First description of a long-term low frequency cluster of a GIM-1-producing E. hormaechei subsp. steigerwaltii in a tertiary care hospital in Germany

Introduction:Enterobacter cloacae complex is a common cause of hospital outbreaks. A retrospective and prospective molecular analysis of multidrug-resistant clinical isolates in a tertiary care centre demonstrated the presence of a GIM-1 metallo-ß-lactamase-producing E. hormaechei subsp. steigerwaltii cluster affecting 23 patients from 2009 to 2015.Methods:Carbapenem-non-susceptible E. cloacae isolates were subsequently analysed by PCR targeting relevant carbapenemase genes (blaIMP, blaVIM, blaGIM-1, blaNDM, blaKPC and blaOXA-48). Genotyping was carried out using DiversiLab, PFGE (XbaI) and MLST. And whole genome sequencing of DNA fragment libraries (Illumoiina) of 33 isolates was performed. Transposon and plasmid sequences were determined by reference mapping and de novo assembly. Epidemiological data was collected about the affected patients and environmental sampling was performed twice on the medical ward with the highest number of patients carrying the E. hormaeichei; in May 2012 and May 2013. Infection control measures introduced to halt the outbreak included admission and discharge screening for multidrug-resistant Gram-negative bacteria of every patient on the ward in a period between May and July 2013.Results:All isolates belonged to one cluster, confirmed by MLST to be sequence type 89. The blaGIM-1-gene was embedded in a class-1-integron (In770) and the Tn21-subgroup transposon Tn6216 (KC511628) on a 25kb-plasmid. Although most cases, stretching discontinuously from 2009 to 2015, were linked to one specific medical ward. Environmental screening detected one colonized sink trap in a service room. Rectal screening throughout the period remained negative and no further blaGIM-1-positive E. hormaechei has been isolated since May 2015.Conclusion:We describe a long-term but low frequency outbreak of a GIM-1-producing E. hormaechei subsp. steigerwaltii cluster. No clear environmental reservoir was detected, with the exception of the one sink, which was thought not to be a likely source of the outbreak. Routine molecular screening of carbapenem-non-susceptible Gram-negative isolates was the key to the detection of the outbreak.