Detection of Klebsiella pneumoniae cfDNA in pleural fluid and its clinical value.

Background: Klebsiella pneumoniae (KP) is an important opportunistic pathogen that can easily cause pneumonia and pleural effusion when body resistance is reduced. However, the positive rate of KP detected from clinical pleural effusion by traditional methods, including bacterial culture, is meager. Therefore, new detection methods are urgently needed to improve the positive detection rate of KP and other bacteria in pleural effusion.

Methods: Simulated pleural fluid of KP infection was first set up. Then circulating cell-free DNA (cfDNA) was extracted from cultured hydrothorax and detected by fluorescence polymerase chain reaction (PCR) to verify KP cfDNA in the pleural fluid. The specificity, sensitivity, and repeatability of this method are verified by detecting the cfDNAs in pleural effusion, samples of malignant pleural effusion, tuberculous pleural effusion, and other common microbial infections. Finally, this method was compared with three traditional methods, pleural effusion, precipitation DNA, sputum culture, and pleural effusion culture to explore the clinical diagnostic value of this method.

Results: KP cfDNA was positive by fluorescence PCR from the simulated KP infected pleural effusion, which confirmed KP cfDNA in pleural effusion. KP cfDNA was positive by fluorescence PCR from the pleural effusion of KP infected patients, while with the same detection method, KP cfDNA in clinical carcinomatous hydrothorax, tuberculosis hydrothorax, and other standard microbial infection samples was negative, which confirmed the method had high specificity, high sensitivity, and reproducibility. Compared with the three traditional methods, this method has a higher positive rate. Compared with the gold standard, sputum bacterial culture, the sensitivity, specificity, positive predictive value, and negative predictive value of this method were 91.67%, 95.45%, 91.7%, and 95.5%, respectively.

Conclusions: The detection of cfDNA by fluorescence PCR is possible. Moreover, the positive rate of this method in clinical pleural effusions is high.