Bacillus globigii Bugbeads: A Model Simulant of a Bacterial Spore

Detection and tracking of a novel genetically tagged biological simulant in the environment

A variant of Bacillus thuringiensis subsp. kurstaki containing a single, stable copy of a uniquely amplifiable DNA oligomer integrated into the genome for tracking the fate of biological agents in the environment was developed. The use of genetically tagged spores overcomes the ambiguity of discerning the test material from pre-existing environmental microflora or from previously released background material. In this study, we demonstrate the utility of the genetically "barcoded" simulant in a controlled indoor setting and in an outdoor release. In an ambient breeze tunnel test, spores deposited on tiles were reaerosolized and detected by real-time PCR at distances of 30 m from the point of deposition. Real-time PCR signals were inversely correlated with distance from the seeded tiles. An outdoor release of powdered spore simulant at Aberdeen Proving Ground, Edgewood, MD, was monitored from a distance by a light detection and ranging (LIDAR) laser. Over a 2-week period, an array of air sampling units collected samples were analyzed for the presence of viable spores and using barcode-specific real-time PCR assays. Barcoded B. thuringiensis subsp. kurstaki spores were unambiguously identified on the day of the release, and viable material was recovered in a pattern consistent with the cloud track predicted by prevailing winds and by data tracks provided by the LIDAR system. Finally, the real-time PCR assays successfully differentiated barcoded B. thuringiensis subsp. kurstaki spores from wild-type spores under field conditions.

Preliminary development of DNA aptamer-Fc conjugate opsonins

Encapsulated bacteria such as virulent strains of Bacillus anthracis impair phagocytosis with their capsules unless opsonized by antibodies. Poly-gamma-D-glutamic acid (gamma-PDGA) is the major component of the B. anthracis capsule. In this work, poly-alpha-D-glutamic acid (alpha-PDGA)-coated magnetic beads (MBs) were used as surrogates to simulate vegetative B. anthracis cells and avoid the hazards of working with virulent bacteria. DNA aptamers were developed against the alpha-linked PDGA-MBs and sequenced. Four of the most frequent candidate aptamer sequences in the pool were coupled at their 5' ends to Fc fragments of murine IgG to act as artificial antibodies. The effects of candidate aptamer-Fc conjugate addition on macrophage attachment and internalization of alpha-PDGA-MBs were tested on P388D1 and RAW 264.7 murine macrophage lines by spectrofluorometric and image analysis techniques. P388D1 cells were not able to internalize the alpha-PDGA-MBs, but attachment to alpha-PDGA-MBs was enhanced by the conjugates to varying degrees. Ingestion of alpha-PDGA-MBs by RAW 264.7 cells in the presence of several different candidate aptamer-Fc conjugates demonstrated a statistically significant (p < 0.01) increase in phagocytic index (P.I.) up to threefold in the first 30 min of exposure to alpha-PDGA-MBs. This preliminary study using alpha-linked instead of gamma-linked PDGA provides proof-of-concept for future work in the new area of hybrid DNA aptamer-protein constructs as potential opsonins.

Implications of limits of detection of various methods for Bacillus anthracis in computing risks to human health

Used for decades for biological warfare, Bacillus anthracis (category A agent) has proven to be highly stable and lethal. Quantitative risk assessment modeling requires descriptive statistics of the limit of detection to assist in defining the exposure. Furthermore, the sensitivities of various detection methods in environmental matrices are vital information for first responders. A literature review of peer-reviewed journal articles related to methods for detection of B. anthracis was undertaken. Articles focused on the development or evaluation of various detection approaches, such as PCR, real-time PCR, immunoassay, etc. Real-time PCR and PCR were the most sensitive methods for the detection of B. anthracis, with median instrument limits of detection of 430 and 440 cells/ml, respectively. There were very few peer-reviewed articles on the detection methods for B. anthracis in the environment. The most sensitive limits of detection for the environmental samples were 0.1 CFU/g for soil using PCR-enzyme-linked immunosorbent assay (ELISA), 17 CFU/liter for air using an ELISA-biochip system, 1 CFU/liter for water using cultivation, and 1 CFU/cm(2) for stainless steel fomites using cultivation. An exponential dose-response model for the inhalation of B. anthracis estimates of risk at concentrations equal to the environmental limit of detection determined the probability of death if untreated to be as high as 0.520. Though more data on the environmental limit of detection would improve the assumptions made for the risk assessment, this study's quantification of the risk posed by current limitations in the knowledge of detection methods should be considered when employing those methods in environmental monitoring and cleanup strategies.

Magnetic microbead-based electrochemical immunoassays

This review provides a summary of recent works concerning electrochemical immunoassays using magnetic microbeads as a solid phase. Recent research activity has led to innovative and powerful detection strategies that have been resulted in sensitive electrochemical detection. Coupling of magnetic microbeads with highly sensitive electrochemical detection provides a useful analytical method for environmental evaluation and clinical diagnostics, etc. The huge surface area and high dispersion capability of magnetic microbeads strongly contributes towards the development of new sensitive, rapid, user-friendly, and miniaturized electrochemical immunoassay systems. Moreover, the immunocomplexes formed on the magnetic microbead surface can be easily detected without pretreatment steps such as preconcentration or purification, which are normally required for standard methods. The discussion in this review is organized in two main subjects that include magnetic-microbead-based assays using enzyme labels and nanoparticle tags.

Rapid ambient mass spectrometric profiling of intact, untreated bacteria using desorption electrospray ionization

Desorption electrospray ionization (DESI) allows the rapid acquisition of highly reproducible mass spectra from intact microorganisms under ambient conditions; application of principal component analysis to the data allows sub-species differentiation.

Bacillus anthracis: toxicology, epidemiology and current rapid-detection methods

B. anthracis, the causative agent for anthrax, has been well studied for over 150 years. Due to the genetic similarities among various Bacillus species, as well as its existence in both a spore form and a vegetative state, the detection and specific identification of B. anthracis have been proven to require complex techniques and/or laborious methods. With the heightened interest in the organism as a potential biological threat agent, a large number of interesting detection technologies have recently been developed, including methods involving immunological and nucleic acid-based assay formats. The technologies range from culture-based methods to portable Total Analysis Systems based on real-time PCR. This review with 170 references provides a brief background on the toxicology and epidemiology of B. anthracis, discusses challenges associated with its detection related to genetic similarities to other species, and reviews immunological and, with greater emphasis, nucleic acid-based detection systems.