Abstract Existence of moonlighting proteins in microorganisms is a known phenomenon, yet still not well understood. Moonlighting proteins have at least two independent biological functions, which must be performed by one polypeptide chain without separation into protein domains. Most of these proteins, beside their role in the cytoplasm, play an important role outside of the cell i.e. they take part in the process of pathogenesis by binding and activating host’s plasminogen. The existence of moonlighting proteins complicates the understanding of pathogenicity and virulence of many common bacteria as well as their role in commensal bacteria. Many of moonlighting proteins occurring in commensal bacteria appear to perform similar functions to proteins discovered in pathogenic bacteria, e.g. binding extracellular matrix. Moonlighting proteins found in bacteria are mostly housekeeping enzymes, especially from the glycolytic pathway, such as enolase, aldolase, dehydrogenase as well as heat-shock proteins and transcriptional factors. 1. Introduction. 2. Involvement of moonlighting proteins in bacterial pathogenesis. 3. Effect of moonlighting proteins on the immune system. 4. Moonlighting proteins in lactic acid bacteria.5. Transportation of moonlighting proteins to the bacterial surface. 6. Evolution of moonlighting proteins. 7. Detection of moonlighting proteins. 8. Summary 1. Wprowadzenie. 2. Udział białek wielofunkcyjnych w bakteryjnej patogenezie. 3. Wpływ białek wielofunkcyjnych na układ odpornościowy. 4. Obecność białek wielofunkcyjnych u bakterii kwasu mlekowego. 5. Transport białek wielofunkcyjnych na powierzchnię komórek bakteryjnych. 6. Ewolucja białek wielofunkcyjnych. 7. Wykrywanie białek wielofunkcyjnych. 8. Podsumowanie