质粒介导的喹诺酮耐药基因qnr的分类、耐药机制及其在国内的流行状况北大核心CSCD

喹诺酮类抗菌药物从早期主要用于治疗尿道感染发展到后来治疗肠道感染和呼吸道感染,目前已在临床、畜牧业和水产业中广泛使用,细菌对其耐药性也逐渐呈蔓延趋势,耐药机制日趋复杂。喹诺酮类耐药机制主要分为染色体介导的耐药和质粒介导的耐药,后者对细菌耐药性的广泛传播起着重要作用。1998年首次报道了质粒介导的喹诺酮类耐药机制,即质粒上qnr基因介导的细菌对氟喹诺酮耐药机制,qnr基因可在不同细菌中迅速水平传播,引发的感染不易控制,使得院内感染大范围的流行。此外,qnr基因通常与β-内酰胺类耐药基因相关或存在于复杂整合子中与其它多重耐药基因共同整合,缩小了临床医生治疗相关细菌感染时选药或联合用药的空间,给我们带来了严峻的挑战。本文就qnr基因的发现历史、耐药机理及在国内的流行状况做了详细概述。     

Contrasting effects of long distance seed dispersal on genetic diversity during range expansion

Currently many attempts are made to reconstruct the colonization history of plant species after the last ice age. A surprising finding is that during the colonization phase genetic diversity did not decrease as much as expected. In this paper we examine whether long distance seed dispersal events could play a role in the unexpected maintenance of genetic diversity during range expansion. This study is based on simulations carried out with a maternally inherited haploid locus using a cellular automaton. The simulations reveal a close relationship between the frequency of long distance seed dispersal events and the amount of genetic diversity preserved during colonization. In particular, when the colonized region is narrow, a complete loss of genetic diversity results from the occurrence of very rare long distance dispersal (LDD) events. We call this phenomenon the 'embolism effect'. However, slightly higher rates of LDD events reverse this effect, up to the point that diversity is better preserved than in a pure diffusion model. This phenomenon is linked to the reorganization of the genetic structure during colonization and is called the 'reshuffling effect'.     

Microbial community succession and bacterial diversity in soils during 77,000 years of ecosystem development

The origins of the biological complexity and the factors that regulate the development of community composition, diversity and richness in soil remain largely unknown. To gain a better understanding of how bacterial communities change during soil ecosystem development, their composition and diversity in soils that developed over c. 77 000 years of intermittent aeolian deposition were studied. 16S rRNA gene clone libraries and fatty acid methyl ester (FAME) analyses were used to assess the diversity and composition of the communities. The bacterial community composition changed with soil age, and the overall diversity, richness and evenness of the communities increased as the soil habitat matured. When analysed using a multivariate Bray-Curtis ordination technique, the distribution of ribotypes showed an orderly pattern of bacterial community development that was clearly associated with soil and ecosystem development. Similarly, changes in the composition of the FAMEs across the chronosequence were associated with biomarkers for fungi, actinomycetes and Gram-positive bacteria. The development of the soil ecosystem promoted the development of distinctive microbial communities that were reminiscent of successional processes often evoked to describe change during the development of plant communities in terrestrial ecosystems.