Blood culture and control bacterial strains
Upon clinical suspicion of BSI, whole blood samples were simultaneously obtained for blood culture and molecular diagnosis. Two sets of blood cultures were collected for each patient according to routine clinical practice, and each set consisted of an aerobic bottle and an anaerobic bottle. The blood cultures were incubated at 37℃ in a BacT/ALERT® 3D System (BioMérieux, France). When the system showed a positive signal, Gram staining was performed, followed by subculture on a Columbia blood agar plate at 37℃ with 5% CO2. Following overnight incubation, the pathogens were further identified by matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF MS) (VITEK® MS system, BioMérieux, France). The positive control bacteria were A. baumannii ATCC 19606 with 5 clinical isolates and K. pneumonia CMCC 46117 with 33 clinical isolates. A total of 131 other clinical isolates that are commonly found in BSI were used as negative controls (Table 1 ).