Development and clinical validation of a droplet digital PCR assay for detecting Acinetobacter baumannii and Klebsiella pneumoniae in patients with suspected bloodstream infections.

The relatively long turnaround time and low sensitivity of traditional blood culture-based diagnosis may delay effective antibiotic therapy for patients with bloodstream infections (BSIs). A rapid and sensitive pathogen detection method is urgently required to reduce the morbidity and mortality associated with BSIs. Acinetobacter baumannii and Klebsiella pneumoniae are two major microorganisms that cause BSIs. Here we report a novel droplet digital polymerase chain reaction (ddPCR) assay that can detect A. baumannii and K. pneumoniae in blood samples within 4 h, with a specificity of 100% for each strain and a limit of detection at 0.93 copies/μl for A. baumannii and 0.27 copies/μl for K. pneumoniae. Clinical validation of 170 patients with suspected BSIs showed that compared to blood cultures that detected four (2.4%) A. baumannii cases and seven (4.1%) K. pneumoniae cases, ddPCR detected 23 (13.5%) A. baumannii cases, 26 (15.3%) K. pneumoniae cases, and four (2.4%) co-infection cases, including the 11 cases detected via blood culture. In addition, patients who tested positive via ddPCR alone (n = 42) had significantly lower serum concentrations of procalcitonin and lactate, SOFA and APACHE II scores, and 28-day mortality than those reported positive via both blood culture and ddPCR (n = 11), suggesting that patients with less severe symptoms can potentially benefit from ddPCR-based diagnosis. In conclusion, our study suggests that ddPCR represents a sensitive and rapid method for identifying causal pathogens in blood samples and guiding treatment decisions in the early stages of BSIs.