The effect of Tween80 on signal intensity of intact proteins by MALDI time-of-flight mass spectrometry

Rapid identification of bacterial and fungal pathogens from positive blood cultures by MALDI-TOF MS

Sepsis is a syndrome characterized by a systemic inflammatory response due to severe infection. Early detection of causal agents and appropriate antimicrobial treatment reduce mortality. Conventional microbiological methods often do not provide time critical results for an optimal early management. We used an in-house protocol based on Tween 80 to process 109 positive blood cultures for bacteria and yeast identification by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS), and results were compared to standard reference or automated methods. MALDI-TOF MS correctly identified 91.7% of the isolates. Correct identification was obtained for 57/62 (91.9%) aerobic/facultative anaerobic Gram-positive isolates, 53 (85.5%) at species level, and 4 (6.4%) at the genus level; 32/32 (100%) aerobic/facultative anaerobic Gram-negative isolates, 31 (96.9%) at species level, and 1 (3.1%) at the genus level; 7/7 (100%) obligate anaerobes, all at the genus level; 3/7 (42.8%) fungi, all at genus level. Overall, the median identification time of MALDI-TOF MS vs reference standard methods was significantly shorter: median (interquartile range) 7.1h (4.7-10.2) vs 48.1h (32.5-50.0), p<0.0001. MALDI-TOF MS is a valuable tool for rapid identification of pathogens in septic patients. An in-house protocol based on Tween 80 can be used to process positive blood cultures.

The effect of sodium dodecyl sulfate and anion-exchange silica gel on matrix-assisted laser desorption/ionization mass spectrometric analysis of proteins

Sodium dodecyl sulfate (SDS), an anionic surfactant, is widely used in peptide and protein sample preparation. When the sample is analyzed by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), this surfactant can often cause signal suppression. We have previously reported an on-probe sample preparation method using a suspension of anion-exchange silica gel and sinapinic acid (i.e., gel-SA suspension) as a matrix, thereby greatly improving the MALDI signal detection of the protein solutions containing SDS. In this study, we found that a certain amount of SDS enhanced the MALDI signal intensity for protein samples. This effect was also observed when using sodium decyl sulfate and sodium tetradecyl sulfate instead of SDS. Furthermore, this on-probe sample preparation method using both SDS and the gel-SA suspension improved the detection limit of protein samples in the MALDI-MS analysis by about ten-fold as compared to that of protein samples without SDS and the gel-SA suspension. This method can be applied not only to the MALDI-MS analysis of samples containing SDS, but also to the examination of proteins at femtomole levels or insoluble proteins such as membrane proteins.

Selected non-ionic biological detergents enhance signal intensity of intact bovine serum albumin by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry

Recently, we showed that the signal intensity of intact protein by matrix-assisted laser desorption/ionisation (MALDI) mass spectro-metry measurement can be enhanced at least an order of magnitude by the addition of Tween80 to the analyte solution. We did not ascertain whether this effect was limited to Tween80 or if it was more universal of biological detergents. This paper discusses our investigations into this question. A variety of chemically diverse detergents were added to analyte solutions containing bovine serum albumin (BSA) to determine whether there was significant signal enhancement. The addition of Tween20, Tween80, Triton X100 and Triton X-114 improved the attainable sensitivity of intact protein MALDI mass spectrometry compared to spectra acquired without detergent. In some cases there was considerable improvement in signal--for example, with Triton X-100 two charge states (the +1 and +2) of BSA (3.9 fmol) could easily be observed. Another advantage of this process is that the detergent can be added directly to the matrix solution reducing sample handling and preparation time. We propose this phenomenon results from the ability of these detergents to increase the solubility of the protein via hydrophobic and hydrophilic interactions between the detergent and protein. The increased solubility allows for more uniform deposition of the analyte/-matrix mixtures producing an evenly distributed layer of analyte especially useful for data acquisition using an automated laser firing sequence.