Force spectroscopy of bonds that form between a Staphylococcus bacterium and silica or polystyrene substrates

Inter- and intra-molecular forces are the driving forces responsible for the creation of an interface between a microorganism and a naturally occurring mineral or man-made material. We have used atomic force microscopy to directly measure forces between a Staphylococcus aureus bacterium and each of two materials (silica and polystyrene) in an electrolyte solution. Force “spectra” were collected by placing a glass or polystyrene bead (∼10 μm diameter) in contact with a living cell and then pulling the two surfaces apart. An attractive, adhesion force was observed in approximately 40 and 50% of the measurements for silica and polystyrene, respectively. The strength of the adhesion bond was 38 ± 4 pN (10−12 N) and 52 ± 9 pN for glass and polystyrene, respectively. The origin of the attractive interaction appears to be non-specific (e.g., van der Waals force) although a small number (2-3%) of force spectra contained distinct sawtooth like profiles indicative of a protein bond between S. aureus and glass or polystyrene.