Simultaneous Gram and viability staining on activated sludge exposed to erythromycin: 3D CLSM time-lapse imaging of bacterial disintegration

Immunofluorescent-aggregation assay based on anti-Salmonella typhimurium IgG-AuNCs, for rapid detection of Salmonella typhimurium

Sensitive and rapid detection of pathogenic bacteria plays an important role in avoiding food poisoning. However, the practical application value of conventional assays for detection of foodborne bacteria, are limited by major drawbacks; these include the laboriousness of pure culture preparation, complexity of DNA extraction for polymerase chain reaction, and low sensitivity of enzyme-linked immunosorbent assay. Herein, we designed a non-complex strategy for the sensitive, quantitative, and rapid detection of Salmonella typhimurium with high specificity, using an anti-Salmonella typhimurium IgG-AuNC-based immunofluorescent-aggregation assay. Salmonella typhimurium was agglutinated with fluorescent anti-Salmonella typhimurium IgG-AuNC on a glass slide, and observed using a fluorescence microscope with photoexcitation and photoemission at 560 nm and 620 nm, respectively. Under optimized reaction conditions, the AuNC-based immunofluorescent-aggregation assay had a determination range between 7.0 × 10³ and 3.0 × 10⁸ CFU/mL, a limit of detection of 1.0 × 10³ CFU/mL and an assay response time of 3 min. The technique delivered good results in assessing real samples.

Vancomycin sorption on activated sludge Gram+ bacteria rather than on EPS; 3D Confocal Laser Scanning Microscopy time-lapse imaging

Antibiotics-bacteria interactions depend on antibiotic concentration at the scale of bacteria. This study investigates how vancomycin penetrates into activated sludge flocs and can be sorbed on the bacteria and extracellular polymeric substances (EPS). The 3D structure of flocs was imaged using EPS autofluorescence. The green fluorescent BODIPY^® FL vancomycin was introduced in a microscopic chamber containing activated sludge and penetration of vancomycin into the flocs by diffusion was observed using time-lapse microscopy. The penetration depended on the floc structure, as long and large pores could go through the whole flocs making preferential path. The antibiotic concentration into the flocs was also found to depend on the sorption rate. BODIPY^® FL vancomycin was found to bind preferentially into Gram⁺ bacteria than on EPS. The vancomycin adsorption constant on bacteria according to the linear adsorption model, Kd_bacteria was estimated to be 5 times higher (SD 2.6) than the adsorption constant on EPS Kd_EPS. These results suggest that antibiotic removal by sorption into wastewater treatment plants could change according to the amount of bacteria in the sludge. Moreover, antibiotic concentration at the scale of bacteria could be significantly higher than the concentration in the bulk solution and this should be taken into account when studying antibiotic activity or biodegradation.

Polyphasic characterization of bacteria obtained from upland rice cultivated in Cerrado soil

This work aimed to characterize 20 isolates obtained from upland rice plants, based on phenotypic (morphology, enzymatic activity, inorganic phosphate solubilization, carbon source use, antagonism), genotypic assays (16S rRNA sequencing) and plant growth promotion. Results showed a great morphological, metabolic and genetic variability among bacterial isolates. All isolates showed positive activity for catalase and protease enzymes and, 90% of the isolates showed positive activity for amylase, catalase and, nitrogenase. All isolates were able to metabolize sucrose and malic acid in contrast with mannitol, which was metabolized only by one isolate. For the other carbon sources, we observed a great variability in its use by the isolates. Most isolates showed antibiosis against Rhizoctonia solani (75%) and Sclerotinia sclerotiorum (55%) and, 50% of them showed antibiosis against both pathogens. Six isolates showed simultaneous ability of antibiosis, inorganic phosphate solubilization and protease activity. Based on phylogenetic analysis of the 16S rRNA gene all the isolates belong to Bacillus genus. Under greenhouse conditions, two isolates (S4 and S22) improved to about 24%, 25%, 30% and 31% the Total N, leaf area, shoot dry weight and root dry weight, respectively, of rice plants, indicating that they should be tested for this ability under field conditions.

Confocal time lapse imaging as an efficient method for the cytocompatibility evaluation of dental composites

It is generally accepted that in vitro cell material interaction is a useful criterion in the evaluation of dental material biocompatibility. The objective of this study was to use 3D CLSM time lapse confocal imaging to assess the in vitro biocompatibility of dental composites. This method provides an accurate and sensitive indication of viable cell rate in contact with dental composite extracts. The ELS extra low shrinkage, a dental composite used for direct restoration, has been taken as example. In vitro assessment was performed on cultured primary human gingival fibroblast cells using Live/Dead staining. Images were obtained with the FV10i confocal biological inverted system and analyzed with the FV10-ASW 3.1 Software. Image analysis showed a very slight cytotoxicity in the presence of the tested composite after 5 hours of time lapse. A slight decrease of cell viability was shown in contact with the tested composite extracts compared to control cells. The findings highlighted the use of 3D CLSM time lapse imaging as a sensitive method to qualitatively and quantitatively evaluate the biocompatibility behavior of dental composites.

Dynamic assessment of the floc morphology, bacterial diversity, and integron content of an activated sludge reactor processing hospital effluent

The treatment of hospital effluents (HE) is a major concern, as they are suspected of disseminating drugs and antibiotic resistance determinants in the environment. In order to assess HE influence on wastewater treatment plant biomass, lab-scale conventional activated sludge systems (CAS) were continuously fed with real HE or urban effluent as a control. To gain insights into the main hurdles linked to HE treatment, we conducted a multiparameter study using classical physicochemical characterization, phase contrast and confocal laser scaning microscopy, and molecular biology (i.e., pyrosequencing) tools. HE caused erosion of floc structure and the production of extracellular polymeric substances attributed to the development of floc-forming bacteria. Adaptation of the sludge bacterial community to the HE characteristics, thus maintaining the purification performance of the biomass, was observed. Finally, the comparative metagenomic analysis of the CAS showed that HE treatment resulted in an increase of class 1 resistance integrons (RIs) and the introduction of Pseudomonas spp. into the bacterial community. HE treatment did not reduce the CAS process performance; nevertheless it increases the risk of dissemination into the environment of bacterial species and genetic determinants (RIs) involved in antibiotic resistance acquisition.

Toxicity evaluation of two dental composites: three-dimensional confocal laser scanning microscopy time-lapse imaging of cell behavior

The purpose of this study was to investigate the in vitro biocompatibility of two dental composites (namely A and B) with similar chemical composition used for direct restoration using three-dimensional confocal laser scanning microscopy (CLSM) time-lapse imaging. Time-lapse imaging was performed on cultured human HGF-1 fibroblast-like cells after staining using Live/Dead®. Image analysis showed a higher mortality rate in the presence of composite A than composite B. The viability rate decreased in a time-dependent manner during the 5 h of exposure. Morphological alterations were associated with toxic effects; cells were enlarged and more rounded in the presence of composite A as shown by F-actin and cell nuclei staining. Resazurin assay was used to confirm the active potential of composites in cell metabolism; results showed severe cytotoxic effects in the presence of both no light-curing composites after 24 h of direct contact. However, extracts of polymerized composites induced a moderate decrease in cell metabolism after the same incubation period. Composite B was significantly better tolerated than composite A at all investigated end points and all time points. The finding confirmed that the used CLSM method was sufficiently sensitive to differentiate the biocompatibility behavior of two composites based on similar methacrylate monomers.