A comparison of immuncapture agglutination and ELISA methods in serological diagnosis of brucellosis

A rapid direct-differential agglutination assay for Brucella detection using antibodies conjugated with functionalized gold nanoparticles

Brucellosis is the most widespread and serious zoonotic disease worldwide which affects livestock, sylvatic wildlife, marine dwellers, and humans. It is acquired through Alphaproteobacteria which belong to the genus Brucella and is categorized as a potential bio-threat agent. In this study, we developed a rapid and direct differential whole cell (WC) agglutination-based assay for its on-field detection. The recombinant outer membrane (rOmp28) protein-derived specific mice IgG polyclonal antibodies (pAbs) of Brucella were purified using affinity chromatography and conjugated with functionalized gold nanoparticles (AuNPs) for rapid agglutination. A positive blot of 32 kDa protein revealed specific immuno-reactivity of rOmp28-pAbs using immunoblot analysis. For the synthesis of AuNPs, the conventional “Turkevich method” was optimized at a concentration < 1 mM of gold precursor for obtaining 50-nm-sized particles. Also, their physico-chemical characteristics were analyzed using UV-visible spectrophotometry, Fourier transform infra-red spectroscopy (FT-IR), Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), dynamic light scattering (DLS), zeta potential (ζ, ZP), and fluorescence spectroscopy. Furthermore, these AuNPs were functionalized with N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) to prepare modified carboxylated AuNPs. For bioconjugation with Brucella rOmp28 IgG pAbs, antibody-conjugated functionalized AuNP constructs were prepared and characterized using FT-IR analysis with strong N–H deformations. Subsequently, these bioconjugated AuNPs were used to develop a direct-differential slide agglutination assay with a detection limit of 104 CFU mL−1. The sensitivity of this assay was compared with standard double-antibody sandwich ELISA (S-ELISA) using rOmp28 IgG pAbs with an LOD of 103 CFU mL−1 and a detection range of 102–108 CFU mL−1. No intraspecies cross-reactivity was observed based on evaluation of its specificity with a battery of closely related bacterial species. In conclusion, the increased sensitivity and specificity of the developed agglutination assay obtained using bioconjugated functionalized AuNPs is ≥ 98% for the detection of Brucella. Therefore, it can be used as an alternate rapid method of direct WC detection of bacteria as it is simple, robust, and cost-effective, with minimal time of reaction in the case of early disease diagnosis.

Evaluating the efficacy of serological testing of clinical specimens collected from patients with suspected brucellosis

BACKGROUND

This study aims to evaluate the efficacy of the standard agglutination test (SAT), the Brucellacapt test and enzyme-linked immunosorbent assay (ELISA) in clinical specimens collected from patients with suspected brucellosis.

METHODS

A prospective study was conducted from December 2020 to December 2021. Brucellosis was diagnosed on the basis of clinical evidence, and confirmed by isolation of Brucella or a four-fold rise in SAT titer. All samples were tested by the SAT, ELISA and the Brucellacapt test. Titers ≥1:100 were considered as SAT positive; ELISA was considered positive when an index greater than 11 was detected, while titers ≥1/160 indicated positivity on the Brucellacapt test. The specificity, sensitivity, and positive (PPVs) and negative predictive values (NPVs) of the three different methods were calculated.

RESULTS

A total of 149 samples were collected from patients with suspected brucellosis. The sensitivities for the SAT, IgG, and IgM detection were 74.42%, 88.37% and 74.42%, respectively. The specificities were 95.24%, 93.65%, and 88.89%, respectively. The simultaneous measurement of IgG and IgM improved the sensitivity (98.84%) but reduced the specificity (84.13%) compared to each antibody test separately. The Brucellacapt test had excellent specificity (100%) and a high PPV (100%); however, the sensitivity and NPV were 88.37% and 86.30%, respectively. The combination of IgG detection by ELISA and the Brucellacapt test had excellent diagnostic performance, with 98.84% sensitivity and 93.65% specificity.

CONCLUSION

This study showed that the simultaneous performance of IgG detection by ELISA and the Brucellacapt test has the potential to overcome the current limitations of detection.

A Label-Based Polymer Nanoparticles Biosensor Combined with Loop-Mediated Isothermal Amplification for Rapid, Sensitive, and Highly Specific Identification of Brucella abortus

Brucella abortus (B. abortus), an important zoonotic pathogen in Brucella spp., is the major causative agent of abortion in cattle (namely, bovine brucellosis). Currently, although the isolation and identification of the Brucella abortus were commonly accepted as the gold standard method, it cannot meet the requirements for early diagnostic strategies. Conventional PCR techniques and immunological tests can realize rapid detection of B. abortus, but the demands for PCR thermal cyclers and/or specific antibodies hinder their application in basic laboratories. Thus, rapid, sensitive, and specific diagnostic strategies are essential to prevent and control the spread of the bovine brucellosis. In this work, a novel detection method for the rapid identification of B. abortus, which uses loop-mediated isothermal amplification (LAMP) combined with a label-based polymer nanoparticles lateral flow immunoassay biosensor (LFIA), was established. One set of specific B. abortus-LAMP primers targeting the BruAb2_0168 gene was designed by the online LAMP primer design tool. The B. abortus-LAMP-LFIA assay was optimized and evaluated using various pathogens and whole blood samples. The optimal amplification temperature and time for B. abortus-LAMP-LFIA were determined to be 65°C and 50 min, respectively. The B. abortus-LAMP-LFIA method limit of detection (LoD) was 100 fg per reaction for pure genomic DNA of B. abortus. Meanwhile, the detection specificity was 100%, and there was no cross-reactivity for other Brucella members and non-Brucella strains. Furthermore, the entire procedure, including the DNA preparation for whole blood samples (30 min), isothermal incubation (50 min), and LFIA detection (2–5 min), can be completed in approximately 85 min. Thus, the B. abortus-LAMP-LFIA assay developed was a simple, rapid, sensitive, and reliable detection technique, which can be used as a screening and/or diagnostic tool for B. abortus in the field and basic laboratories.

Clinical Interpretation of Detection of IgM Anti-Brucella Antibody in the Absence of IgG and Vice Versa; a Diagnostic Challenge for Clinicians

Non-specific and often misleading clinical presentation of active brucellosis has made it a diagnostic puzzle for treating physicians. Clinicians rely greatly on the detection of IgG and IgM anti-Brucella antibodies by ELISA. Different patterns of positivity have been observed for IgG and IgM anti-Brucella antibodies in different cases, which further increases the risk of an erroneous diagnosis. Detailed herein is our two-years data with varied Brucella serology patterns and their clinical interpretation. Between January 2015 to December 2017, 1102 samples were processed in the Immunology Laboratory of KFHU for Brucella serology. 68 samples were positive for both IgG and IgM, 28 samples were positive for IgG and negative for IgM while 15 samples were positive for IgM and negative for IgG antibodies against Brucella. Electronic medical records, history of exposure, signs, symptoms, laboratory data, and the final diagnosis were recorded for all these patients. None of the patients with only positive IgM antibodies was finally diagnosed with brucellosis, while a diagnosis of brucellosis was established for only one patient with IgG antibodies positive in his serum. All the double-positive (IgG- and IgM-positive) serology patterns were diagnosed as having brucellosis. We concluded that determination of single IgM or IgG anti-Brucella-antibodies by ELISA could both be considered as definite and should ideally be interpreted in the context of appropriate clinical scenario and confirmation by other laboratory assays.

Non-specific and often misleading clinical presentation of active brucellosis has made it a diagnostic puzzle for treating physicians. Clinicians rely greatly on the detection of IgG and IgM anti-Brucella antibodies by ELISA. Different patterns of positivity have been observed for IgG and IgM anti-Brucella antibodies in different cases, which further increases the risk of an erroneous diagnosis. Detailed herein is our two-years data with varied Brucella serology patterns and their clinical interpretation. Between January 2015 to December 2017, 1102 samples were processed in the Immunology Laboratory of KFHU for Brucella serology. 68 samples were positive for both IgG and IgM, 28 samples were positive for IgG and negative for IgM while 15 samples were positive for IgM and negative for IgG antibodies against Brucella. Electronic medical records, history of exposure, signs, symptoms, laboratory data, and the final diagnosis were recorded for all these patients. None of the patients with only positive IgM antibodies was finally diagnosed with brucellosis, while a diagnosis of brucellosis was established for only one patient with IgG antibodies positive in his serum. All the double-positive (IgG- and IgM-positive) serology patterns were diagnosed as having brucellosis. We concluded that determination of single IgM or IgG anti-Brucella-antibodies by ELISA could both be considered as definite and should ideally be interpreted in the context of appropriate clinical scenario and confirmation by other laboratory assays.

Review of brucellosis in Nepal

Brucellosis is an abortifacient zoonotic disease that remains prominent in third world countries like Nepal. Brucellosis poses a public health concern, because its incidence in livestock can present substantial economic and health burdens for herders and health professionals. Several cases of bovine and human brucellosis have been reported and the prevalence is higher among livestock than among humans in Nepal. Lack of awareness, unhealthy food habit, traditional husbandry practices, and a lack of surveillance and immunization have been the major factors in maintaining a vicious cycle of propagation of the disease in human and animals. The aim of this paper is to evaluate the current status of the disease, the mechanism of infection, and pathogenesis, its zoonotic potential, diagnostic advances, treatment regimens, and the preventive measures that can be adopted in managing human brucellosis in under-developed countries such as Nepal.

Review of Brucellosis in Nepal

OBJECTIVES

The aim of this paper is to evaluate the current status of the disease, the mechanism of infection, and pathogenesis, its zoonotic potential, diagnostic advances, treatment regimens, and the preventive measures that can be adopted in managing human brucellosis in under-developed countries such as Nepal.

METHODS

We performed a systematic review of all the available literture through Google Scholar, PubMed, Gideon Informatics, World Health Organization and other legitimate sources. Other secondary informations were collected from the government agencies such as department of livestock services and Ministry of Health. The obtained information was then re-analysed and summarized.

RESULTS

Few publications have addressed brucellosis in Nepal and most of those publications have focused on bovine brucellosis with sparse information available on brucellosis in humans and small ruminants. Brucella abortus is the most predominant causative agent followed by B. suis. B. abortus is predominant in cattle accounting for a substantial portion of bovine abortion in the country. Lack of awareness, unhealthy food habit, traditional husbandry practices, and a lack of surveillance and immunization have been the major factors in maintaining a vicious cycle of propagation of the disease in human and animals. Unfortunately, nothing has been done to identify the species of Brucella at the biovar level.

CONCLUSIONS

Although brucellosis has been reported to be endemic in Nepal, neither the distribution nor the economic and public health impact of this disease is well characterized. Robust and well-designed nationwide survey is warranted to assess the prevalence and distribution of disease in livestock and humans. Such data would facilitate the design of appropriate control programmes.

Brucellosis in Nepal - A Potential Threat to Public Health Professionals

Brucellosis is a prominent zoonotic disease affecting humans and animals which with the lack of proper diagnosis and treatment remains dangerous in third world countries like Nepal. Currently, Brucellosis poses a public health concern, whose incidences among entire herds of animals can present substantial economic and health burdens for herders and health professionals. Additionally, factors such as close contact with animals, poor animal husbandry, and unhygienic feeding habits can exacerbate the spread of Brucella and related zoonotic agents. In Nepal, serious cases of bovine and even human brucellosis have been reported, although the topic is yet to be extensively reviewed. This paper evaluates the literatures on human and animal brucellosis in Nepal and other countries, with an emphasis on the impact of Brucella outbreaks on public health professionals. Herein, we summarize the current status of the disease, the mechanism of infection, pathogenesis, zoonotic potential, diagnostic advances, treatment regimens, and the preventive measures that can be adopted in managing human brucellosis in under-developed countries such as Nepal.

Comparison of a New and Rapid Method: Brucella Coombs Gel Test With Other Diagnostic Tests

BACKGROUND

The aim of this study was to detect reliability of Brucella Coombs gel test (BCGT) by comparing with with ELISA (IgG + IgM), Standard agglutination test, and Brucella immunocapture agglutination methods in serological diagnosis of brucellosis.

METHODS

Brucella Coombs gel test (BCGT), Brucella ELISA (IgG + IgM), Standard agglutination test, and Brucella immunocapture agglutination tests of 78 patients with presumptive diagnosis of brucellosis which were sent to Microbiology Laboratory of Konya Numune Hospital from various regions of Konya were studied.

RESULTS

RESULTS

Of 78 patients with ELISA IgG and IgM, STA, BICA and BCGT; 26, 21, 10, 12 and 12 were positive. When compared with BICA, the sensitivity and specifity of BCGT were 100% and 100%, respectively.

CONCLUSION

According to results BCGT can be used as a diagnostic test in routine laboratories after more comprehensive studies in control groups and patients.

Rocket and Two Dimensional Immunoelectrophoresis in Diagnosis of Caprine Brucellosis

BACKGROUND

Brucellosis is a major bacterial zoonosis of global importance with the causative organisms of Gram-negative facultative intracellular pathogens. The aims of this study were to standardize two immunoelectrophoretic techniques, rocket and cross immunoelectrophoresis, and compare their results with other conventional serodiagnostic tests.

METHODS

Sera from 15 sheep, without any history of brucellosis vaccination, infected with Brucella melitensis M16 subcutaneously, were employed in a comparison of culture, precipitating, and immunoelectrophoretic tests. A 125 days serologic follow-up was performed after the infection was started. As a reference, these tests also done in the five healthy sheep.

RESULTS

The results obtained with the rocket immunoelectrophoresis test correlated very well with those of the cross immunoelectrophoresis, whereas results of other tests such as culture, Rose Bengal, standard tube agglutination and 2-mercaptoethanol seruagglutination tests were inferior.

CONCLUSION

As agglutination test shows cross reaction and a prozone phenomenon, and in blood culture, the bacteria is not always detectable, so they are time consuming rocket and cross immunoelectrophoresis are recommended because their results can be obtained in a shorter time.

Genetic and Non-Genetic Inheritance of Natural Antibodies Binding Keyhole Limpet Hemocyanin in a Purebred Layer Chicken Line

Natural antibodies (NAb) are defined as antibodies present in individuals without known antigenic challenge. Levels of NAb binding keyhole limpet hemocyanin (KLH) in chickens were earlier shown to be heritable, and to be associated with survival. Selective breeding may thus provide a strategy to improve natural disease resistance. We phenotyped 3,689 white purebred laying chickens for KLH binding NAb of different isotypes around 16 weeks of age. Heritabilities of 0.12 for the titers of total antibodies (IgT), 0.14 for IgM, 0.10 for IgA, and 0.07 for IgG were estimated. We also estimated high, positive genetic, and moderate to high, positive phenotypic correlations of IgT, IgM, IgA, and IgG, suggesting that selective breeding for NAb can be done on all antibody isotypes simultaneously. In addition, a relatively substantial non-genetic maternal environmental effect of 0.06 was detected for IgM, which may reflect a transgenerational effect. This suggests that not only the genes of the mother, but also the maternal environment affects the immune system of the offspring. Breaking strength and early eggshell whiteness of the mother's eggs were predictive for IgM levels in the offspring, and partly explained the observed maternal environmental effects. The present results confirm that NAb are heritable, however maternal effects should be taken into account.

Detection of IgM antibrucella antibody in the absence of IgGs: a challenge for the clinical interpretation of brucella serology

The use of enzyme-linked immunosorbent assay (ELISA) for the detection of IgG and IgM antibodies antibrucella has become widespread in the diagnosis of human brucellosis. IgM anti-Brucella antibodies are indicative of acute infection. Between 2009-2013, 5307 patients were evaluated for serologic diagnosis at the Microbiology Laboratory of the Albacete General Hospital. A ELISA IgM-positive, IgG-negative anti-Brucella antibody serology pattern was detected in 17 of those patients. Epidemiology data, symptoms, laboratory data, treatment and outcome from these patients were reviewed. Sixteen patients presented with musculoskeletal pain, fatigue and/or fever and 1 was asymptomatic. Five patients received treatment with doxycycline combined with rifampin, gentamycin or streptomycin during 6-12 weeks, with no improvement. None of the 17 patients were finally diagnosed with brucellosis. Our results indicate that anti-Brucella IgM positive serology, per se, is not enough to diagnose acute brucellosis and other methods should be used for confirmation. Brucella serology data should be interpreted taking into account the patient's clinical history and epidemiological context.

Characterization of the immunogenicity and pathogenicity of malate dehydrogenase in Brucella abortus

Brucella abortus is a gram-negative, facultative intracellular pathogen that causes brucellosis, a chronic zoonotic disease resulting in abortion in pregnant cattle and undulant fever in humans. Malate dehydrogenase (MDH), a key enzyme in the tricarboxylic acid cycle, plays important metabolic roles in aerobic energy producing pathways and in malate shuttle. In this study, the MDH-encoding gene for malate dehydrogenase mdh of B. abortus S2308 was cloned, sequenced and expressed. Western blot analysis demonstrated that MDH is an immunogenic membrane-associated protein. In addition, recombinant MDH showed sero-reactivity with 30 individual bovine B. abortus-positive sera by enzyme-linked immunosorbent assay, indicates that MDH may be used as a candidate marker for sero-diagnosis of brucellosis. Furthermore, MDH exhibits fibronectin and plasminogen-binding ability in immunoblotting assay. Inhibition assays on HeLa cells demonstrated that rabbit anti-serum against MDH significantly reduced both bacterial adherence and invasion abilities (p < 0.05), suggesting that MDH play a role in B. abortus colonization. Our results indicated that MDH is not only an immunogenic protein, but is also related to bacterial pathogenesis and may act as a new virulent factor, which will benefit for further understanding the MDH's roles in B. abortus metabolism, pathogenesis and immunity.

Evaluation of ELISA and Brucellacapt tests for diagnosis of human Brucellosis

Background and Objectives

Brucellosis is one of the most common zoonotic diseases in Iran and human brucellosis is endemic in all parts of the country. Because of the difficulty in the diagnosis of brucellosis, particularly in endemic areas, the use of new and feasible diagnostic tests seem to be of great importance for resolving the diagnostic obstacles. We evaluated the usefulness of a new serological test based on an immunocapture-agglutination technique in comparison with ELISA test for serological diagnosis of brucellosis.

Materials and Methods

A total of 11 patients with brucellosis, who had positive blood cultures for Brucella species, and 47 suspected patients were included in this study. Serum samples collected from these patients were tested by brucellacapt and ELISA and the results were, consequently, compared.

Results

In patients with positive blood culture, all the samples gave positive results with brucellacapt test while IgM ELISA, IgG ELISA and (IgG + IgM) ELISA tests were positive in 8, 9 and 11 patients, respectively. Out of the 46 suspected patients, (IgG + IgM) ELISA, Brucellacapt, IgG ELISA and IgM ELISA were positive in 37, 15, 34 and 37 patients, respectively.The best cut-off point of ELISA-IgG was 10.78 IU/ml which produced the maximal sensitivity and specificity for the diagnosis of human brucellosis.

Conclusion

Both the (IgG + IgM) ELISA and Brucellacapt tests demonstrate a high specificity in this study. According to the results of the current study, it is found that both tests are valuable tools for diagnosis of brucellosis in Iran as an endemic area of brucellosis. It is strongly suggested that a combination of both tests to be used for the diagnosis of brucellosis.