Abstract: Calcium montmorillonite (Ca-MMT), sodium ontmorillonite (Na-MMT) and acid-activated montmorillonite (AAM), and their Cu ²⁺ -exchanged ontmorillonites (Cu-MMT), Cu*Ca-MMT, Cu*Na-MMT and Cu*AAM, were used to study the adsorptive activity on Aeromonas hydrophila. The Zeta potentials of MMTs and A. hydrophila are all decreased with increasing pH, and those of Cu-MMTs are increased with increasing pH and transformed from
the negative to positive value when pH=4--6. AAM, Na-MMT and Ca-MMT show some ability to reduce bacterial plate counts by 36.5％, 20.1％ and 14.3％, respectively. The Cu*AAM, Cu*Na-MMT and Cu*Ca-MMT reduce the bacterial plate counts by 99.6％, 93.1％ and 87.4％. The extent of bacterial adsorption onto MMTs is decreased with increasing pH. However, the bacterial adsorption onto Cu-MMTs is decreased with increasing pH and increased with increasing pH when pH>5.0. The study of desorption of Cu2+ by washing with physiological saline for 24h reveals that the washing solutions don’t show a significant reduction of the bacterial counts, while the washed Cu-MMTs retain their full antibacterial activity. The mechanism by which bacterial counts are reduced may involve the enhanced affinity of Cu-MMT for Aeromonas hydrophila and the antibacterial activity of Cu²⁺.

Key words: montmorillonite, copper-bearing montmorillonite, aeromonas hydrophila, adsorption