Cellulase-Linked Immunomagnetic Microbial Assay on Electrodes: Specific and Sensitive Detection of a Single Bacterial Cell.

Pathogen-associated infections represent one of the major threats to human health and require reliable methods for immediate and robust identification of pathogenic microorganisms. Here, an inexpensive cellulase-linked immunomagnetic methodology was developed for the specific and ultrasensitive analysis of bacteria at their single-cell levels within a 3 h procedure. Detection of a model bacterium, Escherichia coli, was performed in a sandwich reaction with E. coli-specific either aptamer or antibody (Ab)-modified magnetic beads (MBs) and Ab/aptamer reporter molecules linked to cellulase. The cellulase-labeled immuno-aptamer sandwich applied onto nitrocellulose-film-modified electrodes digested the film and changed its electrical conductivity. Electrode's chronocoulometric responses at 0.3 V, in the absence of any redox indicators, allowed a single E. coli cell detection and from 1 to 4 × 104 CFU mL-1 E. coli quantification. No interference/cross-reactivity from Salmonella enteritidis, Enterobacter agglomerans, Pseudomonas putida, Staphylococcus aureus, and Bacillus subtilis was observed when the assay was performed on Ab-modified MBs, and E. coli could be quantified in tap water and milk. This electrochemically label-free methodology is sufficiently fast, highly specific, and sensitive to be used in direct in-field applications. The assay can be adapted for specific detection of other bacterial strains of either the same or different species and offers new analytical tools for fast, specific, and reliable analysis of bacteria in the clinic, food, and environment.

Helminth infection in wild boars in Primorye, Russia.

Wild boars have a worldwide distribution and also have major economic, veterinary, and medical importance. Due to a small amount of data on the parasitic fauna of wild boars in the Russian Far East, especially in Prymorye territory, a post-mortem parasitic examination of 20 wild boars was provided. The general prevalence was 25%, and a total of six helminth species, including one larva stage, were found. The most prevalent helminth species were Gnathostoma doloresi (25%) and Metastrongylus elongatus (20%). Followed by Trichuris suis and Ascaris suum (15%). The lowest prevalence was registered for Cysticercus tenuicollis (the larvae stage of T. hydatigena). Parasites were found in each region, with the highest prevalence registered in the Chuguevskii region. Totally 100% of adult boars were positive for helminth infections, instead of 60% of young specimens. Some helminthes found (G. doloresi, T. suis, A. suum) have zoonotic potential and can be involved in the circulation of human parasitic diseases, especially in rural areas. Further research work on parasitic infections in wild boars in Prymorye is necessary due to the high prevalence of helminthes in wild boars.

The organo-metal-like nature of long-range conduction in cable bacteria.

Cable bacteria are filamentous, multicellular microorganisms that display an exceptional form of biological electron transport across centimeter-scale distances. Currents are guided through a network of nickel-containing protein fibers within the cell envelope. Still, the mechanism of long-range conduction remains unresolved. Here, we characterize the conductance of the fiber network under dry and wet, physiologically relevant, conditions. Our data reveal that the fiber conductivity is high (median value: 27 S cm-1; range: 2 to 564 S cm-1), does not show any redox signature, has a low thermal activation energy (Ea = 69 ± 23 meV), and is not affected by humidity or the presence of ions. These features set the nickel-based conduction mechanism in cable bacteria apart from other known forms of biological electron transport. As such, conduction resembles that of an organic semi-metal with a high charge carrier density. Our observation that biochemistry can synthesize an organo-metal-like structure opens the way for novel bio-based electronic technologies.

Femtomolar electroanalysis of a breast cancer biomarker HER-2/neu protein in human serum by the cellulase-linked sandwich assay on magnetic beads.

In cancer diagnostics, specific analysis of blood-circulating proteins biomarkers of cancer is often complicated both by their inherently low concentrations and by strong interference from serum/blood proteins. Here, we report a simple and robust electrochemical cellulase-linked sandwich assay on magnetic beads (MBs) for fM-sensitive analysis of the Human Epidermal growth factor Receptor-2 HER-2/neu protein that is over-expressed in most aggressive breast cancers. In the assay, a sandwich is assembled by capturing HER-2/neu on either antibody (Ab) or aptamer-modified MBs accompanied by reaction with the second Ab or aptamer labelled with cellulase. On application of the sandwiches assembled on MBs onto a cost-effective graphite electrode modified with an insulating nitrocellulose film, the cellulase label digests the film. This results in the pronounced changes in the electrical properties of the modified electrodes. The chronocoulometrically-measured extent of the produced changes was proportional to the 10-15-10-10 M HER-2/neu in the analyzed samples, and down to 1 fM of HER-2/neu could be detected in human serum samples in an overall less than 3 h assay. The developed simple and electrochemically label-free methodology is general and can be easily adapted for testing of any other protein.