Biology Department and CESAM, University of Aveiro, Aveiro, Portugal.
Appl Environ Microbiol. 2012 Jun;78(12):4134-40. doi: 10.1128/AEM.00359-12. Epub 2012 Apr 6.
We compared the resistomes within polluted and unpolluted rivers, focusing on extended-spectrum beta-lactamase (ESBL) genes, in particular bla(CTX-M). Twelve rivers from a Portuguese hydrographic basin were sampled. Physicochemical and microbiological parameters of water quality were determined, and the results showed that 9 rivers were classified as unpolluted (UP) and that 3 were classified as polluted (P). Of the 225 cefotaxime-resistant strains isolated, 39 were identified as ESBL-producing strains, with 18 carrying a bla(CTX-M) gene (15 from P and 3 from UP rivers). Analysis of CTX-M nucleotide sequences showed that 17 isolates produced CTX-M from group 1 (CTX-M-1, -3, -15, and -32) and 1 CTX-M that belonged to group 9 (CTX-M-14). A genetic environment study revealed the presence of different genetic elements previously described for clinical strains. ISEcp1 was found in the upstream regions of all isolates examined. Culture-independent bla(CTX-M)-like libraries were comprised of 16 CTX-M gene variants, with 14 types in the P library and 4 types in UP library, varying from 68% to 99% similarity between them. Besides the much lower level of diversity among CTX-M-like genes from UP sites, the majority were similar to chromosomal ESBLs such as bla(RAHN-1). The results demonstrate that the occurrence and diversity of bla(CTX-M) genes are clearly different between polluted and unpolluted lotic ecosystems; these findings favor the hypothesis that natural environments are reservoirs of resistant bacteria and resistance genes, where anthropogenic-driven selective pressures may be contributing to the persistence and dissemination of genes usually relevant in clinical environments.
我们比较了受污染和未受污染河流中的耐药组，重点关注了扩展谱β-内酰胺酶（ESBL）基因，特别是 bla（CTX-M）。从葡萄牙水文盆地采集了 12 条河流的样本。测定了水质的理化和微生物参数，结果表明 9 条河流被归类为未受污染（UP），3 条河流被归类为受污染（P）。在分离出的 225 株头孢他啶耐药菌株中，有 39 株被鉴定为产 ESBL 菌株，其中 18 株携带 bla（CTX-M）基因（15 株来自 P 河流，3 株来自 UP 河流）。CTX-M 核苷酸序列分析表明，17 株产生 CTX-M 组 1（CTX-M-1、-3、-15 和 -32）和 1 株 CTX-M 属于组 9（CTX-M-14）。遗传环境研究表明，存在先前在临床菌株中描述的不同遗传元件。在所检查的所有分离株的上游区域都发现了 ISEcp1。无培养 bla（CTX-M）样文库包含 16 种 CTX-M 基因变体，P 文库中有 14 种，UP 文库中有 4 种，它们之间的相似度为 68%至 99%。除了 UP 位点的 bla（CTX-M）样基因多样性低外，大多数与染色体 ESBL 如 bla（RAHN-1）相似。结果表明，污染和未污染的流水生态系统中 bla（CTX-M）基因的发生和多样性明显不同；这些发现支持了这样一种假设，即自然环境是耐药细菌和耐药基因的储存库，人为驱动的选择压力可能有助于通常在临床环境中相关的基因的持续存在和传播。
