The mcr-1 gene can be disseminated via multiple mobile elements including Tn6330, its circular intermediate and plasmids harbouring such elements. It is often co-transmitted with other resistance determinants through IncHI2 plasmids. The functional mechanism of Tn6330, a typical composite transposon harbouring mcr-1, should be further investigated.

BackgroundMultidrug resistance (MDR)–encoding plasmids are considered major molecular vehicles responsible for transmission of antibiotic resistance genes among bacteria of the same or different species. Delineating the complete sequences of such plasmids could provide valuable insight into the evolution and transmission mechanisms underlying bacterial antibiotic resistance development. However, due to the presence of multiple repeats of mobile elements, complete sequencing of MDR plasmids remains technically complicated, expensive, and time-consuming.ResultsHere, we demonstrate a rapid and efficient approach to obtaining multiple MDR plasmid sequences through the use of the MinION nanopore sequencing platform, which is incorporated in a portable device. By assembling the long sequencing reads generated by a single MinION run according to a rapid barcoding sequencing protocol, we obtained the complete sequences of 20 plasmids harbored by multiple bacterial strains. Importantly, single long reads covering a plasmid end-to-end were recorded, indicating that de novo assembly may be unnecessary if the single reads exhibit high accuracy.ConclusionsThis workflow represents a convenient and cost-effective approach for systematic assessment of MDR plasmids responsible for treatment failure of bacterial infections, offering the opportunity to perform detailed molecular epidemiological studies to probe the evolutionary and transmission mechanisms of MDR-encoding elements.

The Tn 6330 element located in the phage-like plasmid pHYEC7- mcr1 could be excised from the plasmid and formed a circular intermediate that could be integrated into plasmids containing the IS Apl1 element. This phenomenon indicated that Tn 6330 is a key element responsible for widespread dissemination of mcr-1 among various types of plasmids and bacterial chromosomes. The dissemination rate of such an element may be further enhanced upon translocation into phage-like vectors, which may also be transmitted via transduction events.

e This study reports the increasing prevalence of clinical Escherichia coli of sequence type 167 (ST167) carrying both bla NDM-1 and bla NDM-5 on the conjugative IncX3 plasmid in various parts of China. Close surveillance is needed to monitor the future dissemination of ST167 strains that harbor bla NDM-5 or other bla NDM -like genes.T he continuous emergence of carbapenem-resistant Enterobacteriaceae (CRE) strains in recent years has posed an increasing public health threat worldwide. The dissemination of mobile resistance elements, especially those carrying the New Delhi metallo-␤-lactamase gene (bla NDM-1 ), has been regarded as a major mechanism responsible for causing a dramatic increase in the prevalence of CRE in clinical settings. NDM-producing organisms were first reported on the Indian subcontinent and then in several Middle Eastern and Balkan countries in 2009 (1, 2). This gene has since spread to different species of Enterobacteriaceae and other Gram-negative bacteria throughout the world (3). The rapid increase in the prevalence of CRE may be due to both transmission of bla NDM-1 -carrying elements among the Enterobacteriaceae species and clonal spread of strains containing such elements (4, 5). Current evidence, however, suggests that the transmission of specific mobile resistance elements in CRE has a strong association with specific types of bacterial strains. For example, the bla NDM-1 -like genes are predominantly detected in multilocus sequence typing (MLST) sequence type 131 (ST131) and ST101 strains of Escherichia coli and ST11 strains of Klebsiella pneumoniae (5-8). The underlying mechanisms leading to the clustering of the bla NDM-1 -like genes in specific STs remain to be investigated.In China, bla NDM-1 was reported in 2011 (9). Since then, the gene has become detectable in most species of Enterobacteriaceae in various cities in China, and yet, there is a lack of information on the linkage of specific STs of E. coli to bla NDM-1 carriage due to the sporadic and noncomprehensive nature of CRE-related data in China. Recently, four studies have reported several sporadic cases of clinical infections linked to E. coli ST167 carrying bla NDM-5 in various parts of China (10-12). The gene was shown to be located on the IncX3 plasmid in two studies (11,12).In this work, we have conducted a more comprehensive investigation in order to better understand whether the E. coli ST167 strains are predominantly involved in the transmission of the bla NDM-1 and bla NDM-5 genes in hospitals in various parts of China. Clinical carbapenem-resistant E. coli strains, as determined by the Kirby-Bauer disk diffusion method according to CLSI guidelines, were obtained from 7 hospitals in various locations in China, as shown in Table 1, from 2013 to 2014. A total of 48 carbapenem-resistant E. coli isolates were obtained during the study period and screened for the presence of bla NDM-1 as previously described (13). Twenty-five (52%) were found to carry bla NDM carbapenemase genes, among which 11 were isolated from p...

The recently discovered colistin resistance-encoding element, mcr-1, adds to the list of mobile resistance genes whose products rapidly erode the antimicrobial efficacy of not only the commonly used antibiotics, but also the last line agents of carbapenems and colistin. The relative prevalence of mcr-1-bearing strains in various ecological niches including 1,371 food samples, 480 animal faecal samples, 150 human faecal samples and 34 water samples was surveyed using a novel in-house method. Bacteria bearing mcr-1 were commonly detected in water (71% of samples), animal faeces (51%), food products (36%), and exhibited stable carriage in 28% of human subjects surveyed. Such strains, which exhibited variable antibiotic susceptibility profiles, belonged to various Enterobacteriaceae species, with Escherichia coli being the most dominant in each specimen type. The mcr-1 gene was detectable in the chromosome as well as plasmids of various sizes. Among these, two conjugative plasmids of sizes ca 33 and ca 60 kb were found to be the key vectors that mediated mcr-1 transmission in organisms residing in various ecological niches. The high mcr-1 carriage rate in humans found in this study highlights the importance of continued vigilance, careful antibiotic stewardship, and the development of new antimicrobials.

The fusion plasmid recoverable from the transconjugant was found to be generated as a result of a recombination event that occurred upon interaction between a blaNDM-5-carrying plasmid and another plasmid present in the parental strain. Such recombination events presumably play a potential role in the dissemination of the blaNDM genes among different plasmids and pathogenic bacterial strains.

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This study aimed to characterize novel conjugative plasmids that encode transferable ciprofloxacin resistance in In this study, 157 nonduplicated isolates were recovered from food products, of which 55 were found to be resistant to ciprofloxacin. Interestingly, 37 of the 55 Cip isolates (67%) did not harbor any mutations in the quinolone resistance-determining regions (QRDR). Six isolates were shown to carry two novel types of conjugative plasmids that could transfer the ciprofloxacin resistance phenotype to J53 (azithromycin resistant [Azi]). The first type of conjugative plasmid belonged to the ∼110-kb IncFIB-type conjugative plasmids carrying -bearing and-bearing mobile elements. Transfer of the plasmid between and could confer a ciprofloxacin MIC of 1 to 2 μg/ml. The second type of conjugative plasmid belonged to ∼240-kb IncH1/IncF plasmids carrying a single PMQR gene, Importantly, this type of conjugative ciprofloxacin resistance plasmid could be detected in clinical isolates. The dissemination of these conjugative plasmids that confer ciprofloxacin resistance poses serious challenges to public health and infection control.