Confocal laser scanning microscopic observation of glycocalyx production by Staphylococcus aureus in mouse skin: Does S. aureus generally produce a biofilm on damaged skin?

Background: Bacteria that adhere to damaged tissues encase themselves in a hydrated matrix of polysaccharides, forming a slimy layer known as a biofilm. This is the first report of detection of glycocalyx production by Staphylococcus aureus using confocal laser scanning microscopy (CLSM) on damaged skin tissues. Objectives: To analyse glycocalyx production by S. aureus cells on damaged skin tissues and the influence of polymorphonuclear leucocytes (PMNs) and various antimicrobial agents on its production using CLSM in cyclophosphamide (Cy)-treated (neutropenic) or non-Cy-treated (normal) mice. Methods: S. aureus cells were inoculated on damaged skin tissues in neutropenic or normal mice with or without topical application of antimicrobial agents. S. aureus cells were stained with safranine, and positive staining with fluorescein isothiocyanate-conjugated concanavalin A was considered to indicate the presence of glycocalyx. Results: All S. aureus cells tested on damaged skin tissues formed microcolonies encircled by glycocalyx. The colony counts of S. aureus cells on croton oil dermatitis in normal mice treated with 2% fusidic acid ointment were about 100 times lower than those in neutropenic mice (control). Conclusions: As S. aureus cells can generally produce a biofilm on damaged skin tissues, antimicrobial agents may not eradicate S. aureus cells without the help of PMNs. S. aureus glycocalyx may play a crucial role in colonization and adherence to damaged skin tissues.