Comparative proteomic analysis of listeria monocytogenes isolates from New Zealand

Abstract

Listeria monocytogenes is one of the top ranking foodborne pathogens implicated in a number of foodborne outbreaks that have caused human illness and death. About 90% of the cases of Listeriosis in New Zealand are associated with the consumption of food contaminated with L. monocytogenes. Recently, many researchers have used proteomic approaches to analyse foodborne pathogens, especially L. monocytogenes. Proteomics is a protein-based technology that is the large-scale study of the expressed protein components of an organism’s genome. However, in New Zealand, there have been few studies carried out using proteomic techniques to analyse the protein profile of foodborne pathogens, such as L. monocytogenes, Salmonella and Campylobacter. Comparative proteomic analysis was conducted in this research using 1D SDS-PAGE, 2DE analyses, MALDI-TOF/TOF mass spectrometry and Ion Trap mass spectrometry to identify key differences in protein expression of three strains of L. moncytogenes (V7, SB92/844 and SB92/870) that have different ecological origins. The protein banding patterns generated by 1D SDS PAGE of the three strains of L. monocytogenes showed no significant differences. Visual observations from 2DE gels revealed that certain spots appeared to be expressed differentially/differently?. Key differences in protein expression of the three strains of L. monocytogenes were found using PDQest TM 2D analysis software. One hundred and eighty nine spots were detected using SB92/844 as the reference gel. There were 99 spots in the reference gel that matched the spots in L. monocytogenes strain V7 and 102 spots were detected that were similar in L. monocytogenes strain SB92/870. Seventy out of 189 spots detected (37% of detected spots) were present in all three strains studied. By estimating the relative differences in protein expression, 10 protein spots had decreased expression in SB92/844 relative to V7 and five protein spots were significantly over-expressed. Besides this, 14 protein spots showed no significant protein expression differences in SB92/844 relative to V7. As for the relative protein expression pattern in L. monocytogenes strain SB92/870 relative to V7, five protein spots were significantly over-expressed and six protein spots were down-regulated. Additionally, 11 protein spots showed no differential expression in SB92/870 relative to V7. A comparison of the protein expression of SB92/844 vs SB92/870 showed that 22 protein spots had no significant differences. Only three protein spots were over-expressed and the expression of eight protein spots decreased in SB92/844 relative to SB92/870. The identity of selected protein spots was achieved using MALDI-TOF mass spectrometry and Ion Trap mass spectrometry. It was found that certain proteins (i.e. a major cold shock protein and superoxide dismutase) were expressed differently between the two local strains from New Zealand. The key findings of this study indicated that differentially?? expressed proteins may be related to virulence and pathogenicity. This work also represented the first proteomic study on L. monocytogenes isolates from New Zealand.