Abstract
BackgroundPseudomonas aeruginosa is the major pathogen involved in the decline of lung function in cystic fibrosis (CF) patients. Early aggressive antibiotic therapy has been shown to be effective in preventing chronic colonization. Therefore, early detection is important and sensitive detection methods are warranted. In this study, we used a dilution series of P. aeruginosa positive sputa, diluted in a pool of P. aeruginosa negative sputa, all from CF patients - to mimick as closely as possible the sputa sent to routine laboratories - to compare the sensitivity of three culture techniques versus that of two conventional PCR formats and four real-time PCR formats, each targeting the P. aeruginosa oprL gene. In addition, we compared five DNA-extraction protocols.ResultsIn 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.ConclusionIn 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.
Highlights
Pseudomonas aeruginosa is the major pathogen involved in the decline of lung function in cystic fibrosis (CF) patients
Comparison of culture methods No differences in detection limit could be observed between McConjey Agar (MCA) and Cetrimide Agar (CA), i.e. respectively an average of 2 and 3 colonies were counted at dilution eight
It should be noticed that we found no difference between selective and nonselective culture methods, but this may be due to the fact that no bacteria, other than P. aeruginosa in the two P. aeruginosa positive patients, could be cultured from the sputa of the 8 CF patients
Summary
Pseudomonas aeruginosa is the major pathogen involved in the decline of lung function in cystic fibrosis (CF) patients. To circumvent culture associated limitations, several molecular assays for the detection of Pseudomonas species have been described [8,11,12,13,14,15,16,17,18,19], Döring and colleagues [20] correctly remarked that, because of the influence of sample pretreatment, DNA-extraction protocol and the PCR format, there is a need for validation of the PCR techniques before these can be used in a routine laboratory. To our knowledge, no study systematically compared the sensitivity of different culture, DNA-extraction, PCR and realtime PCR methods for the detection of P. aeruginosa from CF sputum, by using a CF patient sputum based dilution series of P. aeruginosa
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