Coronavirus disease 2019 (COVID-19) emerged in Wuhan, China, in December 2019 and has spread globally with sustained human-to-human transmission outside China. 1,2 To control the spread of COVID-19 and isolate patients as early as possible, the Chinese government requested that close contacts of individuals with COVID-19 must be screened for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. During the screening process, we found some patients whose test results were positive for SARS-CoV-2 but who had no symptoms or signs throughout the course of the disease. Considering that little is known about the differences of clinical features and prognosis between patients who were asymptomatic vs those who were symptomatic, 3,4 this case series aimed to describe the clinical characteristics of patients with SARS-CoV-2 infection confirmed by reverse transcription-polymerase chain reaction (RT-PCR) from 26 transmission cluster series in Wuhan,

IncX4 plasmids are associated with the dissemination of the mcr-1 genes in Enterobacteriaceae. We screened IncX4 plasmids among 2,470 isolates of Enterobacteriaceae and determined the mcr-1 positive isolates. Forty-three isolates were observed to carry IncX4 type plasmid, among which 13 were identified to carry mcr-1 gene. Three representative mcr-1-positive IncX4 plasmids were selected for high-throughput sequencing. Comparative genomics showed that the mcr-1-carrying IncX4 plasmids exhibit remarkable similarity in the backbone, and the major distinction lies in the region containing mcr-1. The major variable regions of all the IncX4 plasmids were fully characterized by PCR-RFLP. The results revealed that the mcr-1 was located on the Variable Region I of IncX4 plasmids in 11 E. coli isolates. Among them, nine E. coli strains possess an epidemic pCSZ4-like IncX4 plasmid containing mcr-1. ISApl1 was presumably involved in the transposition of the mcr-1 cassette and then was lost. Similar genetic contexts were found in different plasmids, even the E. coli chromosome, implying the acquisition of mcr-1 by a unique common mechanism.

c Two Escherichia coli clones (sequence type 648 [ST648] and ST156) that coproduce NDM-5 and MCR-1 were detected from a single fowl in China. The bla NDM-5 gene was found on the two indistinguishable IncX3 plasmids from the two different E. coli isolates, whereas the mcr-1 gene was located on IncHI2 and IncI2 plasmids, respectively, suggesting that bla NDM-5 and mcr-1 have spread in avian intestinal flora. Also, the two strains harbor bla TEM-1 , bla CTX-M-55 , fosA3, and aac(6=)-Ib. The multiresistant E. coli strains (especially the epidemic clone ST648) might raise a potential threat to human health via food chain transmission. Carbapenem-resistant Enterobacteriaceae (CRE) are a global public health problem. The New Delhi metallo-␤-lactamase (NDM) was first described in 2008 (1) and has become one of the most widespread carbapenemases in the world (2-4). Meanwhile, since the recent discovery of the plasmid-mediated colistin resistance gene mcr-1 in China (5), several studies have confirmed its dissemination in different humans and animals (6-10). In addition, the coproduction of carbapenemase and MCR-1 was detected in a few bacteria (6,8,(11)(12)(13), which poses a serious concern to public health. Here, we report the first case of NDM-5-and MCR-1-producing Escherichia coli clones sequence type 648 (ST648) and ST156 from a single fowl.In May 2015, a rectal swab was collected from a 1-month-old Muscovy duck (Cairina moschata) with colibacillosis to study carbapenemase-encoding genes from animals in China. The diseased duck was sent to the veterinary clinical diagnosis laboratory in South China Agricultural University from a duck farm in Guangdong Province, China. Carbapenem-producing isolates were selected in MacConkey medium supplemented with meropenem (1 g/ml). Two E. coli isolates (NDM131 and NDM132) with diverse morphological characteristics were isolated and were identified by the Axima matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometer (Shimadzu-Biotech Corp., Kyoto, Japan).Antibiotic susceptibility testing was performed using the agar dilution method (14) and interpreted according to the Clinical and Laboratory Standards Institute guidelines (15). The EUCAST breakpoints for Enterobacteriaceae for colistin and tigecycline were applied (16).Both E. coli isolates (NDM131 and NDM132) were resistant to cefoxitin, ceftazidime, cefotaxime, imipenem, meropenem, ertapenem, gentamicin, tobramycin, ciprofloxacin, tetracycline, fosfomycin, trimethoprim-sulfamethoxazole, and colistin but susceptible to tigecycline (see Table S1 in the supplemental material). NDM131 was also resistant to aztreonam and amikacin. The double-disk synergy test and biochemical Carba NP test confirmed extended-spectrum ␤-lactamase (ESBL) and carbapenemase production in both isolates.PCR analyses were performed to confirm carbapenemase, ESBLs, plasmid-mediated AmpC cephalosporinase-encoding genes, 16S rRNA methyltransferase genes, and fosfomycin resistance genes. The complete coding sequence of the NDM g...

Carbapenem and colistin are the last-resort antibiotics used for treating multidrug-resistant Gram-negative pathogens. Here, we report, for the first time, co-transfer of resistance to both classes of antibiotics by a mobile IncX3-X4 hybrid plasmid in an Escherichia coli isolate. Spread of such a plasmid is of great concern for clinical therapy, and heightened efforts are needed to control its dissemination.

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