Effect of insulin on microbial growth

The ability of insulin to affect the growth kinetics of Escherichia coli, Staphylococcus aureus, Enterococcus faecalis, and Pseudomonas aeruginosa was measured. For all organisms, insulin, in the absence of a metabolizable sugar source, i.e., glucose or starch in Mueller-Hinton medium, had no effect on generation time as compared with a homologous control. Response to insulin, in the form of increased or decreased generation times, for both Gram-positive and Gram-negative bacteria, was dependent on the concentration of insulin, the concentration of glucose present, and the initial concentration of bacteria exposed to the glucose and insulin.