Robotic Nucleic Acid Isolation Using a Magnetic Bead Resin and an Automated Liquid Handler for Biological Agent Simulants

Rapid-viability PCR method for detection of live, virulent Bacillus anthracis in environmental samples

In the event of a biothreat agent release, hundreds of samples would need to be rapidly processed to characterize the extent of contamination and determine the efficacy of remediation activities. Current biological agent identification and viability determination methods are both labor- and time-intensive such that turnaround time for confirmed results is typically several days. In order to alleviate this issue, automated, high-throughput sample processing methods were developed in which real-time PCR analysis is conducted on samples before and after incubation. The method, referred to as rapid-viability (RV)-PCR, uses the change in cycle threshold after incubation to detect the presence of live organisms. In this article, we report a novel RV-PCR method for detection of live, virulent Bacillus anthracis, in which the incubation time was reduced from 14 h to 9 h, bringing the total turnaround time for results below 15 h. The method incorporates a magnetic bead-based DNA extraction and purification step prior to PCR analysis, as well as specific real-time PCR assays for the B. anthracis chromosome and pXO1 and pXO2 plasmids. A single laboratory verification of the optimized method applied to the detection of virulent B. anthracis in environmental samples was conducted and showed a detection level of 10 to 99 CFU/sample with both manual and automated RV-PCR methods in the presence of various challenges. Experiments exploring the relationship between the incubation time and the limit of detection suggest that the method could be further shortened by an additional 2 to 3 h for relatively clean samples.

Evaluation of the Cepheid GeneXpert system for detecting Bacillus anthracis

AIMS

The Cepheid GeneXpert is a four-site, automated sample preparation and real-time PCR detection system. In this study, the capability of the GeneXpert to isolate and detect nucleic acid from Bacillus anthracis Ames spores was assessed.

METHODS AND RESULTS

A four-plex, dried-down bead cartridge containing PCR reagents specific for the pXO1 and pXO2 plasmids as well as sample processing and inhibition controls was evaluated. For B. anthracis Ames spores harbouring pXO1 and pXO2, samples containing 68 CFU per ml (148 spores per ml) were positive in all four replicates. A limited cross-reactivity panel, which included closely related Bacillus species, was also tested to determine the specificity of the pXO1 and pXO2 assays. No cross-reactivity occurred. Further, B. anthracis Sterne spore samples were analysed to compare results when processed using the GeneXpert to those run directly on the Cepheid SmartCycler without sample processing. The GeneXpert detection capability was three logs lower than the SmartCycler indicating the benefit of incorporating a nucleic acid extraction procedure.

CONCLUSIONS

This study demonstrates that the GeneXpert is a rapid and reliable system for simultaneously detecting the B. anthracis virulence plasmids pXO1 and pXO2.

SIGNIFICANCE AND IMPACT OF THE STUDY

The GeneXpert is the only platform currently available that is capable of both nucleic acid purification and real-time PCR detection enclosed within a single system. Further, all sample manipulations are automated, thus reducing errors associated with manual processing.

Automated Screening for Biological Weapons in Homeland Defense

Biological threat detection programs that collect air samples and monitor for large-scale release of biowarfare agents generate large numbers of samples that must be quickly and accurately screened for the presence of biological agents. An impediment to the rapid analysis of large numbers of environmental biological samples is that manual laboratory processes are time-consuming and require resources to maintain infrastructure, trained personnel, and adequate supplies of testing reagents. An ideal screening system would be capable of processing multiple samples rapidly, cost-effectively, and with minimal personnel. In the present study, we evaluated the Automated Biological Agent Testing System (ABATS) to explore the capability of automation to increase sample throughput, maximize system accuracy, and reduce the analysis costs associated with biological threat agent screening in environmental samples. This study demonstrates the utility of this concept and the potential of an automated system to address the growing environmental monitoring needs of the United States.