Unveiling and Characterizing Early Bilateral Interactions between Biofilm and the Mouse Innate Immune System

Abstract

A very substantial progress has been made in our understanding of infectious diseases caused by invasive bacteria. Under their planktonic forms, bacteria transiently reside in the otherwise sterile mammal body tissues, as the physiological inflammation insures both their clearance and repair of any tissue damage. Yet, the bacteria prone to experience planktonic to biofilm developmental transition still need to be studied. Of note, sessile bacteria not only persist but also concur preventing the effectors and regulators of the physiological inflammation to operate. Thus, it is urgent to design biologically sound experimental approaches aimed to extract, at the earliest stage, immune signatures of mono-bacteria planktonic to biofilm developmental transition in vivo and ex vivo. Indeed, the transition is often the first event to which succeeds the “chronicization” process whereby classical bacteria-targeting therapies are no more efficacious. An in vivo model of micro-injection of Staphylococcus aureus planktonic or biofilm cells in the ear pinna dermis of laboratory transgenic mice with fluorescent immune cells is proposed. It allows visualizing, in real time, the range of the early interactions between the S. aureus and myeloid cell subsets- the resident macrophages and dendritic cells, the recruited neutrophil granulocytes/polymorphonuclear neutrophils, monocytes otherwise known to differentiate as macrophages or dendritic cells. One main objective is to extract contrasting immune signatures of the modulation of the physiological inflammation with respect to the two bacterial lifestyles.

Intravital Multiphoton Examination of Implant-Associated Staphylococcus aureus Biofilm Infection

“…The mouse ear pinna is a proven site for assessing immune responses and infection progression (Li et al, 2012 ; Abtin et al, 2014 ; Forestier et al, 2017 ). Thus, we sought to establish an ear pinna interdermal implant model of S. aureus biofilm infection.…”

“…To assess the cellular activities and interactions occurring during biofilm infection, several studies have employed confocal or epifluorescent microscopy (Forestier et al, 2017 ; Abdul Hamid et al, 2020 ). Unfortunately, these experiments are restricted to a limited depth penetration and single short-wavelength excitatory light that rapidly damages animal tissues.…”

A mouse ear skin model to study the dynamics of innate immune responses against Staphylococcus aureus biofilms

“…After 24 h, the inflammatory response was considerable and comparable for the two bacterial forms. In rodent models, neutrophils are usually the most rapidly recruited, and therefore most abundant, cells in the proximity of biofilms [7]. In a catheter-related model, however, monocytes were the first cells to be recruited [18].…”

“…These results were mostly obtained during experiments performed in vitro in which biofilms were exposed to monocytes or neutrophils, or both [6]. In the few experiments performed in vivo with different rodent models, several parameters vary, such as the presence of a biomedical device, the tissue(s) that were inoculated or implanted with a bacteria-free or loaded device, the bacteria delivery mode and the inoculum dose [7]. These studies illustrate the importance of both neutrophils and monocytes/macrophages as a first line of defence against biofilm infections.…”

“…In particular, it allows the analysis of cellular behaviour in an inflamed tissue [8]. We previously developed a concept that was potentially able to extract the biologically relevant features of the host and invasive bacteria after injection of either the planktonic or biofilm form of bacteria in the ear pinna [7]. In the present study, it was decided to use the transgenic fluorescent reporter laboratory mice line LysM-EGFP.…”