Laboratorio de Investigaciones de los Mecanismos de Resistencia a Antibióticos, Facultad de Medicina, Instituto de Microbiología y Parasitología Médica, UBA-CONICET, Universidad de Buenos Aires, Ciudad Autónoma de Buenos Aires, Argentina.
PLoS One. 2012;7(6):e39223. doi: 10.1371/journal.pone.0039223. Epub 2012 Jun 22.
Class 1 integrons are one of the most successful elements in the acquisition, expression and spread of antimicrobial resistance genes (ARG) among clinical isolates. Little is known about the gene flow of the components of the genetic platforms of class 1 integrons within and between bacterial communities. Thus it is important to better understand the interactions among "environmental" intI1, its genetic platforms and its distribution with human activities.
METHODOLOGY/PRINCIPAL FINDINGS: An evaluation of two types of genetic determinants, ARG (sul1 and qacE1/qacEΔ1 genes) and lateral genetic elements (LGE) (intI1, ISCR1 and tniC genes) in a model of a culture-based method without antibiotic selection was conducted in a gradient of anthropogenic disturbances in a Patagonian island recognized as being one of the last regions containing wild areas. The intI1, ISCR1 genes and intI1 pseudogenes that were found widespread throughout natural communities were not associated with urbanization (p>0.05). Each ARG that is embedded in the most common genetic platform of clinical class 1 integrons, showed different ecological and molecular behaviours in environmental samples. While the sul1 gene frequency was associated with urbanization, the qacE1/qacEΔ1 gene showed an adaptive role to several habitats.
CONCLUSIONS/SIGNIFICANCE: The high frequency of intI1 pseudogenes suggests that, although intI1 has a deleterious impact within several genomes, it can easily be disseminated among natural bacterial communities. The widespread occurrence of ISCR1 and intI1 throughout Patagonian sites with different degree of urbanization, and within different taxa, could be one of the causes of the increasing frequency of multidrug-resistant isolates that have characterized Argentina for decades. The flow of ARG and LGE between natural and clinical communities cannot be explained with a single general process but is a direct consequence of the interaction of multiple factors operating at molecular, ecological, phylogenetic and historical levels.
1 类整合子是临床分离株中获得、表达和传播抗生素耐药基因（ARG）的最成功元素之一。关于 1 类整合子遗传平台的组成部分在细菌群落内部和之间的基因流动知之甚少。因此，更好地了解“环境”intI1 及其遗传平台及其与人类活动的分布之间的相互作用非常重要。
方法/主要发现：在巴塔哥尼亚一个被认为是最后一个拥有野生地区的岛屿的人为干扰梯度中，采用一种不进行抗生素选择的基于培养的方法模型，对两种遗传决定因素（ARG（sul1 和 qacE1/qacEΔ1 基因）和侧位遗传元件（LGE）（intI1、ISCR1 和 tniC 基因）进行了评估。在自然群落中广泛存在的 intI1、ISCR1 基因和 intI1 假基因与城市化无关（p>0.05）。每个嵌入临床 1 类整合子最常见遗传平台的 ARG 都表现出不同的生态和分子行为在环境样本中。虽然 sul1 基因的频率与城市化有关，但 qacE1/qacEΔ1 基因表现出对多种栖息地的适应性作用。
结论/意义：intI1 假基因的高频率表明，尽管 intI1 对几个基因组有有害影响，但它很容易在自然细菌群落中传播。ISCR1 和 intI1 在巴塔哥尼亚不同城市化程度的地点以及不同分类群中广泛存在，可能是几十年来阿根廷多药耐药分离株频率增加的原因之一。ARG 和 LGE 在自然和临床群落之间的流动不能用单一的一般过程来解释，而是分子、生态、系统发育和历史水平上多种因素相互作用的直接结果。
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