178. Endemic Carbapenem Resistance Driven By Clonal and Horizontal Spread of blaIMP-4 Across Diverse Enterobacterales: Jumping Genes, Promiscuous Plasmids and Killer Clones

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


Endemic Carbapenem Resistance Driven By Clonal and Horizontal
Background. Carbapenem-resistant Enterobacterales (CRE) have become endemic and cause significant morbidity and mortality globally. The metallo-beta-lactamase gene bla IMP-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 bla IMP-4 in clinical and environmental isolates from 2008 -2020 at our institution.
Methods. We performed whole genome sequencing on 219 bla IMP-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 bla IMP-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, bla IMP-4 was present on IncC plasmids in Serratia marcescens and Klebsiella pneumoniae. We noted small outbreaks of Pseudomonas aeruginosa ST111 with chromosomal integration of bla IMP-4 from 2008-2018 (16 isolates) and Enterobacter cloacae complex ST114 with bla IMP-4 on IncFIB(K)/ IncFIA(HI1) plasmids from 2011-2020 (19 isolates). From 2016-2020, there was an explosion of diverse IncHI2 plasmids carrying bla IMP-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 bla IMP-4 , these plasmids carried mcr-9.1, a colistin resistance gene, and resistance determinants to nearly all key classes of Gram-negative antimicrobials. 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. 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. Background. In January 2021, a California acute care hospital (ACH A), a sentinel site for Acinetobacter baumannii (AB) surveillance, identified OXA-48-like-carbapenemase producing (CP) AB in a patient admitted from a ventilator-equipped skilled nursing facility (vSNF A); OXA-48-like AB had not been previously reported in the United States.

Identification and Whole Genome Sequencing Analysis of an Oxacillinase (OXA)-48-like-producing Acinetobacter baumannii
Methods. Our investigation included onsite infection control (IC) assessments, contact tracing, and point prevalence surveys (PPS) at vSNF A. The Antibiotic Resistance (AR) Laboratory Network performed carbapenemase testing on AB isolates (including those from ACH A) and PPS swabs. A case was defined as a patient with an OXA-48-like AB isolate, or an epidemiologically-linked patient with an OXA-48-like gene detected via screening. We performed whole genome sequencing (WGS) of OXA-48-like AB and other CP organisms on the Illumina MiSeq and Oxford Nanopore MinION for short and long read sequencing, respectively.
Results. Since January 2021, we have identified five OXA-48-like AB cases (including the index), six OXA-48-like cases (no organism recovered), and six patients with other CP organisms at ACH A and vSNF A. Since August 2019, vSNF A has concurrently been experiencing an OXA-109 AB outbreak. A second vSNF A patient, Patient 2, who overlapped with the index patient, had OXA-48-like Klebsiella pneumoniae (KP) (November 2019) and OXA-109 AB (May 2020) isolates. WGS of the index patient's AB and Patient 2's KP isolates identified a rare OXA-48-like gene located on the AB chromosome and a KP plasmid. The OXA-48-like AB was also carrying an OXA-109 gene, and hqSNP analysis indicated it varied by 9-44 single-nucleotide polymorphisms (SNPs) from 14 OXA-109 AB isolates linked to that outbreak, and 0-3 SNPs from the other OXA-48-like AB case isolates.