Growth-dependent cr(VI) reduction by Alteromonas sp. ORB2 under haloalkaline conditions: toxicity, removal mechanism and effect of heavy metals.

Bacterial reduction of hexavalent chromium (VI) to chromium (III) is a sustainable bioremediation approach. However, the Cr(VI) containing wastewaters are often characterized with complex conditions such as high salt, alkaline pH and heavy metals which severely impact the growth and Cr(VI) reduction potential of microorganisms. This study investigated Cr(VI) reduction under complex haloalkaline conditions by an Alteromonas sp. ORB2 isolated from aerobic granular sludge cultivated from the seawater-microbiome. Optimum growth of Alteromonas sp. ORB2 was observed under haloalkaline conditions at 3.5-9.5% NaCl and pH 7-11. The bacterial growth in normal culture conditions (3.5% NaCl; pH 7.6) was not inhibited by 100 mg/l Cr(VI)/ As(V)/ Pb(II), 50 mg/l Cu(II) or 5 mg/l Cd(II). Near complete reduction of 100 mg/l Cr(VI) was achieved within 24 h at 3.5-7.5% NaCl and pH 8-11. Cr(VI) reduction by Alteromonas sp. ORB2 was not inhibited by 100 mg/L As(V), 100 mg/L Pb(II), 50 mg/L Cu(II) or 5 mg/L Cd(II). The bacterial cells grew in the medium with 100 mg/l Cr(VI) contained lower esterase activity and higher reactive oxygen species levels indicating toxicity and oxidative stress. In-spite of toxicity, the cells grew and reduced 100 mg/l Cr(VI) completely within 24 h. Cr(VI) removal from the medium was driven by bacterial reduction to Cr(III) which remained in the complex medium. Cr(VI) reduction was strongly linked to aerobic growth of Alteromonas sp. The Cr(VI) reductase activity of cytosolic protein fraction was pronounced by supplementing with NADPH in vitro assays. This study demonstrated a growth-dependent aerobic Cr(VI) reduction by Alteromonas sp. ORB2 under complex haloalkaline conditions akin to wastewaters.

Fungal infections: Pathogenesis, antifungals and alternate treatment approaches.

Increasing incidence of fungal infections of recent times requires immediate intervention. Fungal infections are seldom construed at initial stages that intensify the severity of infections and complicate the treatment procedures. Fungal pathogens employ various mechanisms to evade the host immune system and to progress the severity of infections. For the treatment of diverse superficial and systemic infections, antifungal drugs from the available repertoire are administered. However, well documented evidence of fungal resistance to most of the antifungal drugs hampers disease control and poses challenges in antifungal therapy. Several physiological adaptations and genetic mutations followed by their selection in presence of antifungal agents drive the resistance development in fungi. The availability of limited antifungal arsenal, emergence of resistance and biofilm-conferred resistance drives the need for development of novel drugs and alternate approaches for the better treatment outcome against mycoses. This graphical review explicitly shed light on various fungal infections and causative organisms, pathogenesis, different antifungal drugs and resistance mechanisms including host immune response and evasion strategies. Here, we have highlighted recent developments on novel antifungal agents and other alternate approaches for fighting against fungal infections.

Assessment of alkylimidazolium chloride ionic liquid formulations for cleaning and disinfection of environmental surfaces.

BACKGROUND: Surface disinfection is fundamental to good environmental hygiene and preventing infections. Development of newer formulations that can effectively kill and remove microorganisms from the surfaces is desired. METHODS: Here, we assessed the efficacy of 1-hexadecyl-3-methylimidazolium chloride [C16MIM][Cl] ionic liquid (IL) and its formulation in ethanol for killing and removing bacteria from different environmental surfaces. Efficacy of IL and its formulation was determined on known monospecies bacterial cultures and unknown multispecies bacterial cultures on environmental surfaces. RESULT: The surface disinfection efficacy of [C16MIM][Cl] was concentration dependent and achieved 41 to 100% reduction in total viable bacterial counts of Gram positive and Gram negative bacteria at varied concentrations. The treatment of wooden surface with 0.1% [C16MIM][Cl] caused 98% reduction in bacterial load within 20 s contact time as against mere 45% reduction (20 s) with 70% ethanol. Antibacterial and surface disinfection activities of [C16MIM][Cl] have increased markedly when prepared in 70% ethanol, suggesting synergistic activity. A formulation comprising of 0.01% [C16MIM][Cl] in 70% ethanol showed effective surface disinfection and achieved 95% to 98% reduction in bacterial load on different surfaces. CONCLUSION: Ionic liquids are potent candidates for disinfection of environmental surfaces.

Alkylimidazolium Ionic Liquids as Antifungal Alternatives: Antibiofilm Activity Against Candida albicans and Underlying Mechanism of Action.

Candida albicans is an opportunistic pathogen causes fungal infections that range from common skin infections to persistent infections through biofilm formation on tissues, implants and life threatening systemic infections. New antifungal agents or therapeutic methods are desired due to high incidence of infections and emergence of drug-resistant strains. The present study aimed to evaluate (i) the antifungal and antibiofilm activity of 1-alklyl-3-methyl imidazolium ionic liquids ([CnMIM]+[X]-, n = 4, 12 and 16) against Candida albicans ATCC 10231 and two clinical C. albicans strains and (ii) the mechanism of action of promising antifungal ionic liquid on C. albicans. Two of the tested compounds were identified as more effective in preventing growth and biofilm formation. These ionic liquid compounds with -dodecyl and -hexadecyl alkyl groups effectively prevented biofilm formation by fluconazole resistant C. albicans 10231 and two other clinical C. albicans strains. Although both the compounds caused viability loss in mature C. albicans biofilms, an ionic liquid with -hexadecyl group ([C16MIM]+[Cl]-) was more effective in dispersing mature biofilms. This promising ionic liquid compound ([C16MIM]+[Cl]-) was chosen for determining the underlying mode of action on C. albicans cells. Light microscopy showed that ionic liquid treatment led to a significant reduction in cell volume and length. Increased cell membrane permeability in the ionic liquid treated C. albicans cells was evident in propidium iodide staining. Leakage of intracellular material was evident in terms of increased absorbance of supernatant and release of potassium and calcium ions into extracellular medium. A decrease in ergosterol content was evident when C. albicans cells were cultured in the presence of antifungal ionic liquid. 2',7'-Dichlorodihydrofluorescein acetate assay revealed reactive oxygen species generation and accumulation in C. albicans cells upon treatment with antifungal ionic liquid. The effect of antifungal ionic liquid on mitochondria was evident by decreased membrane potential (measured by Rhodamine 123 assay) and loss of metabolic activity (measured by MTT assay). This study demonstrated that imidazolium ionic liquid compound exert antifungal and antibiofilm activity by affecting various cellular processes. Thus, imidazolium ionic liquids represent a promising antifungal treatment strategy in lieu of resistance development to common antifungal drugs.

Textile dye biodecolourization and ammonium removal over nitrite in aerobic granular sludge sequencing batch reactors.

Biodecolourization of azo dye and removal of ammonium by aerobic granular sludge (AGS) was investigated under different growth conditions. AGS not previously exposed to azo dye was able to effectively decolourize azo dye under anaerobic and microaerophilic conditions. Azo dye, total organic carbon and ammoniacal nitrogen removal efficiencies of 89-100%, 79-95% and 92-100%, respectively, were achieved in the AGS reactor operated for 80days under microaerophilic conditions. Removal of carbon, nitrogen and phosphorus was not impacted by azo dye loading. Azo dye, organic carbon and ammonium were majorly removed in the anoxic period wherein bulk dissolved oxygen was ranged from 0.5 and <0.08mgL-1. Removal of 60mgL-1 NH4+-N was associated only with smaller amounts of nitrite build-up (∼5mgL-1 NO2--N) and negligible nitrate concentrations. Profiles of nitrogen compounds in individual sequencing batch reactor cycles supported the occurrence of ammonium removal over nitrite pathway. Bacterial community analysis showed enrichment of specific microorganisms capable of decolourizing azo dyes in the dye-decolourizing AGS. Dye decolourization and nutrient removal by AGS under microaerophilic conditions is a novel finding and can be further developed for treating textile wastewaters onsite or after dilution with sewage.

Long alkyl-chain imidazolium ionic liquids: Antibiofilm activity against phototrophic biofilms.

Biofilm formation is problematic and hence undesirable in medical and industrial settings. In addition to bacteria, phototrophic organisms are an integral component of biofilms that develop on surfaces immersed in natural waters. 1-Alkyl-3-methyl imidazolium ionic liquids (IL) with varying alkyl chain length were evaluated for their influence on the formation of monospecies (Navicula sp.) and multispecies biofilms under phototrophic conditions. An IL with a long alkyl side chain, 1-hexadecyl-3-methylimidaazolium chloride ([C16(MIM)][Cl]) retarded growth, adhesion and biofilm formation of Navicula sp. at concentrations as low as 5µM. Interestingly, [C16(MIM)][Cl] was very effective in preventing multispecies phototrophic biofilms on fibre reinforced plastic surfaces immersed in natural waters (fresh and seawater). SYTOX® Green staining and chlorophyll leakage assay confirmed that the biocidal activity of the IL was exerted through cell membrane disruption. The data show that [C16(MIM)][Cl] is a potent inhibitor of phototrophic biofilms at micromolar concentrations and a promising agent for biofilm control in re-circulating cooling water systems. This is the first report that ionic liquids inhibit biofilm formation by phototrophic organisms which are important members of biofilms in streams and cooling towers.

The ionic liquid 1-alkyl-3-methylimidazolium demonstrates comparable antimicrobial and antibiofilm behavior to a cationic surfactant.

Biofilms are problematic in health and industry because they are resistant to various antimicrobial treatments. Ionic liquids are a novel class of low temperature liquid salts consisting of discrete anions and cations, and have attracted considerable interest as safer alternatives to organic solvents. Ionic liquids have interesting antimicrobial properties and some could find use in the development of novel antiseptics, biocides and antifouling agents. The antimicrobial and antibiofilm activity of 1-dodecyl-3-methylimiazolium iodide ([C(12)MIM]I) was studied using the clinically important bacterial pathogens, Staphylococcus aureus SAV329 and Pseudomonas aeruginosa PAO1. The ionic liquid increased cell membrane permeability in both S. aureus and P. aeruginosa cells and impaired their growth, attachment and biofilm development. The ionic liquid exhibited superior antimicrobial and antibiofilm activity against the Gram-positive S. aureus compared to the Gram-negative P. aeruginosa cells. BacLight™ staining and confocal microscope imaging confirmed that the ionic liquid treatment increased the cell membrane permeability of both the Gram-positive and Gram-negative bacteria. In addition, the antimicrobial and antibiofilm properties of [C(12)MIM]I were similar or superior to those of cetyltrimethylammonium bromide (CTAB), a well-known cationic surfactant. It is concluded that the ionic liquid induced damage to bacterial cells by disrupting cell membrane, leading to inhibition of growth and biofilm formation. Overall, the results indicate that the ionic liquid 1-dodecyl-3-methylimiazolium iodide was effective in preventing S. aureus and P. aeruginosa biofilms and could have applications in the control of bacterial biofilms.