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Extended-spectrum- β -lactamases (ESBLs)-producing Escherichia coli conferred resistance to most β -lactams, except for carbapenems. To date, the transmission mechanism of bla CTX-M , as the most common ESBLs subtype, in E. coli has received sustained attention around the worldwide, but the research on the pathogenicity of bla CTX-M -bearing E. coli is still scarce. The aims of this study were to discern the spread characteristics of ColV (encoding colicin V) plasmids in bla CTX-M -positive E. coli. The multi-drug resistance traits, phylogroups, and ColV plasmid profilings were screened in 76 bla CTX-M -positive E. coli. Thereafter, the genetic profiles of E. coli G12 and GZM7 were determined by whole genome sequencing, conjugation and S1-pulsed-field gel electrophoresis. The median lethal dose was analyzed in E. coli G12 and TG12A, the ColV-plasmid transconjugant of G12. Of all 76 bla CTX-M -bearing E. coli , 67.11% exhibited resistance to at least 2 drugs in addition to ceftiofur, 14.47% carried ColV-positive plasmids, and 53.95% were phylogroup C. Further studies demonstrated that the bla CTX-M -bearing E. coli G12 was assigned to the predominant lineage O78:H4-ST117 of phylogroup G. In addition, its ColV-positive plasmid simultaneously carried multiple resistance genes, and could be independently transferred to confer partial pathogenicity on its host by plasmid mating. E. coli GZM7 was O53:H9-ST23 of phylogroup C, which belonged to another representative lineage of APEC (avian pathogenic E. coli). Its ColV-positive plasmid could complete conjugation with the help of the other coexisting-resistance conjugative plasmid, although it failed to transfer alone. Our findings highlight the flexibly horizontal transfer of ColV plasmids along with multidrug-resistant genes among bla CTX-M -bearing E. coli poses a threat to poultry health and food safety, which contributes to elucidate the concept of "One Health" and deserves particular concern. [ABSTRACT FROM AUTHOR]

Aim of this study was to investigate the prevalence and genetic environment of the oxazolidinone resistance gene optrA in Streptococcus suis (S. suis) isolates from diseased pigs in China. A total of 178 S. suis isolates were screened for the optrA gene by PCR. The phenotypes and genotypes of optrA -positive isolates were investigated by antimicrobial susceptibility testing, core genome Multilocus Sequence Typing (cgMLST), capsular serotypes determination and whole-genome sequencing (WGS). Fifty-one (28.7%) S. suis isolates were positive for optrA. Phylogenetic analysis indicated that the spread of the optrA among S. suis isolates was primarily due to horizontal transfer. Analysis of S. suis serotypes from diseased pigs revealed substantial diversity. The genetic environment of optrA was complex and diverse and could be divided into 12 different types. Interestingly, we identified a novel integrative and conjugative element ICE Ssu 988S, carrying optrA and erm (T) genes. This is to the best of our knowledge the first report of the optrA and erm (T) co-located on an ICE in S. suis. Our results showed a high prevalence of optrA gene in S. suis isolates in China. Further research is needed to evaluate the importance of ICEs, as they horizontally propagate important clinical resistance genes. [ABSTRACT FROM AUTHOR]

This study was designed to depict prevalence and antimicrobial resistance characteristics of Proteus mirabilis ( P. mirabilis ) strains in 4 chicken farms and to probe the transfer mechanism of resistance genes. A total of 187 P. mirabilis isolates were isolated from 4 chicken farms. The susceptibility testing of these isolates to 14 antimicrobials showed that the multidrug resistance (MDR) rate was as high as 100%. The β-lactamase resistance genes bla OXA-1 , bla CTX-M-1G , bla CTX-M-9G and colistin resistance gene mcr-1 were highly carried in the P. mirabilis isolates. An MDR strain W47 was selected for whole genome sequencing (WGS) and conjugation experiment. The results showed that W47 carried 23 resistance genes and 64 virulence genes, and an SXT/R391 integrated conjugative elements (ICEs) named ICE Pmi Chn5 carrying 17 genes was identified in chromosome. ICE Pmi Chn5 was able to be excised from the chromosome of W47 forming a circular intermediate, but repeated conjugation experiments were unsuccessful. Among 187 P. mirabilis isolates, 144 (77.01%, 144/187) isolates carried ICE Pmi Chn5-like ICEs, suggesting that ICEs may be the major vector for the transmission of resistance genes among MDR chicken P. mirabilis strains in this study. The findings were conducive to insight into the resistance mechanism of chicken P. mirabilis strains and provide a theoretical basis for the use of antibiotics for the treatment of MDR P. mirabilis infections in veterinary clinic. [ABSTRACT FROM AUTHOR]

• This study characterized a novel integrative and conjugative element, carrying eight resistance genes and seven IS elements, from a serovar 2 Glaesserella parasuis ST279 isolate. • Tn6743, a novel transposon carrying six resistance genes, was identified. • This study characterized a novel insertion element ISGpa1, which is the first characterized example in G. parasuis. ICE Gpa1804 was identified in the genome of a serovar 2, ST279 isolate EHP1804 carrying eight different resistance genes from 200 Glaesserella parasuis strains isolated from swine with lower respiratory tract infection in seven provinces of China. Susceptibility testing for EHP1804 was determined by broth microdilution, and its genetic profile was determined by whole-genome sequencing. The complete ICE Gpa1804 was analysed by polymerase chain reaction, conjugation assay and bioinformatics tools. The conjugation assay was performed using EHP1804 as the donor and G. parasuis V43 (rifampicin-resistant) as the recipient. ICE Gpa1804 has a size of 71,880 bp and contains 83 genes, including eight resistance genes [ tet (B), bla Rob-1 , aphA1, strA, strB, aac(3)-IId, catA3 and sul2 ]. The conjugation assay showed that ICE Gpa1804 could be transferred to G. parasuis V43 with frequencies of 4.3 × 10−7. To the best of the authors' knowledge, this is the first study to identify a novel integrative and conjugative element (ICE) carrying eight resistance genes and seven insertion sequence (IS) elements from a G. parasuis isolate. Tn 6743 , a novel transposon carrying six resistance genes, was identified. Moreover, IS Gpa1 , a novel IS 256 family insertion element, is the first characterized example of a G. parasuis insertion element. Multiple mobile genetic elements involved in resistance genes were located in chromosomal ICE Gpa1804 , which showed that ICEs may serve as a vital platform for the accumulation of resistance genes. [ABSTRACT FROM AUTHOR]

It has been recognized that colistin resistance is a growing problem that seriously impairs the clinical efficacy of colistin against bacterial infections. One strategy that has been proven to have therapeutic effect is to overcome the widespread emergence of antibiotic-resistant pathogens by combining existing antibiotics with promising non-antibiotic agents. In this work, antibiotic susceptibility testing, checkerboard assays and time-kill curves were used to investigate the antibacterial activity of the individual drugs and the potential synergistic activity of the combination. The molecular mechanisms of tetrandrine in combination with colistin were analyzed using fluorometric assay and Real-time PCR. To predict possible interactions between tetrandrine and MCR-1, molecular docking assay was taken. Finally, we evaluated the in vivo efficacy of tetrandrine in combination with colistin against MCR-positive Salmonella. Overall, the combination of tetrandrine and colistin showed significant synergistic activity. In-depth mechanistic analysis showed that the combination of tetrandrine with colistin enhances the membrane-damaging ability of colistin, undermines the functions of proton motive force (PMF) and efflux pumps in MCR-positive bacteria. The results of molecular docking and RT-PCR analyses showed that tetrandrine not only affects the expression of mcr -1 but is also an effective MCR-1 inhibitor. Compared with colistin monotherapy, the combination of tetrandrine with colistin significantly reduced the bacterial load in vivo. Our findings demonstrated that tetrandrine serves as a potential colistin adjuvant against MCR-positive Salmonella. • In our study, the combination of tetrandrine and colistin drastically enhanced colistin bactericidal activity compared with monotreatment. • In-depth mechanistic analysis showed that tetrandrine potentiated colistin activity through enhancing the membrane-damaging ability of colistin. • Tetrandrine dramatically undermines the function of PMF and result in decreased intracellular ATP levels. In addition, the activity of efflux pump was significantly inhibited by the addition of tetrandrine in both single or combination treatments. • Tetrandrine not only affects the expression of mcr -1 but also as an effective MCR-1 inhibitor. • The discovery of tetrandrine as a potential adjuvant for colistin therapy in combination therapy for severe infections caused by MCR-1 positive Salmonella. [ABSTRACT FROM AUTHOR]

This study was undertaken to discern the transmission characteristics of mcr-1 and bla CTX-M-type in one multidrug-resistant Escherichia coli LWY24 from chicken in China. The genetic profiles of LWY24 isolate were determined by conjugation, S1-pulsed-field gel electrophoresis, southern blot hybridization, and whole genome sequencing analysis. Meanwhile, co-transfer of plasmids in LWY24 isolate was screened by dual conjugation assays. The LWY24 isolate was identified as ST93, and harbored 3 conjugative plasmids, pLWY24J-3 (bla CTX-M-55 -bearing IncFⅡ), pLWY24J- mcr-1 (mcr-1 -carrying IncI2), and pLWY24J-4 (non-resistance-conferring IncI1), and one nonconjugative plasmid pLWY24 (bla CTX-M-14 -containing IncHI2/IncHI2A). Numerous resistance genes, insertion sequences (especially IS 26), and transposons were found in the 4 plasmids, suggesting that horizontal transmission have occurred by plasmid mating, homologous recombination, and transpositions. Under the selection pressure of cefotaxime and colistin or cefotaxime alone, the mcr-1 -bearing plasmid and the bla CTX-M-55 -harboring plasmid could be co-transferred at a similar frequency, with 8.00 × 10−4 or 9.00 × 10−4 transconjugants per donor cell, respectively. The specific shufflon region in mcr-1 -encoding plasmid could generate up to 6 diverse PilV structures, which may further accelerate the horizontal transfer of plasmid. In conclusion, the transmission characteristics of mcr-1 and bla CTX-M-type in LWY24 isolate could due to clonal spread of ST93, selective pressure of cefotaxime, IS 26 -mediate homologous recombination and transposition, and the specific shufflon region. [ABSTRACT FROM AUTHOR]