Genetic elements carrying erm(B) in Streptococcus pyogenes and association with tet(M) tetracycline resistance gene
Genetic elements carrying erm(B) in Streptococcus pyogenes and association with tet(M) tetracycline resistance gene
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DOI：
10.1128/aac.01484-06
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发表时间：
2007-04-01
影响因子：
4.9
通讯作者：
Giovanettil, Eleonora
中科院分区：
文献类型：
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作者：
Brenciani, Andrea;Bacciaglia, Alessandro;Giovanettil, Eleonora
本研究旨在鉴定化脓性链球菌中携带甲基化酶基因 erm(B) 的遗传元件，该基因编码核糖体修饰介导的对大环内酯、林可酰胺和链霉素 B (MLS) 抗生素的耐药性。在该物种中，erm(B) 负责组成型抗性分离株（cMLS 表型）和诱导抗性分离株的子集（iMLS-A）中的 MLS 抗性。总共研究了 125 株 erm(B) 阳性菌株，其中 81 株 iMLS-A（对四环素均敏感）和 44 株 cMLS（29 株对四环素耐药，15 株对四环素敏感）。尽管所有四环素抗性分离株均携带 tet(M) 基因，但在大多数四环素敏感分离株（81/81 iMLS-A 和 7/15 cMLS）中也检测到了 tet(M) 序列。在 8 个 tet(M) 阴性 cMLS 分离株中的 2 个中，erm(B) 由位于质粒的 Tn917 样转座子携带。通过 PCR 检测 erm(B) 和 tet(M) 阳性分离株是否存在与 Tn916 家族的接合转座子相关的基因 int（整合酶）、xis（切除酶）和 tndX（分解酶）。在使用不同表型和基因型特征组合的代表作为供体的交配实验中，erm（B）和tet（M）一致地共转移，表明它们在个体遗传元件中的联系。通过脉冲场凝胶电泳和杂交研究证实了这种联系，并且通过扩增和测序实验检测和表征了与不同表型/基因型不同相关的不同元件。在所有 iMLS-A 和一些 cMLS 分离株中观察到一种先前未报道的遗传组织，其特点是含有 erm (B) 的 DNA 插入到有缺陷的 Tn5397（一种 Tn916 相关转座子）的 tet(M) 基因中。这种新元素被命名为 Tn1116。之前在化脓性链球菌中未描述过的遗传元件还包括 Tn6002（一种未发表的转座子，其完整序列可在 GenBank 中找到）和 Tn3872（一种由 Tn917 转座子插入 Tn916 产生的复合元件）[与在一些 cMLS 分离株中表达但在其他分离株中沉默的 tet(M) 基因相关]。四环素敏感表型和 tet(M) 基因之间的高关联性表明，Tn916 家族的转座子（迄今为止通常仅与四环素抗性表型相关）在化脓性链球菌中可能比目前认为的更广泛。
This study was directed at characterizing the genetic elements carrying the methylase gene erm(B), encoding ribosome modification-mediated resistance to macrolide, lincosamide, and streptogramin B (MLS) antibiotics, in Streptococcus pyogenes. In this species, erm(B) is responsible for MLS resistance in constitutively resistant isolates (cMLS phenotype) and in a subset (iMLS-A) of inducibly resistant isolates. A total of 125 erm(B)-positive strains were investigated, 81 iMLS-A (uniformly tetracycline susceptible) and 44 cMLS (29 tetracycline resistant and 15 tetracycline susceptible). Whereas all tetracycline-resistant isolates carried the tet(M) gene, tet(M) sequences were also detected in most tetracycline-susceptible isolates (81/81 iMLS-A and 7/15 cMLS). In 2 of the 8 tet(M)-negative cMLS isolates, erm(B) was carried by a plasmid-located Tn917-like transposon. erm(B)- and tet(M)-positive isolates were tested by PCR for the presence of genes int (integrase), xis (excisase), and tndX (resolvase), associated with conjugative transposons of the Tn916 family. In mating experiments using representatives of different combinations of phenotypic and genotypic characteristics as donors, erm(B) and tet(M) were consistently cotransferred, suggesting their linkage in individual genetic elements. The linkage was confirmed by pulsed-field gel electrophoresis and hybridization studies, and different elements, variably associated with the different phenotypes/genotypes, were detected and characterized by amplification and sequencing experiments. A previously unreported genetic organization, observed in all iMLS-A and some cMLS isolates, featured an erm (B)-containing DNA insertion into the tet(M) gene of a defective Tn5397, a Tn916-related transposon. This new element was designated Tn1116. Genetic elements not previously described in S. pyogenes also included Tn6002, an unpublished transposon whose complete sequence is available in GenBank, and Tn3872, a composite element resulting from the insertion of the Tn917 transposon into Tn916 [associated with a tet(M) gene expressed in some cMLS isolates and silent in others]. The high frequency of association between a tetracycline-susceptible phenotype and tet(M) genes suggests that transposons of the Tn916 family, so far typically associated solely with a tetracycline-resistant phenotype, may be more widespread in S. pyogenes than currently believed.