Use of high-resolution melting and melting temperature-shift assays for specific detection and identification of Bacillus anthracis based on single nucleotide discrimination

Enzyme-Linked Phage Receptor Binding Protein Assays (ELPRA) Enable Identification of Bacillus anthracis Colonies

Bacteriophage receptor binding proteins (RBPs) are employed by viruses to recognize specific surface structures on bacterial host cells. Recombinant RBPs have been utilized for detection of several pathogens, typically as fusions with reporter enzymes or fluorescent proteins. Identification of Bacillus anthracis, the etiological agent of anthrax, can be difficult because of the bacterium's close relationship with other species of the Bacillus cereussensu lato group. Here, we facilitated the identification of B. anthracis using two implementations of enzyme-linked phage receptor binding protein assays (ELPRA). We developed a single-tube centrifugation assay simplifying the rapid analysis of suspect colonies. A second assay enables identification of suspect colonies from mixed overgrown solid (agar) media derived from the complex matrix soil. Thus, these tests identified vegetative cells of B. anthracis with little processing time and may support or confirm pathogen detection by molecular methods such as polymerase chain reaction.

A novel A > G polymorphism in the intron 2 of TBX3 gene is significantly associated with body size in donkeys

T-box transcription factor 3 (TBX3) gene encodes a transcriptional suppressor and plays an important role in embryonic development, which belongs to the T-box family. TBX3 also has been found to be associated with body size traits in horse that is a relative of donkey. Therefore, TBX3 is considered as a promising candidate gene for economic traits of donkey. This study aimed to reveal the significant variation of TBX3 gene in Dezhou donkey and explores the relationship between genotypes and body sizes. In this study, an A > G mutation was found in the intron 2 of TBX3 gene by sequencing, and three genotypes (AA, GG and AG) were identified in 380 Dezhou donkey individuals with Tm-shift method. Association analysis illustrated that there were significant differences between AA and GG genotype in body length, body height, chest depth, chest circumference, body weight, hucklebone width and rump length. Our results demonstrated that the polymorphism of TBX3 is significantly associated with body size traits, which can serve as a marker to improve donkey production performance.

Establishment of a Tm-shift Method for Detection of Cat-Derived Hookworms

Melting temperature shift (T_m-shift) is a new detection method that analyze the melting curve on real-time PCR thermocycler using SYBR Green I fluorescent dye. To establish a T_m-shift method for the detection of Ancylostoma ceylanicum and A. tubaeforme in cats, specific primers, with GC tail of unequal length attached to their 5′ end, were designed based on 2 SNP loci (ITS101 and ITS296) of the internal transcribed spacer 1 (ITS1) sequences. The standard curve of T_m-shift was established using the standard plasmids of A. ceylanicum (AceP) and A. tubaeforme (AtuP). The T_m-shift method stability, sensitivity, and accuracy were tested with reference to the standard curve, and clinical fecal samples were also examined. The results demonstrated that the 2 sets of primers based on the 2 SNPs could accurately distinguish between A. ceylanicum and A. tubaeforme. The coefficient of variation (CV) of T_m-values of AceP and AtuP was 0.07% and 0.06% in ITS101 and was 0.06% and 0.08% in ITS296, respectively. The minimum detectable DNA concentration was 5.22×10⁻⁶ and 5.28×10⁻⁶ ng/μl samples of AceP and AtuP, respectively. The accuracy of T_m-shift method reached 100% based on examination of 10 hookworm DNA samples with known species. In the clinical detection of hookworm in 69 stray cat fecal sample, the T_m-shift detection results were consistent with the microscopic examination and successfully differentiated between the 2-hookworm species. In conclusion, the developed method is a rapid, sensitive and accurate technique and can provide a promising tool for clinical detection and epidemiological investigation of cat-derived hookworms.

Tm-Shift Detection of Dog-Derived Ancylostoma ceylanicum and A. caninum

To develop a T_m-shift method for detection of dog-derived Ancylostoma ceylanicum and A. caninum, three sets of primers were designed based on three SNPs (ITS71, ITS197, and ITS296) of their internal transcribed spacer 1 (ITS1) sequences. The detection effect of the T_m-shift was assessed through the stability, sensitivity, accuracy test, and clinical detection. The results showed that these three sets of primers could distinguish accurately between A. ceylanicum and A. caninum. The coefficient of variation in their T_m values on the three SNPs was 0.09% and 0.15% (ITS71), 0.18% and 0.14% (ITS197), and 0.13% and 0.07% (ITS296), respectively. The lowest detectable concentration of standard plasmids for A. ceylanicum and A. caninum was 5.33 × 10⁻⁶ ng/μL and 5.03 × 10⁻⁶ ng/μL. The T_m-shift results of ten DNA samples from the dog-derived hookworms were consistent with their known species. In the clinical detection of 50 fecal samples from stray dogs, the positive rate of hookworm detected by T_m-shift (42%) was significantly higher than that by microscopic examination (34%), and the former can identify the Ancylostoma species. It is concluded that the T_m-shift method is rapid, specific, sensitive, and suitable for the clinical detection and zoonotic risk assessment of the dog-derived hookworm.

Development of T m -shift genotyping method for detection of cat-derived Giardia lamblia

To develop T _m -shift genotyping method for detection of cat-derived Giardia lamblia, two sets of primers with two GC-rich tails of unequal length attached to their 5'-end were designed according to two SNPs (BG434 and BG170) of β-giardin (bg) gene, and specific PCR products were identified by inspection of a melting curve on real-time PCR thermocycler. A series of experiments on the stability, sensitivity, and accuracy of T _m -shift method was tested, and clinical samples were also detected. The results showed that two sets of primers based on SNP could distinguish accurately between assemblages A and F. Coefficient of variation of T _m values of assemblage A and F was 0.14 and 0.07% in BG434 and 0.10 and 0.11% in BG170, respectively. The lowest detection concentration was 4.52 × 10^-5 and 4.88 × 10^-5 ng/μL samples of assemblage A and F standard plasmids. The T _m -shift genotyping results of ten DNA samples from the cat-derived G. lamblia were consistent with their known genotypes. The detection rate of clinical samples by T _m -shift was higher than that by microscopy, and their genotyping results were in complete accordance with sequencing results. It is concluded that the T _m -shift genotyping method is rapid, specific, and sensitive and may provide a new technological mean for molecular detection and epidemiological investigation of the cat-derived G. lamblia.

Nested Machine Learning Facilitates Increased Sequence Content for Large-Scale Automated High Resolution Melt Genotyping

High Resolution Melt (HRM) is a versatile and rapid post-PCR DNA analysis technique primarily used to differentiate sequence variants among only a few short amplicons. We recently developed a one-vs-one support vector machine algorithm (OVO SVM) that enables the use of HRM for identifying numerous short amplicon sequences automatically and reliably. Herein, we set out to maximize the discriminating power of HRM + SVM for a single genetic locus by testing longer amplicons harboring significantly more sequence information. Using universal primers that amplify the hypervariable bacterial 16 S rRNA gene as a model system, we found that long amplicons yield more complex HRM curve shapes. We developed a novel nested OVO SVM approach to take advantage of this feature and achieved 100% accuracy in the identification of 37 clinically relevant bacteria in Leave-One-Out-Cross-Validation. A subset of organisms were independently tested. Those from pure culture were identified with high accuracy, while those tested directly from clinical blood bottles displayed more technical variability and reduced accuracy. Our findings demonstrate that long sequences can be accurately and automatically profiled by HRM with a novel nested SVM approach and suggest that clinical sample testing is feasible with further optimization.

Evaluation of up-converting phosphor technology-based lateral flow strips for rapid detection of Bacillus anthracis Spore, Brucella spp., and Yersinia pestis

Bacillus anthracis, Brucella spp., and Yersinia pestis are zoonotic pathogens and biowarfare- or bioterrorism-associated agents that must be detected rapidly on-site from various samples (e.g., viscera and powders). An up-converting phosphor technology-based lateral flow (UPT-LF) strip was developed as a point-of-care testing (POCT) to satisfy the requirements of first-level emergency response. We developed UPT-LF POCT to quantitatively detect the three pathogens within 15 min. Sample and operation-error tolerances of the assay were comprehensively evaluated. The sensitivity of UPT-LF assay to bacterial detection reached 10(4) cfu · mL(-1) (100 cfu/test), with a linear quantitative range of 4 to 6 orders of magnitude. Results revealed that the UPT-LF assay exhibited a high specificity with the absence of false-positive results even at 10(9) cfu · mL(-1) of non-specific bacterial contamination. The assay could tolerate samples with a wide pH range (2 to 12), high ion strengths (≥ 4 mol · L(-1) of NaCl), high viscosities (≤ 25 mg · mL(-1) of PEG20000 or ≥ 20% of glycerol), and high concentrations of bio-macromolecule (≤ 200 mg · mL(-1) of bovine serum albumin or ≥ 80 mg · mL(-1) of casein). The influence of various types of powders and viscera (fresh and decomposed) on the performance of UPT-LF assay was determined. The operational error of liquid measurement exhibited few effects on sensitivity and specificity. The developed UPT-LF POCT assay is applicable under field conditions with excellent tolerance to sample complexity and operational error.

Genetic diversity of Bacillus anthracis in Europe: genotyping methods in forensic and epidemiologic investigations

Bacillus anthracis, the etiological agent of anthrax, a zoonosis relatively common throughout the world, can be used as an agent of bioterrorism. In naturally occurring outbreaks and in criminal release of this pathogen, a fast and accurate diagnosis is crucial to an effective response. Microbiological forensics and epidemiologic investigations increasingly rely on molecular markers, such as polymorphisms in DNA sequence, to obtain reliable information regarding the identification or source of a suspicious strain. Over the past decade, significant research efforts have been undertaken to develop genotyping methods with increased power to differentiate B. anthracis strains. A growing number of DNA signatures have been identified and used to survey B. anthracis diversity in nature, leading to rapid advances in our understanding of the global population of this pathogen. This article provides an overview of the different phylogenetic subgroups distributed across the world, with a particular focus on Europe. Updated information on the anthrax situation in Europe is reported. A brief description of some of the work in progress in the work package 5.1 of the AniBioThreat project is also presented, including (1) the development of a robust typing tool based on a suspension array technology and multiplexed single nucleotide polymorphisms scoring and (2) the typing of a collection of DNA from European isolates exchanged between the partners of the project. The know-how acquired will contribute to improving the EU's ability to react rapidly when the identity and real origin of a strain need to be established.

An association study between genetic polymorphism in the interleukin-6 receptor gene and coronary heart disease

The goal of our study is to test the association of IL6R rs7529229 polymorphism with CHD through a case-control study in Han Chinese population and a meta-analysis. Our result showed there is a lack of association between IL6R rs7529229 polymorphism and CHD on both genotype and allele levels in Han Chinese (P > 0.05). However, a meta-analysis among 11678 cases and 12861 controls showed that rs7529229-C allele was significantly associated with a decreased risk of CHD, especially in Europeans (P < 0.0001, odds ratio = 0.93, 95% confidential interval = 0.89–0.96). Since there is significant difference among different populations, further studies are warranted to test the contribution of rs7529229 to CHD in other ethnic populations.

In silico and in vitro evaluation of PCR-based assays for the detection of Bacillus anthracis chromosomal signature sequences

Bacillus anthracis, the causative agent of anthrax, is a zoonotic pathogen that is relatively common throughout the world and may cause life threatening diseases in animals and humans. There are many PCR-based assays in use for the detection of B. anthracis. While most of the developed assays rely on unique markers present on virulence plasmids pXO1 and pXO2, relatively few assays incorporate chromosomal DNA markers due to the close relatedness of B. anthracis to the B. cereus group strains. For the detection of chromosomal DNA, different genes have been used, such as BA813, rpoB, gyrA, plcR, S-layer, and prophage-lambda. Following a review of the literature, an in silico analysis of all signature sequences reported for identification of B. anthracis was conducted. Published primer and probe sequences were compared for specificity against 134 available Bacillus spp. genomes. Although many of the chromosomal targets evaluated are claimed to be specific to B. anthracis, cross-reactions with closely related B. cereus and B. thuringiensis strains were often observed. Of the 35 investigated PCR assays, only 4 were 100% specific for the B. anthracis chromosome. An interlaboratory ring trial among five European laboratories was then performed to evaluate six assays, including the WHO recommended procedures, using a collection of 90 Bacillus strains. Three assays performed adequately, yielding no false positive or negative results. All three assays target chromosomal markers located within the lambdaBa03 prophage region (PL3, BA5345, and BA5357). Detection limit was further assessed for one of these highly specific assays.