Does low hydroxyl group surface density explain less bacterial adhesion on porous alumina?

Background: Bacterial adhesion depends on surface materials. Recently it was suggested that ceramic-on-ceramic bearings could be less prone to infection than other bearings. We examined the possibility that porous alumina ceramic could be less susceptible to bacterial adhesion. Hypothesis: As hydroxyl groups (OH) on material surface are a major factor governing the surface properties (for example: adsorption, first non-specific step of bacterial adhesion), we hypothesized that alumina had lower OH group density than other material. Thus, we asked (i) if bacterial adhesion was lower on alumina than on titanium alloy, stainless steel and polyethylene and (ii) if OH group density was also lower on alumina. Material and methods: We performed (i) in vitro bacterial cultures on porous alumina, titanium, stainless steel and polyethylene using Staphylococcus aureus and Pseudomonas aeruginosa, known to adhere to surfaces. Bacterial cultures were done 3 times in duplicate for each material and each strain. Colony Forming Units (CFU) per cm(2) were measured; (ii) Neutral red reagent helped obtaining OH density estimates using spacer arms. UV-visible spectrophotometry method with Neutral red test, reproduced twice for each surface, provided mu g/cm(2) measurements of OH density. Results: There was significantly less P. aeruginosa adherent on porous alumina (2.25x10(4) CFU/cm(2)) than on titanium (4.27x10(5) CFU/cm(2), p=0.01), on stainless steel (2.44x10(5) CFU/cm(2), p=0.02) and on polyethylene (7.29x10(5) CFU/cm(2), p<0.001). S. aureus was significantly less adherent on porous alumina (3.22x10(5) CFU/cm(2)) than on polyethylene (5.23x10(6) CFU/cm(2), p=0.01), but there was no difference with titanium (1.64x10(6) CFU/cm(2), p=0.08) and stainless steel (1.79x10(6) CFU/cm(2), p=0.1). There was significantly lower Neutral red grafted on porous alumina (0.09 mu g/cm(2)) than on titanium (8.88 mu g/cm(2), p<0.0001), on stainless steel (39.8 mu g/cm(2), p=0.002) and on polyethylene (4.5 mu g/cm(2), p<0.01). However, no correlation was found between bacterial adherence and OH group density. Discussion: Bacterial adherence on porous alumina was lower than on other bearings. Although there were less surface OH groups on porous alumina, we failed establishing a statistical correlation between bacterial adherence and OH group density. (C) 2018 Elsevier Masson SAS. All rights reserved.