Abstract
Matrix-Assisted Laser Desorption:lonisation Time of Flight Mass Spectrometry (MALDI-TOF-MS) as a tool for differentiating bacterial species was examined using reference strains representing gram-positive and gram-negative taxa. Initially, the effect of differences in medium composition on spectral profile was examined. The results indicated that growth on Columbia blood agar resulted in a larger spectrum of ionized residues and was therefore used for the cultivation of all strains in the rest of the study. The stability of the obtained mass spectral profiles against differences in batch and media processing suggested that no significant alterations to the profiles occurred in response to changes in media sources. The established conditions from these initial experiments were used to standardize subsequent experiments. The MALDI-TOF-MS profiles of 15 reference strains were compared and species characteristic markers were identified. The potential of using MALDI-TOF-MS as a tool for probing clonal diversity was examined using well characterized but clonally variable isolates of Bacteroides fragilis. Comparative analysis of the profiles of 20 strains revealed 5 clusters within the species but compared to other taxa such as Bacteroides merdae and Salmonella arizonae they form a closely related lineage. These results obtained strongly support the potential to use MALDI-TOF-MS as a tool for exploring bacterial surfaces for characteristic biomarkers and species-specific signatures.