Clusters of genetically similar isolates of Pseudomonas aeruginosa from multiple hospitals in the UK

Variable number tandem repeat (VNTR) analysis at nine loci of isolates of Pseudomonas aeruginosa submitted to the national reference laboratory from UK hospitals, from over 2000 patients, between June 2010 and June 2012 revealed four widely found types that collectively were received from approximately a fifth of patients, including from those with cystic fibrosis. These types were also prevalent among related submissions from the clinical environment and were received from up to 54 (out of 143) hospitals. Multi-locus sequence typing and blaOXA-50-like sequencing confirmed the clonal relationship within each cluster, and representatives from multiple centres clustered within about 70 % by pulsed-field gel electrophoresis. Illumina sequencing of 12 isolates of cluster A of VNTR profile 8, 3, 4, 5, 2, 3, 5, 2, x (where the repeat number at the last, most discriminatory locus is variable) revealed a large number of variably present targets in the accessory genome and seven of these were sought by PCR among a larger set of isolates. Representatives from patients within a single centre mostly had distinct accessory gene profiles, suggesting that these patients acquired the strain independently, while those with clear epidemiological links shared the same profile. Profiles also varied between representatives from different centres. Epidemiological investigations of widely found types such as these require the use of finer-typing methods, which increasingly will be informed by next generation sequencing.