Several Acinetobacter spp. act as opportunistic pathogens causing healthcare-associated infections worldwide, and in this respect their ability to resist antimicrobial compounds has certainly boosted up their global propagation. Acinetobacter clinical strains have demonstrated a remarkable ability to evolve and become resistant to almost all available drugs in the antimicrobial arsenal, including the last-resort carbapenem β-lactams. The dissemination of antimicrobial resistant genes (ARG), heavy metals-detoxification systems and other traits such as virulence factors is facilitated by mobile genetic elements (MGE) through horizontal gene transfer. Among them, plasmids have been shown to play a critical role in this genus. Despite the continuous increase of Acinetobacter plasmid sequences present in databases, there are no reports describing the basic traits carried by these MGE. To fill this gap, a broad analysis of the Acinetobacter plasmidome was performed. A search for Acinetobacter complete plasmids indicated that 905 sequences have been deposited in the NCBI-GenBank public database, of which 492 are harbored by Acinetobacter baumannii strains. Plasmid-classification schemes based on Rep proteins homology have so far described 23 different groups for A. baumannii (GR1-23), and 16 Acinetobacter Rep3 Groups (AR3G1-16) for the complete genus. Acinetobacter plasmids size ranges from 1.3 to 400 kb. Interestingly, widespread plasmids which are < 20 kb make up 56% of the total present in members of this genus. This led to the proposal of Acinetobacter plasmid assignation to two groups according to their size (< 20 kb and > 20 kb). Usually, smaller plasmids are not self-transmissible, and thereby employ alternative mechanisms of dissemination. For instance, a subgroup of < 20 kb-plasmids belonging to the pRAY-family, lack a rep gene, but encode a relaxase enabling their mobilization by conjugative plasmids. Other subgroup, including small GR2 Acinetobacter plasmids, does not encode a relaxase gene. However, they could still be mobilized by conjugative plasmids which recognize an oriT region carried by these small plasmids. Also, these < 20 kb-plasmids usually carry accessory genes bordered by XerC/D-recombinases recognition sites which have been hypothesized to mediate plasmid plasticity. Conversely, many cases of larger plasmids are self-transmissible and might encode virulence factors and their regulators, thus controlling strain pathogenicity. The ARGs carried by the > 20 kb-plasmids are usually encoded within other MGEs such as transposons, or as part of integrons. It has been recently noted that some of the > 20 kb-plasmids are derived from excised phages, and thus dubbed as phage-like plasmids. All in all, the plethora of plasmids found in strains of this genus and the multiple strategies promoting their evolution and dissemination have certainly contributed to survival of the Acinetobacter members in different habitats, including the clinical environment.

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我们对不动杆菌属成员携带的质粒了解多少？

几种不动杆菌属。作为机会性病原体在全球范围内引起医疗保健相关感染，在这方面，它们抵抗抗菌化合物的能力无疑促进了它们的全球传播。不动杆菌临床菌株已证明具有显着的进化能力，并对抗菌武器库中几乎所有可用的药物产生耐药性，包括最后的碳青霉烯β-内酰胺类药物。移动遗传元件 (MGE) 通过水平基因转移促进了抗微生物基因 (ARG)、重金属解毒系统和毒力因子等其他特征的传播。其中，质粒已被证明在该属中起着关键作用。尽管数据库中存在的不动杆菌质粒序列不断增加，没有报告描述这些 MGE 所携带的基本特征。为了填补这一空白，我们对不动杆菌质粒组进行了广泛的分析。对不动杆菌完整质粒的搜索表明 905 个序列已存放在 NCBI-GenBank 公共数据库中，其中 492 个序列包含鲍曼不动杆菌菌株。迄今为止，基于 Rep 蛋白同源性的质粒分类方案已描述了鲍曼不动杆菌 (GR1-23) 的 23 个不同组和完整属的 16 个不动杆菌 Rep3 组 (AR3G1-16)。不动杆菌质粒大小范围为 1.3 至 400 kb。有趣的是，< 20 kb 的广泛质粒占该属成员总数的 56%。这导致提议将不动杆菌质粒根据它们的大小（< 20 kb 和 > 20 kb）分为两组。通常，较小的质粒不能自我传播，因此采用其他传播机制。例如，属于 pRAY 家族的 < 20 kb 质粒亚群缺乏 rep 基因，但编码一种松弛酶，使它们能够通过接合质粒进行动员。其他亚群，包括小 GR2 不动杆菌质粒，不编码松弛酶基因。然而，它们仍然可以被识别这些小质粒携带的 oriT 区域的接合质粒动员。此外，这些小于 20 kb 的质粒通常携带由 XerC/D 重组酶识别位点接壤的辅助基因，这些位点已被假设为介导质粒可塑性。相反，许多较大的质粒是自我传播的，可能编码毒力因子及其调节因子，从而控制菌株的致病性。>携带的ARGs 20 kb 质粒通常在其他 MGE 中编码，例如转座子，或作为整合子的一部分。最近注意到一些> 20 kb 的质粒来自切下的噬菌体，因此被称为噬菌体样质粒。总而言之，在该属菌株中发现的大量质粒以及促进其进化和传播的多种策略无疑有助于不动杆菌成员在不同栖息地（包括临床环境）中的生存。