Anti-protective antigen IgG enzyme-linked immunosorbent assay for diagnosis of cutaneous anthrax in India. Clin Vaccine Immunol. 2012;19:1238-1242. [PMID: 22718130 DOI: 10.1128/cvi.00154-12]

New bacteriophage-derived lysins, LysJ and LysF, with the potential to control Bacillus anthracis

Bacillus anthracis is an etiological agent of anthrax, a severe zoonotic disease that can be transmitted to people and cause high mortalities. Bacteriophages and their lytic enzymes, endolysins, have potential therapeutic value in treating infections caused by this bacterium as alternatives or complements to antibiotic therapy. They can also be used to identify and detect B. anthracis. Endolysins of two B. anthracis Wbetavirus phages, J5a and F16Ba which were described by us recently, differ significantly from the best-known B. anthracis phage endolysin PlyG from Wbetavirus genus bacteriophage Gamma and a few other Wbetavirus genus phages. They are larger than PlyG (351 vs. 233 amino acid residues), contain a signal peptide at their N-termini, and, by prediction, have a different fold of cell binding domain suggesting different structural basis of cell epitope recognition. We purified in a soluble form the modified versions of these endolysins, designated by us LysJ and LysF, respectively, and depleted of signal peptides. Both modified endolysins could lyse the B. anthracis cell wall in zymogram assays. Their activity against the living cells of B. anthracis and other species of Bacillus genus was tested by spotting on the layers of bacteria in soft agar and by assessing the reduction of optical density of bacterial suspensions. Both methods proved the effectiveness of LysJ and LysF in killing the anthrax bacilli, although the results obtained by each method differed. Additionally, the lytic efficiency of both proteins was different, which apparently correlates with differences in their amino acid sequence. KEY POINTS: • LysJ and LysF are B. anthracis-targeting lysins differing from lysins studied so far • LysJ and LysF could be overproduced in E. coli in soluble and active forms • LysJ and LysF are active in killing cells of B. anthracis virulent strains.

Alternate Antimicrobial Therapies and Their Companion Tests

New antimicrobial approaches are essential to counter antimicrobial resistance. The drug development pipeline is exhausted with the emergence of resistance, resulting in unsuccessful trials. The lack of an effective drug developed from the conventional drug portfolio has mandated the introspection into the list of potentially effective unconventional alternate antimicrobial molecules. Alternate therapies with clinically explicable forms include monoclonal antibodies, antimicrobial peptides, aptamers, and phages. Clinical diagnostics optimize the drug delivery. In the era of diagnostic-based applications, it is logical to draw diagnostic-based treatment for infectious diseases. Selection criteria of alternate therapeutics in infectious diseases include detection, monitoring of response, and resistance mechanism identification. Integrating these diagnostic applications is disruptive to the traditional therapeutic development. The challenges and mitigation methods need to be noted. Applying the goals of clinical pharmacokinetics that include enhancing efficacy and decreasing toxicity of drug therapy, this review analyses the strong correlation of alternate antimicrobial therapeutics in infectious diseases. The relationship between drug concentration and the resulting effect defined by the pharmacodynamic parameters are also analyzed. This review analyzes the perspectives of aligning diagnostic initiatives with the use of alternate therapeutics, with a particular focus on companion diagnostic applications in infectious diseases.

Characterization of the adaptive immune response of donors receiving live anthrax vaccine

Live anthrax vaccine containing spores from attenuated strains STI-1 of Bacillus anthracis is used in Russia and former CIS (Commonwealth of Independent States) to prevent anthrax. In this paper we studied the duration of circulation of antibodies specific to spore antigens, the protective antigen (PA), the lethal factor (LF) and their domains (D) in donors’ blood at different times after their immunization with live anthrax vaccine. The relationship between the toxin neutralization activity level and the level of antibodies to PA, LF and their domains was tested. The effect of age, gender and number of vaccinations on the level of adaptive post-vaccination immune response has been studied. It was shown that antibodies against PA-D1 circulate in the blood of donors for 1 year or more after immunization with live anthrax vaccine. Antibodies against all domains of LF and PA-D4 were detected in 11 months after vaccination. Antibodies against the spores were detected in 8 months after vaccination. A moderate positive correlation was found between the titers of antibodies to PA, LF, or their domains, and the TNA of the samples of blood serum from the donors.

Development of ELISA based on Bacillus anthracis capsule biosynthesis protein CapA for naturally acquired antibodies against anthrax

Anthrax is a zoonotic disease caused by the gram-positive spore-forming bacterium Bacillus anthracis. Detecting naturally acquired antibodies against anthrax sublethal exposure in animals is essential for anthrax surveillance and effective control measures. Serological assays based on protective antigen (PA) of B. anthracis are mainly used for anthrax surveillance and vaccine evaluation. Although the assay is reliable, it is challenging to distinguish the naturally acquired antibodies from vaccine-induced immunity in animals because PA is cross-reactive to both antibodies. Although additional data on the vaccination history of animals could bypass this problem, such data are not readily accessible in many cases. In this study, we established a new enzyme-linked immunosorbent assay (ELISA) specific to antibodies against capsule biosynthesis protein CapA antigen of B. anthracis, which is non-cross-reactive to vaccine-induced antibodies in horses. Using in silico analyses, we screened coding sequences encoded on pXO2 plasmid, which is absent in the veterinary vaccine strain Sterne 34F2 but present in virulent strains of B. anthracis. Among the 8 selected antigen candidates, capsule biosynthesis protein CapA (GBAA_RS28240) and peptide ABC transporter substrate-binding protein (GBAA_RS28340) were detected by antibodies in infected horse sera. Of these, CapA has not yet been identified as immunoreactive in other studies to the best of our knowledge. Considering the protein solubility and specificity of B. anthracis, we prepared the C-terminus region of CapA, named CapA322, and developed CapA322-ELISA based on a horse model. Comparative analysis of the CapA322-ELISA and PAD1-ELISA (ELISA uses domain one of the PA) showed that CapA322-ELISA could detect anti-CapA antibodies in sera from infected horses but was non-reactive to sera from vaccinated horses. The CapA322-ELISA could contribute to the anthrax surveillance in endemic areas, and two immunoreactive proteins identified in this study could be additives to the improvement of current or future vaccine development.

Development of a PCR Lateral Flow Assay for Rapid Detection of Bacillus anthracis, the Causative Agent of Anthrax

Bacillus anthracis, the causative agent of anthrax is one of the most potent listed biological warfare agents. The conventional microbiological methods of its detection are labor intensive and time consuming, whereas molecular assays are fast, sensitive and specific. PCR is one of the most reliable diagnostic tools in molecular biology. The combination of PCR with lateral flow strips can reduce the diagnostic/detection time. It gives an alternative to gel electrophoresis and offers easy and clear interpretation of results. In the present study, a PCR Lateral flow (PCR-LF) assay targeting cya gene present on pXO1 plasmid of B. anthracis has been developed. The forward and reverse primers were tagged with 6-carboxyflourescein (6-FAM) and biotin, respectively, at 5' end. The dual labeled PCR products were detected using lateral flow (LF) strips developed in this study. The PCR-LF assay could detect ≥ 5 pg of genomic DNA and ≥ 500 copies of target DNA harboured in a recombinant plasmid. The assay was able to detect as few as 10³ and 10 CFU/mL of B. anthracis Sterne cells spiked in human blood after 6 and 24 h of enrichment, respectively.

Toxin-neutralizing antibodies elicited by naturally acquired cutaneous anthrax are elevated following severe disease and appear to target conformational epitopes

Understanding immune responses to native antigens in response to natural infections can lead to improved approaches to vaccination. This study sought to characterize the humoral immune response to anthrax toxin components, capsule and spore antigens in individuals (n = 46) from the Kayseri and Malatya regions of Turkey who had recovered from mild or severe forms of cutaneous anthrax infection, compared to regional healthy controls (n = 20). IgG antibodies to each toxin component, the poly-γ-D-glutamic acid capsule, the Bacillus collagen-like protein of anthracis (BclA) spore antigen, and the spore carbohydrate anthrose, were detected in the cases, with anthrax toxin neutralization and responses to Protective Antigen (PA) and Lethal Factor (LF) being higher following severe forms of the disease. Significant correlative relationships among responses to PA, LF, Edema Factor (EF) and capsule were observed among the cases. Though some regional control sera exhibited binding to a subset of the tested antigens, these samples did not neutralize anthrax toxins and lacked correlative relationships among antigen binding specificities observed in the cases. Comparison of serum binding to overlapping decapeptides covering the entire length of PA, LF and EF proteins in 26 cases compared to 8 regional controls revealed that anthrax toxin-neutralizing antibody responses elicited following natural cutaneous anthrax infection are directed to conformational epitopes. These studies support the concept of vaccination approaches that preserve conformational epitopes.

Gel green fluorescence ssDNA aptasensor based on carbon nanotubes for detection of anthrax protective antigen

Bacillus anthracis, the causative agent of anthrax, is a harmful pathogen with potential ability as a biological weapon which persuades scientists to develop novel methods to detect anthrax from infected resources. In this study, a multi-walled carbon nanotube (MWCNTs)-based fluorescence aptasensor was fabricated to detect the recombinant protective antigen domain 4 (rPAD4) of Bacillus anthracis as the most important key factor in development of anthrax. First, PAD4 was recombinant expressed in E. coli and purified by Ni-NTA column. Second, the affinity of aptamer to rPAD4 was confirmed by ELAA assay. In aptasensor design, the aptamer was labeled with Gel Green and immobilized on MWCNTs. Upon the adsorption of labeled aptamer on MWCNTs, fluorescence emission was quenched. In contrast, by adding rPAD4 to hybridization reaction and incubation for 10 min, the fluorescence emission was significantly recovered to 85% compared to the control. Detection limit for the sensitivity and specificity of the aptasensor was determined 20 ng/ml and 62.5 ng/ml purified and unpurified rPAD4 protein, respectively. Also, applicability of aptasensor was showed in mouse serum sample. Finally, results indicated that nanosensor has the potential to be developed as a high-sensitive, cost-effective and fast-acting system for measuring of PA in anthrax diagnostic tests.

Development of a novel chimeric PA-LF antigen of Bacillus anthracis, its immunological characterization and evaluation as a future vaccine candidate in mouse model

Tremendous efforts are being made to develop an anthrax vaccine with long term protection. The main component of traditional anthrax vaccine is protective antigen (PA) with the trace amount of other proteins and bacterial components. In this study, we developed a recombinant PA-LF chimera antigen of Bacillus anthracis by fusing the PA domain 2-4 with lethal factor (LF) domain 1 and evaluated its protective potential against B. anthracis in mouse model. The anti-PA-LF chimera serum reacted with both PA and LF antigen, individually. The chimera elicited a strong antibody titer in mice with predominance of IgG1 isotype followed by IgG2b, IgG2a and IgG3. Cytokines were assessed in splenocytes of immunized mice and a significant up-regulation in the expression of IL-4, IL-10, IFN-γ and TNF-α was observed. The PA-LF chimera immunized mice exhibited 80% survival after challenge with virulent spores of B. anthracis. Pathological studies showed normal architecture in vital organs (spleen, lung, liver and kidney) of recovered immunized mice on 20 DPI after spore challenge. These findings suggested that PA-LF chimera of B. anthracis elicited good humoral as well as cell mediated immune response in mice, and thus, can be a potent vaccine candidate against anthrax.

An ELISA using a recombinant chimera of protective antigen and lethal factor for serodiagnosis of cutaneous anthrax in India

In this study, an ELISA was developed for simultaneous detection of antibodies against both the important toxins of B. anthracis i.e. protective antigen (PA) and lethal factor (LF). A chimera of PA and LF was made by fusion and cloned and expressed in E. coli. The purified recombinant protein was used in plate ELISA for serodiagnosis of anthrax. The chimera could detect antibodies against both the toxins of Bacillus anthracis. The human serum samples (n = 98) collected from anthrax endemic and non-endemic areas were tested employing ELISA. The ELISA gave sensitivity of 100% (95% Confidence Interval [CI], 92.13 to 100) and specificity of 97.78% (95% Confidence Interval [CI], 88.23 to 99.94) with a J index of 0.97. The efficiency of ELISA was found to be 98.9% with the positive predictive value (PPV) and negative predictive value (NPV) of 97.8% and 100%, respectively. The chimera of PA and LF could be a better diagnostic antigen for serodiagnosis as the assay detects antibodies against both the toxins in early as well delayed infection cases of anthrax. Therefore, it can be a very useful tool for the surveillance as well as for confirmation of cutaneous anthrax cases.

Enhanced production and purification of recombinant surface array protein (Sap) for use in detection of Bacillus anthracis

Surface array protein (Sap) can be an important biomarker for specific detection of Bacillus anthracis, which is released by the bacterium during its growth in culture broth. In the present work, we have cloned and expressed Sap in Escherichia coli. The culture conditions and cultivation media were optimized and used in batch fermentation process for scale up of Sap in soluble form. The recombinant Sap was purified employing affinity chromatography followed by diafiltration. The final yield of purified protein was 20 and 46 mg/l of culture during shake flasks and batch fermentation, respectively. The protein purity and its reactivity were confirmed employing SDS-PAGE and Western blot, respectively. The antibodies raised against purified Sap were evaluated by Western blotting for detection of Sap released by B. anthracis. Our results showed that the Sap could be a novel marker for detection and confirmation of B. anthracis.

Evaluation of clinical and serological findings for diagnosis of cutaneous anthrax infection after an outbreak

PURPOSE

Anthrax, caused by the bacterium Bacillus anthracis, is one of the oldest documented infectious diseases in both livestock and humans. We aimed to evaluate clinical findings and risk factors of patients with cutaneous anthrax infection and report anti-lethal factor (LF) IgG and anti-protective antigen (PA) IgG titers in the serologic diagnosis of disease.

METHODS

In this study, serum samples of 18 cutaneous anthrax patients were collected and anti-LF IgG and anti-PA IgG titers were measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Twelve (67%) males and 6 (33%) females, with a mean age of 36.06 ± 16.58 years were included in the study. Risk factors identified in the patient population studied were slaughtering (28%), flaying (56%), chopping meat (67%), burying diseased animal corpses (17%) and milking (6%) livestock. Black eschar formation (94%), pruritus (78%) and painful lymphadenopathy (61%) were first three common clinical signs and symptoms, respectively. Fourteen (78%) patients produced a positive IgG response against PA, 11 (61%) patients produced against LF. Three (17%) patients had no response to either antigen.

CONCLUSIONS

A detailed history of contact with sick animals or animal products along with clinical findings should be taken at the first step for the diagnosis of cutaneous anthrax infection. Serologic detection of anti-LF IgG and anti-PA IgG with ELISA may be useful auxillary method for establishing the diagnosis.

Development & validation of a quantitative anti-protective antigen IgG enzyme linked immunosorbent assay for serodiagnosis of cutaneous anthrax

Background & objectives:

Anthrax caused by Bacillus anthracis is primarily a disease of herbivorous animals, although several mammals are vulnerable to it. ELISA is the most widely accepted serodiagnostic assay for large scale surveillance of cutaneous anthrax. The aims of this study were to develop and evaluate a quantitative ELISA for determination of IgG antibodies against B. anthracis protective antigen (PA) in human cutaneous anthrax cases.

Methods:

Quantitative ELISA was developed using the recombinant PA for coating and standard reference serum AVR801 for quantification. A total of 116 human test and control serum samples were used in the study. The assay was evaluated for its precision, accuracy and linearity.

Results:

The minimum detection limit and lower limit of quantification of the assay for anti-PA IgG were 3.2 and 4 µg/ml, respectively. The serum samples collected from the anthrax infected patients were found to have anti-PA IgG concentrations of 5.2 to 166.3 µg/ml. The intra-assay precision per cent CV within an assay and within an operator ranged from 0.99 to 7.4 per cent and 1.7 to 3.9 per cent, respectively. The accuracy of the assay was high with a per cent error of 6.5 - 24.1 per cent. The described assay was found to be linear between the range of 4 to 80 ng/ml (R²=0.9982; slope=0.9186; intercept = 0.1108).

Interpretation & conclusions:

The results suggested that the developed assay could be a useful tool for quantification of anti-PA IgG response in human after anthrax infection or vaccination.

Ultrasensitive electrochemical immunoassay for surface array protein, a Bacillus anthracis biomarker using Au-Pd nanocrystals loaded on boron-nitride nanosheets as catalytic labels

Bacillus anthracis, the causative agent of anthrax, is a well known bioterrorism agent. The determination of surface array protein (Sap), a unique biomarker for B. anthracis can offer an opportunity for specific detection of B. anthracis in culture broth. In this study, we designed a new catalytic bionanolabel and fabricated a novel electrochemical immunosensor for ultrasensitive detection of B. anthracis Sap antigen. Bimetallic gold-palladium nanoparticles were in-situ grown on poly (diallyldimethylammonium chloride) functionalized boron nitride nanosheets (Au-Pd NPs@BNNSs) and conjugated with the mouse anti-B. anthracis Sap antibodies (Ab2); named Au-Pd NPs@BNNSs/Ab2. The resulting Au-Pd NPs@BNNSs/Ab2 bionanolabel demonstrated high catalytic activity towards reduction of 4-nitrophenol. The sensitivity of the electrochemical immunosensor along with redox cycling of 4-aminophenol to 4-quinoneimine was improved to a great extent. Under optimal conditions, the proposed immunosensor exhibited a wide working range from 5 pg/mL to 100 ng/mL with a minimum detection limit of 1 pg/mL B. anthracis Sap antigen. The practical applicability of the immunosensor was demonstrated by specific detection of Sap secreted by the B. anthracis in culture broth just after 1h of growth. These labels open a new direction for the ultrasensitive detection of different biological warfare agents and their markers in different matrices.

Development of a Sterne-Based Complement Fixation Test to Monitor the Humoral Response Induced by Anthrax Vaccines

Anthrax is a zoonotic disease caused by Bacillus anthracis spore-forming bacterium. Since it is primarily a disease of animals, the control in animals, and humans depend on the prevention in livestock, principally cattle, sheep, and goats. Most veterinary vaccines utilize the toxigenic, uncapsulated (pXO1+/pXO2–) B. anthracis strain 34F₂ which affords protection through the production of neutralizing antibodies directed to the toxin components Protective Antigen (PA), Lethal Factor (LF), and Edema Factor (EF). The titration of specific antibodies in sera of vaccinated animals is crucial to evaluate the efficacy of the vaccination and to obtain epidemiological information for an effective anthrax surveillance. In this study, we developed a Sterne-based Complement Fixation Test (CFT) to detect specific antibodies induced in animals vaccinated with Sterne 34F₂. We assessed its efficacy in laboratory animals and under field conditions by monitoring the humoral response induced by vaccination in cattle. The results indicated that the Sterne-based CFT is able to correctly identify vaccinated animals. It proved to be a very sensitive and specific test. Moreover, the Sterne-based CFT offers many benefits with regard to costs, standardization and reproducibility of the assay procedure.

Advances in Anthrax Detection: Overview of Bioprobes and Biosensors

Anthrax is an infectious disease caused by Bacillus anthracis. Although anthrax commonly affects domestic and wild animals, it causes a rare but lethal infection in humans. A variety of techniques have been introduced and evaluated to detect anthrax using cultures, polymerase chain reaction, and immunoassays to address the potential threat of anthrax being used as a bioweapon. The high-potential harm of anthrax in bioterrorism requires sensitive and specific detection systems that are rapid, field-ready, and real-time monitoring. Here, we provide a systematic overview of anthrax detection probes with their potential applications in various ultra-sensitive diagnostic systems.

Anthrax: A disease of biowarfare and public health importance

Bioterrorism has received a lot of attention in the first decade of this century. Biological agents are considered attractive weapons for bioterrorism as these are easy to obtain, comparatively inexpensive to produce and exhibit widespread fear and panic than the actual potential of physical damage. Bacillus anthracis (B. anthracis), the etiologic agent of anthrax is a Gram positive, spore forming, non-motile bacterium. This is supposed to be one of the most potent BW agents because its spores are extremely resistant to natural conditions and can survive for several decades in the environment. B. anthracis spores enter the body through skin lesion (cutaneous anthrax), lungs (pulmonary anthrax), or gastrointestinal route (gastrointestinal anthrax) and germinate, giving rise to the vegetative form. Anthrax is a concern of public health also in many countries where agriculture is the main source of income including India. Anthrax has been associated with human history for a very long time and regained its popularity after Sept 2001 incidence in United States. The present review article describes the history, biology, life cycle, pathogenicity, virulence, epidemiology and potential of B. anthracis as biological weapon.

A field usable qualitative anti-protective antigen enzyme-linked immunosorbent assay for serodiagnosis of human anthrax

Although all mammals, including humans, are vulnerable when they come into direct contact with infected animals, anthrax is primarily a disease of herbivorous animals. In countries like India, cutaneous anthrax is a public health problem in several regions. Hence, a simple and efficacious serodiagnostic assay for large scale surveillance of endemic populations is required. In the present study, a field-usable, qualitative ELISA was developed for serodiagnosis of human anthrax. Results are assessed on a visual basis and no sophisticated instruments are required. Anti-protective antigen (PA) IgG was determined by visual examination of ELISA results of 225 human serum samples (160 from healthy humans, 5 from PA vaccinated individuals and 60 from confirmed anthrax cases). Comparison of the ELISA results with the results obtained from optical density values showed compatible sensitivity and specificity. Assay sensitivity, specificity, and positive and negative predictive values were found to be 100%. The developed assay could be a very useful tool for serological diagnosis of anthrax infection in humans.

Detection of protective antigen, an anthrax specific toxin in human serum by using surface plasmon resonance

In this study, surface plasmon resonance (SPR) technology was used for the sensitive detection of protective antigen (PA), an anthrax specific toxin in spiked human serum samples. A monoclonal antibody raised against Bacillus anthracis PA was immobilized on carboxymethyldextran-modified gold chip, and its interaction with PA was characterized in situ by SPR. By using kinetic evaluation software, KD (equilibrium constant) and Bmax (maximum binding capacity of analyte) were found to be 20 fM and 18.74 m°, respectively. The change in Gibb's free energy (∆G= -78.04 kJ/mol) confirmed the spontaneous interaction between antigen and antibody. The assay could detect 1 pg/mL purified PA. In PA-spiked human serum samples, 10 pg/mL of PA could be detected. Presence of PA in blood samples serves as an important early diagnostic marker for B. anthracis infections. Thus, SPR test can be a sensitive assay for detection of anthrax at early stages of infection.

Serodiagnosis of human cutaneous anthrax in India using an indirect anti-lethal factor IgG enzyme-linked immunosorbent assay

Anthrax, caused by Bacillus anthracis, is primarily a zoonotic disease. Being a public health problem also in several developing countries, its early diagnosis is very important in human cases. In this study, we describe the use of an indirect enzyme-linked immunosorbent assay (ELISA) for detection of anti-lethal factor (anti-LF) IgG in human serum samples. A panel of 203 human serum samples consisting of 50 samples from patients with confirmed cutaneous anthrax, 93 samples from healthy controls from areas of India where anthrax is nonendemic, 44 samples from controls from an area of India where anthrax is endemic, and 16 patients with a disease confirmed not to be anthrax were evaluated with an anti-LF ELISA. The combined mean anti-LF ELISA titer for the three control groups was 0.136 ELISA unit (EU), with a 95% confidence interval (CI) of 0.120 to 0.151 EU. The observed sensitivity and specificity of the ELISA were 100% (95% CI, 92.89 to 100%) and 97.39% (95% CI, 93.44 to 99.28%), respectively, at a cutoff value of 0.375 EU, as decided by receiver operating characteristic (ROC) curve analysis. The likelihood ratio was found to be 49.98. The positive predictive value (PPV), negative predictive value (NPV), efficiency, and Youden's index (J) for reliability of the assay were 92.5%, 100%, 98.02%, and 0.97, respectively. The false-positive predictive rate and false-negative predictive rate of the assay were 2.61% and 0%. The assay could be a very useful tool for early diagnosis of cutaneous anthrax cases, as antibodies against LF appear much earlier than those against other anthrax toxins in human serum samples.

Surface Plasmon Resonance Biosensor for Detection of Bacillus anthracis, the Causative Agent of Anthrax from Soil Samples Targeting Protective Antigen

Bacillus anthracis, the causative agent of anthrax is one of the most important biological warfare agents. In this study, surface plasmon resonance (SPR) technology was used for indirect detection of B. anthracis by detecting protective antigen (PA), a common toxin produced by all live B. anthracis bacteria. For development of biosensor, a monoclonal antibody raised against B. anthracis PA was immobilized on carboxymethyldextran modified gold chip and its interaction with PA was characterized in situ by SPR and electrochemical impedance spectroscopy. By using kinetic evaluation software, KD (equilibrium constant) and Bmax (maximum binding capacity of analyte) were found to be 20 fM and 18.74, respectively. The change in Gibb's free energy (∆G = -78.04 kJ/mol) confirmed the spontaneous interaction between antigen and antibody. The assay could detect 12 fM purified PA. When anthrax spores spiked soil samples were enriched, PA produced in the sample containing even a single spore of B. anthracis could be detected by SPR. PA being produced only by the vegetative cells of B. anthracis, confirms indirectly the presence of B. anthracis in the samples. The proposed method can be a very useful tool for screening and confirmation of anthrax suspected environmental samples during a bio-warfare like situation.