Doublet Benoît, Praud Karine, Bertrand Sophie, Collard Jean-Marc, Weill François-Xavier, Cloeckaert Axel
Centre National de Référence des Salmonella, Laboratoire des Bactéries Pathogènes Entériques, Institut Pasteur, 28 Rue du Docteur Roux, 75724 Paris Cedex 15, France.
Antimicrob Agents Chemother. 2008 Oct;52(10):3745-54. doi: 10.1128/AAC.00525-08. Epub 2008 Aug 1.
Salmonella genomic island 1 (SGI1) is an integrative mobilizable element that harbors a multidrug resistance (MDR) gene cluster. Since its identification in epidemic Salmonella enterica serovar Typhimurium DT104 strains, variant SGI1 MDR gene clusters conferring different MDR phenotypes have been identified in several S. enterica serovars and classified as SGI1-A to -O. A study was undertaken to characterize SGI1 from serovar Kentucky strains isolated from travelers returning from Africa. Several strains tested were found to contain the partially characterized variant SGI1-K, recently described in a serovar Kentucky strain isolated in Australia. This variant contained only one cassette array, aac(3)-Id-aadA7, and an adjacent mercury resistance module. Here, the uncharacterized part of SGI1-K was sequenced. Downstream of the mer module similar to that found in Tn21, a mosaic genetic structure was found, comprising (i) part of Tn1721 containing the tetracycline resistance genes tetR and tet(A); (ii) part of Tn5393 containing the streptomycin resistance genes strAB, IS1133, and a truncated tnpR gene; and (iii) a Tn3-like region containing the tnpR gene and the beta-lactamase bla(TEM-1) gene flanked by two IS26 elements in opposite orientations. The rightmost IS26 element was shown to be inserted into the S044 open reading frame of the SGI1 backbone. This variant MDR region was named SGI1-K1 according to the previously described variant SGI1-K. Other SGI1-K MDR regions due to different IS26 locations, inversion, and partial deletions were characterized and named SGI1-K2 to -K5. Two new SGI1 variants named SGI1-P1 and -P2 contained only the Tn3-like region comprising the beta-lactamase bla(TEM-1) gene flanked by the two IS26 elements inserted into the SGI1 backbone. Three other new variants harbored only one IS26 element inserted in place of the MDR region of SGI1 and were named SGI1-Q1 to -Q3. Thus, in serovar Kentucky, the SGI1 MDR region undergoes recombinational and insertional events of transposon and insertion sequences, resulting in a higher diversity of MDR gene clusters than previously reported and consequently a higher diversity of MDR phenotypes.
沙门氏菌基因组岛1（SGI1）是一种整合型可移动元件，携带一个多药耐药（MDR）基因簇。自其在流行的肠炎沙门氏菌鼠伤寒血清型DT104菌株中被鉴定以来，已在几种肠炎沙门氏菌血清型中鉴定出赋予不同MDR表型的变异SGI1 MDR基因簇，并将其分类为SGI1-A至-O。开展了一项研究，以对从非洲返回的旅行者中分离出的肯塔基血清型菌株中的SGI1进行表征。测试的几种菌株被发现含有部分特征化的变异体SGI1-K，最近在澳大利亚分离出的一株肯塔基血清型菌株中有所描述。该变异体仅包含一个盒式阵列aac(3)-Id-aadA7和一个相邻的汞抗性模块。在此，对SGI1-K未表征的部分进行了测序。在与Tn21中发现的mer模块相似的mer模块下游，发现了一种镶嵌遗传结构，包括：（i）含有四环素抗性基因tetR和tet(A)的Tn1721的一部分；（ii）含有链霉素抗性基因strAB、IS1133和一个截短的tnpR基因的Tn5393的一部分；以及（iii）一个类似Tn3的区域，含有tnpR基因和β-内酰胺酶bla(TEM-1)基因，两侧是两个方向相反的IS26元件。最右侧的IS26元件被证明插入到SGI1主干的S044开放阅读框中。根据先前描述的变异体SGI1-K，将这个变异的MDR区域命名为SGI1-K1。由于不同的IS26位置、倒位和部分缺失，对其他SGI1-K MDR区域进行了表征，并命名为SGI1-K2至-K5。两个新的SGI1变异体SGI1-P1和-P2仅包含类似Tn3的区域，该区域由插入到SGI1主干中的两个IS26元件侧翼的β-内酰胺酶bla(TEM-1)基因组成。另外三个新变异体仅含有一个插入到SGI1的MDR区域位置的IS26元件，被命名为SGI1-Q1至-Q3。因此，在肯塔基血清型中，SGI1 MDR区域经历了转座子和插入序列的重组和插入事件，导致MDR基因簇的多样性比先前报道的更高，从而MDR表型的多样性也更高。
