Effects of Cadmium on Peptide Profiles and Biotyper Score Value of Escherichia coli O157:H7 Identified by Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass-Spectrometry (MALDI-TOF/MS)

Abstract

Matrix-assisted laser desorption/ionization time-of-flight mass-spectrometry (MALDI-TOF/MS) based biotyping is a high-throughput technique for microbial identification. It has been used to replace existing cultivation techniques in clinical diagnosis laboratory in many hospitals of Thailand. On another aspect, contamination of foods by various kinds of heavy metals is a major inevitable situation in Thailand. However, there has been no report on the effects of heavy metals such as cadmium ions on expression pattern of peptides and biotyper score value upon identification of bacterial genus and species by MALDI-TOF MS. Herein, we studied the Maldi-TOF peptide profiles and biotyper score value of the important pathogenic bacteria Escherichia coli O157:H7 culturing in various concentrations of CdCl₂ ranging from 0.0016 mM to 1 mM, which was previously shown  to cover all the concentrations under and over of heavy metal tolerant ability. Under the cadmium stress condition, MALDI-TOF MS can specify the type of E. coli O157:H7 and provide a reliable score. The score values were trendy decreasing with the increasing CdCl₂ concentrations (p<0.005). In conclusion, the results showed a drastic effect of cadmium ions on the peptide pattern identified by MALDI-TOF MS while exerting no significant effect on the score values used for the genus, species or strain identification. This study provides information and confidence for laboratory personnel who work with the MALDI-TOF/MS in identifying the pathogenic bacteria isolated from the areas that are suspected to be contaminated with heavy metals.