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a Iwata S, Tada T, Hishinuma T, et al: Antimicrob Agents Chemother, 2020; 64.18)size (bp)4.65M4.34M205K4.70M85K4.35M205K4.42M153KAntibioticBML24961664samples of five patients in Japan in 201818). All five were multidrug-resistant, being resistant to amino-glycosides, carbapenems and fluoroquinolones18). These isolates harbored genes encoding aminogly-coside modifying enzymes, including aac(6’)-Ib4 and aac(6’)-Iae, and MBL genes encoding carbap-enemases; including IMP-1, IMP-11 and IMP-70 (Table 2). They also had three mutations with amino acid substitutions in GyrA and ParC, which were associated with quinolone resistance (Table 2). One isolate harbored aminoglycoside- and carbap-enem-resistant genes on the chromosome, whereas the other four harbored these genes on plasmids. Carbepenemase activities of IMP-1 MBL variantsAll five P. rettgeri and P. stuartii clinical isolates were resistant to imipenem and meropenem, and three, two P. rettgeri isolates and one P. stuartii isolate, were highly resistant to both carbapenems, with minimum inhibitory concentrations (MICs) of 512 μg/ml (Table 3). These three highly carbape-nem-resistant isolates harbored blaIMP-70, whereas, of the other two, one harbored blaIMP-1 and the other harbored blaIMP-11. IMP-70 is a variant of IMP-1 with two amino acid substitutions, Val67Phe isolatesgenomeP. rettgeri BML2496chromosomeP. rettgeri BML2526chromosomeplasmidP. rettgeri BML2531chromosomeplasmidP. rettgeri BML2576chromosomeplasmidP. stuartii BML2537chromosomeplasmidImipenemMeropenemTable 2　Genetic characterization of carbapenem-resistant Providencia species isolatesaTable 3　Drug susceptibility profiles of Providencia species clinical isolatesantibiotic resistance genesaminoglycosidescarbapenemaseaac(6’)-Ib4aac(6’)-Iaeaac(6’)-Ilaac(6’)-Iaeaac(2’)-Iaaac(6’)-IaeMIC(μg/ml)P. rettgeriBML2531BML25263232512512and Phe87Val; IMP-10 is a variant of IMP-1 with one amino acid substitution, Val67Phe; and IMP- 1(F87V) is a variant of IMP-1 with one amino acid substitution, Phe87Val. E. coli expressing blaIMP-1, blaIMP-10, blaIMP-1(Phe87Val), and blaIMP-70 showed signifi-cantly higher MICs for all carbapenems tested than a vector control (Table 4). The MICs for all carbap-enems of the vector control ranged from ≤0.06 to 0.125. E. coli expressing blaIMP-70 showed higher MICs for doripenem and meropenem, but the same MICs for imipenem and panipenem, than E. coli expressing blaIMP-1. E. coli expressing blaIMP-10 showed a significantly higher MIC for doripenem and an increased MIC for meropenem. Assessment of the carbepenemase activities of recombinant IMP-1, IMP-10, IMP-1(Phe87Val) and IMP-70 showed that IMP-10 had greater hydrolytic activi-ties than IMP-1 against meropenem, with the kcat/Km values of IMP-70 and IMP-10 being 2.3- and 3.4-fold higher, respectively, than those of IMP-1 (Table 5). In contrast IMP-70 and IMP-1 showed similar carbapenemase activities against doripenem, imipenem and panipenem, and IMP-1(Phe87Val) showed similar or reduced carbapenemase activi-ties against all carbapenems tested.quinolone resistance genesGyrAParCblaIMP-1Ser83IleAsp87AlaSer83Ile Asp87GlublaIMP-70Ser83Ile Asp87GlublaIMP-11Ser83Ile Asp87GlublaIMP-70Ser83Ile Asp87GlublaIMP-70P. stuartiiBML2537BML2576512512>512512Ser87IleSer87IleSer87IleSer87IleSer87Arg203