Mechanistic study of the bactericidal action of silver-loaded chabasite on Acidithiobacillus thiooxidans

The bactericidal action of silver-loaded chabasite against Acidithiobacillus thiooxidans was evaluated by measuring the variations in biogenic sulfate, ATP and biomass dry cell weight (DCW). The experiment was conducted using concrete specimens powder coated with 2.6% (Z-Ag-2.6%) or 18% (Z-Ag-18%) by wt. silver-loaded chabasite. Uncoated (UC) and blank chabasite-coated without silver-loading (ZC) served as control specimens. The growth of the bacterium was not hampered upon exposure to UC and ZC as confirmed by an increase in biomass DCW and cellular ATP. In Z-Ag-2.6%, cellular ATP declined to zero at the end of the experiment and the value of DCW did not increase from an initial value of 100 mg−1. While there was an active biofilm in the UC with a maximum value of 0.1 mg DCW cm−2 and cellular ATP of 0.01 mg cm−2, there was no significant biofilm development in all the zeolite coated specimens. In Z-Ag-2.6% and Z-Ag-18%, a progressive decrease in soluble silver (Ag-S) was observed due to uptake of silver by the bacteria as confirmed by the increase in particulate silver (Ag-P) from 0 to 4 × 10−2 mg Ag per mg DCW and 0 to 1.14 × 10−3 mg Ag per mg DCW, respectively. The half-life, T1/2, for Z-Ag-18% was calculated to be 60 d compared to 700 d for Z-Ag-2.6%.