Abstract
OBJECTIVES: A carbapenem-resistant Providencia rettgeri (PR1) isolate was recovered from a wound infection in Missouri, USA. This isolate possessed an EDTA-inhibitable carbapenemase that was unidentified using the Xpert CARBA-R assay. Our objective was to elucidate the molecular determinant of carbapenem resistance in this isolate. We then sought to test the transmissibility of bla(IMP-27) loci in clinical P. rettgeri and Proteus mirabilis isolates. METHODS: In October 2016 the novel ambler Class B carbapenemase bla(IMP-27), was reported in two different Proteus mirabilis (PM185 and PM187) isolates. Broth mating assays for transfer of carbapenemase activity were performed for the three clinical isolates with recipient sodium azide-resistant Escherichia coli J53. Antibiotic susceptibility testing and phenotypic carbapenemase activity testing were performed on the clinical isolates, J53 and transconjugants using the Kirby-Bauer disc diffusion method according to CLSI guidelines. Plasmid DNA from PM187, PR1 and their transconjugants were used as input for Nextera Illumina sequencing libraries and sequenced on a NextSeq platform. RESULTS: PR1 was resistant to both imipenem and meropenem. PM187 and PR1 could transfer resistance to E. coli through plasmid conjugation (pPM187 and pPR1). pPM187 had a virB/virD4 type IV secretion system whereas pPR1 had a traB/traD type IV secretion system. CONCLUSION: Two of three bla(IMP-27)-bearing clinical isolates tested could conjugate resistance into E. coli. The resulting transconjugants became positive for phenotypic carbapenemase production but did not pass clinical resistance breakpoints. bla(IMP-27) can be transmitted on different plasmid replicon types that rely on distinct classes of type IV secretion system for horizontal transfer.