**Abstract**

Disulfide bond isomerase proteins (Dsbs) have been extensively characterized in gram-negative bacteria. Recently research efforts is being placed on their biology in gram-positive species. Modern "omics" technologies, allowed assessment of the contribution of the Dsbs to bacterial pathogenesis. The author cloned and characterized the *dsbA* 1 protein from *Pseudomonas aeruginosa* in the late 1990s. The global proteome analysis demonstrated that the *dsbA* gene is under the direct regulatory control of the extracytoplasmic function (ECF) sigma factor AlgT(U) or sigma-22. This is unique to *P. aeruginosa*. Disruption of *dsbA* gene results in pleiotropic phenotype: defect in assembly of cysteine disulfide bond containing proteins-as shown in many others. Recently, omics-based approaches identified expression changes in *dsbA* gene under different physiological states of bacterial pathogens-primarily in free-living, biofilm state, or under infectious disease conditions. Involvement of *dsbA* function in biofilm formation was shown using *dsbA* gene disruption mutants. This chapter documents past and current findings and concludes with future trends in research on Dsbs including peptidomimetics.

**Keywords:** bacterial pathogenesis, disulfide isomerase, OMICS technology, proteomics, extracytoplasmic function (ECF) sigma factors, thiol status, Sigma factors, microarrays, metatranscriptomics, metabolomics, animal models of disease
