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Due to the development of resistance to antimicrobial agents, bacterium Acinetobacter baumanniiis nowadays a leading cause of nosocomial outbreaks. Clinically relevant A. baumanniioutside hospital settings including natural soils affected by human waste represents a public-health risk for humans and animals. The aim of this study was to investigate the potential of metal-loaded zeolites to eliminate viable A. baumanniifrom artificially contaminated natural soils. A. baumanniiisolate was subjected to the activity of natural zeolitised tuff (NZ) and Cu-modified (CuNZ) or Ag-modified zeolite (AgNZ) in wet, slightly acidic terra rossaand slightly alkaline red palaeosol. A. baumanniisurvived in terra rossaand red palaeosol supplemented with 1 wt% of NZ for seven days and four months, respectively. The addition of 1 wt% of CuNZ to terra rossaand red palaeosol shortened the survival of A. baumanniito three and 14 days, respectively. The addition of 0.1 wt% of AgNZ to both soils resulted in complete removal of viable A. baumanniiwithin 1 h of contact, while the total native heterotrophic bacterial counts remained high. Since AgNZ is prepared with a simple modification of cost-effective and environmentally friendly natural zeolite, it is a promising material for the remediation of soils contaminated with pandrug-resistant A. baumannii.

Antibacterial activity of a natural zeolite, clinoptilolite (Z), enriched with about 0.4–0.5 mmol of Ag (Ag–Z), Cu (Cu–Z) or Zn (Zn–Z) was tested toward two strains of Gram-negative bacteria – Escherichia coli and Acinetobacter baumannii – in natural seawater from Adriatic Sea (Croatia). The Ag–Z and Cu–Z exhibited bactericidal activity toward E. coli and A. baumannii after 3 and 6 h of exposure, respectively. The Zn–Z showed antibacterial activity toward both strains, but lacking the bactericidal effect even after 24 h of exposure. All studied samples released metal cations in seawater. Concentration of Ag and Zn leached from Ag–Z and Zn–Z was higher than maximum allowable concentrations (MAC) for drinking water, whereas concentration of Cu was below MAC. Due to high concentration of Na+in seawater (about 1.2 g Na+dm–3) an ion-exchange process can be responsible for the leaching of the studied cations. The lowest extent of leaching from Cu–Z was ascribed to different position and geometry of sites occupied by Cu(II) in the clinoptilolite lattice. The antibacterial activity of M–Z was attributed to the metal cations leached from the zeolite lattice into seawater. The obtained results indicate that Cu–Z can be considered as a promising disinfectant for treatment of seawater.