A prolonged multispecies outbreak of IMP-6 carbapenemase-producing Enterobacterales due to horizontal transmission of the IncN plasmid

Abstract

A multispecies outbreak of IMP-6 carbapenemase-producing Enterobacterales (IMP-6-CPE) occurred at an acute care hospital in Japan. This study was conducted to understand the mechanisms of IMP-6-CPE transmission by pulsed-field gel electrophoresis (PFGE), multilocus sequence typing and whole-genome sequencing (WGS), and identify risk factors for IMP-6-CPE acquisition in patients who underwent abdominal surgery. Between July 2013 and March 2014, 22 hospitalized patients infected or colonized with IMP-6-CPE (Escherichia coli [n = 8], Klebsiella oxytoca [n = 5], Enterobacter cloacae [n = 5], Klebsiella pneumoniae [n = 3] and Klebsiella aerogenes [n = 1]) were identified. There were diverse PFGE profiles and sequence types (STs) in most of the species except for K. oxytoca. All isolates of K. oxytoca belonged to ST29 with similar PFGE profiles, suggesting their clonal transmission. Plasmid analysis by WGS revealed that all 22 isolates but one shared a ca. 50-kb IncN plasmid backbone with bla_IMP-6 suggesting interspecies gene transmission, and typing of plasmids explained epidemiological links among cases. A case-control study showed pancreatoduodenectomy, changing drains in fluoroscopy room, continuous peritoneal lavage and enteric fistula were associated with IMP-6-CPE acquisition among the patients. Plasmid analysis of isolates in an outbreak of IMP-6-CPE suggested interspecies gene transmission and helped to clarify hidden epidemiological links between cases.

Figure 1

Basic characteristics of cases of IMP-6 carbapenemase-producing Enterobacterales and its isolates, Osaka, Japan, June 2013-March 2014, and the timeline of detection. Horizontal lines indicate durations of hospitalization and nodes indicate detection of isolates. Asterisks indicate the cases included in the case-control study. The cases with type A1 plasmid are shown on a background of pink, and the cases with type A2 plasmid are shown on a background of blue. Case 9 was admitted to ward E11 of the Department of Neurosurgery on 20 January and was treated there until 17 February 2014. ICCU: intensive cardiac care unit.

Figure 2

Dendrogram of pulsed-field gel electrophoresis (PFGE) profiles, multilocus sequence typing (MLST) data and plasmid types for the 22 isolates from IMP-6 carbapenemase-producing Enterobacterales cases. (a) Escherichia coli, (b) Klebsiella oxytoca, (c) Enterobacter cloacae, (d) Klebsiella pneumoniae. MLST:Multilocus sequence typing.

Figure 3

Possible relationship between 23 plasmid types in the 22 isolates from IMP-6 carbapenemase-producing Enterobacterales cases, Osaka, Japan, 2013–2014 and eight other isolates in the database. Plasmid clustering was performed on the basis of gene presence–absence pattern and intI1 structure (intact or pseudogene). Red and black bars in the heatmap indicate gene presence and absence, respectively. Information on the samples is listed in the table to the right of the heatmap. Information on the isolates from the database that had no relationship with this outbreak is shown as N/A in the column named ‘ID’. N/A: not available; ST: sequence type by multilocus sequence typing.