Direct and Subcultured MALDI-TOF MS for Microbial Identification

For direct MALDI-TOF MS analysis (using Sepsityper™ kit and IH protocol), duplicate 1 μL of extracted protein supernatant from the last centrifugation were applied to the polished steel target plate and once dried, were immediately overlaid with 1 μL α-cyano-4-hydroxycinnamic acid (HCCA) matrix (Bruker Daltonics, Bremen, Germany) solution before MALDI-TOF MS analysis. The final score used for interpretation for each sample was the higher one from two measurements. For MALDI-TOF MS analysis after BC subculture (standard method), a small portion of a single colony (after 24 or 48 h of incubation) was smeared onto the ground steel target plate using a wooden cocktail stick, and covered with 1 μL HCCA matrix solution immediately. Measurements were performed with the Bruker Biotyper MALDI-TOF MS system using FlexControl 3.3 and MALDI Biotyper V.3.3.1.2 software (Bruker Daltonics) as previously described (Zhou et al., 2016 (link)).