Topical Insulin and Infectious Keratitis: An In Vitro Microbial Growth Study.

PURPOSE: Topical insulin eye drops are used clinically to promote corneal epithelial healing in persistent epithelial defects. Given these benefits, insulin may also aid epithelial recovery in infectious keratitis. However, it remains unclear whether insulin impacts the growth of common ocular pathogens. This study aimed to evaluate the effect of insulin on microbial growth dynamics in vitro.

METHODS

Regular and rapid insulin were tested at 1 IU/mL and 10 IU/mL in tryptic soy broth (TSB) and lubricating eyedrops. A single clinical isolate of each organism (Staphylococcus aureus, Staphylococcus epidermidis, Pseudomonas aeruginosa, Candida albicans, Fusarium spp. and Aspergillus spp.) was included. Preparations with insulin, TSB alone, and Systane alone were inoculated in triplicate. Growth kinetics were assessed by optical density to calculate area under the curve (AUC), lag phase duration, and maximum specific growth rate (μ).

RESULTS

Insulin at either concentration in TSB did not enhance microbial growth compared to controls. No growth was observed in artificial tear groups.

CONCLUSION

Insulin, whether regular or rapid, at 1 IU/mL or 10 IU/mL, did not increase growth of tested pathogens in vitro. These findings suggest that topical insulin unlikely promotes microbial proliferation in vitro and may be considered a potentially safe adjunct, although in vivo validation remains necessary.