Insulin Acts as Stimulatory Agent in Diabetes-Related Escherichia Coli Pathogenesis

Background: In general, diabetic patients are more prone to microbial infections, which is believed to be caused due to high glucose levels in blood which compromise components of the immune system. However, it is little known about role of therapeutic insulin administration on dissemination of infectious diseases in people with diabetes mellitus. Methods: The study included the clinically isolated strains of Escherichia coli (E. coli) with biofilm forming capacity as well as referent non-biofilm former E. coli strain as control. Metabolic activity, level of virulence and biofilm forming capacity of tested E. coli strains were investigated in vitro conditions under presence of human hormone insulin at different incubation time points. Results: Administration of hormone insulin in concentration of 2.5 U/ml resulted in significant increase in proliferation of all tested E. coli strains under in vitro conditions at 37 °C. Presence of insulin also stimulated expression of E. coli virulent factor enzyme aspartyl proteinase, which in synergism with human insulin served as signal molecules for bacterial quorum sensing and biofilm formation. Conclusion: Results of this study present first report about direct effect of hormone insulin on elevated metabolic activity of E. coli in a linkage with its biofilm forming capability. This opens a new look at understanding the cause of various bacterial infections in diabetic patients, as well as their multi-resistance to antibiotics that occurs due to changed bacterial metabolism and their newly acquired colonization abilities.