Comparison of Pulsed-field Gel Electrophoresis and Whole Genome Sequencing to Determine Transmission Rate of ESBL-producing E.Coli

Pulse-field gel electrophoresis (PFGE) was considered the reference standard to determine transmission events of extended-spectrum Beta-Lactamase (ESBL) producing E.coli . However, this technique lacks the resolution to differentiate closely related strains, which is needed to identify ESBL-transmission. Furthermore, PFGE is not able to distinguish mobile genetic elements. In contrast, whole genome sequencing (WGS) allows the identification of single-nucleotide polymorphisms (SNPs) that differentiate bacterial strains and mobile genetic elements, such as plasmids at the highest possible resolution, therefore enabling investigation of their relatedness by phylogenetic analyses and ultimately detailed exploration of transmission pathways. As WGS is now readily available and affordable, the investigators aim to reinvestigate transmission events in the 24 index-contact patient-pairs identified after cessation of contact precautions by reassessing the genetic relatedness of both strains and mobile genetic elements by sequencing all 48 recovered ESBL- E.coli strains. The investigators hypothesize that the number of transmission events as defined by transmission of ESBL-producing E. coli strains may have been overestimated by PFGE as compared to WGS, as PFGE lacks the resolution to differentiate closely related strains. However, transmission of mobile genetic elements may have been missed by PFGE as this technology is not able to identify the genetic relatedness of plasmids, genes and other mobile genetic elements. Thus WGS may reveal additional transmission events defined as the transmission of mobile genetic elements. Different sequencing approaches may yield different results in terms of detection of transmission events. The investigators hypothesize that short-read sequencing may suffice to reliably detect relatedness of strains but that additional long-read sequencing approaches are needed to detect transmission of mobile genetic elements.