Acceleration of the direct identification of versus coagulase-negative staphylococci from blood culture material: a comparison of six bacterial DNA extraction methods
Résumé
To accelerate differentiation between and coagulase-negative staphylococci (CNS), this study aimed to compare six different DNA extraction methods from two commonly used blood culture materials, i.e. BACTEC and BacT/ALERT. Furthermore, we analysed the effect of reduced blood culture incubation for the detection of staphylococci directly from blood culture material. A real-time polymerase chain reaction (PCR) duplex assay was used to compare the six different DNA isolation protocols on two different blood culture systems. Negative blood culture material was spiked with methicillin-resistant (MRSA). Bacterial DNA was isolated with automated extractor easyMAG (three protocols), automated extractor MagNA Pure LC (LC Microbiology Kit M), a manual kit MolYsis Plus and a combination of MolYsis Plus and the easyMAG. The most optimal isolation method was used to evaluate reduced bacterial incubation times. Bacterial DNA isolation with the MolYsis Plus kit in combination with the specific B protocol on the easyMAG resulted in the most sensitive detection of , with a detection limit of 10 CFU/ml, in BacT/ALERT material, whereas using BACTEC resulted in a detection limit of 100 CFU/ml. An initial or CNS load of 1 CFU/ml blood can be detected after 5 h of incubation in BacT/ALERT 3D by combining the sensitive isolation method and the LightCycler assay.
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