A proteomic approach for fast identification of staphylococcus aureus isolates by Matrix Assisted Laser Desorption Ionization Time of Flight (MALDI-TOF) based protein mass fingerprinting. (c2011)

Abstract

Staphylococcus aureus is an important human pathogen that is capable of causing a wide range of diseases, from relatively mild skin infections to deep systemic infections such as pneumonia. Identification and typing of S. aureus is currently based on various genomic and phenotypic methods; however, these methods are time-consuming, expensive and sometimes lack accuracy. A total of 14 S. aureus isolates were previously identified by conventional methods including multiple locus sequence typing (MLST), SCCmec typing and spa typing. Our purpose is to evaluate the use of Matrix Assisted Laser Desorption Ionization Time of Flight (MALDI-TOF) for rapid identification and analysis of these S. aureus isolates. Formic acid extraction was used to extract proteins which were then subjected to MALDI-TOF analysis. An identification profile for each isolate was created and 2 programs were developed for further analysis of the obtained data. With this approach setting stringent parameters on reproducibility of data, we were able to identify the masses of 5 peaks (4823, 6428, 6612, 8903, and 9644 m/z) that are common to all S. aureus isolates. To determine whether these 5 peaks were unique to S. aureus, the same procedure of protein extraction and data analysis was applied on S. epidermidis and Escherichia coli. Compared to the m/z list of S. aureus, 3 peaks were discovered to be common in S. epidermidis but none in E. coli. Thus we were able to identify 3 peaks unique for the genus Staphylococcus and 2 peaks unique for the species S. aureus. Also, our results suggest that the program developed is valid and very powerful in analyzing high-through put data obtained from MALDI analysis. Moreover, MALDI-TOF MS has high potential to be used as a proteomic tool for the identification of bacteria. Future work includes identification of peaks specific at the strain level and Tandem-MS of the unique peaks to determine their nature.