The metallo-beta-lactamase GIM-1 has been found in various bacterial host species nearly exclusivley in Western Germany. However, not much is known about the epidemiology of GIM-1-positive Serratia marcescens. Here we report on a surprisingly protracted regional dissemination. In-hospital transmission was investigated by using conventional epidemiological tools to identify spatiotemporal links. Strain typing was performed using PFGE and whole genome sequencing (WGS). Bayesian phylogeny was used to infer the time axis of the observed occurence. Thirteen S. marcescens strains from 10 patients of 6 different German hospitals were investigated. Suspected in-hospital transmissions were confirmed by molecular typing at a higher resolution using WGS compared to PFGE. A detailed sequence analysis demonstrated a spread of one predominant strain variant, but also provided evidence for gene transfer of the blaGIM-1 gene cassette between different strains. A Bayesian phylogenetic analysis showed that the most recent common ancestor of the identified clonal cluster can be dated back to April 1993 (95% highest posterior density interval: January 1973 - March 2003), and that this strain might have harboured the blaGIM-1 already at that time, and therewith years before the first detection of this resistance gene in clinical specimens. This study shows a longstanding clonal and plasmid-mediated expansion of GIM-1-producing S. marcescens that might have gone unnoticed in the absence of a standardized and effective molecular screening for carbapenmases. Systematic and early detection of resistance is thus highly advisable, especially for the prevention of potentially long-term dissemination that may progress beyond control.
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