Chromosomal Integration of blaKPC-2 in Proteus mirabilis Clinical Isolates

Introduction Over these years, KPC-type beta-lactamases have become one of the most prevalent acquired carbapenemases in Enterobacteriaceae, with the highest incidence in Mediterranean countries, especially Italy and Greece. Historically, blaKPC has been largely reported in high-risk clones of K. pneumoniae (KPC-Kp), which have spread rapidly in several areas worldwide. Here we describe the first Italian detection of a small set of Proteus mirabilis clinical isolates (AOUC-001 to -006) harbouring blaKPC-2 from a setting of high-level endemicity of KPC-Kp. Multidrug-resistance in P. mirabilis is commonly associated with the production of extended-spectrum beta-lactamases or the AmpC-type cephalosporinase, but acquisition of blaKPC is still sporadically reported to date. Materials and Methods Antimicrobial susceptibility was determined by standard broth microdilution. All KPC-positive P. mirabilis were fully sequenced using Illumina MiSeq and, for two isolates (AOUC-001 and -004), the PacBio technology. In silico identification of antimicrobial resistance genes was obtained by ResFinder. Complete characterization of blaKPC genetic context was achieved by NGS data validated by PCR mapping and Sanger sequencing. Results P. mirabilis AOUC-004 was virtually resistant to all tested antibiotics (i.e. PDR) while the others (AOUC-001 to -006) exhibited resistance to all except for carbapenems. Genome sequencing revealed that 5 out of 6 strains were strictly related each other, while AOUC-004 showed a higher genetic distance. In addition to blaKPC-2, the 5 related strains also carried the armA and blaCMY-16 genes. Strikingly, such strains harbored two copies of blaKPC-2, both embedded within two Tn4401a transposons. Conversely, AOUC-004 did not possess blaCMY-16 and had a double copy of blaKPC-2 aboard Tn4401a derivative elements. In all studied strains, acquisition of blaKPC occurred through the chromosomal integration of a KPC-encoding plasmid strictly related to pKpQIL and pKPN101-IT, although targeting different loci within the genome of AOUC-004 and the remaining 5 related strains. Discussion and Conclusions Here we characterized six clinical isolates of P. mirabilis encoding KPC-2 and explored the different genetic mechanisms at the basis of the chromosomal integration of blaKPC. These results expand the current knowledge about the acquisition and integration of carbapenemase-encoding genes in P. mirabilis that, differently from what is generally observed among Enterobacteriaceae, is not an uncommon event. From a clinical perspective, acquisition of carbapenem and aminoglycosides resistance in P. mirabilis could represent a serious threat, considering its intrinsic resistance to several molecules such as tigecycline and colistin.