Influence of surface porosity and pH on bacterial adherence to hydroxyapatite and biphasic calcium phosphate bioceramics

Abstract

Hydroxyapatite (HA) and biphasic calcium phosphate (BCP) ceramic materials are widely employed as bone substitutes due to their porous and osteoconductive structure. Their porosity and the lowering of surrounding pH as a result of surgical trauma may, however, predispose these materials to bacterial infections. For this reason, the influence of porosity and pH on the adherence of common Gram-positive bacteria to the surfaces of these materials requires investigation. Mercury intrusion porosimetry measurements revealed that the pore size distribution of both bioceramics had, on a logarithmic scale, a sinusoidal frequency distribution ranging from 50 to 300 nm, with a mean pore diameter of 200 nm. Moreover, total porosity was 20 % for HA and 50 % for BCP. Adherence of Staphylococcus aureus and Staphylococcus epidermidis was studied at a physiological pH of 7.4 and at a pH simulating bone infection of 6.8. Moreover, the effect of pH on the f potential of HA, BCP and of both staphylococci was evaluated. Results showed that when pH decreased from 7.4 to 6.8, the adherence of both staphylococci to HA and BCP surfaces decreased significantly, although at the same time the negative f-potential values of the ceramic surfaces and both bacteria diminished. At both pH values, the number of S. aureus adhered to the HA surface appeared to be lower than that for BCP. A decrease in pH to 6.8 reduced the adherence of both bacterial species (mean 57 %). This study provides evidence that HA and BCP ceramics do not have pores sufficiently large to allow the internalization of staphylococci. Their anti-adherent properties seemed to improve when pH value decreased, suggesting that HA and BCP bioceramics are not compromised upon orthopaedic use.

Influence of cell surface characteristics on adhesion of Saccharomyces cerevisiae to the biomaterial hydroxylapatite

“…This method has been described previously for recovery of yeast cells from non-porous supports (Vernhet and Bellon-Fontaine 1995) and cell recovery was confirmed by the absence of methylene-blue stained cells on sonicated tablets. Similar methods have been used to recover cells from HAP tablets including sonication for staphylococci (Kinnari et al 2009) and vortexing used to remove Candida sp. (Pereira-Cenci et al 2008) with enumeration by plate counts.…”

Zwitterionic ceramics for biomedical applications

“…aureus bacterial adhesion in zwitter-SBA15 compared to pristine SBA-15. In this case the bacterial adhesion was determined both qualitatively and quantitatively, by confocal microscopy studies and the counting of colony forming units (CFUs) [52], respectively.…”

Resistance of Staphylococcus aureus to the cationic antimicrobial agent poly(2-(dimethylamino ethyl)methacrylate) (pDMAEMA) is influenced by cell-surface charge and hydrophobicity

“…Bacterial zeta potentials were determined using a Malvern Zetasizer Nano ZS (Malvern Instruments). Zeta potentials were calculated from the electrophoretic mobility by Smoluchowski's equation at 25 uC, with five repeats per sample (Heimenz, 1986;Kinnari et al, 2009). The dielectric constant of the dispersant was set at 78.54.…”