Whole-genome sequencing identifies highly related Pseudomonas aeruginosa strains in multiple washbasin U-bends at several locations in one hospital: evidence for trafficking of potential pathogens via wastewater pipes

ABSTRACT Background Hand washbasin U-bends have increasingly been associated with nosocomial outbreaks by Gram-negative bacteria, including Pseudomonas aeruginosa which is virtually ubiquitous in U-bends. Wastewater networks servicing U-bends are potential highways for trafficking pathogenic bacteria. Aim To use P. aeruginosa to investigate trafficking of bacteria between hospital washbasin U-bends. Methods Twenty-five washbasin U-bends in five locations in Dublin Dental University Hospital (DDUH) were investigated for trafficking of P. aeruginosa: 10 in Clinic 2 (C2), 10 in the Accident & Emergency Department (A&E) and five in three other locations. In addition, washbasin tap samples (N=80) and mains and tap water samples (N=72) were cultured for P. aeruginosa. Selected P. aeruginosa isolates recovered over 29 months underwent whole-genome sequencing, and relatedness was interpreted using whole-genome multi-locus sequence typing and pairwise single nucleotide polymorphism (SNP) analysis. Findings P. aeruginosa was recovered from all U-bends but not from taps or water. Eighty-three isolates yielded 10 sequence types (STs), with ST560 and ST179 from A&E, C2 and two other locations predominating (70%). ST560 was also recovered from a common downstream pipe. Isolates within ST560 and ST179 were highly related regardless of source. ST560 was divided into Cluster I (N=25) and Cluster II (N=2) with average allelic differences and SNPs of 3 and 0, and 2 and 5, respectively. The 31 ST179 isolates exhibited an average allelic difference and SNPs of 3 and 12, respectively. Conclusion Highly related P. aeruginosa strains were identified in multiple U-bends in several DDUH locations, indicating trafficking via the wastewater network.