BackgroundThe Liverpool epidemic strain (LES) ofPseudomonas aeruginosais widespread among patients with cystic fibrosis (CF) in specialist centers around Liverpool and elsewhere in the UK. This study evaluates a new diagnostic PCR assay based on a unique DNA sequence (PS21) of LES, for its identification of colonies directly from sputum.MethodsOne hundred and fifty-eight sputum samples from 92 patients were cultured andP. aeruginosaisolates were typed by PS21 PCR and pulsed-field gel electrophoresis (PFGE). Subsequently, PS21 PCR was performed directly on sputum and the results were compared with culture, PFGE, and PS21 PCR typing.ResultsEighty patients were colonized withP. aeruginosa, 63 by LES (79%). There was 100% concordance between PS21 PCR on colonies and PFGE typing. The sensitivity and specificity of PS21 PCR directly on sputum was 98.2% and 93.6%, respectively.ConclusionsThis study shows that PS21 PCR can be used for simple and rapid screening of LES colonization in CF patients.