AUTHOR=Maurin Corantin , Courrier Emilie , He Zhiguo , Rigaill Josselin , Josse Jérôme , Laurent Frédéric , Gain Philippe , Thuret Gilles , Verhoeven Paul O. 

TITLE=Key Role of Staphylococcal Fibronectin-Binding Proteins During the Initial Stage of Staphylococcus aureus Keratitis in Humans

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=11

YEAR=2021

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2021.745659

DOI=10.3389/fcimb.2021.745659

ISSN=2235-2988

ABSTRACT=<sec><title>Objectives</title><p><italic>Staphylococcus aureus</italic> is one of the main causes of bacterial keratitis in humans. This study was aimed at investigating the mechanisms of <italic>S. aureus</italic> adhesion to the human corneal epithelium involved during the initial stage of infectious keratitis.</p></sec><sec><title>Methods</title><p>Human corneas stored in a specific active storage machine that restores a normal pluristratified epithelium were used to assess <italic>S. aureus</italic> adhesion level to intact and injured tissues using immunostaining. <italic>S. aureus</italic> adhesion to immobilized fibronectin was measured in microtiter plate. Internalization of <italic>S. aureus</italic> clinical isolates recovered from keratitis was assessed on human corneal epithelial HCE-2 cells.</p></sec><sec><title>Results</title><p>Superficial corneal injury unmasked fibronectin molecules expressed within the human corneal epithelium. <italic>S. aureus</italic> adhesion level was increased by 117-fold in the area of injured epithelium (<italic>p</italic> &lt; 0.0001). The deletion of staphylococcal <italic>fnbA/B</italic> genes decreased by 71% the adhesion level to immobilized fibronectin (<italic>p</italic> &lt; 0.001). The deletion of <italic>fnbA/B</italic> genes and the incubation of the corneas with anti-fibronectin blocking antibodies prior to the infection significantly reduced the <italic>S. aureus</italic> adhesion level to injured corneal epithelium (<italic>p</italic> &lt; 0.001). Finally, <italic>S. aureus</italic> clinical isolates triggered its internalization in human corneal epithelial cells as efficiently as the 8325-4 wt.</p></sec><sec><title>Conclusion</title><p><italic>S. aureus</italic> was almost unable to bind the intact corneal epithelium, whereas a superficial epithelial injury of the corneal epithelium strongly increased <italic>S. aureus</italic> adhesion, which is mainly driven by the interaction between staphylococcal fibronectin-binding proteins and unmasked fibronectin molecules located underneath the most superficial layer of the corneal epithelium.</p></sec>