We have recovered one blaNDM-1-harboring bacterial strain, designated as XM1570, from a sputum sample obtained from a fatal case of pneumonia in China. Biochemical profiling, 16S rRNA sequencing and antimicrobial susceptibility testing were performed. Conjugation experiments were conducted to determine transmissibility of resistance. Pulsed-field gel electrophoresis and whole genome sequencing were performed to identify strain-specific features. The isolate XM1570 was identified as Acinetobacter calcoaceticus. Whole genome sequencing identified two plasmids, pXM1 and pXM2. Comparative analysis showed >99% similarity between XM1570 and A. calcoaceticus PHEA-2. Plasmid pXM1 carried the carbapenemase gene blaNDM-1 and displayed high homology with previously described plasmids isolated from different Acinetobacter spp., which were collected from human or livestock distributed in China and worldwide. The blaNDM-1 gene was located on this conjugative plasmid in a transposon-like region flanked by two copies of the insertion sequence ISAba125; and resistance to all tested β-lactams was observed. Transferability of resistance from pXM1 to the transconjugants was identified. Plasmid pXM2 had an insertion sequence ISAba125 and a −35 region of the blaNDM-1 gene promoter but the blaNDM-1 gene was not present. A chromosomally located carbapenemase-encoding gene blaOXA-75 was detected; however, this gene was interrupted by an insertion sequence ISAba22 belonging to IS3 family. Location of blaNDM-1 on different self-transmissible plasmids could facilitate geographically broad dissemination and host range expansion of the blaNDM-1 gene via horizontal gene transfer. Our findings of this normally environmental species A. calcoaceticus XM1570 further underline the significant clinical challenge and the essential need for surveillance including molecular methods and plasmid analyses.

In this study, we discovered a novel mobilized colistin resistance (mcr-1) gene variant, named mcr-1.9, which was identified in a colistin-resistant enterotoxigenic Escherichia coli (ETEC) strain from a clinical diarrhea case. The mcr-1.9 gene differs from mcr-1 at position 1036 due to a single nucleotide polymorphism (G→A), which results in an aspartic acid residue being replaced by an asparagine residue (Asp346→Asn) in the MCR-1 protein sequence. Antimicrobial susceptibility testing showed that the mcr-1.9-harboring ETEC strain is resistant to colistin at a minimum inhibitory concentration of 4 μg/ml. Plasmid profiling and conjugation experiments also suggest that the mcr-1.9 variant can be successfully transferred into the E. coli strain J53, indicating that the gene is located on a transferable plasmid. Bioinformatics analysis of data obtained from genome sequencing indicates that the mcr-1.9 gene is located on a 64,005 bp plasmid which has been named pEC26. This plasmid was found to have high similarity to the mcr-1-bearing IncI2-type plasmids pWF-5-19C (99% identity and 99% coverage) and pmcr1-IncI2 (99% identity and 98% coverage). The mcr-1.9-harboring ETEC also shows multidrug resistance to nine classes of antibiotics, and contains several virulence and antimicrobial-resistance genes suggested by the genome sequence analysis. Our report is the first to identify a new mcr-1 variant in an ETEC isolated from a human fecal sample, raising concerns about the existence of more such variants in human intestinal flora. Therefore, we believe that an undertaking to identify new mcr-1 variants in the bacterial communities of human intestines is of utmost importance, and that measures need to be taken to control the spread of mcr-1 and its variants in human intestinal microflora.

Extended-spectrum β-lactamases, especially CTX-M enzymes, play a critical role in cephalosporin resistance in several bacterial species. The ISEcp1 insertion sequence, a mobile genetic element, regulates the high expression and horizontal transfer of the bla_CTX-M gene. Diverse types of spacer regions exist, the length of which varies across the different types of bla_CTX-M genes and their upstream ISEcp1 elements. In this study, we aimed to investigate the distribution and role of ISEcp1 and different length spacers in antibiotic-resistant Shigella. We selected 1393 cephalosporin-resistant Shigella strains isolated from China between 2004 and 2016 to analyse the distribution of ISEcp1 and spacers using polymerase chain reaction and sequencing. To functionally evaluate the role of these elements, we designed different combinations of ISEcp1, spacer sequences, and bla_CTX-M gene fragments to generate and express recombinant plasmids containing these fragments in Escherichia coli. We then assessed the cephalosporin resistance phenotype of recombinant clones using the E-TEST method. The carriage rate of ISEcp1 in cephalosporin-resistant Shigella was 90.09%, with an ISEcp1-CTX-M element carriage rate of 67.19%, and was significantly higher in the bla_CTX-M-9 group than that in the bla_CTX-M-1 group. Moreover, E. coli strains containing different combinations exhibited varying bacterial resistance to β-lactam antibiotics, indicating the regulatory role of ISEcp1 and spacers. Our results demonstrate that the configuration of ISEcp1, spacer sequences, and bla_CTX-M in plasmids fosters a robust resistance phenotype against various cephalosporins, providing new insights into antimicrobial resistance mechanisms and an important basis for developing novel anti-resistance drugs.

Background: Enterovirus 71 (EV71), one of the most important neurotropic EVs, has caused death and long-term neurological sequelae in hundreds of thousands of young children in the Asia-Pacific region in the past decade. The neurological diseases are attributed to infection by EV71 inducing an extensive peripheral and central nervous system (CNS) inflammatory response with abnormal cytokine production and lymphocyte depletion induced by EV71 infection. In the absence of specific antiviral agents or vaccines, an effective immunosuppressive strategy would be valuable to alleviate the severity of the local inflammation induced by EV71 infection. Presentation of the hypothesis: The complement system plays a pivotal role in the inflammatory response. Inappropriate or excessive activation of the complement system results in a severe inflammatory reaction or numerous pathological injuries. Previous studies have revealed that EV71 infection can induce complement activation and an inflammatory response of the CNS. CR2-targeted complement inhibition has been proved to be a potential therapeutic strategy for many diseases, such as influenza virus-induced lung tissue injury, postischemic cerebral injury and spinal cord injury. In this paper, a mouse model is proposed to test whether a recombinant fusion protein consisting of CR2 and a region of Crry (CR2-Crry) is able to specifically inhibit the local complement activation induced by EV71 infection, and to observe whether this treatment strategy can alleviate or even cure the neurogenic inflammation. Testing the hypothesis: CR2-Crry is expressed in CHO cells, and its biological activity is determined by complement inhibition assays. 7-day-old ICR mice are inoculated intracranially with EV71 to duplicate the neurological symptoms. The mice are then divided into two groups, in one of which the mice are treated with CR2-Crry targeted complement inhibitor, and in the other with phosphate-buffered saline. A group of mice deficient in complement C3, the breakdown products of which bind to CR2, are also infected with EV71 virus. The potential bioavailability and efficacy of the targeted complement inhibitor are evaluated by histology, immunofluorescence staining and radiolabeling. Implications of the hypothesis: CR2-Crry-mediated targeting complement inhibition will alleviate the local inflammation and provide an effective treatment for the severe neurological diseases associated with EV71 infection.