Responses of Staphylococcus aureus to mechanical and chemical stresses

Initial bacterial adhesion to soft or hard surfaces in the human body and emergent properties leading to biofilm formation play a critical role in bacterial infections, which can occur when bacteria adhere to mammalian cells, teeth, or to biomaterial-implant surfaces. One of the most common, clinically-relevant infectious bacteria are staphylococci. Staphylococcus aureus is a biofilm-forming organism involved in infection associated with biomaterial implants and devices, pneumonia, meningitis and osteomyelitis amongst others. While already difficult to treat due to their biofilm-mode of growth, further challenges in infection control and prevention are constituted by the development of “superbugs”, resistant to multiple antibiotics.

Hitherto, the majority of in vitro studies on antibiotic efficacy has been performed on planktonic bacteria. This neglects both the protection offered by the biofilm-mode of growth occurring when bacteria adhere to surfaces and embed themselves in a matrix and the nanoscopic deformations of the bacterial cell wall arising from the adhesion forces between bacteria and the surfaces to which they adhere. Bacteria adhering to surfaces can experience not only a mechanical stress due to nanoscopic deformations but also a chemical stress arising from antibiotic treatments.

The aim of this thesis is to gain insight into responses of S. aureus strains to mechanical and chemical stresses, as governed by physico-chemical properties of the substratum surfaces to which they adhere, grow and form a biofilm on.

Accordingly, this thesis represents the first comprehensive description of the role of physico-chemistry in explaining biofilm formation from initial adhesion to emergent surface-programmed biofilm properties.