Quantification of E. coli adhesion to polyamides and polystyrene with atomic force microscopy

Atomic force microscopy (AFM) was used to measure adhesion forces between E. coli bacteria and surfaces consisting of a series of polyamides and polystyrene, materials that are prominent in carpeting, upholstery, and other indoor surfaces. Bioparticle adhesion to such surfaces in air is poorly understood, yet these interactions are thought to play a key role in their accumulation and release as indoor air pollutants. The polymers employed were polyamide 6 (PA6), polyamide 6,6 (PA66), polyamide 12 (PA12) and polystyrene (PS). We report the interaction forces between immobilized E. coli and AFM tips coated with each polymer. The adhesion forces for the tip–bacterial interactions were in the range between 2.9 and 6.7 nN, which is of the same magnitude as the polymer–polymer interactions for the same series of polymers. Polystyrene had stronger adhesion with E. coli than any of the three polyamides, by an average factor of 1.4. The work of adhesion and Hamaker constants of the probe–surface interactions were calculated using a square-pyramid flat-surface model developed previously. A drag-force analysis suggests that model spheres with the same adhesion force as E. coli–poly(amide) (F ∼ 4 nN) will remain adherent under normal foot traffic (F ∼ 0.2 nN), but will release during vacuum cleaning (F ≥ 30 nN).