Selective and specific detection of sulfate-reducing bacteria using potentiometric stripping analysis

A fast, sensitive and reliable potentiometric stripping analysis (PSA) is described for the selective detection of the marine pathogenic sulfate-reducing bacterium (SRB), Desulforibrio caledoiensis. The chemical and electrochemical parameters that exert influence on the deposition and stripping of lead ion, such as deposition potential, deposition time and pH value were carefully studied. The concentration of SRB was determined in acetate buffer solution (pH 5.2) under the optimized condition (deposition potential of −1.3 V, deposition time of 250 s, ionic strength of 0.2 mol L⁻¹ and oxidant mercury (II) concentration of 40 mg L⁻¹). A linear relationship between the stripping response and the logarithm of the bacterial concentration was observed in the range of 2.3 × 10 to 2.3 × 10⁷ cfu mL⁻¹. In addition, the potentiometric stripping technique gave a distinct response to the SRB, but had no obvious response to Escherichia coli. The measurement system has a potential for further applications and provides a facile and sample method for detection of pathogenic bacteria.     

Effect of Contact Area and Shape of Anode Current Collectors on Bacterial Community Structure in Microbial Fuel Cells

Low electrical conductivity of carbon materials is a source of potential loss for large carbonaceous electrode surfaces of MFCs due to the long distance traveled by electrons to the collector. In this paper, different configurations of titanium current collectors were used to connect large surfaces of carbon cloth anodes. The current collectors had different distances and contact areas to the anode. For the same anode surface (490 cm²), increasing the contact area from 28 cm² to 70 cm² enhanced power output from 58 mW·m⁻² to 107 mW·m⁻². For the same contact area (28 cm²), decreasing the maximal distance of current collectors to anodes from 16.5 cm to 7.75 cm slightly increased power output from 50 mW·m⁻² to 58 mW·m⁻². Molecular biology characterization (qPCR and 16S rRNA gene sequencing) of anodic bacterial communities indicated that the Geobacter number was not correlated with power. Moreover, Geobacter and Desulfuromonas abundance increased with the drop in potential on the anode and with the presence of fermentative microorganisms. Electrochemical impedance spectroscopy (EIS) showed that biofilm resistance decreased with the abundance of electroactive bacteria. All these results showed that the electrical gradient arising from collectors shapes microbial communities. Consequently, current collectors influence the performance of carbon-based anodes for full-scale MFC applications.     

Antimony biomethylation by mixed cultures of micro-organisms under anaerobic conditions

The volatile antimony compound trimethylantimony (TMA) was detected in headspace gases over anaerobic soil enrichment cultures spiked with potassium antimony tartrate. The presence of TMA was variable (12 positives from 104 cultures) and dependent upon both the inoculum source (environmental sample) and enrichment culture conditions. Positives for TMA formation were obtained with variable frequency for four of the six soils tested and for three types of enrichment culture, designed to encourage growth of nitrate-reducing, methane-producing or fermentative bacteria. The identity of the volatile antimony compound produced in each of the three types of enrichment culture was confirmed by gas chromatography–mass spectrometry and gas chromatography–atomic absorption spectroscopy. There was no evidence of any other volatile antimony compound in the headspace gases. These data suggest that the capability to generate TMA is widely distributed in the terrestrial environment and is attributable to different metabolic types of micro-organisms. © 1998 John Wiley & Sons, Ltd.     

Characterization of Microbial Degradation Products of Steviol Glycosides

Steviol glycosides were subjected to bacteria present in a soil sample collected from a Stevia plantation in Paraguay. During the incubation experiments, next to the aglycon steviol, steviol degradation products were also formed. X-ray analysis and NMR methods in combination with chemical synthesis and GIAO NMR calculations were used to fully characterize the structure of these compounds as a tricyclic ketone and the corresponding reduced form. They were nicknamed monicanone and monicanol. The latter has the (S)-configuration at the alcohol site.     

Bioprospecting the Antibiofilm and Antimicrobial Activity of Soil and Insect Gut Bacteria

Antimicrobial resistance is a growing concern in public health and current research shows an important role for bacterial biofilms in recurrent or chronic infections. New strategies, therefore, are necessary to overcome antimicrobial resistance, through the development of new therapies that could alter or inhibit biofilm formation. In this sense, antibiofilm natural products are very promising. In this work, a bioprospection of antimicrobial and antibiofilm extracts from Uruguayan soil bacteria and insect gut bacteria was carried out. Extracts from extracellular broths were tested for their ability to inhibit planktonic cell growth and biofilm formation. Genomic analysis of Bacillus cereus ILBB55 was carried out. All extracts were able to inhibit the growth of, at least, one microorganism and several extracts showed MICs lower than 500 µg mL⁻¹ against microorganisms of clinical relevance (Staphylococcus aureus, Pseudomonas aeruginosa, and Enterobacter cloacae). Among the extracts evaluated for biofilm inhibition only ILBB55, from B. cereus, was able to inhibit, S. aureus (99%) and P. aeruginosa (62%) biofilms. Genomic analysis of this strain showed gene clusters similar to other clusters that code for known antimicrobial compounds. Our study revealed that extracts from soil bacteria and insect gut bacteria, especially from B. cereus ILBB55, could be potential candidates for drug discovery to treat infectious diseases and inhibit S. aureus and P. aeruginosa biofilms.     

一种乳酸菌胞外多糖糖链结构解析

以分离纯化得到的一种嗜热链球菌分泌的胞外多糖EPS03-1gm为研究对象, 采用气相色谱、分光光度及核磁共振技术对该多糖重复单位结构进行了解析. 结果表明, EPS03-1gm的单糖组成是葡萄糖和半乳糖, 不含糖醛酸和蛋白成分, 其重复单位中有4个糖基单元且都是6C糖. DEPT谱说明每个重复单位中有4个CH2, 用二维核磁共振谱和HMQC及HMBC谱分别对4个糖单元中的H和C进行了归属. 确定该多糖重复单位的糖链结构为: →3)-α-D-Galp-(1→3)-β-D-Galf-(1→3)-β-D-Glcp-(1→6)-β-D-Glcp-(1→.     

乌头碱的代谢产物去氧乌头碱的生物转化及其电喷雾串联质谱

采用人肠内细菌和乌头碱体外温孵的方法, 探讨去氧乌头碱在人肠内的生物转化. 利用离子阱和傅里叶变换离子回旋共振质谱直接分析去氧乌头碱的转化产物. 乌头类生物碱及其代谢产物在正离子电喷雾质谱条件下形成质子化分子([M+H]+), 通过多级串联质谱进行结构表征. 去氧乌头碱可被人肠内细菌转化, 通过脱酰基、脱甲基脱羟基以及酯化反应产生新型的单酯型、双酯型和脂类生物碱等10余种代谢产物. 双酯型的去氧乌头碱的毒性较高, 当它被肠内细菌转化为单酯型和脂类生物碱时会使其毒性降低.     

Immunomodulatory Efficacy-Mediated Anti-HCV and Anti-HBV Potential of Kefir Grains; Unveiling the In Vitro Antibacterial,Antifungal, and Wound Healing Activities

The utilization of fermented foods with health-promoting properties is becoming more popular around the world. Consequently, kefir, a fermented milk beverage made from kefir grains, was shown in numerous studies to be a probiotic product providing significant health benefits. Herein, we assessed the antibacterial and antifungal potential of kefir against a variety of pathogenic bacteria and fungi. This study also showed the effectiveness of kefir in healing wounds in human gastric epithelial cells (GES-1) by (80.78%) compared with control (55.75%) within 48 h. The quantitative polymerase chain reaction (qPCR) results of kefir-treated HCV- or HBV- infected cells found that 200 µg/mL of kefir can eliminate 92.36% of HCV and 75.71% of HBV relative to the untreated infected cells, whereas 800 µg/mL (the highest concentration) completely eradicated HCV and HBV. Moreover, the estimated IC₅₀ values of kefir, at which HCV and HBV were eradicated by 50%, were 63.84 ± 5.81 µg/mL and 224.02 ± 14.36 µg/mL, correspondingly. Kefir can significantly suppress the elevation of TNF-α and upregulate IL-10 and INF-γ in both treated HCV- and HBV-infected cells. High-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS) analysis of kefir revealed the presence of numerous active metabolites which mainly contribute to the antimicrobial, antiviral, and immunomodulatory activities. This study demonstrated, for the first time, the anti-HBV efficacy of kefir while also illustrating the immunomodulatory impact in the treated HBV-infected cells. Accordingly, kefir represents a potent antiviral agent against both viral hepatitis C and B, as well as having antimicrobial and wound healing potential.     

Detection of Bacterial α-l-Fucosidases with an Ortho-Quinone Methide-Based Probe and Mapping of the Probe-Protein Adducts

Fucosidases are associated with several pathological conditions and play an important role in the health of the human gut. For example, fucosidases have been shown to be indicators and/or involved in hepatocellular carcinoma, breast cancer, and helicobacter pylori infections. A prerequisite for the detection and profiling of fucosidases is the formation of a specific covalent linkage between the enzyme of interest and the activity-based probe (ABP). The most commonly used fucosidase ABPs are limited to only one of the classes of fucosidases, the retaining fucosidases. New approaches are needed that allow for the detection of the second class of fucosidases, the inverting type. Here, we report an ortho-quinone methide-based probe with an azide mini-tag that selectively labels both retaining and inverting bacterial α-l-fucosidases. Mass spectrometry-based intact protein and sequence analysis of a probe-labeled bacterial fucosidase revealed almost exclusive single labeling at two specific tryptophan residues outside of the active site. Furthermore, the probe could detect and image extracellular fucosidase activity on the surface of live bacteria.     

Fluoroquinolones’ Biological Activities against Laboratory Microbes and Cancer Cell Lines

Development of novel derivatives to rein in and fight bacteria have never been more demanding, as microbial resistance strains are alarmingly increasing. A multitude of new fluoroquinolones derivatives with an improved spectrum of activity and/or enhanced pharmacokinetics parameters have been widely explored. Reporting novel antimicrobial agents entails comparing their potential activity to their parent drugs; hence, parent fluoroquinolones have been used in research as positive controls. Given that these fluoroquinolones possess variable activities according to their generation, it is necessary to include parent compounds and market available antibiotics of the same class when investigating antimicrobial activity. Herein, we provide a detailed guide on the in vitro biological activity of fluoroquinolones based on experimental results published in the last years. This work permits researchers to compare and analyze potential fluoroquinolones as positive control agents and to evaluate changes occurring in their activities. More importantly, the selection of fluoroquinolones as positive controls by medicinal chemists when investigating novel FQs analogs must be correlated to the laboratory pathogen inquest for reliable results.