Detection of anthrax protective antigen (PA) using europium labeled anti-PA monoclonal antibody and time-resolved fluorescence.

Inhalation anthrax is a rare but acute infectious disease following adsorption of Bacillus anthracis spores through the lungs. The disease has a high fatality rate if untreated, but early and correct diagnosis has a significant impact on case patient recovery. The early symptoms of inhalation anthrax are, however, non-specific and current anthrax diagnostics are primarily dependent upon culture and confirmatory real-time PCR. Consequently, there may be a significant delay in diagnosis and targeted treatment. Rapid, culture-independent diagnostic tests are therefore needed, particularly in the context of a large scale emergency response. The aim of this study was to evaluate the ability of monoclonal antibodies to detect anthrax toxin proteins that are secreted early in the course of B. anthracis infection using a time-resolved fluorescence (TRF) immunoassay. We selected monoclonal antibodies that could detect protective antigen (PA), as PA83 and also PA63 and LF in the lethal toxin complex. The assay reliable detection limit (RDL) was 6.63×10(-6)µM (0.551ng/ml) for PA83 and 2.51×10(-5)µM (1.58ng/ml) for PA63. Despite variable precision and accuracy of the assay, PA was detected in 9 out of 10 sera samples from anthrax confirmed case patients with cutaneous (n=7), inhalation (n=2), and gastrointestinal (n=1) disease. Anthrax Immune Globulin (AIG), which has been used in treatment of clinical anthrax, interfered with detection of PA. This study demonstrates a culture-independent method of diagnosing anthrax through the use of monoclonal antibodies to detect PA and LF in the lethal toxin complex.

Evaluation of automated and manual DNA purification methods for detecting Ricinus communis DNA during ricin investigations.

In April of 2013, letters addressed to the President of United States and other government officials were intercepted and found to be contaminated with ricin, heightening awareness about the need to evaluate laboratory methods for detecting ricin. This study evaluated commercial DNA purification methods for isolating Ricinus communis DNA as measured by real-time polymerase chain reaction (PCR). Four commercially available DNA purification methods (two automated, MagNA Pure compact and MagNA Pure LC, and two manual, MasterPure complete DNA and RNA purification kit and QIAamp DNA blood mini kit) were evaluated. We compared their ability to purify detectable levels of R. communis DNA from four different sample types, including crude preparations of ricin that could be used for biological crimes or acts of bioterrorism. Castor beans, spiked swabs, and spiked powders were included to simulate sample types typically tested during criminal and public health investigations. Real-time PCR analysis indicated that the QIAamp kit resulted in the greatest sensitivity for ricin preparations; the MasterPure kit performed best with spiked powders. The four methods detected equivalent levels by real-time PCR when castor beans and spiked swabs were used. All four methods yielded DNA free of PCR inhibitors as determined by the use of a PCR inhibition control assay. This study demonstrated that DNA purification methods differ in their ability to purify R. communis DNA; therefore, the purification method used for a given sample type can influence the sensitivity of real-time PCR assays for R. communis.

Comparison of DNA extraction kits for detection of Burkholderia pseudomallei in spiked human whole blood using real-time PCR.

Burkholderia pseudomallei, the etiologic agent of melioidosis, is endemic in northern Australia and Southeast Asia and can cause severe septicemia that may lead to death in 20% to 50% of cases. Rapid detection of B. pseudomallei infection is crucial for timely treatment of septic patients. This study evaluated seven commercially available DNA extraction kits to determine the relative recovery of B. pseudomallei DNA from spiked EDTA-containing human whole blood. The evaluation included three manual kits: the QIAamp DNA Mini kit, the QIAamp DNA Blood Mini kit, and the High Pure PCR Template Preparation kit; and four automated systems: the MagNAPure LC using the DNA Isolation Kit I, the MagNAPure Compact using the Nucleic Acid Isolation Kit I, and the QIAcube using the QIAamp DNA Mini kit and the QIAamp DNA Blood Mini kit. Detection of B. pseudomallei DNA extracted by each kit was performed using the B. pseudomallei specific type III secretion real-time PCR (TTS1) assay. Crossing threshold (C T ) values were used to compare the limit of detection and reproducibility of each kit. This study also compared the DNA concentrations and DNA purity yielded for each kit. The following kits consistently yielded DNA that produced a detectable signal from blood spiked with 5.5×10(4) colony forming units per mL: the High Pure PCR Template Preparation, QIAamp DNA Mini, MagNA Pure Compact, and the QIAcube running the QIAamp DNA Mini and QIAamp DNA Blood Mini kits. The High Pure PCR Template Preparation kit yielded the lowest limit of detection with spiked blood, but when this kit was used with blood from patients with confirmed cases of melioidosis, the bacteria was not reliably detected indicating blood may not be an optimal specimen.

Swab protocol for rapid laboratory diagnosis of cutaneous anthrax.

The clinical laboratory diagnosis of cutaneous anthrax is generally established by conventional microbiological methods, such as culture and directly straining smears of clinical specimens. However, these methods rely on recovery of viable Bacillus anthracis cells from swabs of cutaneous lesions and often yield negative results. This study developed a rapid protocol for detection of B. anthracis on clinical swabs. Three types of swabs, flocked-nylon, rayon, and polyester, were evaluated by 3 extraction methods, the swab extraction tube system (SETS), sonication, and vortex. Swabs were spiked with virulent B. anthracis cells, and the methods were compared for their efficiency over time by culture and real-time PCR. Viability testing indicated that the SETS yielded greater recovery of B. anthracis from 1-day-old swabs; however, reduced viability was consistent for the 3 extraction methods after 7 days and nonviability was consistent by 28 days. Real-time PCR analysis showed that the PCR amplification was not impacted by time for any swab extraction method and that the SETS method provided the lowest limit of detection. When evaluated using lesion swabs from cutaneous anthrax outbreaks, the SETS yielded culture-negative, PCR-positive results. This study demonstrated that swab extraction methods differ in their efficiency of recovery of viable B. anthracis cells. Furthermore, the results indicated that culture is not reliable for isolation of B. anthracis from swabs at ≥ 7 days. Thus, we recommend the use of the SETS method with subsequent testing by culture and real-time PCR for diagnosis of cutaneous anthrax from clinical swabs of cutaneous lesions.

Multi-platform comparison of ten commercial master mixes for probe-based real-time polymerase chain reaction detection of bioterrorism threat agents for surge preparedness.

The Centers for Disease Control and Prevention and United States Army Research Institute for Infectious Diseases have developed real-time PCR assays for the detection of bioterrorism threat agents. These assays all rely on a limited number of approved real-time PCR master mixes. Because the availability of these reagents is a critical element of bioterrorism preparedness, we undertook a joint national preparedness exercise to address the potential surge needs resulting from a large-scale bio-emergency. We identified 9 commercially-available potential alternatives to an existing approved master mix (LightCycler FastStart DNA Master HybProbes): the TaqMan Fast Universal PCR master mix, OmniMix HS, FAST qPCR master mix, EXPRESS qPCR SuperMix kit, QuantiFast Probe PCR kit, LightCycler FastStart DNA Master(PLUS) HybProbe, Brilliant II FAST qPCR master mix, ABsolute Fast QPCR Mix and the HotStart IT Taq master mix. The performances of these kits were evaluated by the use of real-time PCR assays for four bioterrorism threat agents: Bacillus anthracis, Brucella melitensis, Burkholderia mallei and Francisella tularensis. The master mixes were compared for target-specific detection levels, as well as consistency of results among three different real-time PCR platforms (LightCycler, SmartCycler and 7500 Fast Dx). Real-time PCR analysis revealed that all ten kits performed well for agent detection on the 7500 Fast Dx instrument; however, the QuantiFast Probe PCR kit yielded the most consistently positive results across multiple real-time PCR platforms. We report that certain combinations of commonly used master mixes and instruments are not as reliable as others at detecting low concentrations of target DNA. Furthermore, our study provides laboratories the option to select from the commercial kits we evaluated to suit their preparedness needs.

The etiology of severe acute gastroenteritis among adults visiting emergency departments in the United States.

BACKGROUND: Acute gastroenteritis (AGE) remains a common cause of clinic visits and hospitalizations in the United States, but the etiology is rarely determined. METHODS: We performed a prospective, multicenter emergency department-based study of adults with AGE. Subjects were interviewed on presentation and 3-4 weeks later. Serum samples, rectal swab specimens, and/or whole stool specimens were collected at presentation, and serum was collected 3-4 weeks later. Fecal specimens were tested for a comprehensive panel of viral, bacterial, and parasitic pathogens; serum was tested for calicivirus antibodies. RESULTS: Pathogens were detected in 25% of 364 subjects, including 49% who provided a whole stool specimen. The most commonly detected pathogens were norovirus (26%), rotavirus (18%), and Salmonella species (5.3%). Pathogens were detected significantly more often from whole stool samples versus a rectal swab specimen alone. Nine percent of subjects who provided whole stool samples had >1 pathogen identified. CONCLUSIONS: Viruses, especially noroviruses, play a major role as agents of severe diarrhea in adults. Further studies to confirm the unexpectedly high prevalence of rotaviruses and to explore the causes of illness among patients from whom a pathogen cannot be determined are needed. Studies of enteric pathogens should require the collection of whole stool samples.

Comparative evaluation of automated and manual commercial DNA extraction methods for detection of Francisella tularensis DNA from suspensions and spiked swabs by real-time polymerase chain reaction.

This study evaluated commercial automated and manual DNA extraction methods for the isolation of Francisella tularensis DNA suitable for real-time polymerase chain reaction (PCR) analysis from cell suspensions and spiked cotton, foam, and polyester swabs. Two automated methods, the MagNA Pure Compact and the QIAcube, were compared to 4 manual methods, the IT 1-2-3 DNA sample purification kit, the MasterPure Complete DNA and RNA purification kit, the QIAamp DNA blood mini kit, and the UltraClean Microbial DNA isolation kit. The methods were compared using 6 F. tularensis strains representing the 2 subspecies which cause the majority of reported cases of tularemia in humans. Cell viability testing of the DNA extracts showed that all 6 extraction methods efficiently inactivated F. tularensis at concentrations of ≤106 CFU/mL. Real-time PCR analysis using a multitarget 5' nuclease assay for F. tularensis revealed that the PCR sensitivity was equivalent using DNA extracted by the 2 automated methods and the manual MasterPure and QIAamp methods. These 4 methods resulted in significantly better levels of detection from bacterial suspensions and performed equivalently for spiked swab samples than the remaining 2. This study identifies optimal DNA extraction methods for processing swab specimens for the subsequent detection of F. tularensis DNA using real-time PCR assays. Furthermore, the results provide diagnostic laboratories with the option to select from 2 automated DNA extraction methods as suitable alternatives to manual methods for the isolation of DNA from F. tularensis.

Analysis of active ricin and castor bean proteins in a ricin preparation, castor bean extract, and surface swabs from a public health investigation.

In late February 2008, law enforcement officials in Las Vegas, Nevada, discovered in a hotel room, a copy of The Anarchist Cookbook, suspected castor beans and a "white powder" thought to be a preparation of ricin. Ricin is a deadly toxin from the seed of the castor bean plant (Ricinus communis). The United States regulates the possession, use, and transfer of ricin and it is the only substance considered a warfare agent in both the Chemical and the Biological Weapons Conventions. Six samples obtained from the hotel room were analyzed by laboratories at the Centers for Disease Control and Prevention using a panel of biological and mass spectrometric assays. The biological assays (real time-PCR, time resolved fluorescence and cytotoxicity) provided presumptive evidence of active ricin in each of the samples. This initial screen was followed by an in-depth analysis using a novel, state-of-the-art mass spectrometry-based ricin functional assay and high sensitivity tandem mass spectrometry for protein identification. Mass spectrometric analysis positively identified ricin and confirmed that in each of the samples it was enzymatically active. The tandem mass spectrometry analysis used here is the most selective method available to detect ricin toxin. In each sample, ricin was unequivocally identified along with other R. communis plant proteins, including the highly homologous protein RCA120. Although database searches using tandem mass spectra acquired from the samples indicated that additional controlled substances were not present in these samples, the mass spectrometric results did provide extensive detail about the sample contents. To the best of our knowledge following a review of the available literature, this report describes the most detailed analysis of a white powder for a public health or forensic investigation involving ricin.

Cross-platform evaluation of commercial real-time reverse transcription PCR master mix kits using a quantitative 5'nuclease assay for Ebola virus.

Selection of optimal reaction master mix reagents is essential to obtain the best performance with diagnostic real-time reverse transcription polymerase chain reaction (RT-PCR) assays. Every year the number of commercially available master mix kits increases, so it is prudent to periodically evaluate kits on the market. In this study we evaluated five commercial real-time RT-PCR master mix kits, the RealMasterMix RT-PCR ROX kit, the AgPath-ID One-Step RT-PCR kit, the SuperScript III Platinum One-step Quantitative RT-PCR system, the QuantiTect Probe RT-PCR kit, and the LightCycler RNA HybProbe amplification kit, using a 5'nuclease assay for Ebola virus. The kits were evaluated using the manufacturer's recommended conditions, as well as conditions which have been used with the Ebola virus assay during outbreaks. When evaluated for use in Ebola virus RNA detection, the AgPath-ID kit resulted in the greatest sensitivity in comparison to the other four kits. The efficacy of the AgPath-ID kit was instrument-independent in the five real-time PCR platforms tested. This study demonstrated that Ebola virus RNA detection was not equivalent among the master mix reagents studied and, thus, that this variable can affect real-time RT-PCR assay sensitivity. Furthermore, this study rates the master mix reagents for their suitability, providing diagnostic laboratories the option to select from these kits to suit their specific laboratory needs for real-time RT-PCR.

Optimal swab processing recovery method for detection of bioterrorism-related Francisella tularensis by real-time PCR.

Francisella tularensis, the etiological agent of tularemia, is regarded as a potential bioterrorism agent. The advent of bioterrorism has heightened awareness of the need for validated methods for processing environmental samples. In this study we determined the optimal method for processing environmental swabs for the recovery and subsequent detection of F. tularensis by the use of real-time PCR assays. Four swab processing recovery methods were compared: heat, sonication, vortexing, and the Swab Extraction Tube System (SETS). These methods were evaluated using cotton, foam, polyester and rayon swabs spiked with six pathogenic strains of F. tularensis. Real-time PCR analysis using a multi-target 5'nuclease assay for F. tularensis showed that the use of the SETS method resulted in the best limit of detection when evaluated using multiple strains of F. tularensis. We demonstrated also that the efficiency of F. tularensis recovery from swab specimens was not equivalent for all swab processing methodologies and, thus, that this variable can affect real-time PCR assay sensitivity. The effectiveness of the SETS method was independent of the automated DNA extraction method and real-time PCR platforms used. In conclusion, diagnostic laboratories can now potentially incorporate the SETS method into specimen processing protocols for the rapid and efficient detection of F. tularensis by real-time PCR during laboratory bioterrorism-related investigations.

Evaluation of automated and manual commercial DNA extraction methods for recovery of Brucella DNA from suspensions and spiked swabs.

This study evaluated automated and manual commercial DNA extraction methods for their ability to recover DNA from Brucella species in phosphate-buffered saline (PBS) suspension and from spiked swab specimens. Six extraction methods, representing several of the methodologies which are commercially available for DNA extraction, as well as representing various throughput capacities, were evaluated: the MagNA Pure Compact and the MagNA Pure LC instruments, the IT 1-2-3 DNA sample purification kit, the MasterPure Complete DNA and RNA purification kit, the QIAamp DNA blood mini kit, and the UltraClean microbial DNA isolation kit. These six extraction methods were performed upon three pathogenic Brucella species: B. abortus, B. melitensis, and B. suis. Viability testing of the DNA extracts indicated that all six extraction methods were efficient at inactivating virulent Brucella spp. Real-time PCR analysis using Brucella genus- and species-specific TaqMan assays revealed that use of the MasterPure kit resulted in superior levels of detection from bacterial suspensions, while the MasterPure kit and MagNA Pure Compact performed equally well for extraction of spiked swab samples. This study demonstrated that DNA extraction methodologies differ in their ability to recover Brucella DNA from PBS bacterial suspensions and from swab specimens and, thus, that the extraction method used for a given type of sample matrix can influence the sensitivity of real-time PCR assays for Brucella.

Evaluation of five commercial nucleic acid extraction kits for their ability to inactivate Bacillus anthracis spores and comparison of DNA yields from spores and spiked environmental samples.

This study evaluated five commercial extraction kits for their ability to recover DNA from Bacillus anthracis spores and spiked environmental samples. The kits evaluated represent the major types of methodologies which are commercially available for DNA or total nucleic acid extraction, and included the ChargeSwitch gDNA Mini Bacteria Kit, NucliSens Isolation Kit, Puregene Genomic DNA Purification Kit, QIAamp DNA Blood Mini Kit, and the UltraClean Microbial DNA Isolation Kit. Extraction methods were performed using the spores of eight virulent strains of B. anthracis. Viability testing of nucleic acid extracts showed that the UltraClean kit was the most efficient at depleting samples of live B. anthracis spores. TaqMan real-time PCR analysis revealed that the NucliSens, QIAamp and UltraClean kits yielded the best level of detection from spore suspensions. Comparisons of processed samples from spiked swabs and three powder types indicated that DNA extraction using the UltraClean kit resulted in the most consistently positive results and the lowest limit of detection. This study demonstrated that different nucleic extraction methodologies, represented here by various commercial extraction kits, differ in their ability to inactivate live B. anthracis spores as well as DNA yield and purity. In addition, the extraction method used can influence the sensitivity of real-time PCR assays for B. anthracis.

A simple method for the rapid removal of Bacillus anthracis spores from DNA preparations.

This study establishes a filtration method for the safe removal of Bacillus anthracis spores which may contaminate DNA preparations. Centrifugal filtration with 0.1-microm filter units can be used following extraction of DNA from B. anthracis spores to render samples safe without compromising the sensitivity of diagnostic real-time PCR assays for B. anthracis.

Gamma irradiation can be used to inactivate Bacillus anthracis spores without compromising the sensitivity of diagnostic assays.

The use of Bacillus anthracis as a biological weapon in 2001 heightened awareness of the need for validated methods for the inactivation of B. anthracis spores. This study determined the gamma irradiation dose for inactivating virulent B. anthracis spores in suspension and its effects on real-time PCR and antigen detection assays. Strains representing eight genetic groups of B. anthracis were exposed to gamma radiation, and it was found that subjecting spores at a concentration of 10(7) CFU/ml to a dose of 2.5 x 10(6) rads resulted in a 6-log-unit reduction of spore viability. TaqMan real-time PCR analysis of untreated versus irradiated Ames strain (K1694) spores showed that treatment significantly enhanced the detection of B. anthracis chromosomal DNA targets but had no significant effect on the ability to detect targets on the pXO1 and pXO2 plasmids of B. anthracis. When analyzed by an enzyme-linked immunosorbent assay (ELISA), irradiation affected the detection of B. anthracis spores in a direct ELISA but had no effect on the limit of detection in a sandwich ELISA. The results of this study showed that gamma irradiation-inactivated spores can be tested by real-time PCR or sandwich ELISA without decreasing the sensitivity of either type of assay. Furthermore, the results suggest that clinical and public health laboratories which test specimens for B. anthracis could potentially incorporate gamma irradiation into sample processing protocols without compromising the sensitivity of the B. anthracis assays.

Comparing serologic response against enteric pathogens with reported diarrhea to assess the impact of improved household drinking water quality.

We evaluated enteric infection serology as an alternative outcome measure to diarrhea prevalence in a randomized controlled trial of household-based drinking water treatment; 492 households were randomly assigned to 5 household-based water treatment interventions or control. Individuals were followed weekly over 52 weeks to measure diarrhea prevalence. Study subjects of age