质粒介导黏菌素耐药机制研究进展

黏菌素是一种多肽类抗生素,对革兰阴性菌具有较强的抗菌活性。由于其副作用大,一直以来黏菌素在临床中很少被使用。近年来,随着多重耐药菌,特别是耐碳青霉烯类肠杆菌的产生,黏菌素耐药基因mcr的研究逐渐受到重视。过去通常认为,黏菌素耐药性由染色体介导,无法在细菌间水平传播。mcr-1基因的发现证明黏菌素耐药性还可能通过质粒介导水平传播。本文将介绍多种黏菌素耐药基因mcr及其流行特征、MCR作用机制和分类特点,为黏菌素的合理使用提供理论支持,以及采取针对性的预防措施。     

Synthesis and characterization of the colistin peptide polymyxin E1 and related antimicrobial peptides.

Two strategies were developed to synthesize the acylated cyclic peptides know as polymyxins. Synthesis of polymyxin E1 and several analogs enabled us to evaluate the minimum inhibitory concentration of individual compounds against Gram-negative bacteria. In this study we also report the first identification of two component peptides in the complex polymyxin fermentation product colistin, a Thr2Ser isoform and an acyl group isomer. Both of these peptides, as well as a known component peptide, Leu7Ile, were similar to polymyxin E1 in potency, suggesting that conservative mutations in the colistin family are functionally inconsequential. In contrast, the acyclic analogs of all of these peptides were inactive, indicating that the characteristic lariat structure of the polymyxins is necessary for antimicrobial activity.     

Tryptamine derivatives disarm colistin resistance in polymyxin-resistant gram-negative bacteria

The last three decades have seen a dwindling number of novel antibiotic classes approved for clinical use and a concurrent increase in levels of antibiotic resistance, necessitating alternative methods to combat the rise of multi-drug resistant bacteria. A promising strategy employs antibiotic adjuvants, non-toxic molecules that disarm antibiotic resistance. When co-dosed with antibiotics, these compounds restore antibiotic efficacy in drug-resistant strains. Herein we identify derivatives of tryptamine, a ubiquitous biochemical scaffold containing an indole ring system, capable of disarming colistin resistance in the Gram-negative bacterial pathogens Acinetobacter baumannii, Klebsiella pneumoniae, and Escherichia coli while having no inherent bacterial toxicity. Resistance was overcome in strains carrying endogenous chromosomally-encoded colistin resistance machinery, as well as resistance conferred by the mobile colistin resistance-1 (mcr-1) plasmid-borne gene. These compounds restore a colistin minimum inhibitory concentration (MIC) below the Clinical & Laboratory Sciences Institute (CLSI) breakpoint in all resistant strains.     

质粒介导的黏菌素耐药基因mcr-1研究进展

mcr-1基因是迄今为止国际上首次发现的质粒介导的黏菌素耐药基因,可介导肠杆菌科细菌对多粘菌素类药物产生耐药并可通过质粒进行水平转移。最新研究表明该基因已通过IncI2、IncX4和IncHI2等流行性质粒以及可移动元件,在全球35个不同国家和地区的人、动物和环境源多种肠杆菌中广泛传播。这些研究对于深入了解mcr-1基因介导的黏菌素耐药和传播机制、全球流行分布特征奠定了基础,丰富了耐药性形成理论。文章主要介绍了不同来源肠杆菌科细菌中mcr-1的分布流行情况、耐药和传播机制、基因环境等方面的研究进展,探讨了其临床风险性以及后续应对措施,以期为相关科研人员和临床工作者提供参考,共同应对抗生素耐药日益严峻的局面。     

Structural and functional insights into MCR-2 mediated colistin resistance

正Dear Editor,The spread of antibiotic resistance genes among bacteria is a serious and growing threat to global health(Peleg and Hooper, 2010). One emerging case is transferable genes found in bacteria-encoding enzymes resistant to colistin.     

A novel type of colistin resistance genes selected from random sequence space

Antibiotic resistance is a rapidly increasing medical problem that severely limits the success of antibiotic treatments, and the identification of resistance determinants is key for surveillance and control of resistance dissemination. Horizontal transfer is the dominant mechanism for spread of resistance genes between bacteria but little is known about the original emergence of resistance genes. Here, we examined experimentally if random sequences can generate novel antibiotic resistance determinants de novo. By utilizing highly diverse expression libraries encoding random sequences to select for open reading frames that confer resistance to the last-resort antibiotic colistin in Escherichia coli, six de novo colistin resistance conferring peptides (Dcr) were identified. The peptides act via direct interactions with the sensor kinase PmrB (also termed BasS in E. coli), causing an activation of the PmrAB two-component system (TCS), modification of the lipid A domain of lipopolysaccharide and subsequent colistin resistance. This kinase-activation was extended to other TCS by generation of chimeric sensor kinases. Our results demonstrate that peptides with novel activities mediated via specific peptide-protein interactions in the transmembrane domain of a sensory transducer can be selected de novo, suggesting that the origination of such peptides from non-coding regions is conceivable. In addition, we identified a novel class of resistance determinants for a key antibiotic that is used as a last resort treatment for several significant pathogens. The high-level resistance provided at low expression levels, absence of significant growth defects and the functionality of Dcr peptides across different genera suggest that this class of peptides could potentially evolve as bona fide resistance determinants in natura.     

Farm animals and aquaculture: significant reservoirs of mobile colistin resistance genes

Colistin resistance has attracted substantial attention after colistin was considered as a last-resort drug for the treatment of infections caused by carbapenem-resistant and/or multidrug-resistant (MDR) Gram-negative bacteria in clinical settings. However, with the discovery of highly mobile colistin resistance (mcr) genes, colistin resistance has become an increasingly urgent issue worldwide. Despite many reviews, which summarized the prevalence, mechanisms, and structures of these genes in bacteria of human and animal origin, studies on the prevalence of mobile colistin resistance genes in aquaculture and their transmission between animals and humans remain scarce. Herein, we review recent reports on the prevalence of colistin resistance genes in animals, especially wildlife and aquaculture, and their possibility of transmission to humans via the food chain. This review also gives some insights into the routine surveillance, changing policy and replacement of polymyxins by polymyxin derivatives, molecular inhibitors, and traditional Chinese medicine to tackle colistin resistance.     

Induced colistin resistance as an identifying marker for Aeromonas phenospecies groups

AIMS: To investigate the taxonomic interest of colistin resistance as an identifying marker for Aeromonas phenospecies groups. METHODS AND RESULTS: Colistin resistance was investigated in 387 Aeromonas isolates identified at species level using a 14-test format protocol with miniaturized tests combined with determination of urocanic acid utilization whenever necessary. Colistin resistance, determined by the disc diffusion method, was unreliable when compared with minimum inhibitory concentration (MIC) determination. In some strains, the MIC values and resistance rates of colistin could be increased after overnight induction with a 50- microg colistin disc in 20 ml of Mueller-Hinton broth (2.5 mg l(-1)). Colistin-induced resistance level was raised to 85.8% in the Aeromonas hydrophila complex, 2.1% in the A. caviae complex and 2.5% in the A. veronii complex except for A. jandaei (100% colistin resistant). This new marker allowed the identification of 96.2 and 93.6% of Aeromonas isolates to phenospecies and species level, respectively. CONCLUSIONS: Colistin-induced colistin resistance is a new phenotypic marker for Aeromonas isolates. SIGNIFICANCE AND IMPACT OF THE STUDY: With the present protocol, colistin resistance determination may improve the identification of Aeromonas isolates to phenogroup level, when results obtained by conventional biochemical methods are ambiguous.     

粘杆菌素发酵液微滤膜分离处理过程研究

粘杆菌素由于其药性强、残留低、对人畜无害被认为是最安全的畜禽抗生素之一。利用微滤对粘杆菌素发酵液进行预处理,根据发酵液的特性,选择孔径为0．2μm、膜面积为0．06M。的管式陶瓷膜为微滤膜,研究了操作参数的适宜值：压力为0．2MPa,流量为20L／min,在浓缩倍数达到3．5倍时连续两次加入与浓缩液体等量的水,得率为96％。经微滤处理后,滤液的吸光度Abs（470nm）为0．394,N-NH,含量为115mg／100mL,有效地去除了菌体、胶体蛋白及部分色素等,效果优于工业生产中板框过滤滤液的质量标准。     

Some properties of cefoxitin-induced spheroplasts of Proteus species, including sensitivity to colistin

Spheroplasts of various Proteus species could be induced by cefoxitin in nutrient broth alone or in broth containing 0–33 mol/l sucrose and 4 times 10^-3 mol/l magnesium sulphate. Spheroplasts induced in the latter medium were lysed when diluted into water, but osmotically stable if transferred to broth or other appropriate menstrua. High concentrations of colistin were needed to induce lysis of cefoxitin-induced spheroplasts and it was concluded that, contrary to earlier findings with benzylpenicillin-induced spheroplasts, peptidoglycan had little, if any, role to play in acting as a barrier to the entry of polymyxins into Proteus cells.