深圳社区感染沙门菌耐药基因调查与同源性分析

Analysis of antimicrobial resistant mechanisms and genetic homogeny of Salmonella from community acquired infections in Shenzhen

目的调查深圳社区感染沙门菌耐药特点和分子机制，并进行同源性分析。方法收集深圳市人民医院2002--2007年临床分离沙门菌共93株，PCR和DNA测序分析沙门菌gyrA、gyrB、parC和pare基因QRDR的突变，PCR检测质粒介导喹诺酮耐药基因qnr和aac（6’）-Ib—CF，B内酰胺酶基因blaTEE、blaSHV、blaOKA和blaCTX-M基因，以及I类整合子，PFGE对沙门菌进行分子分型。结果伤寒沙门菌和甲型副伤寒沙门菌对氨苄西林、氯霉素、复方磺胺甲嗯唑、头孢曲松和环丙沙星敏感率为96％-100％；52％（13／25）伤寒沙门菌和95％（61／64）甲型副伤寒沙门菌对萘啶酸耐药。24％（6／25）萘啶酸耐药伤寒沙门菌和94％（60／64）萘啶酸耐药甲型副伤寒沙门菌对环丙沙星敏感性降低（MIC0．125—1μg／mL）。75株萘啶酸耐药环丙沙星敏感沙门菌仅GyrA的QRDR均存在第83位或87位单个氨基酸替代，其中Ser83Phe突变占91％（68／75）。2株环丙沙星耐药沙门菌在QRDR中均携带GyrA上2个点突变和parC上1个点突变。93株沙门菌均未发现质粒介导的qnr和aac（6’）-，6-基因。1株头孢曲松耐药甲型副伤寒沙门菌检测到blaCTX-M-14。基因，且该基因上游存在插入序列ISEcpl。3株多重耐药沙门菌均存在一个1900bp的I类整合子，其基因盒均为dhfrXII-orfF—aadA2，同时携带blaTEM-1或blaOXA-30基因。25株伤寒沙门菌共有22种不同的PFGE带型，64株甲型副伤寒沙门菌的PFGE带型平均相似性为91％。90例患者均系社区感染，6例甲型副伤寒患者发病前30天内曾前往外地旅行。结论深圳社区感染伤寒和甲型副伤寒沙门菌对萘啶酸耐药率较高，沙门菌GyrA的QRDR点突变是萘啶酸耐药的重要机制，甲型副伤寒沙门菌菌株问遗传同源性极高，来自同一克隆。

Objective To investigate the antimicrobial resistance mechanisms and genetic homogeny of Salmonella from community acquired infections in Shenzhen, China. Methods Ninety-three of Salmonella were isolated from 2002 to 2007 at Shenzhen People＇s Hospital, China. PCR and DNA sequencing were used to investigate the mutation in QRDR of the gyrA, gyrB, parC and parE. Plasmid mediated quinolone resistance genes including qnr and aac （6＇） -Ib-cr, β-lactamase genes including blaTEM, blaSHV,blaoxo, blacTX-M, and class 1 integron were detected. All isolates were typed by PFGE. Results S. enterica typhi and S. enterica paratyphi A were susceptible to ampicillin, chloramphenicol, trimethoprim/ sulfamethoxazole, ceftriaxone and ciprofloxacin, with the susceptible rate of 96%-100%. Fifty-two percent （13/25） of S. enterica typhi and 95% （61/64） of S. enterica paratyphi A were resistant to nalidixic acid. Twenty-four percent （6/25） of nalidixic acid-resistant S. enterica typhi and 94% （60/64） of nalidixic acid-resistant S. enterica paratyphi A showed decreased susceptibility to ciprofloxacin （MIC of 0. 125-1 μg/ml）. All nalidixic acid-resistant （susceptible to ciprofloxacin ） Salmonella （NARS） isolates bad a single substitution in the QRDR of GyrA, and 91% （68/75） of these isolates carried the substitutiml Ser83Phe in GyrA. Two mutations in the QRDR of GyrA were detected in both of two ciprofloxacin-resistant Salmonella, with the additional one mutation in the QRDR ofparC. Plasmid mediated quinolone resistance genes including qnr and aac （6＇）-Ib-cr were not detected in any isolate. The blacTX-M-14 gene was detected in a ceftriaxone- resistant isolate of S. enterica paratyphi A, with ISEcpl located on the upstream of it. Three multidrug- resistant strains of Salmonella all carried one I 900 bp class I integron gene cassette dhfrXlI-orfF-aadA2, with the additional one β-1actamase gene of blaTEM,t or blaoxa-30. Twenty-two distinct PFGE patterns were observed among twenty-five S. enterica typhi. The PFGE patterns of sixty-four S. enterica paratyphi A showed limited genetic diversity （average similarity of 91% ）. Ninety investigated inpatients were infected in the community. Six patients infected by S. enterica paratyphi A had a travel history before infection. Conclusions Nalidixic acid-resistant S. enterica typhi and S. enterica paratyphi A are highly prevalent in Shenzhen, China. The mutation in the QRDR of GyrA is the prevalent mechanism responsible for the resistance to nalidixic acid in Slmonella. The great genetic similarity among S. enterica paratyphi A isolates indicates endemic disease from the presence of a single clone over 6-year period.