The Influence of Material Surface Properties on Initial Bacterial Attachment and Biofilm Formation on Built Environment Surfaces

Key results

1. 01

   SuggestedMaterial had no significant effect on initial attachment efficiency (α) across six polymers and stainless steel. α showed no trend with wettability, roughness or surface charge, and all α values were low.

   In a two-way ANOVA (material, organism, interaction), material was not significant for α (Table S.6.1), and plots of α against material properties showed no trend (Figure S.8.1). All α values were below 0.05, although the materials ranged from hydrophilic (SS) to hydrophobic (HDPE, HIPS), in roughness from 50.9 ± 9.9 nm (SS) to 769 ± 474.7 nm (HDPE), and in zeta potential from -7.9 to -18.7 mV. · Effect of Material Surfaces on Initial Bacterial…; Characterization of Material Surface Properties

2. 02

   ShownBacterial species, not material, set initial attachment: both Gram-negative species attached more efficiently than both Gram-positive ones (the authors call it an order of magnitude; pooled values show a smaller gap for some pairs). α did not track cell charge, hydrophobicity or lab vs hospital origin.

   Pooled over seven materials, α was 0.029 (E. coli) and 0.026 (P. aeruginosa) vs 0.0056 (B. subtilis) and 0.011 (S. aureus). In the two-way ANOVA the species effect was significant (Table S.6.1). Bonferroni pairwise comparisons separated each Gram-negative species from each Gram-positive one at p ≤ 0.0001 (standard error from 14 measurements). · Effect of Bacterial Cell Properties on Initial…; Figure legends

3. 03

   ShownUnlike initial attachment, 24 h biofilm biomass depended on material. Stainless steel, the smoothest and most hydrophilic surface, carried significantly more biofilm than the plastics. This runs against literature trends that favour rough, hydrophobic surfaces.

   Crystal violet assay (absorbance at 585 nm normalized to surface area, triplicates) for E. coli and B. subtilis on all seven materials. Two-way ANOVA found significant species and material effects (Table S.6.3). Bonferroni comparisons ranked SS (roughness 50.9 ± 9.9 nm) above the plastic materials (Table S.6.4). · Material Impacts on Biofilm Formation; Characterization of Material Surface Properties; Evaluation of Biofilm Formation; Figure legends

4. 04

   ShownE. coli exceeded B. subtilis in both attachment and biofilm formation, but the gap was much smaller for biofilm. The authors suggest that weak initial attachment limits B. subtilis biofilm here, even though B. subtilis is usually the stronger biofilm former.

   α was 0.029 ± 0.0029 for E. coli vs 0.0056 ± 0.0023 for B. subtilis. The paper states about 6.4-fold higher attachment and 1.7-fold higher biofilm formation for E. coli. The 6.4-fold figure does not match the reported α values. · Material Impacts on Biofilm Formation

5. 05

   SuggestedDextran, used as a stand-in for extracellular polymeric substances (EPS), adsorbed preferentially to stainless steel. The authors propose that this kind of surface conditioning, not initial attachment, drives the material dependence of biofilm.

   In an adsorption experiment (Figure S.7.1), dextran adsorption is reported to correlate well with biofilm formation and to favour SS; the main text gives no adsorption values. A second explanation, stress from contact with stainless steel raising EPS output, is proposed but not tested. · Material Impacts on Biofilm Formation; ENVIRONMENTAL IMPLICATIONS