Concerns have been raised in recent years regarding co-selection for antibiotic resistance among bacteria exposed to heavy metals, particularly copper and zinc, used as growth promoters for some livestock species. In this study, 25 IncHI2 plasmids harboring oqxAB (20/25)/blaCTX-M (18/25) were found with sizes ranging from ∼260 to ∼350 kb and 22 belonged to the ST3-IncHI2 group. In addition to blaCTX-M and oqxAB, pcoA-E (5/25) and silE-P (5/25), as well as aac(6′)-Ib-cr (18/25), floR (16/25), rmtB (6/25), qnrS1(3/25) and fosA3 (2/25), were also identified on these IncHI2 plasmids. The plasmids carried pco and sil contributed to increasing in the MICs of CuSO4 and AgNO3. The genetic context surrounding the two operons was well conserved except some variations within the pco operon. The ~32 kb region containing the two operons identified in the IncHI2 plasmids was also found in chromosomes of different Enterobacteriaceae species. Further, phylogenetic analysis of this structure showed that Tn7-like transposon might play an important role in cross-genus transfer of the sil and pco operons among Enterobacteriaceae. In conclusion, co-existence of the pco and sil operons, and oqxAB/blaCTX-M as well as other antibiotic resistance genes on IncHI2 plasmids may promote the development of multidrug-resistant bacteria.

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.

Antibiotic resistance in bacteria has become a great threat to global public health. Tigecycline is a next‐generation tetracycline that is the final line of defense against severe infections by pan‐drug‐resistant bacterial pathogens. Unfortunately, this last‐resort antibiotic has been challenged by the recent emergence of the mobile Tet(X) orthologs that can confer high‐level tigecycline resistance. As it is reviewed here, these novel tetracycline destructases represent a growing threat to the next‐generation tetracyclines, and a basic framework for understanding the molecular epidemiology and resistance mechanisms of them is presented. However, further large‐scale epidemiological and functional studies are urgently needed to better understand the prevalence and dissemination of these newly discovered Tet(X) orthologs among Gram‐negative bacteria in both human and veterinary medicine.

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.

Campylobacter is a major foodborne pathogen and is commonly present in food producing animals. This pathogenic organism is highly adaptable and has become increasingly resistant to various antibiotics. Recently, both the Centers for Disease Control and Prevention and the World Health Organization have designated antibiotic-resistant Campylobacter as a serious threat to public health. For the past decade, multiple mechanisms conferring resistance to clinically important antibiotics have been described in Campylobacter, and new resistance mechanisms constantly emerge in the pathogen. Some of the recent examples include the erm(B) gene conferring macrolide resistance, the cfr(C) genes mediating resistance to florfenicol and other antimicrobials, and a functionally enhanced variant of the multidrug resistance efflux pump, CmeABC. The continued emergence of new resistance mechanisms illustrates the extraordinary adaptability of Campylobacter to antibiotic selection pressure and demonstrate the need for innovative strategies to control antibiotic-resistant Campylobacter. In this review, we will briefly summarize the trends of antibiotic resistance in Campylobacter and discuss the mechanisms of resistance to antibiotics used for animal production and important for clinical therapy in humans. A special emphasis will be given to the newly discovered antibiotic resistance.

BackgroundThe association of PMQR and ESBLs in negative-bacteria isolates has been of great concern. The present study was performed to investigate the prevalence of co-transferability of oqxAB and bla CTX-M genes among the 696 Escherichia coli (E. coli) isolates from food-producing animals in South China, and to characterize these plasmids.MethodsThe ESBL-encoding genes (bla CTX-M, bla TEM and bla SHV), and PMQR (qnrA, qnrB, qnrS, qnrC, qnrD, aac(6’)-Ib-cr, qepA, and oqxAB) of these 696 isolates were determined by PCR and sequenced directionally. Conjugation, S1 nuclease pulsed-field gel electrophoresis (PFGE) and Southern blotting experiments were performed to investigate the co-transferability and location of oqxAB and bla CTX-M. The EcoRI digestion profiles of the plasmids with oqxAB-bla CTX-M were also analyzed. The clonal relatedness was investigated by PFGE.ResultsOf the 696 isolates, 429 harbored at least one PMQR gene, with oqxAB (328) being the most common type; 191 carried bla CTX-M, with bla CTX-M-14 the most common. We observed a significant higher prevalence of bla CTX-M among the oqxAB-positive isolates (38.7%) than that (17.4%) in the oqxAB-negative isolates. Co-transferability of oqxAB and bla CTX-M was found in 18 of the 127 isolates carrying oqxAB-bla CTX-M. These two genes were located on the same plasmid in all the 18 isolates, with floR being on these plasmids in 13 isolates. The co-dissemination of these genes was mainly mediated by F33:A-: B- and HI2 plasmids with highly similar EcoRI digestion profiles. Diverse PFGE patterns indicated the high prevalence of oqxAB was not caused by clonal dissemination.Conclusion bla CTX-M was highly prevalent among the oqxAB-positive isolates. The co-dissemination of oqxAB-bla CTX-M genes in E. coli isolates from food-producing animals is mediated mainly by similar F33:A-: B- and HI2 plasmids. This is the first report of the co-existence of oqxAB, bla CTX-M, and floR on the same plasmids in E. coli.

cWe report the complete nucleotide sequence of a plasmid, pA31-12, carrying bla CTX-M-55 and mcr-1 from a chicken Escherichia coli isolate. pA31-12 has an IncI2 replicon that displays extensive sequence similarity with pHN1122-1-borne bla CTX-M-55 and pHNSHP45-borne mcr-1. Insertion sequences ISEcp1 and ISApl1 are responsible for the mobilization of bla CTX-M-55 and mcr-1, respectively. The colocalization of mcr-1 with an extended-spectrum ␤-lactamase gene on a conjugative plasmid may accelerate the dissemination of both genes by coselection.