178. Endemic Carbapenem Resistance Driven By Clonal and Horizontal Spread of blaIMP-4 Across Diverse Enterobacterales: Jumping Genes, Promiscuous Plasmids and Killer Clones
Authors: Macesic Nenad , Blakeway Luke , Jenney Adam W , Peleg Anton 
Published: December 2021

Abstract

Background
Carbapenem-resistant Enterobacterales (CRE) have become endemic and cause significant morbidity and mortality globally. The metallo-beta-lactamase gene blaIMP-4 is a key CRE resistance determinant in Australia and Asia but its genomic context remains unknown. We aimed to determine the genomic epidemiology of blaIMP-4 in clinical and environmental isolates from 2008 – 2020 at our institution.

Methods
We performed whole genome sequencing on 219 blaIMP-4-carrying isolates from 134 patients (219 short-read and 75 long-read). Multi-locus sequence types (MLSTs), resistance determinants and plasmid replicons were assessed. High-quality de novo hybrid assemblies were used to identify location of blaIMP-4 gene. We conducted phylogenetic analysis for key MLSTs and plasmids.

Results
Bla IMP-4 was noted on a class I integron also harboring aminoglycoside, sulfamethoxazole, chloramphenicol and quaternary ammonium compound resistance genes. This integron was able to migrate over time to 10 bacterial species (42 STs) and 6 different plasmid types (Figure 1 and Figure 2). From 2008-2020, blaIMP-4 was present on IncC plasmids in Serratia marcescens and Klebsiella pneumoniae. We noted small outbreaks of Pseudomonas aeruginosa ST111 with chromosomal integration of blaIMP-4 from 2008-2018 (16 isolates) and Enterobacter cloacae complex ST114 with blaIMP-4 on IncFIB(K)/IncFIA(HI1) plasmids from 2011-2020 (19 isolates). From 2016-2020, there was an explosion of diverse IncHI2 plasmids carrying blaIMP-4. This was driven by clonal expansion of E. cloacae complex ST93/ST190 (79 isolates), with spillover of IncHI2 plasmids to Klebsiella spp (13 isolates), Citrobacter spp (2 isolates), S. marcescens (1 isolate), Escherichia coli (4 isolates). In addition to blaIMP-4, these plasmids carried mcr-9.1, a colistin resistance gene, and resistance determinants to nearly all key classes of Gram-negative antimicrobials.
Figure 1. Bacterial species harboring blaIMP-4 2008-2020

BlaIMP-4 was noted in diverse bacterial species over the study period. Serratia marcescens and Klebsiella pneumoniae were present throughout. Outbreaks of Enterobacter cloacae complex ST114, ST190 and ST93 and Pseudomonas aeruginosa ST111 were noted.
Figure 2. Diverse plasmids associated with blaIMP-4 carriage determined by de novo hybrid assembly

Presence of blaIMP-4 on diverse plasmids that varied through the study period was noted. Plasmids were charaterised by analysing de novo hybrid assembly data and co-location of blaIMP-4 and plasmid replicons on the same contigs.

Conclusion
Bla IMP-4 spread on a class I integron was responsible for endemic carbapenem resistance at our institution. This mobile genetic element was able to persist due to both clonal spread and entry into diverse plasmids. Concerningly, we noted a large outbreak driven by IncHI2 plasmids harboring colistin resistance genes with spread to multiple bacterial species.

Disclosures
All Authors: No reported disclosures