pvl gene was more associated with SSTIs than with pneumonia （52.7 % vs 27.5 %,x2 =8.186,P =0.004）.Expression of hla in isolates from invasive infections was higher than that in isolates from non-invasive infections（t =2.433,P =0.0163）.Conclusions The distribution of virulence genes among epidemic MRSA strains isolated from children was different.CA-MRSA expressed hla,psmα,and RNA Ⅲ in much higher levels,especially ST59 strains,which might lead to their enhanced pathogenicity.The fnbB gene might be associated with pneumonia,while the pvl gene is associated with SSTIs,and the hla gene might be associated with invasive infection.