Metal uptake systems underpin Enterococcus faecalis virulence in both non-diabetic and diabetic wound infection models.

Abstract

Wound infections remain an important medical problem, which is aggravated by the prevalence of multidrug-resistant bacteria. Among them, Enterococcus faecalis is a major pathogen of surgical site incisional and diabetic chronic wounds, but factors driving its colonization and persistence in wounds remain poorly understood. Iron, manganese, and zinc are essential cofactors in cellular processes, prompting the host to restrict their availability through mobilization of metal-sequestering proteins, a defense known as nutritional immunity. Previously, we showed that E. faecalis strains lacking key iron (Δ5Fe), manganese (Δ3Mn), or zinc (Δ2Zn) uptake systems have impaired virulence. Here, we used an excisional wound model in normoglycemic (C57Bl/6J or B6) and diabetic (C57Bl/6J lepR -/- or DB) mice to examine the role of these metal import systems in wounds. The strong upregulation of metal import genes and reduced wound colonization by Δ3Mn, Δ5Fe, and Δ2Zn strains in B6 mice indicate that iron, manganese, and zinc are limited during wound infection. While Δ2Zn and Δ3Mn strains showed no improved colonization in diabetic wounds, the Δ5Fe strain exhibited a temporary colonization advantage over non-diabetic mice. Quantifications of metal-sequestering proteins lactoferrin, transferrin, calprotectin, and psoriasin from intact skin and infected wounds indicated that nutritional immunity, especially iron restriction, is delayed in diabetes. In conclusion, this study underscores the crucial role of trace metal acquisition in E. faecalis wound colonization and suggests differences in metal bioavailability between diabetic and non-diabetic wounds, helping to explain the increased susceptibility of diabetic wounds to chronic infection.