Proteomics of enterococci: An “-omic” tool for understanding antibiotic resistance and stress environments

Proteomics, the study of the proteome, was first mentioned in the 1990s, referring to the protein complement expressed by the genome or by the cell or tissue at any one time. Since cells are constantly responding to environmental stimuli, their protein expression profiles are persistently changing. The separation of proteins and peptides is therefore a key element in proteomic analyses. Two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) has become a popular and quite powerful way to characterize whole protein extracts of a particular sample. As 2-DE is a core component of this chapter, it is important to specifically highlight the advances in gel electrophoretic separation methods, such as difference gel electrophoresis (DIGE), which complements traditional 2-DE with superior sensitivity, dynamic range and quantitation applied to microbial case studies. A successful model of protein function and regulation pathways in the cell requires a broad understanding of both protein interaction and cellular metabolism. The intention of this chapter is to present an overview of the major achievements of proteomic approaches to study Enterococcus spp. and its adaptation networks that are crucial for bacteria. Special focus is placed on the stress induced by antibiotic treatment and stressful environments. Finally, recent developments related to the enterococci proteome and technological determinants used as biomarkers are discussed.