2187. Earliest Description of Mobile Genetic Elements (MGEs) Involved in Establishing bla(NDM) Persistence Following its Spread From Acinetobacter spp. to Enterobacterales

BACKGROUND: bla (NDM) is the most prevalent carbapenemase worldwide. It originated in Acinetobacter spp. and spread to Enterobacterales on MGEs despite bottlenecks in MGE transfers between, and persistence within, these phylogenetically distinct bacteria. To elucidate how this transfer and successful expansion were achieved, we investigated MGEs among the earliest NDM-positive Gram-negative bacteria (GNB), isolated in India in 2007. METHODS: Thirteen polymerase chain reaction-confirmed NDM-positive GNB underwent whole-genome sequencing (Illumina NovaSeq and Oxford Nanopore Technologies MinION) and computational analyses: assembly (Unicycler and Trycycler), annotation (RAST), identification (Kraken2), plasmid incompatibility (PlasmidFinder). RESULTS: Single copies of bla(NDM-1) were found in 12 Enterobacterales (6 K. pneumoniae; 3 E. coli; 2 E. cloacae; 1 E. hormaechei) and 1 A. baumannii (Ab), located on plasmids in 11/13 strains: 6 IncC, 3 IncFII, 2 IncFIB (Figure 1). Partial or complete ISAba125 was found upstream of all bla(NDM), with a second complete downstream copy forming Tn125 only in Ab. bla(NDM)'s genetic environment was highly diverse including the earliest evidence of its association with MGEs that participated in its global dissemination: insertion sequence common region 1 (ISCR1, n=5) and Tn3000 (n=4). IS3000, present in 2 copies bracketing Tn3000, was also found in single copies in 4 strains at varying distances upstream of bla(NDM). In 3/4 of these, ISCR1 was downstream of bla(NDM). These hybrid constructs may represent precursors leading to the formation of these MGEs, or degenerate structures. Figure 1: Genetic environment surrounding blaNDM in 13 Gram-negative bacteria isolated in India in 2007. [Figure: see text] Acibau: Acinetobacter baumannii; Entclo: Enterobacter cloacae; Enthor: Enterobacter hormaechei; Esccol: Escherichia coli; Klepne: Klebsiella pneumoniae. CONCLUSION: We present evidence of early, rapid and diverse adaptation of bla(NDM)’s genetic environment following its transfer from Acinetobacter spp. to Enterobacterales. We identify for the first time potentially intermediate genetic structures in the transition between the ancestral Tn125 structure from Acinetobacter spp., and both ISCR1 and Tn3000, which overtook Tn125 as the predominant MGEs among NDM-positive Enterobacterales. Additional sequencing of early NDM-positive isolates could shed more light on the genetic events leading to the formation of MGEs associated with bla(NDM), furthering our understanding of the emergence of MGEs carrying antibiotic-resistance genes. DISCLOSURES: All Authors: No reported disclosures