Interplay between ESKAPE Pathogens and Immunity in Skin Infections: An Overview of the Major Determinants of Virulence and Antibiotic Resistance

Abstract

The skin is the largest organ in the human body, acting as a physical and immunological barrier against pathogenic microorganisms. The cutaneous lesions constitute a gateway for microbial contamination that can lead to chronic wounds and other invasive infections. Chronic wounds are considered as serious public health problems due the related social, psychological and economic consequences. The group of bacteria known as ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter sp.) are among the most prevalent bacteria in cutaneous infections. These pathogens have a high level of incidence in hospital environments and several strains present phenotypes of multidrug resistance. In this review, we discuss some important aspects of skin immunology and the involvement of ESKAPE in wound infections. First, we introduce some fundamental aspects of skin physiology and immunology related to cutaneous infections. Following this, the major virulence factors involved in colonization and tissue damage are highlighted, as well as the most frequently detected antimicrobial resistance genes. ESKAPE pathogens express several virulence determinants that overcome the skin's physical and immunological barriers, enabling them to cause severe wound infections. The high ability these bacteria to acquire resistance is alarming, particularly in the hospital settings where immunocompromised individuals are exposed to these pathogens. Knowledge about the virulence and resistance markers of these species is important in order to develop new strategies to detect and treat their associated infections.

Keywords: chronic wounds; hypervirulent phenotypes; multidrug resistance; skin infections.

Figure 1

A schematic view of bacterial skin infection, derived from a loss in epidermis integrity. (1) An injury provokes a skin lesion that constitutes a gateway for microbial contamination. (2) Bacteria colonize the skin and produce a biofilm. (3) Bacteria secrete toxins that extend the tissue degradation, reaching dermis layer. (4) Resident immune cells recognize the bacteria and secrete immune mediators to neutralize the pathogens and recruit other immune cells. (5) Cell debris (damage-associated molecular patterns (DAMPS) and lipid mediators) activate immune cells and serve as chemoattractors. (6) Blood leukocytes are recruited to combat the pathogens. (7) Effector substances released by immune cells also promote tissue damage and amplify the inflammation.