The peptidoglycan and biofilm matrix of Staphylococcus epidermidis undergo structural changes when exposed to human platelets

Abstract

Staphylococcus epidermidis is a bacterium frequently isolated from contaminated platelet concentrates (PCs), a blood product used to treat bleeding disorders in transfusion patients. PCs offer an accidental niche for colonization of S. epidermidis by forming biofilms and thus avoiding clearance by immune factors present in this milieu. Using biochemical and microscopy techniques, we investigated the structural changes of the peptidoglycan (PG) and the biofilm matrix of S. epidermidis biofilms formed in whole-blood derived PCs compared to biofilms grown in glucose-supplemented trypticase soy broth (TSBg). Both, the PG and the biofilm matrix are primary mechanisms of defense against environmental stress. Here we show that in PCs, the S. epidermidis biofilm matrix is mainly of a proteinaceous nature with extracellular DNA, in contrast to the predominant polysaccharide nature of the biofilm matrix formed in TSBg cultures. PG profile studies demonstrated that the PG of biofilm cells remodels during PC storage displaying fewer muropeptides variants than those observed in TSBg. The PG muropeptides contain two chemical modifications (amidation and O-acetylation) previously associated with resistance to antimicrobial agents by other staphylococci. Our study highlights two key structural features of S. epidermidis that are remodeled when exposed to human platelets and could be used as targets to reduce septic transfusions events.

The staphylococcal exopolysaccharide PIA – Biosynthesis and role in biofilm formation, colonization, and infection

“…By representing a major component of the extracellular matrix, PIA fixes staphylococcal cells in the fibrous net it produces and thereby builds up biofilm mass [114] , which leads to increased resistance of the biofilm to mechanical force. Accordingly, PIA is crucial for biofilm formation under high-shear flow conditions like those found inside catheters [40] , [115] , [116] , [117] , [118] , [119] , but it becomes less important under low-shear conditions like those in subcutaneously implanted tissue [120] , ocular infections [121] , or platelet concentrate [122] . Single-cell force spectroscopy data demonstrated multivalent electrostatic interaction of the cationic PIA polymer with the negatively charged wall teichoic acids on staphylococcal cells, confirming on the molecular level that the cationic character previously shown to be crucial for PIA function [63] has an important role in the attachment of PIA to the cell surface and PIA-mediated intercellular adhesion [123] .…”

Staphylococcus aureus cell wall structure and dynamics during host-pathogen interaction

“…It has been hypothesised that in S . epidermidis PG synthesis is reduced when exposed to human platelets, creating a less complex PG structure [ 41 ]. This allows energy to be used in other processes, allowing proliferation of bacteria in a harsh, restrictive environment such as infection [ 41 ].…”

“…A reduced muropeptide diversity was presented in this study (Fig 2 and S4 Table ), suggesting that PG from S. aureus has less complexity and crosslinking during an infection. It has been hypothesised that in S. epidermidis PG synthesis is reduced when exposed to human platelets, creating a less complex PG structure [41]. This allows energy to be used in other processes, allowing proliferation of bacteria in a harsh, restrictive environment such as infection [41].…”

“…It has been hypothesised that in S. epidermidis PG synthesis is reduced when exposed to human platelets, creating a less complex PG structure [41]. This allows energy to be used in other processes, allowing proliferation of bacteria in a harsh, restrictive environment such as infection [41]. Salmonella enterica serovar Typhimurium cultured within human epithelial cells possesses a unique PG structure, with a reduction in glycine containing muropeptides and a decrease in crosslinking [60].…”

“…Several studies have utilised “pseudo in vivo ” conditions to mimic the complex environment of an infection. Staphylococcus epidermidis PG isolated from an in vitro biofilm in platelet concentrates show substitutions in the pentaglycine bridge, with glycine being substituted for serine or alanine residues, as well as increased O-acetylation, providing resistance to lysostaphin and lysozyme [ 14 , 41 ].…”