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.Peer reviewe

Survival of ESKAPE pathogen Acinetobacter baumannii in water of different temperatures and pH

Bacterium Acinetobacter baumannii is an emergent pathogen associated with nosocomial infections, which can be also found in natural waters. The impact of ecological factors on A. baumannii is insufficiently investigated. The aim was to examine the influence of temperatures (−20 to 80 °C) and pH values (2 to 12) on the survival of environmental and clinical isolates of A. baumannii in nutrient-deprived spring water (SW) and nutrient-rich diluted nutrient broth during 5 months. A. baumannii successfully survived at −20 to 44 °C and neutral pH for 5 months, which is consistent with the persistence of this pathogen in the hospital environment. At temperatures 50 to 80 °C the survival of A. baumannii ranged from 5 days to 5 min. The pH 2 was the most lethal with survival time up to 3 hours, suggesting that acidic conditions are promising for disinfection of water contaminated with A. baumannii. Although the type of media was not statistically significant for long-time survival, the extensively resistant or pandrug-resistant isolates survived better in SW than susceptible or multidrug-resistant isolates. Two distinct colony phenotypes were recorded at extreme temperatures and pH values. The results of this study provide insight into the behaviour of this emerging pathogen in the environment.The Croatian Science Foundation (project no. IP-2014-09-5656).http://wst.iwaponline.com2019-05-01hj2018Anatomy and Physiolog

Resistance of bioparticles formed of phosphate-accumulating bacteria and zeolite to harsh environmental conditions

<div><p>Extreme environmental conditions, such as pH fluctuations, high concentrations of toxicants or grazing of protozoa, can potentially be found in wastewater treatment systems. This study was carried out to provide specific evidence on how ‘bioparticles’ can resist these conditions. The term ‘bioparticle’ is used to describe a particle comprising natural zeolitized tuff with a developed biofilm of the phosphate-accumulating bacterial species, <i>Acinetobacter junii</i>, on the surface. The bacteria in the biofilm were protected from the negative influence of extremely low pH, high concentrations of benzalkonium-chloride and grazing by <i>Paramecium caudatum</i> and <i>Euplotes affinis</i>, even under conditions that caused complete eradication of planktonic bacteria. During an incubation of 24 h, the biofilms were maintained and bacteria detached from the bioparticles, thus bioaugmenting the wastewater. The bioparticles provided a safe environment for the survival of bacteria in harsh environmental conditions and could be used for successful bioaugmentation in wastewater treatment plants.</p> </div

Perlite as a Biocarrier for Augmentation of Biogas-Producing Reactors from Olive (<i>Olea europaea</i>) Waste

Biogas is mainly produced by anaerobic digestion (AD), and in the EU, the widely used substrate for AD is maize silage. Due to a rise in silage prices, the intention is to gradually replace maize with lignocellulose biomass. In the Mediterranean area, the olive industry produces large amounts of lignocellulose wastes, namely olive cake and pruned biomass. Still, due to its high lignin content, it is resistant to biodegradation. This issue could be resolved by adding targeted microorganisms that enhance the substrate’s primary degradation, and the cells’ attachment to suitable biocarriers could boost the augmentation process. A microbial consortium customized for biodegradation of olive cake and pruned biomass was isolated, propagated and immobilized onto the biocarrier, perlite, a naturally occurring aluminosilicate material. The perlite proved to be a suitable biocarrier with numbers of immobilized bacteria as high as 2.1 ± 0.9 × 1011 and 3.4 ± 0.6 × 1010 CFU g−1 when preparation was performed in aerobic and anaerobic conditions, respectively. Bioaugmentation of AD reactors significantly increased the biogas yield, but only if olive cake, not the pruned biomass, was used as a substrate

Antibacterial Properties of Non-Modified Wool, Determined and Discussed in Relation to ISO 20645:2004 Standard

Wool is considered to possibly exhibit antibacterial properties due to the ability of wool clothing to reduce the build-up of odor, which arises from the microbial activity of skin microbiota. Indeed, when tested with a widely used agar diffusion plate test method, even wool or other textiles not treated with any antimicrobial agent can be interpreted to show certain antibacterial effects due to the lack of growth under the specimen, as instructed in ISO 20645:2004 standard. Therefore, we analyzed in detail what happens to bacterial cells in contact with untreated wool and cotton fabric placed on inoculated agar plates by counting viable cells attached to the specimens after 1 and 24 h of contact. All wool and several cotton samples showed no growth under the specimen. Nevertheless, it was shown without a doubt that neither textile material kills bacteria or inhibits cell multiplication. A reasonable explanation is that bacterial cells firmly attach to wool fibers forming a biofilm during multiplication. When the specimen was lifted off the nutrient agar surface, the cells in the form of biofilm remained attached to the wool fibers, removing the biomass and resulting in a clear, no growth zone underneath it. By imaging the textile specimens with X-ray microtomography, we concluded that the degree of attachment could be dependent on surface topography. The results indicate that certain textiles, in this case, wool, could exhibit antibacterial properties by removing excess bacteria that grow on the textile/skin interface when taken off the body

Première visualisation de biofilms bactériens dans des milieux poreux en 3D par microtomographie neutronique sans agent de contraste

International audienc

Development and evaluation of an experimental protocol for 3-D visualization and characterization of the structure of bacterial biofilms in porous media using laboratory X-ray tomography

International audienc