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ABSTRACT: Objectives: KHM-1-metallo-β-lactamase-producing Enterobacterales strains, of which only a few have been found, were isolated from four inpatients in Osaka, Japan during 2016 to 2020. We compared whole genomes of the four KHM-1-producing isolates, including one Enterobacter hormaechei subsp. hoffmannii, one Escherichia coli, and two Citrobacter freundii. Methods: These isolates were characterized by whole-genome sequencing, comparative analysis of blaKHM-1-encoding plasmids with earlier reported plasmids, and antimicrobial susceptibility tests. Results: Multilocus sequence typing classified the E. hormaechei subsp. hoffmannii isolate to ST78, the E. coli isolate to ST354, and the two C. freundii isolates to ST95. These isolates harboured various antimicrobial resistance genes aside from blaKHM-1 on their chromosomes and plasmids. In all four isolates, blaKHM-1 was located on 137 kbp to 213 kbp plasmids of IncC replicon type. Although there were common resistance genes such as blaKHM-1-ISEc68, class I integron cassette, and fosG, the four blaKHM-1-encoding plasmids were distinguishable into two lineages based on differences of the resistance gene components and their surrounding regions. Conclusion: Because no epidemiological contact was observed among the inpatients, the blaKHM-1-encoding IncC plasmids might have spread horizontally to multiple bacterial species through repeated recombination and insertion.

It has been shown that an evolutionary tradeoff between vertical (host growth rate) and horizontal (plasmid conjugation) transmissions contributes to global plasmid fitness. As conjugative IncC plasmids are important for the spread of multidrug resistance (MDR), in a broad range of bacterial hosts, we investigated vertical and horizontal transmissions of two multidrug-resistant IncC plasmids according to their backbones and MDR-region rearrangements, upon plasmid entry into a new host. We observed plasmid genome deletions after conjugation in three diverse natural Escherichia coli clinical strains, varying from null to high number depending on the plasmid, all occurring in the MDR region. The plasmid burden on bacterial fitness depended more on the strain background than on the structure of the MDR region, with deletions appearing to have no impact. Besides, we observed an increase in plasmid transfer rate, from ancestral host to new clinical recipient strains, when the IncC plasmid was rearranged. Finally, using a second set of conjugation experiments, we investigated the evolutionary tradeoff of the IncC plasmid during the critical period of plasmid establishment in E. coli K-12, by correlating the transfer rates of deleted or non-deleted IncC plasmids and their costs on the recipient strain. Plasmid deletions strongly improved conjugation efficiency with no negative growth effect. Our findings indicate that the flexibility of the MDR-region of the IncC plasmids can promote their dissemination, and provide diverse opportunities to capture new resistance genes. In a broader view, they suggest that the vertical-horizontal transmission tradeoff can be manipulated by the plasmid to improve its fitness., Competing Interests: The authors declare no conflict of interest.

Salmonella Thompson is a prevalent foodborne pathogen and a major threat to food safety and public health. This study aims to reveal the dissemination mechanism of S. Thompson with co-resistance to ceftriaxone and ciprofloxacin. In this study, 181 S. Thompson isolates were obtained from a retrospective screening on 2118 serotyped Salmonella isolates from foods and patients, which were disseminated in 12 of 16 districts in Shanghai, China. A total of 10 (5.5 %) S. Thompson isolates exhibited resistance to ceftriaxone (MIC ranging from 8 to 32 μg/mL) and ciprofloxacin (MIC ranging from 2 to 8 μg/mL). The AmpC β-lactamase gene bla CMY-2 and plasmid-mediated quinolone resistance (PMQR) genes of qnr S and qep A were identified in the 9 isolates. Conjugation results showed that the co-transfer of bla CMY-2 , qnr S, and qep A occurred on the IncC plasmids with sizes of ∼150 (n = 8) or ∼138 (n = 1) kbp. Three typical modules of IS Ecp1 - bla CMY-2 - blc-sugE , IS 26 -IS 15DIV-qnr S-IS Kpn19 , and IS CR3 - qep A-intl1 were identified in an ST3 IncC plasmid pSH11G0791. Phylogenetic analysis indicated that IncC plasmids evolved into Lineages 1, 2, and 3. IncC plasmids from China including pSH11G0791 in this study fell into Lineage 1 with those from the USA, suggesting their close genotype relationship. In conclusion, to our knowledge, it is the first report of the co-existence of bla CMY-2 , qnr S, and qep A in IncC plasmids, and the conjugational transfer contributed to their dissemination in S. Thompson. These findings underline further challenges for the prevention and treatment of Enterobacteriaceae infections posed by IncC plasmids bearing bla CMY-2 , qnr S, and qep A. • Ceftriaxone and ciprofloxacin co-resistance was found in Salmonella Thompson. • Co-transfer of blaCMY-2, qnrS and qepA occurred on the IncC plasmids. • ISEcp1-blaCMY-2-blc-sugE, IS26-IS15DIV-qnrS-ISKpn19 and ISCR3-qepA-intl1 were found. • IncC plasmids from China fell into Lineage 1 with those from the USA. [ABSTRACT FROM AUTHOR]

Objectives: KHM-1-metallo-β-lactamase-producing Enterobacterales strains, of which only a few have been found, were isolated from four inpatients in Osaka, Japan during 2016 to 2020. We compared whole genomes of the four KHM-1-producing isolates, including one Enterobacter hormaechei subsp. hoffmannii, one Escherichia coli, and two Citrobacter freundii., Methods: These isolates were characterized by whole-genome sequencing, comparative analysis of bla KHM-1 -encoding plasmids with earlier reported plasmids, and antimicrobial susceptibility tests., Results: Multilocus sequence typing classified the E. hormaechei subsp. hoffmannii isolate to ST78, the E. coli isolate to ST354, and the two C. freundii isolates to ST95. These isolates harboured various antimicrobial resistance genes aside from bla KHM-1 on their chromosomes and plasmids. In all four isolates, bla KHM-1 was located on 137 kbp to 213 kbp plasmids of IncC replicon type. Although there were common resistance genes such as bla KHM-1 -ISEc68, class I integron cassette, and fosG, the four bla KHM-1 -encoding plasmids were distinguishable into two lineages based on differences of the resistance gene components and their surrounding regions., Conclusion: Because no epidemiological contact was observed among the inpatients, the bla KHM-1 -encoding IncC plasmids might have spread horizontally to multiple bacterial species through repeated recombination and insertion., (Copyright © 2024 The Author(s). Published by Elsevier Ltd.. All rights reserved.)