Advances in the Applications of Clinoptilolite-Rich Tuffs.

Adsorptive, catalytic, and antibacterial properties of clinoptilolite-rich tuffs (ZT) are presented here. ZT transformed into Fe-containing ZT (Fe-ZT) removes various organic and inorganic anions from water. Fe-ZT, which contains selenium, is beneficial for growing Pleurotus ostreatus mushrooms. The fungi convert inorganic Se from Fe-ZT into a more useful organically bonded form. ZT and Fe-ZT as supplements retain nitrogen and potassium in sandy, silty loam and silty clay soils. ZT shows an affinity toward toxic metal cations, which are essential for cleaning contaminated water. The adsorption of atenolol, acetylsalicylic, and salicylic acid onto M-ZT (M-Cu2+, Mn2+, Ni2+, or Zn2+) from water solutions suggests that both the natures of M and pharmaceuticals have a significant impact on the adsorption mechanism and determine the adsorption capability of the ZT. ZT is an excellent carrier for ultrafine (2-5 nm) nano oxide particles, which have been shown to have catalytic activity in different chemical processes and photodegradation reactions of organic pollutants. ZT can also be transformed into SO4-SnO2-ZT, which is catalytically active as a solid acid. M-ZT is an effective carrier of valuable bacteria. Ag-ZT possesses beneficial bactericidal activity in disinfecting water and soil remediation.

Antibacterial activity of silver doped hydroxyapatite toward multidrug-resistant clinical isolates of Acinetobacter baumannii.

Bacteria Acinetobacter baumannii is a persistent issue in hospital-acquired infections due to its fast and potent development of multi-drug resistance. To address this urgent challenge, a novel biomaterial using silver (Ag+) ions within the hydroxyapatite (HAp) lattice has been developed to prevent infections in orthopedic surgery and bone regeneration applications without relying on antibiotics. The aim of the study was to examine the antibacterial activity of mono-substituted HAp with Ag+ ions and a mixture of mono-substituted HAps with Sr2+, Zn2+, Mg2+, SeO32- and Ag+ ions against the A. baumannii. The samples were prepared in the form of powder and disc and analyzed by disc diffusion, broth microdilution method, and scanning electron microscopy. The results from the disc-diffusion method have shown a strong antibacterial efficacy of the Ag-substituted and mixture of mono-substituted HAps (Sr, Zn, Se, Mg, Ag) toward several clinical isolates. The Minimal Inhibitory Concentrations for the powdered HAp samples ranged from 32 to 42 mg/L (Ag+ substituted) and 83-167 mg/L (mixture of mono-substituted), while the Minimal Bactericidal Concentrations after 24 h of contact ranged from 62.5 (Ag+) to 187.5-292 mg/L (ion mixture). The lower substitution level of Ag+ ions in a mixture of mono-substituted HAps was the cause of lower antibacterial effects measured in suspension. However, the inhibition zones and bacterial adhesion on the biomaterial surface were comparable. Overall, the clinical isolates of A. baumannii were effectively inhibited by substituted HAp samples, probably in the same amount as by other commercially available silver-doped materials, and such materials may provide a promising alternative or supplementation to antibiotic treatment in the prevention of infections associated with bone regeneration. The antibacterial activity of prepared samples toward A. baumannii was time-dependent and should be considered in potential applications.

Metal-loaded zeolite remediation of soils contaminated with pandrug-resistant Acinetobacter baumannii.

Due to the development of resistance to antimicrobial agents, bacterium Acinetobacter baumannii is nowadays a leading cause of nosocomial outbreaks. Clinically relevant A. baumannii outside 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. baumannii from artificially contaminated natural soils. A. baumannii isolate was subjected to the activity of natural zeolitised tuff (NZ) and Cu-modified (CuNZ) or Ag-modified zeolite (AgNZ) in wet, slightly acidic terra rossa and slightly alkaline red palaeosol. A. baumannii survived in terra rossa and red palaeosol supplemented with 1 wt% of NZ for seven days and four months, respectively. The addition of 1 wt% of CuNZ to terra rossa and red palaeosol shortened the survival of A. baumannii to three and 14 days, respectively. The addition of 0.1 wt% of AgNZ to both soils resulted in complete removal of viable A. baumannii within 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.

Characterization of Acinetobacter baumannii from water and sludge line of secondary wastewater treatment plant.

The elimination of potentially pathogenic bacteria in wastewater treatment plants (WWTPs) attracts much attention in public health. Reports on the occurrence of the emerging hospital pathogen Acinetobacter baumannii in wastewaters do not include a continuous monitoring at all WWTP stages. The objective of this study was to characterize A. baumannii recovered from the water and sludge line of the secondary WWTP in Zagreb, Croatia over the period of one year. Recovery of A. baumannii was performed using CHROMagar Acinetobacter plates. Antimicrobial susceptibility testing was performed with broth microdilution and results interpreted using EUCAST breakpoints for clinical isolates of A. baumannii. Molecular characterization was performed by WGS and cgMLST. The secondary WWTP treating the urban wastewater is constantly receiving viable A. baumannii along with genes encoding carbapenem resistance, and emitting them via effluent into the environment. Furthermore, A. baumannii from influent are incorporated into activated sludge flocs in aeration basin. A. baumannii can survive the technological process of anaerobic mesophilic sludge digestion, and is finally destroyed in alkaline lime-treated stabilized sludge. The majority (102/119) of A. baumannii isolates were carbapenem-resistant, while antibiotic-susceptible isolates (17/119) were rarely recovered from all WWTP stages. Carbapenem-resistant isolates belonged to international clonal lineage IC2 carrying OXA-23 and IC1 carrying OXA-72, while the susceptible isolates belonged to IC5 or were unclustered. Increased resistance to antibiotics, together with the appearance of carbapenem- and even pandrug-resistant isolates in effluent as compared to influent wastewater, suggests the need of additional disinfection of effluent prior to its discharge into the natural recipient.

The fate of carbapenem-resistant bacteria in a wastewater treatment plant.

Wastewater treatment plants have been considered potential sources of antibiotic resistance gene exchange and release into the environment. The aim of our study was to quantify environmental and human-associated carbapenem-resistant bacterial populations (CRBPs) across wastewater treatment stages and correlate bacterial counts to physicochemical and other bacteriological parameters in order to see their behaviour in wastewater and sludge and their potential dissemination in the environment. Samples were taken from five sites (treatment stages) of the largest Croatian wastewater treatment plant (20 per site) over 10 months of monitoring. CRBPs were found at all wastewater treatment stages save for the lime-treated, stabilised sludge, which underlines the importance of effluent and digested sludge disinfection. Secondary sludge settling removed 99% of CRBP from the effluent, but the relative proportion of CRBP in the total bacterial count significantly increased in the effluent (0.0020%) and digested sludge (0.0019%) compared to the influent (0.0006%), indicating selection for resistant bacteria in these settings. CRBP counts did not correlate with measured carbapenem concentrations in wastewater, which suggests that antibiotic concentrations were not the reason for CRBP selection. Negative correlation between activated sludge retention time and CRBP indicated that their number could be reduced by increasing the retention time during secondary treatment. Despite the indications that WWTPs select for antibiotic-resistant bacteria, wastewater treatment is very efficient in reducing their absolute numbers, and proper effluent and sludge disinfection can significantly reduce dissemination of antibiotic-resistant bacteria into the environment.