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Introduction: This study aimed to investigate the genetic factors promoting widespread Q6 dissemination of tet(X4) between Escherichia coli and to characterize the genetic contexts of tet(X4). Methods: We isolated E. coli from feces, water, soil and flies collected across a largescale chicken farm in China in 2020. Antimicrobial susceptibility testing and PFGE typing were used to identify tigecycline resistance and assess clonal relationships among isolates. Plasmids present and genome sequences were analyzed by conjugation, S1 pulsed-field gel electrophoresis (PFGE), plasmid stability testing and whole-genome sequencing. Results: A total of 204 tigecycline-resistant E. coli were isolated from 662 samples. Of these, we identified 165 tet(X4)-carrying E. coli and these strains exhibited a high degree of multidrug resistance. Based on the geographical location distribution of the sampled areas, number of samples in each area and isolation rate of tigecyclineresistant strains and tet(X4)-carrying isolates, 72 tet(X4)-positive isolates were selected for further investigation. Tigecycline resistance was shown to be mobile in 72 isolates and three types of tet(X4)-carrying plasmids were identified, they were IncHI1 (n= 67), IncX1 (n= 3) and pO111-like/IncFIA(HI1) (n= 2). The pO111-like/IncFIA(HI1) is a novel plasmid capable of transferring tet(X4). The transfer efficiency of IncHI1 plasmids was extremely high in most cases and IncHI1 plasmids were stable when transferred into common recipient strains. The genetic structures flanked by IS1, IS26 and ISCR2 containing tet(X4) were complex and varied in different plasmids. Discussion: The widespread dissemination of tigecycline-resistant E. coli is a major threat to public health. This data suggests careful use of tetracycline on farms is important to limit spread of resistance to tigecycline. Multiple mobile elements carrying tet(X4) are in circulation with IncHI1 plasmids the dominant vector in this setting. [ABSTRACT FROM AUTHOR]

Klebsiella pneumoniae simultaneously carrying genes encoding carbapenem resistance and hypervirulence causes fatal infections, representing a severe threat to human health. These carbapenem-resistant and hypervirulent K. pneumoniae (hvCRKP) strains are increasingly reported worldwide and have been found to belong to a variety of sequence types (STs). In this study, we report and characterized an hvCRKP strain of ST592, an uncommon ST, which caused a fatal infection in intensive care unit (ICU) in China and represents a novel type of hvCRKP. We demonstrated that this novel hvCRKP type emerged from the carbapenem-susceptible hypervirulent K. pneumoniae (hvKP) lineage of the K57 capsular type. K57 hvKP contains a pLVPK-like virulence plasmid and then acquired a conjugative bla KPC–2-carrying plasmid to form hvCRKP. The pLVPK-like virulence plasmid contains no complete conjugation module but was able to be transferred by fusion with the conjugative bla KPC–2-carrying plasmid during conjugation. This represents a new mechanism of simultaneous transfer genetic determinants of carbapenem resistance and virulence and highlights the undergoing expansion of hvCRKP, which requires rigorous monitoring and novel countermeasures to curb plasmid-mediated transmission. [ABSTRACT FROM AUTHOR]

The newly emerging NDM-5 confers increased antibiotic resistance and attracts extensive global attention, but the prevalence, dissemination mechanism, and clinical significance of NDM-5 among clinical Escherichia coli (E. coli) infections have not been thoroughly characterized to date. In the present study, 109 unique carbapenem-resistant E. coli (CR-EC) isolates were collected in Southwest China, from 2013 to 2017, among which 41 (37.61%) CR-EC isolates were identified as NDM-5-producers, with most isolates carrying the IncF-type plasmids. Molecular epidemiological studies revealed ST167 being the most common sequence type (ST). Moreover, we described the first report of a clinical CR-EC isolate co-harboring bla KPC–2 and bla NDM–5, which showed a higher level of resistance to carbapenems. In addition, bla NDM–5 plasmid transformation and conjugation indicated that bla NDM–5 itself did confer resistance to carbapenems. Complete sequencing of the bla NDM–5-harboring IncF plasmid revealed highly conserved regions (ble MBL- trpF - tat) and some transposons around bla NDM–5. Our findings revealed a new potential threat of NDM-5-postive CR-EC in mainland China and emphasized an urgent need to control their further spread. [ABSTRACT FROM AUTHOR]

High prevalence rates of sulfonamide resistance genes sul1 , sul2 , and sul3 have been observed in Gram-negative bacteria isolated from humans, domestic animals, and aquaculture species worldwide. We investigated the distribution characteristics, location, conjugative transferability, and genetic environments of sul genes from Escherichia coli isolates collected from Penaeus vannamei and pork samples from three large markets in Zhejiang, China. The prevalence rates of sul genes in sulfonamide-resistant E. coli isolates from P. vannamei and pork samples were 90.0 and 88.6%, respectively, and the prevalence of sul1 and sul2 was significantly higher than that of sul3 (p < 0.05). Twenty-four representative sul -positive E. coli isolates were analyzed in detail. Southern blot hybridization confirmed that sul genes of E. coli isolates were located on plasmids and/or chromosomes. Transfer of resistance through conjugation was observed in all 18 E. coli isolates harboring sul genes on plasmids. Replicon typing identified seven different incompatibility groups and IncF was the dominant replicon type among sul gene-containing plasmids from both sources. PCR walking analysis indicated that 87.5% (35/40) of sul gene-related fragments carried insertion sequences (ISs) belonging to a variety of families in diverse sites, with IS 26 occurring most frequently. In addition, the sul1 gene was detected mainly in fragments carrying class 1 integrons. Co-location on the same fragment with resistance genes that may contribute to the persistence and dissemination of sul1 and/or sul2 genes. The diversity of mobile genetic elements and resistance genes adjacent to sul3 was much lower than those adjacent to sul1 and sul2 , especially those located in chromosomes, which reduced the transmission potential of the sul3 gene. In conclusion, combined with the results of clonal relatedness analysis by PFGE and MLST of 24 representative E. coli isolates from P. vannamei and pork samples, it showed that a small number of sul genes were vertically transmitted among E. coli from P. vannamei and that horizontal gene transfer was likely the main transmission mechanism of sul genes from both sources. Our results provide important information to better understand the risk of transmission of sul genes from seafood and meat to humans. [ABSTRACT FROM AUTHOR]

Highlights • Two new aac(6′)-aph(2″) transposon structures were found in Enterococcus faecalis from Beijing, China. • Truncated aac(6′)-aph(2″) transposons were not always related to high plasmid location rate and high transfer efficiency. • Truncated aph(2″)-Ia region was identified upstream of a type III transposon with different rates among transposon groups. • Truncated aph(2″)-Ia region had similar positive rate trend as transposon plasmid location and conjugation-positive rates. ABSTRACT Transfer of aac(6′)-aph(2″) transposons mediating high-level gentamicin resistance (HLGR) in Enterococcus faecalis is a serious problem in the clinic. However, factors affecting the transfer of aac(6′)-aph(2″) have not yet been elucidated. The current study aimed to examine the genetic and molecular basis of HLGR in E. faecalis strains isolated in Beijing (China) and to clarify the relationship between transfer efficiency of aac(6′)-aph(2″) transposons and the transposon structure/location. A total of five transposon structures were identified by PCR mapping of the corresponding transposon regions, including a Tn 5281 -like non-truncated transposon and four truncated transposons. A plasmid location study of aac(6′)-aph(2″) by Southern blot following S1-PFGE and filter mating conjugation experiments demonstrated that plasmid location rates correlated with conjugation-positive rates. Chromosome walking to identify the sequence upstream of a representative type III truncated transposon found a truncated aph(2″)-Ia region, and further PCR analysis of this region among strains from different groups revealed similar a positive rate trend as the transposon plasmid location rate and conjugation-positive rate. In conclusion, aac(6′)-aph(2″) transposons were of different structures in E. faecalis strains from Beijing, with two new transposon structures that have not been reported elsewhere. Presence of the truncated aph(2″)-Ia region upstream of some truncated transposons suggests recombination between aminoglycoside-modifying enzyme genes. Possible links exist among plasmid location, conjugation and the presence of truncated aph(2″)-Ia upstream of the transposon. [ABSTRACT FROM AUTHOR]

Toxicokinetics and bioconcentration of eight common bisphenol analogues, including bisphenol A (BPA), -B, –C, -E, –S, -Z, -AF, and -AP in common carp (Cyprinus carpio) were investigated. Both free (BP free) and total forms (BP total) of the bisphenols were measured in various fish tissues. The conjugated forms of bisphenols were calculated based on BP free and BP total. The calculated bioconcentration factors (BCFs) based on the total bisphenols (BP total) in the carp whole body were in the range of 0.3–320, agreeing with previous field results from Taihu Lake, China. The elimination rate constant (k e) positively correlated with the fraction of conjugated form (f conjugated), which displayed negative correlation with their log K ow (r = −0.861, p < 0.05), indicating that conjugation facilitated their elimination and those with higher hydrophobicity were more difficult to be eliminated. Except BPA, the concentrations of all bisphenols in the carp tissues were in the order of kidney > liver ≫ muscle. The uptake rate constants (k u) in kidney (r = 0.836, p < 0.05) and in liver (r = 0.863, p < 0.05) displayed significantly positive correlations with BCFs, and k u in kidney was greater than in liver except BPA. These results indicated that kidney and liver played important roles in accumulating bisphenols in carp, and kidney made more contribution than liver for most bisphenols. Biliary excretion predominated for elimination of most bisphenols while BPA and BPS were mainly through urinary excretion. Image 1 • The BP free /BP total positively correlated with the log K ow of the bisphenols. • The calculated BCFs based on BP total in carp agreed with those measured in field. • Formation of conjugated forms facilitated elimination of bisphenols from fish. • Kidney made more contributions relative to liver for uptake of most BPA alternatives. • Biliary excretion was a more important exclusion pathway for most BPA alternatives. [ABSTRACT FROM AUTHOR]

Strains of the environmental bacterium Myroides odoratimimus can cause human infections. However, treating M. odoratimimus infections can be difficult because of multidrug resistance in this organism. In this study, we isolated strain M. odoratimimus G13 from pastureland in Tibet, China. The minimum inhibitory concentration analysis suggested that strain G13 has resistance to multiple antibiotics, with an MIC for tetracycline of 168 mg/L. Whole-genome sequencing and bioinformatic analysis revealed that the genome of G13 was rich in virulence factor-encoding genes and antibiotic resistance genes (ARGs). The mobilizable genomic island MGI1313 was also identified and characterized, and six resistance genes related to four types of antibiotics were annotated in MGI1313. Conjugation assays indicated that MGI1313 could be transferred from G13 to Escherichia coli 25DN by horizontal gene transfer, resulting in multidrug-resistant E. coli conjugants. In conclusion, multidrug-resistant M. odoratimimus G13 and the mobility of MGI1313 raise the risk of difficult-to-treat bacterial infections and should be under close surveillance., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020. Published by Elsevier B.V.)

Objective: The purpose of this study was to investigate the molecular characteristics of ESBL-encoding conjugative plasmid identified in muti-drug resistant Escherichia coli isolated from food. Methods: 465 Escherichia coli isolates were collected from national foodborne disease surveillance net from 2013 to 2014 (salad, n= 159; meat, n= 102; processed meat, n= 95; cakes/rice, n= 46; cooked dish, n= 63). ESBLs strain was detected by Mueller-Hinton agar plate, and then its drug resistance was tested by agar dilution method. Polymerase chain reaction (PCR) and DNA sequencing were performed to identify the corresponding ESBL genes. Plasmids were typed by PCR-based replicon typing and their characteristics were determined by S1-nuclease pulsed-field gel electrophoresis method. Broth mating assays were carried out for all isolates to determine whether the ESBL marker could be transferred by conjugation. Results: 12 E. coli were found to be resistant to cefotaxime, and all of which were confirmed as ESBLs. The 12 isolates all carried different types of CTX-M genes resistant to drug, and 7 of which carried TEM type as well. All 12 isolates contained at least one plasmid and some had four plasmids, with size ranging from 47-to 220-kb by S1-PFGE anaylsis. Seven isolates demonstrated the ability to transfer their cefotaxime resistance marker to the recotper strain J53 by only one plasmid. Conclusion: This study highlights the diversity of the multi-drug resistant E. coli and also the diversity of ESBL genes in China. Plasmids carrying these genes poses a serious threat to food safety in China.