Gram-negative bacteria have evolved an array of secretion systems for protein transport across their membranes. The ability to secrete a diverse set of proteins to their target of choice provides bacteria with a menacing tool for pathogenesis. This work aims to enhance our understanding of bacterial pathogenesis by characterizing key aspects of bacterial secretion systems using mass spectrometry. Chapter 1 provides a general introduction of protein secretion pathways in Gran-negative bacteria, with a special emphasis on type III and type VI secretion systems. Chapter 2 highlights chemical...