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As a newly emerging Klebsiella pathogen, more and more Klebsiella michiganensis drug resistant strains have been reported in recent years, which posed serious threats to public health. Here we first reported a multidrug-resistant K. michiganensis strain 12084 with two bla SIM-1 and one mcr-9.2 genes isolated from the sputum specimen of a patient in the Second Affiliated Hospital of Zhejiang University School of Medicine and analyzed its genetic basis and drug-resistance phenotypes. Genetic analysis showed that this strain harbored three different incompatibility groups (IncHI2, IncHI5, and IncFII pKPHS2 :IncFIB-4.1) of plasmids (p12084-HI2, p12084-HI5, and p12084-FII). A total of 26 drug-resistance genes belonging to 12 classes of antibiotics were identified, most of which (24) were located on two plasmids (p12084-HI2 and p12084-HI5). Interestingly, two bla SIM-1 genes were identified to locate on p12084-HI2 and p12084-HI5, respectively, both of which were embedded in In630, indicating their genetic homogeny. It was noting that one bla SIM-1 gene was situated in a novel unit transposon (referred to as Tn 6733 ) on the p12084-HI5 plasmid. We also discovered an mcr-9.2 gene on the p12084-HI2 plasmid. To the best of our knowledge, this is the first report of a bla SIM-1 and mcr-9.2 harboring K. michiganensis strain. We then investigated the population structure/classification, and antibiotic resistance for all 275 availably global K. michiganensis genomes. Population structure revealed that K. michiganensis could be divided into two main clades (Clade 1 and Clade 2); the most popular ST29 was located in Clade 1, while other common STs (such as ST50, ST27, and ST43) were located in Clade 2. Drug-resistance analysis showed 25.5% of the K. michiganensis strains (70/275) harboring at least one carbapenemase gene, indicating severe drug resistance of K. michiganensis beyond our imagination; this is a dangerous trend and should be closely monitored, especially for ST27 K. michiganensis with the most drug-resistant genes among all the STs. Overall, we reported a bla SIM-1 and mcr-9.2 harboring K. michiganensis strain, and further revealed the population structure/classification, and drug-resistance of K. michiganensis , which provided an important framework, reference, and improved understanding of K. michiganensis ., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Li, Jiang, Li, Ju, Yue, Chen, Hu, Wang, Hu, Tuohetaerbaike, Wen, Zhang, Zhou, Yin and Chen.)

In this study, a detailed genetic dissection of the huge and complex bla NDM -carrying genetic elements and their related mobile genetic elements was performed in Enterobacteriaceae. An extensive comparison was applied to 12 chromosomal genetic elements, including six sequenced in this study and the other six from GenBank. These 12 genetic elements were divided into five groups: a novel IME Tn 6588 ; two related IMEs Tn 6523 (SGI1) and Tn 6589 ; four related ICEs Tn 6512 (R391), Tn 6575 (ICE Pvu ChnBC22), Tn 6576 , and Tn 6577 ; Tn 7 and its derivatives Tn 6726 and 40.7-kb Tn 7 -related element; and two related IMEs Tn 6591 (GI sul2 ) and Tn 6590 . At least 51 resistance genes, involved in resistance to 18 different categories of antibiotics and heavy metals, were found in these 12 genetic elements. Notably, Tn 6576 carried another ICE Tn 6582 . In particular, the six bla NDM -carrying genetic elements Tn 6588 , Tn 6589 , Tn 6575 , Tn 6576 , Tn 6726 , and 40.7-kb Tn 7 -related element contained large accessory multidrug resistance (MDR) regions, each of which had a very complex mosaic structure that comprised intact or residual mobile genetic elements including insertion sequences, unit or composite transposons, integrons, and putative resistance units. Core bla NDM genetic environments manifested as four different Tn 125 derivatives and, notably, two or more copies of relevant Tn 125 derivatives were found in each of Tn 6576 , Tn 6588 , Tn 6589 , and 40.7-kb Tn 7 -related element. The huge and complex bla NDM -carrying genetic elements were assembled from complex transposition and homolog recombination. Firstly identified were eight novel mobile elements, including three ICEs Tn 6576 , Tn 6577 , and Tn 6582 , two IMEs, Tn 6588 and Tn 6589 , two composite transposons Tn 6580a and Tn 6580b , and one integron In1718., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Luo, Yin, Zeng, Hu, Jiang, Jing, Chen, Wang, Song, Yang and Zhou.)

Haemophilus parasuis ( H. parasuis ) is a kind of opportunistic pathogen of the upper respiratory tract of piglets. Under certain circumstances, virulent strains can breach the mucosal barrier and enter the bloodstream, causing severe Glässer's disease. Many virulence factors are found to be related to the pathogenicity of H. parasuis strain, but the pathogenic mechanism remains unclear. LuxS/AI-2, as a kind of very important quorum sensing system, affects the growth characteristics, biofilm formation, antibiotic production, virulence, and metabolism of different strains. In order to investigate the effect of luxS/AI-2 quorum sensing system on the virulence of H. parasuis , a deletion mutant strain (ΔluxS) and complemented strain (C-luxS) were constructed and characterized. The results showed that the luxS gene participated in regulating and controlling stress resistance, biofilm formation and virulence. Compared with wild-type strain, ΔluxS strain decreased the production of AI-2 molecules and the tolerance toward oxidative stress and heat shock, and it reduced the abilities of autoagglutination, hemagglutination, and adherence, whereas it increased the abilities to form biofilm in vitro. In vivo experiments showed that ΔluxS strain attenuated its virulence about 10-folds and significantly decreased its tissue burden of bacteria in mice, compared with the wild-type strain. Taken together, the luxS/AI-2 quorum sensing system in H. parasuis not only plays an important role in growth and biofilm formation, but also affects the pathogenicity of H. parasuis .