Comparison between silver- and copper-modified zeolite-rich tuffs as microbicide agents for Escherichia coli and Candida albicans.

Zeolite-rich tuff from the State of Chihuahua was modified with silver or copper ions (ZChAg and ZChCu) to evaluate its microbicidal effect against Escherichia coli (E. coli) and Candida albicans (C. albicans) suspended in an aqueous solution in order to compare the microbial disinfection kinetics between bacteria and yeast. The zeolite-rich tuff was treated with AgNO3 or CuCl2 solutions. The materials obtained were characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and the textural properties were also determined by BET-analyses. The concentration of Ag and Cu was verified in the zeolitic materials using neutron activation analysis. The experimental data were adjusted to both Chick and Chik-Watson models to describe the kinetic behavior of the process. It was found that when the mass of ZChAg increased, the survival microorganisms notably decreased. The E. coli and C. albicans showed higher resistance in contact with ZChCu even when the mass of such material was 10-20 times higher than the mass of ZChAg. Chick and Chik-Watson constants showed that the kinetics of the disinfection process depended on the desorption of the exchange ion that modified the structure of the zeolitic material, its concentration in aqueous medium, its oligodynamic properties, and each microorganism's characteristics (Gram-negative bacteria and yeast). The kinetic desorption of Ag and Cu from the corresponding modified-zeolite-rich tuffs was also considered in this work. In this case, the Higuchi and Korsmeyer-Peppas models were applied.

Adherence of Streptococcus mutans to orthodontic band cements.

BACKGROUND: The aim of this study was to quantitatively determine the adherence of Streptococcus mutans to orthodontic band cements. METHODS: Two hundred and ten blocks of seven different band cements for orthodontic prescription were made using a Teflon mould (4 × 4 × 1 mm). The obtained blocks were slightly polished and cleansed ultrasonically. Certified S. mutans ATCC 25175 were cultured with conventional methods for growth in Petri dishes and trypticase soy broth. Quantitative analysis was carried out with radioactive markers to codify the bacteria ((3) H). Subsequently, a combustion system was used to capture the residues, the radioactivity of the samples was measured, and the values recorded in disintegrations per minute (dpm). One-way analysis of variance (ANOVA) with a Scheffé test for multiple comparisons was realized with a significance level of ≤0.05. RESULTS: Significant differences were found among different band cement materials (p < 0.001). Two band cement materials showed statistically lower values than the others (Transbond Plus Band Cem and Ketac Cem). In contrast, GC Fuji Ortho Band presented the highest adherence of S. mutans. CONCLUSIONS: Among the cements evaluated, Transbond Plus Band Cem and Ketac Cem showed lower adherence of S. mutans.

Antibacterial behavior of silver-modified clinoptilolite-heulandite rich tuff on coliform microorganisms from wastewater in a column system.

The water disinfecting behavior of silver-modified clinoptilolite-heulandite rich tuff (ZSAg) as an antibacterial agent against coliform microorganisms from water in a continuous mode was investigated. Silver recovery from the disinfected effluents by the sodium-modified clinoptilolite-heulandite rich tuff (ZSNa) was also considered. Escherichia coli (ATCC 8739) and total coliform microorganisms, as indicators of microbiological contamination of water, were chosen to achieve the disinfection of synthetic wastewater or municipal wastewater. Ammonium (NH(4)(+)) and chloride (Cl(-)) ions were added to the synthetic wastewater as an interfering chemical species on the disinfection processes. The antibacterial activity of the ZSAg as a bactericide was measured by the coliform concentration as evaluated by the APHA method. The amount of silver in the disinfected effluents was determined using atomic absorption spectroscopy. The inactivation of the ZSAg was calculated from the breakthrough curves based on the model reported by Gupta et al. It was found that when the silver concentration in the effluent is less than 0.6 microg/mL, the bacterial survival percentage increased and the volume of disinfected water diminished. The total silver amounts found in the effluent at the end of the disinfection processes varied depending on the water treated (synthetic or municipal wastewater). The presence of NH(4)(+) ions in synthetic wastewater influent notably improved the disinfected water volume (zero NVC/100mL), in comparison to the disinfection of the same influent without NH(4)(+) ions. A contrary water disinfection behavior was observed in the presence of Cl(-) ions. The silver recovery does not depend on the mass of the sodium zeolitic bed according with the wastewater to be treated (synthetic or municipal wastewater) and the presence of NH(4)(+) or Cl(-) ions in the influent also influenced the silver recovery from wastewater. The ZSNa did not have antibacterial activity. Therefore the amount of bactericide agent (silver-modified natural zeolite), coliform microorganisms from water (E. coli or consort of coliform microorganisms) as well as the water quality (synthetic wastewater or municipal wastewater) influenced both the disinfection process and the silver recovery in a column system.