Development of a nondestructive fluorescence-based enzymatic staining of microcolonies for enumerating bacterial contamination in filterable products

Active particles as mobile microelectrodes for selective bacteria electroporation and transport

Self-propelling micromotors are emerging as a promising micro- and nanoscale tool for single-cell analysis. We have recently shown that the field gradients necessary to manipulate matter via dielectrophoresis can be induced at the surface of a polarizable active ("self-propelling") metallodielectric Janus particle (JP) under an externally applied electric field, acting essentially as a mobile floating microelectrode. Here, we successfully demonstrated that the application of an external electric field can singularly trap and transport bacteria and can selectively electroporate the trapped bacteria. Selective electroporation, enabled by the local intensification of the electric field induced by the JP, was obtained under both continuous alternating current and pulsed signal conditions. This approach is generic and applicable to bacteria and JP, as well as a wide range of cell types and micromotor designs. Hence, it constitutes an important and novel experimental tool for single-cell analysis and targeted delivery.

Digital, Rapid, Accurate, and Label-Free Enumeration of Viable Microorganisms Enabled by Custom-Built On-Glass-Slide Culturing Device and Microscopic Scanning

Accurately measuring the number of viable microorganisms plays an essential role in microbiological studies. Since the conventional agar method of enumerating visible colonies is time-consuming and not accurate, efforts have been made towards overcoming these limitations by counting the invisible micro-colonies. However, none of studies on micro-colony counting was able to save significant time or provide accurate results. Herein, we developed an on-glass-slide cell culture device that enables rapid formation of micro-colonies on a 0.38 mm-thick gel film without suffering from nutrient and oxygen deprivation during bacteria culturing. Employing a phase contrast imaging setup, we achieved rapid microscopic scanning of micro-colonies within a large sample area on the thin film without the need of fluorescent staining. Using Escherichia coli (E. coli) as a demonstration, our technique was able to shorten the culturing time to within 5 h and automatically enumerate the micro-colonies from the phase contrast images. Moreover, this method delivered more accurate counts than the conventional visible colony counting methods. Due to these advantages, this imaging-based micro-colony enumeration technique provides a new platform for the quantification of viable microorganisms.

The rebirth of culture in microbiology through the example of culturomics to study human gut microbiota

Bacterial culture was the first method used to describe the human microbiota, but this method is considered outdated by many researchers. Metagenomics studies have since been applied to clinical microbiology; however, a "dark matter" of prokaryotes, which corresponds to a hole in our knowledge and includes minority bacterial populations, is not elucidated by these studies. By replicating the natural environment, environmental microbiologists were the first to reduce the "great plate count anomaly," which corresponds to the difference between microscopic and culture counts. The revolution in bacterial identification also allowed rapid progress. 16S rRNA bacterial identification allowed the accurate identification of new species. Mass spectrometry allowed the high-throughput identification of rare species and the detection of new species. By using these methods and by increasing the number of culture conditions, culturomics allowed the extension of the known human gut repertoire to levels equivalent to those of pyrosequencing. Finally, taxonogenomics strategies became an emerging method for describing new species, associating the genome sequence of the bacteria systematically. We provide a comprehensive review on these topics, demonstrating that both empirical and hypothesis-driven approaches will enable a rapid increase in the identification of the human prokaryote repertoire.

Anisotropic core-shell Fe3 O4 @Au magnetic nanoparticles and the effect of the immunomagnetic separation volume on the capture efficiency

The aim of this study was to synthesize in high product yield of anisotropic core-shell Fe3 O4@Au magnetic nanoparticles and to investigate the effect of the immunomagnetic separation (IMS) volume on the capture efficiency. For these purposes and for the first time, we synthesized polyhedral magnetic nanoparticles composed of Fe3 O4 core Au shell. To synthesize magnetic gold anisotropic core-shell particles, the seed-mediated synthetic method was carried out. By choosing an appropriate amount of iron particles and growth solution the fine control of the seed-mediated approach is enabled. This led to the high product yield of anisotropic nanoparticles. The magnetic separation of these nanoparticles was easily accomplished, and the resulting nanoparticles were characterized with transmission electron microscopy (TEM), ultraviolet visible spectroscopy (UV–vis), near edge absorption fine structure (NEXAFS) spectroscopy, and X-ray diffraction (XRD). Additionally, the magnetic properties of the nanoparticles were examined. The magnetic nanoparticles (MNPs) were modified with antibody and interacted with Escherichia coli (E. coli). The high capture efficiency between the magnetic nanoparticles and E. coli is evidenced by SEM images. The capture efficiency decreases with an increase of volumes, and the highest capture efficiency was observed for E. coli in an experiment volume of 100 μL for magnetic nanoparticles. The percentage of captured E. coli for polyhedral nanoparticles was found to be approximately 95 % and for spherical nanoparticles 88 %, respectively.

Fluorescence-based rapid detection of microbiological contaminants in water samples

Microbiological contamination of process waters is a current issue for pharmaceutical industries. Traditional methods require several days to obtain results; therefore, rapid microbiological methods are widely requested to shorten time-to-result. Milliflex Quantum was developed for the rapid detection and enumeration of microorganisms in filterable samples. It combines membrane filtration to universal fluorescent staining of viable microorganisms. This new alternative method was validated using European and United States Pharmacopeia definitions, with sterile water and/or sterile water artificially contaminated with microorganisms. The Milliflex Quantum method was demonstrated to be reliable, robust, specific, accurate, and linear over the whole range of assays following these guidelines. The Milliflex Quantum system was challenged to detect natural contaminants in different types of pharmaceutical purified process waters. Milliflex Quantum was demonstrated to detect accurately contaminants 3- to 7-fold faster than traditional membrane filtration method. The staining procedure is nondestructive allowing downstream identification following a positive result. The Milliflex Quantum offers a fast, sensitive, and robust alternative to the compendial membrane filtration method.

A comparison of TO-PRO-1 iodide and 5-CFDA-AM staining methods for assessing viability of planktonic algae with epifluorescence microscopy

Two fluorescent dyes, TO-PRO-1 iodide and 5-CFDA-AM, were evaluated for LIVE/DEAD assessment of unicellular marine algae Brachiomonas submarina and Tetraselmis suecica. Epifluorescence microscopy was used to estimate cell viability in predetermined mixtures of viable and non-viable algal cells and validated using microplate growth assay as reference measurements. On average, 5-CFDA-AM underestimated live cell abundance by ~25% compared with viability estimated by the growth assay, whereas TO-PRO-1 iodide provided accurate viability estimates. Furthermore, viability estimates based on staining with TO-PRO-1 iodide were not affected by a storage period of up to one month in -80°C, making the assay a good candidate for routine assessment of phytoplankton populations in field and laboratory studies.