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Institutional outbreak involving multiple clades of IMP-producing Enterobacter cloacae complex sequence type 78 at a
Sohei Harada1,2, Kotaro Aoki3, Daisuke Ohkushi4
1Department of Infection Control and Prevention, The University of Tokyo Hospital, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8655, Japan. haradas-tky@umin.ac.jp.
Background:
Information about the clinical and microbiological characteristics of IMP-producing Enterobacterales has been limited. Here, we describe an institutional outbreak of IMP-producing Enterobacter cloacae complex (ECC) involving multiple clades of ECC sequence type (ST) 78 strains.
Methods:
Antimicrobial susceptibility testing, whole-genome sequencing, and conjugation experiments of 18 IMP-producing ECC strains isolated during four-year study period were performed. Species and subspecies were determined by average nucleotide identity analysis and clonal relatedness of the isolates was analyzed with multilocus sequence typing and core-genome single nucleotide polymorphism (SNP) analysis. Relevant clinical information was extracted from medical records.
Results:
Fourteen of 18 IMP-producing ECC isolates were determined as Enterobacter hormaechei ST78. Sixteen isolates, including 13 isolates belonging to ST78, carried blaIMP-1 in In316-like class 1 integron and also carried IncHI2 plasmids. Conjugation experiments were successful for 12 isolates carrying blaIMP-1 on IncHI2 plasmids and for an isolate carrying blaIMP-11 on an IncL/M plasmid. Although isolation of ST78 strains was clustered in a 14-months period suggesting nosocomial transmission, these strains were subdivided into three clades by SNP analysis: clade A (n = 10), clade B (n = 1), clade C (n = 3). A part of clonal relatedness was unexpected by the epidemiological information at the time of isolation of the strains. Most of the IMP-producing ECC strains were susceptible to non-β-lactam antibiotics and had relatively low minimum inhibitory concentrations to carbapenems (≤4 μg/mL). Five of six infections caused by IMP-producing ECC were treated successfully.
Conclusions:
Whole-genome sequencing analysis revealed the outbreak was caused by three different clades of ST78 strains, where patients had favorable treatment outcome of the infections compared with that caused by Enterobacterales producing other carbapenemases, possibly due to their non-multidrug-resistant phenotype.
Insights
An institutional outbreak of IMP-producing Enterobacter cloacae complex (ECC) involved three clades of ST78 strains. Infections showed favorable treatment outcomes, possibly due to a non-multidrug-resistant phenotype.
Area of Science:
- Microbiology
- Infectious Diseases
- Genomics
Background:
- Limited data exists on the clinical and microbiological features of IMP-producing Enterobacterales.
- This study details an institutional outbreak of IMP-producing Enterobacter cloacae complex (ECC) involving multiple clades of ECC sequence type (ST) 78 strains.
Purpose of the Study:
- To characterize the clinical and microbiological aspects of an IMP-producing ECC outbreak.
- To investigate the genetic relatedness and resistance mechanisms of the involved strains.
Main Methods:
- Whole-genome sequencing (WGS) and antimicrobial susceptibility testing were performed on 18 IMP-producing ECC strains.
- Multilocus sequence typing (MLST) and core-genome single nucleotide polymorphism (SNP) analysis were used to assess clonal relatedness.
- Conjugation experiments were conducted to confirm plasmid-mediated resistance transfer.
Main Results:
- Fourteen of 18 isolates were identified as Enterobacter hormaechei ST78.
- Most IMP-producing ECC strains carried blaIMP-1 within an In316-like class 1 integron on IncHI2 plasmids.
- SNP analysis revealed three distinct clades (A, B, and C) within the ST78 strains, despite a 14-month isolation cluster suggesting nosocomial transmission.
- The isolates exhibited susceptibility to non-β-lactam antibiotics and low carbapenem minimum inhibitory concentrations (MICs).
Conclusions:
- The outbreak was caused by three distinct clades of ST78 strains, as determined by WGS.
- Patients infected with these IMP-producing ECC strains experienced favorable treatment outcomes compared to those with other carbapenemase-producing Enterobacterales.
- The favorable outcomes may be attributed to the non-multidrug-resistant nature of these specific strains.
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