Peirano Gisele, Agersø Yvonne, Aarestrup Frank M, dos Reis Eliane Moura Falavina, dos Prazeres Rodrigues Dalia
Oswaldo Cruz Institute Avenida Brasil 4365, 21045-900 Rio de Janeiro, Brazil.
J Antimicrob Chemother. 2006 Aug;58(2):305-9. doi: 10.1093/jac/dkl248. Epub 2006 Jun 16.
To determine the occurrence of antimicrobial resistance genes and role of integrons among 135 antimicrobial-resistant Salmonella enterica from Brazil.
The presence of antimicrobial resistance genes, class 1 and 2 integrons and gene cassettes was analysed by PCR and sequencing. The genetic location of class 1 integrons was determined in 25 isolates by hybridization and plasmid transfer experiments.
Fifty-five of the isolates were positive for class 1 integrons. Integron-positive isolates represented 17 different serovars and were mainly from human (n=28) and animal (n=13) sources. The gene cassette arrangements could be determined in 51 of the positive isolates, which harboured one [dfrA22, aadA1 or orf3 (putative trimethoprim resistance)], two [aadA1-dfrA1, aac(6')-Ib-orf1 (unknown function) or aacA4-aadA1], three [dfrA15b-cmlA4-aadA2, orf2 (unknown function)-dfrA5-orfD] or four [orf4-aacA4-blaOXA-30 (interrupted by an IS1 element)-aadA1] cassettes in their variable region. Only one isolate harboured a class 2 integron with the gene cassette array dfrA1-sat-aadA1. Several integron unrelated resistance genes were also detected in the isolates. Sulphonamide resistance was primarily mediated by sul2 and sul3, tetracycline resistance by tet(B) and tet(A), chloramphenicol resistance by catA1, streptomycin resistance by strA and ampicillin resistance by blaTEM. blaCTX and blaCMY-2 were found in cephalosporin-resistant isolates. Mating and hybridization experiments demonstrated that a high-molecular-weight plasmid mediated the gene transfer of integrons and additional resistance determinants.
The present study revealed that integron-mediated resistance genes contributed to the multiresistance phenotype observed in the isolates, but most resistance genes were located outside the integron structure, as independent genes. However, they might be located on the same conjugative plasmid.
确定来自巴西的135株耐抗菌药物肠炎沙门氏菌中抗菌药物耐药基因的出现情况及整合子的作用。
通过聚合酶链反应（PCR）和测序分析抗菌药物耐药基因、1类和2类整合子及基因盒的存在情况。通过杂交和质粒转移实验确定25株分离株中1类整合子的基因定位。
55株分离株1类整合子呈阳性。整合子阳性分离株代表17种不同血清型，主要来自人类（n = 28）和动物（n = 13）来源。51株阳性分离株的基因盒排列可确定，其可变区含有一个[二氢叶酸还原酶基因A22（dfrA22）、氨基糖苷腺苷转移酶基因A1（aadA1）或开放阅读框3（orf3，推测为甲氧苄啶耐药）]、两个[aadA1-dfrA1、6'-乙酰转移酶-Ib-开放阅读框1（aac(6')-Ib-orf1，功能未知）或乙酰转移酶A4-氨基糖苷腺苷转移酶基因A1（aacA4-aadA1）]、三个[二氢叶酸还原酶基因A15b-氯霉素乙酰转移酶基因4-氨基糖苷腺苷转移酶基因A2（dfrA15b-cmlA4-aadA2）、开放阅读框2（orf2，功能未知）-二氢叶酸还原酶基因A5-开放阅读框D（orfD）]或四个[开放阅读框4-乙酰转移酶A4-超广谱β-内酰胺酶OXA-30（被IS1元件中断）-氨基糖苷腺苷转移酶基因A1（orf4-aacA4-blaOXA-30-aadA1）]基因盒。仅1株分离株含有2类整合子，其基因盒阵列是二氢叶酸还原酶基因A1-链霉素乙酰转移酶-氨基糖苷腺苷转移酶基因A1（dfrA1-sat-aadA1）。在分离株中还检测到几个与整合子无关的耐药基因。磺胺类耐药主要由磺胺类耐药基因2（sul2）和磺胺类耐药基因3（sul3）介导，四环素耐药由四环素耐药基因B（tet(B)）和四环素耐药基因A（tet(A)）介导，氯霉素耐药由氯霉素乙酰转移酶基因A1（catA1）介导，链霉素耐药由链霉素耐药基因A（strA）介导，氨苄西林耐药由β-内酰胺酶TEM（blaTEM）介导。在耐头孢菌素分离株中发现了头孢菌素酶CTX（blaCTX）和头孢菌素酶CMY-2（blaCMY-2）。接合和杂交实验表明，一种高分子量质粒介导了整合子和其他耐药决定簇的基因转移。
本研究表明，整合子介导的耐药基因促成了分离株中观察到的多重耐药表型，但大多数耐药基因位于整合子结构之外，为独立基因。然而，它们可能位于同一接合性质粒上。
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