Influence of surface oxides on the adhesion of a wild strain of Pseudomonas sp to aluminium brass

The adhesion of a wild strain of Pseudomonas sp. to aged aluminium brass was evaluated modifying the pH and ionic strength of the electrolyte solution. Ionic strengths of 0.1 and 0.6 M NaCl, and pH values of 2, 4, 6, and 8 were tested. The surface oxides composition was analysed in situ by reflectance spectroscopy and the water contact angle of oxides under n-hexane was determined. At low ionic strength the adhesion of bacteria increased as pH values raised. The occurrence of adhesion was correlated to the formation of an oxide layer on the samples. The presence of copper and zinc oxides was detected in the layer at pH values greater than or equal to 4 at both ionic strengths. At low ionic strength the formation of (hydro)oxides was also observed. At high ionic strength (0.6 M), the adhesion was strongly diminished throughout the range of pH values tested. No evidences of hydration of the oxide layer were found at this condition. The acid-base interaction capacity of the metal surface was observed to increase with the raising of pH accounting for both, the bacterial adhesion increase and the oxides hydration. (C) 2002 Elsevier Science Ltd. All rights reserved.