The identification of the multi-drug resistant organisms, vancomycin resistant enterococci (VRE) and extended spectrum β-lactamase producing Enterobacteriaceae (ESBL-E), in the ICU: examining the interplay between patient colonisation and environmental contamination.

The role of the environment in the dissemination and acquisition of multi-drug resistant organisms (MDRO) is a debated topic in the literature. In this thesis, we sought to identify and characterise extended spectrum beta lactamase producing Enterobactericeae (ESBL-E) and vancomycin resistant enterococcus (VRE) reservoirs in the environment of the intensive care unit (ICU) of a tertiary referral hospital in North Dublin. In a prospective study, we took 1722 samples from the ICU environment over the course of 20 months. We found 9% of environmental sites tested were positive for VRE and 0.6% of sites were positive for ESBL-E. We identified that older isolation rooms were the most contaminated areas in the ICU.

We also quantified the burden of ESBL-E and VRE carriage among patients admitted to the ICU over this time period and examined the interplay between environmental and patient isolates. Of 157 patients who were included in the study, 9.5% were colonised with ESBL-E and 19.1% were colonised with VRE. There were no epidemiological links between the patient and environmental isolates for the ESBL-E isolates. There were a number of epidemiologically linked isolates among the VRE from both the environmental and patient samples.

Genetic characterisation of a selection of vancomycin resistant Enterococcus faecium (VREfm) isolates, by pulsed-field gel (PFGE) and next generation sequencing (NGS), showed that there was genetic diversity among the patient isolates, but that the environmental isolates displayed more clonal relationships. NGS demonstrated that despite the clonality of the environmental isolates, there were a variety of strain matches identified, and indeed the reverse was true for the patient isolates, highlighting the complexity of enterococcal populations and transmission in the hospital milieu.