Comparison of the sensitivity of culture, PCR and quantitative real-time PCR for the detection of Pseudomonas aeruginosa in sputum of cystic fibrosis patients

In our hands, all three culture methods and the bioMérieux easyMAG Nuclisens protocol Generic 2.0.1, preceded by proteinase K pretreatment and followed by any of the 3 real-time PCR formats with probes were most sensitive and able to detect P. aeruginosa up to 50 cfu/ml, i.e. the theoretical minimum of one cell per PCR mixture, when taking into account the volumes used in this study of sample for DNA-extraction, of DNA-elution and of DNA-extract in the PCR mixture.In this study, no difference in sensitivity could be found for the detection of P. aeruginosa from sputum between microbiological culture and optimized DNA-extraction and real-time PCR. The results also indicate the importance of the optimization of the DNA-extraction protocol and the PCR format.Patients with cystic fibrosis (CF), an autosomal recessively inherited disease caused by a mutation in the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene, are particularly susceptible to pulmonary infections with Pseudomonas aeruginosa [1,2]. Colonization of the airways of CF patients with P. aeruginosa results in higher morbidity and mortality because of the faster decline of the lung function, especially from the chronic infection phase onwards [3-5]. Detection of colonization and infection by this pathogen as early as possible enables to postpone the chronic infective stage and eventually to achieve the eradication of P. aeruginosa through early treatment. Indeed, early aggressive antibiotic therapy is now generally accepted as an efficient means to postpone chronic colonization [6,7].In most routine laboratories detection of bacterial species in respiratory samples is achieved by culture. However, it has been shown that routine culture of sputa from CF patients yields limited microbiological information since it frequently fails to identify the pathogens, which were shown to be present by means of PCR [8]. Furthermore, the correct detection and identification of P. aeruginosa, although in gener