Victoria Kostenko

Impact of Silver-Containing Wound Dressings on Bacterial Biofilm Viability and Susceptibility to Antibiotics during Prolonged Treatment

ABSTRACT The long-term antimicrobial efficacy of silver dressings against bacterial biofilms was investigated in a 7-day treatment in vitro model where the protein-rich medium was refreshed daily in order to mimic the conditions found in a wound bed. The use of plate-to-plate transfer assays demonstrated measurable differences in the effectivenesses of several silver dressings on the viability of biofilm bacteria and their susceptibility to antibiotics. Whereas after the first day of treatment, all dressings used resulted in a significant reduction in the number of viable cells in the biofilms and disruption of the biofilm colonies, during prolonged treatment, the efficacy of dressings with hydrophilic base materials diminished with daily transfers, and bacterial populations recovered. For dressings with hydrophobic base materials, the level of efficacy correlated with the silver species loaded. Biofilm bacteria, which survived the initial silver treatment, were susceptible to tobramycin, ciprofloxacin, and trimethoprim-sulfamethoxazole, in contrast to untreated biofilms, which were highly tolerant to the same antibiotics. This acquired susceptibility was unaffected by the longevity of pretreatment with the silver dressings but depended on the dressing used. The antimicrobial efficacy of the dressings correlated with the type of the dressing base material and silver species loaded.

Relation between the activity of anaerobic microbial populations in oil sands tailings ponds and the sedimentation of tailings

Oil sands tailings ponds contain a variety of anaerobic microbes, including methanogens, sulfate- and nitrate-reducing bacteria. Methanogenic activity in samples from a tailings pond and its input streams was higher with trimethylamine (TMA) than with acetate. Methanogens closely affiliated to Methanomethylovorans hollandica were found in the TMA enrichments. Tailings sedimentation increased with methanogenic activity, irrespective whether TMA or acetate was used to stimulate methanogenesis. Increased sedimentation of autoclaved tailings was observed with added pure cultures under methanogenic, as well as under nitrate-reducing conditions, but not under sulfate-reducing conditions. Scanning electron microscopy and energy-dispersive X-ray spectroscopy indicated the presence of microbes and of extracellular polymeric substances in tailings particle aggregates, especially under methanogenic and nitrate-reducing conditions. Hence different classes of microorganisms growing in tailings ponds contribute to increased tailings aggregation and sedimentation. Because addition of nitrate is known to lower methane production by methanogenic consortia, these observations offer the potential to combine lower methane emissions with improved microbially-induced tailings sedimentation.

Staphylococcus aureus biofilm formation and tolerance to antibiotics in response to oscillatory shear stresses of physiological levels

Bacterial infections in the blood system are usually associated with blood flow oscillation generated by some cardiovascular pathologies and insertion of indwelling devices. The influence of hydrodynamically induced shear stress fluctuations on the Staphylococcus aureus biofilm morphology and tolerance to antibiotics was investigated. Fluctuating shear stresses of physiologically relevant levels were generated in wells of a six-well microdish agitated by an orbital shaker. Numerical simulations were performed to determine the spatial distribution and local fluctuation levels of the shear stress field on the well bottom. It is found that the local biofilm deposition and morphology correlate strongly with shear stress fluctuations and maximum magnitude levels. Tolerance to killing by antibiotics correlates with morphotype and is generally higher in high shear regions.

Nutrient media optimization for simultaneous enhancement of the laccase and peroxidases production by coculture of Dichomitus squalens and Ceriporiopsis subvermispora

Coculturing of two white‐rot fungi, Dichomitus squalens and Ceriporiopsis subvermispora, was explored for the optimization of cultivation media for simultaneous augmentation of laccase and peroxidase activities by response surface methodology (RSM). Nutrient parameters chosen from our previous studies with the monocultures of D. squalens and C. subvermispora were used to design the experiments for the cocultivation study. Glucose, arabinose, sodium nitrate, casein, copper sulfate (CuSO4), and manganese sulfate (MnSO4) were combined according to central composite design and used as the incubation medium for the cocultivation. The interaction of glucose and sodium nitrate resulted in laccase and peroxidase activities of approximately 800 U/g protein. The addition of either glucose or sodium nitrate to the medium also modifies the impact of other nutrients on the ligninolytic activity. Both enzyme activities were cross‐regulated by arabinose, casein, CuSO4, and MnSO4 as a function of concentrations. Based on RSM, the optimum nutrient levels are 1% glucose, 0.1% arabinose, 20 mM sodium nitrate, 0.27% casein, 0.31 mM CuSO4, and 0.07 mM MnSO4. Cocultivation resulted in the production of laccase of 1,378 U/g protein and peroxidase of 1,372 U/g protein. Lignin (16.9%) in wheat straw was degraded by the optimized enzyme mixture.

Enhanced Delignification of Wheat Straw by the Combined Effect of Hydrothermal and Fungal Treatments

Delignification is the crucial step for the conversion of lignocelluloses to biofuel. In this work, wheat straw delignification was enhanced by a two-step process, comprising hydrothermal and fungal treatments. Wheat straw was exposed to hydrothermal treatment at subcritical temperatures and then subjected to fungal treatment. Lignocellulose hydrolysis rate was significantly higher during the hydrothermal treatment compared to the slower fungal delignification. However, by-products of lignin degradation via hydrothermal treatment were re-deposited on the cellulose fibers as the substrate was cooled to room temperature. It is shown that post-treatment fungi can enhance delignification by degradation of the residual lignin by-products. The effect of fungal delignification of hydrothermally treated substrate was a function of temperature of the hydrothermal process. Compared to the hydrothermal treatment, the novel combined approach, proposed in this study, resulted in two-fold higher delignification and promises to be an effective method for delignified substrate preparation for conversion to biofuel.

Impact of Oil-Based Drilling Fluids Emulsification on Tolerance and Hydrocarbon-Degrading Potential of Ralstonia pickettii and Alcaligenes piechandii

Biodegradability of drilling fluid waste is essential in the development of environmentally compatible oil and gas drilling. Biodegradation is determined not only by the enzymatic potential, but also microbial tolerance to hydrocarbons. The present study investigated the hydrocarbon degradation and tolerance of Ralstonia pickettii BP20 and Alcaligenes piechandii KN1 to drilling fluids with diesel and low-aromatic continuous phases in respect to their state: non-emulsified oil, direct (O/W) and invert (W/O) emulsions; and the concentrations affecting microbial activity and viability. In general, A. piechaudii KN1demonstrated higher tolerance than R. picketti BP20 did; but, the impacts of different drilling fluids on viability and activity of both microbial strains had similar trends. Microbial growth and hydrocarbons degradation rates increased when diesel was replaced with low aromatic oil, and emulsified. The higher productivity was observed in direct (O/W) emulsions than in invert (W/O) emulsions. Similarly, viability of microorganisms in low aromatic fluids and emulsions was higher than in corresponding diesel drilling fluids. Tolerance to low aromatic fluids increased in the order: non-emulsifier oil < invert emulsion < direct emulsion. In contrast, for diesel based drilling fluids, direct emulsion enhanced, but invert emulsion reduced microbial viability compared to non-emulsified oil.

Pseudomonas putida Biofilm Facilitates Fine Solids, Water and Oil Separation from Oil Sands Tailings

Aims: The generation of the tailings, poor settling slurry contaminated with emulsified bitumen, significantly increases the negative impact of oil sands operations on the environment and human health (contamination of surface and ground water with hydrocarbons and naphthenic acids, methane emission), as well as operation cost. Poor effectiveness of conventional tailings settling and clean-up technologies contributes to the daily increase of the quantity of tailings deposited in ponds covering now more than 130 km. There is an urgent need for development of novel tailings settling technologies. The aim of the present study is a comparative analysis of the impact of Pseudomonas putida planktonic and biofilm populations on oil, solids and water separation in tailings, and the investigation of the mechanisms involved in bioseparation. Methodology: Mature fine tailings (MFT) were exposed to Pseudomonas putida planktonic populations and biofilms at agitation followed by static conditions for settling. Oil-solids-water separation was determined by water and oil release from MFT in comparison with untreated tailings. Interaction of tailings with microbial populations was Research Article Kostenko et al.; JSRR, Article no. JSRR.2014.004 111 investigated with scanning electron microscopy (SEM), confocal scanning laser microscopy (CSLM) and energy-dispersive X-ray (EDAX) spectroscopy. Results: The exposure of mature fine tailings to microbial cultures, and especially to biofilms, significantly increase tailings densification, dewatering and bitumen release. The separation efficiency is associated with fine clay aggregation due to the interaction with the microbial cells, biofilm colonies and extracellular polymeric substances (EPS). Conclusion: The mechanism driving the observed biodensification is the aggregation of fine solids via flocculation by biofilm-produced EPS and bacterial cells. Microorganisms were also observed to destabilize emulsions and enhanced residual bitumen release from tailings.

Escherichea coli Biofilm Formation and Susceptibility in Response to Increased Shear Stresses

The development of biofilms, well organized communities of bacterial cells embedded in a self-generated extra-cellular polymeric matrix, on medical devices (vascular or urinary catheters, surgical implants) and surrounding tissue poses a great challenge for modern medicine. The biofilm environment confers onto bacterial cells resistance to antimicrobials and the host immune system that leads to persistent and recurrent device-associated infections, deterioration of patient life quality, and often replacement of the device [1].Copyright

Rough Substratum Surface Facilitates Methicillin-Resistant Staphylococcus aureus Biofilm Formation in the Presence of Antibiotics

Despite a variety of approaches developed to prevent bacterial colonization and biofilm formation on indwelling medical devices, implant-associated infections remain responsible for about 65% of nosocomial diseases, including MRSA infections [1].Copyright