Comparison of culture and PCR for the detection of Brucella melitensis in blood and lymphoid tissues of serologically positive and negative slaughtered sheep

Polyphasic Characterization of Brucella spp. in Livestock Slaughtered from Abattoirs in Eastern Cape, South Africa

In livestock, brucellosis is mainly an asymptomatic disease except when abortion occurs; therefore, two serological tests are used for diagnosis as no single test is suitable. Abattoir samples enable a combination of culture, molecular, and serological tests to detect brucellosis. This study assessed Brucella-specific PCR (ITS-PCR) to detect brucellosis and to conduct a molecular characterization of Brucella spp. isolated from PCR-positive livestock (n = 565) slaughtered at abattoirs and the appropriate sample tissue(s). ITS-PCR detected Brucella DNA in 33.6% of cattle, 14.5% of sheep, and 4.7% of pig tissues. Impure Brucella cultures from PCR-positive tissues were 43.6% (44/94) of cattle, 51.7% (15/29) of sheep, and 50% (2/4) of pigs with predominantly B. abortus identification with AMOS-PCR and low isolation of mixed B. abortus and B. melitensis in all species. In cattle, 33% of isolates were from lymph nodes, while in sheep 38.0% were from the liver and kidney and only from tonsils in pigs (2/4). Brucella infections identified with AMOS-PCR were present in seropositive and mainly seronegative (75.6-100%) livestock with the potential to cause brucellosis during pregnancy or breeding. This study demonstrated the value of the polyphasic approach, especially with chronic infections and the potential risk of these asymptomatic animals.

The outer membrane proteins based seroprevalence strategy for Brucella ovis natural infection in sheep

Introduction

The diagnosis of brucellosis largely relies on tiger red plate agglutination test (RBPT). However, it is difficult to distinguish between natural infection antibody positive and vaccination antibody positive, nevertheless, the identification of specific Brucella species natural infection.

Methods

Here, we analyzed the structure of main outer membrane proteins (OMPs), OMP25 and OMP31 from Brucella ovis (B. ovis) and Brucella melitensis (B. melitensis), which are the main pathogens of sheep brucellosis, and found the OMP25 and OMP31 could be used as the differential antigens for B. ovis and B. melitensis antibody. Then we expressed the OMP25 from B. ovis (OMP25o) and OMP31 from B. melitensis (OMP31m).

Results

They have equally efficiency in antibody detection of vaccinated sheep serum, consistent with the RBPT results. However, through epidemiological investigations, we found some RBPT positive samples were negative by the OMP31m based serum antibody detection, but these samples gave positive results by the OMP25o. We verified these OMP31m negative but OMP25o positive samples by B. ovis and B. melitensis specific primers based PCR detection, and all these samples were B. melitensis negative. However, four out of six samples are B. ovis positive. These results showed that we could use the OMP25o and OMP31m to diagnose sheep brucellosis antibody, especially to discriminate the infection of the B. ovis.

Discussion

Currently, China has not yet approved a vaccine based on B. ovis and B. ovis positive samples should be naturally infected. There should be some implicit transmission of B. ovis in Jilin province. Further epidemiological investigation should be conducted to monitor the B. ovis natural infection.

Evaluation of a Real-time PCR in Combination with a Cultivation Method for the Detection of Brucella Abortus in Organs of Infected Cattle in Southern Italy

Introduction

Brucellosis is a widespread zoonosis of great economic importance for livestock farming in many areas of the world. It is a highly infectious disease which is diagnosed using conventional serological and microbiological methods. The aim of this study was to assess the efficiency of a specific real-time PCR in combination with broth cultivation in detecting Brucella spp. in organs of infected cattle, in order to compare the sensitivity of the two approaches and the time needed in them until a correct diagnosis is made.

Material and Methods

We examined 67 organs collected from 10 cattle slaughtered following a brucellosis outbreak which occurred in February 2016 in southern Italy. The research was carried out by enrichment broth cultivations in combination with a real-time PCR every week for six weeks.

Results

Brucella strains were isolated by cultivation from 44 enrichment broths of organs. All isolates were later identified as Brucella abortus by real-time PCR. Using this method in combination with cultivation made it possible to identify the same percentage of infected animals faster than by cultivation alone. Moreover, the same diagnostic results were obtained, on average two weeks before they would have been using only cultivation. In almost all cases, Brucella was detected by real-time PCR after the first week of cultivation in pre-enrichment Brucella broth, while the bacterial growth was evident usually after 2 or 3 weeks.

Conclusion

Real-time PCR has allowed results to be obtained faster than in the classical microbiological method, reducing the response times to identify positive animals by half.

Molecular detection of Brucella spp. in clinical samples of seropositive ruminants in Bosnia and Herzegovina

Brucellosis is one of the most common zoonotic diseases worldwide that is endemic to Bosnia and Herzegovina (B&H) and remains an emerging public and animal health concern in this country. Diagnostic testing of brucellosis in ruminants in B&H relies exclusively on serological methods. The present study was conducted to determine the presence of Brucella spp. in clinical samples of seropositive ruminants by Real-time PCR assay. Of the 135 samples tested, 37% were positive by Real-time PCR. The frequency of detection of Brucella-DNA in the samples collected from aborted animals (n = 20/20; 100%) was significantly higher (P < 0.00001) when compared to asymptomatic animals (n = 30/115; 26%). Among asymptomatic animals, 31.1% of cattle were positive for Brucella-DNA, followed by sheep (23.4%) and goats (16.6%). The results of this research underline the limitations of the current control policy and indicate the need for additional diagnostic methods required for more effective brucellosis control program.

Molecular detection of Brucella spp. in ruminant herds in Greece

Brucellosis is a worldwide distributed infectious disease. Ruminants and other animal species (swine, dogs, equids, etc.), as well as wild mammals, can be affected. The disease can be transmitted to humans through the food chain or by direct contact with infected animals. Because of the relatively high economic burden due to abortions within a herd, significant efforts have been employed and hence the disease in most European countries has been eradicated. Accordingly, Greece applies both control and eradication programs concerning small ruminants (sheep and goats) and bovines depending on the geographical area. Current challenges in the standard antibody-based laboratory methods used for Brucella detection are the failure to differentiate antibodies against the wild strain from the ones against the vaccine strain Rev1 and antibodies against B. melitensis from those against B. abortus. The aim of the study was to reexamine and combine previously published protocols based on PCR analysis and to generate a rapid, not expensive, and easy to perform diagnostic tool able to confirm the doubtful results delivered from serology. For this reason, 264 samples derived from 191 ruminants of the farm and divided in 2 groups (male/female) were examined with a modified DNA extraction and PCR protocol. Molecular examination revealed the presence of Brucella spp. in 39 out of 264 samples (derived from 30 animals). In addition, Brucella spp. was detected in infected tissues such as testicles, inguinal lymph nodes, fetal liver, and fetal stomach content.

Genotyping of Brucella strains isolated from humans and cattle of different geographical regions of Pakistan using MLVA-15

Background

Prevalence of brucellosis and MLVA genotyping in animals and humans, isolated from different regions of Pakistan was performed. Animals having history of brucellosis from the field and local farms of Bannu, Mardan, Peshawar, Swat, Lahore and Islamabad were selected for blood collection. Humans that work with them were also selected for sampling in this study. Total of 600 samples were taken from cattle and humans and subjected to Rose Bengal plate Test (RBPT) for the initial screening of positive samples. Designed primers of B.abortus for cattle and B.melitensis for humans were utilised to perform PCR. Culturing and isolation was carried to further to perform MLVA genotyping assay through the selection of two panels of primer markers.

Results

RBPT showed more number of cases of brucellosis in animals and humans compared to the PCR findings. Genotyping findings based upon MLVA‐15 set of markers demonstrated that the isolated strains of B.abortus fall in the same clade with strain A1, P8 and A2 from Pakistan and also similar with BCCN#02‐45 strain from India. On the other hand, B.melitensis isolated from different districts of Pakistan shared the same clade with BwIM‐AFG 63, BwIM‐AFG 44 strains from Afghanistan and BwIM IRN 37 strain from Iran. Selected VNTR alleles were sequenced for calibration purposes.

Conclusion

It is concluded that Brucella is prevalent in animals and humans in studied districts of Pakistan. Moreover, A1, P8, BwIM‐AFG 63, BwIM‐AFG 44 and A2 were found the common genotypes in Pakistan.

Direct diagnosis of Brucella species through multiplex PCR formed by a new method

This study aimed to develop direct PCR methods, which enable the diagnosis of brucellosis agents from ruminant aborted fetus samples at species and genus levels, and determine the applicability of the newly developed methods. For this purpose, 137 lung, 137 liver, and 52 fetal stomach fluid samples belonging to 166 ruminant aborted fetuses (326 samples in total) were examined. Firstly, agent isolation and identification were performed and species-specific multiplex PCR (m-PCR) from the culture was applied to the samples. In addition, the Mayer-Scholl m-PCR method was modified and termed 'modified Mayer-Scholl', and genus specific Bcsp31 PCR was also modified with minor changes. Four different methods were applied to direct examination samples and the obtained results were compared. The conventional culture method was set as the standard method to which sensitivities and specificities of the molecular methods were calculated. According to the assessments on the basis of fetus (n = 166), sensitivity and specificity values for modified Mayer-Scholl m-PCR method were 94.11% and 98.76%, and the same indicators for the modified Bcsp31 PCR were 95.29% and 98.76%, respectively. When all organ samples were taken into account (n = 326), sensitivity and specificity values for the modified Mayer-Scholl m-PCR method were 85.38% and 98.06%, and for the modified Bcsp31 PCR, they were 83.62% and 98.06%, respectively. As a result, it was found that the diagnostic power of the tests were 'high' when results were evaluated at fetus level. On the other hand, it was found to be 'clinically useful' when evaluated at organ level. We concluded that species level identifications can be made through the modified Mayer-Scholl method, which is a direct m-PCR method, with a high diagnostic power by specifying DNAs belonging to Brucella species directly from clinical samples.

High Shedding Potential and Significant Individual Heterogeneity in Naturally-Infected Alpine ibex (Capra ibex) With Brucella melitensis

Wildlife reservoirs of infectious diseases raise major management issues. In Europe, brucellosis has been eradicated in domestic ruminants from most countries and wild ruminants have not been considered important reservoirs so far. However, a high prevalence of Brucella melitensis infection has been recently identified in a French population of Alpine ibex (Capra ibex), after the emergence of brucellosis was confirmed in a dairy cattle farm and two human cases. This situation raised the need to identify the factors driving the persistence of Brucella infection at high prevalence levels in this ibex population. In the present paper, we studied the shedding pattern of B. melitensis in ibex from Bargy Massif, French Alps. Bacteriological examinations (1-15 tissues/samples per individual) were performed on 88 seropositive, supposedly infected and euthanized individuals. Among them, 51 (58%) showed at least one positive culture, including 45 ibex with at least one Brucella isolation from a urogenital sample or a lymph node in the pelvic area (active infection in organs in the pelvic area). Among these 45 ibex, 26 (30% of the total number of necropsied animals) showed at least one positive culture for a urogenital organ and were considered as being at risk of shedding the bacteria at the time of capture. We observed significant heterogeneity between sex-and-age classes: seropositive females were most at risk to excrete Brucella before the age of 5 years, possibly corresponding to abortion during the first pregnancy following infection such as reported in the domestic ruminants. The high shedding potential observed in young females may have contributed to the self-sustained maintenance of infection in this population, whereas males are supposed to play a role of transmission between spatial units through venereal transmission during mating. This heterogeneity in the shedding potential of seropositive individuals should be considered in the future to better evaluate management scenarios in this system as well as in others.

Examining the Possibility of Detecting Brucella Canis from Tissue Samples Using Bruce-Ladder Multiplex PCR Assay

The goal of this study was to compare the results of serological and conventional bacteriological methods with the results obtained using multiplex PCR Bruce-ladder assay. Based on the obtained results, the usability of the assay was assessed in regard to rapid diagnosis of canine brucellosis directly from the samples of reproductive organs of infected dogs. Out of 225 blood samples, 33 (14.67%) had a positive agglutination reaction. In this study, out of the 225 assayed reproductive organs of dogs, B. canis was isolated from 3 samples (1.33%), while the PCR Bruce-ladder assay detected two positive samples (0.88%). Two dogs from which B. canis was isolated, an antibody titer of 1/200 was established in blood serums, and third dog from which B. canis was isolated was negative using the tube agglutination test. From a total of 225 assayed organ samples, a positive PCR reaction was obtained from two samples. The obtained results show that the tube agglutination method remains the first choice for the detection of dogs infected with B. canis. In addition, whenever possible, it is necessary to try isolation. It is desirable to attempt the detection of B. canis in tissues using PCR, but the results may not be treated as definitive and reliable.

Use of <i>Brucella abortus</i> species specific polymerase chain reaction assay for the diagnosis of bovine brucellosis

Serology is primarily used in the diagnosis of bovine brucellosis. Bacterial culture and isolation is the gold standard in diagnosing brucellosis but, like serology, it does not offer complete (100%) diagnostic sensitivity and specificity. Polymerase chain reaction (PCR) has been suggested to offer better specificity and sensitivity. In this study, we evaluated the performance of Brucella abortus species specific (BaSS) PCR directly from different samples in the diagnosis of bovine brucellosis in naturally infected cattle in KwaZulu-Natal province of South Africa with known infectious status from culture. The BaSS PCR had a low diagnostic sensitivity (DSe) of 70%, but was able to identify vaccine strains using abomasal fluid from aborted foetuses and detect Brucella DNA from decomposing samples. The best sample for the BaSS PCR was abomasal fluid.

Mucosal bacterial dissemination in a rhesus macaque model of experimental brucellosis

Animals were experimentally infected with Brucella melitensis via aerosol. B. melitensis was cultured from the saliva and vaginal vault of infected animals, corresponding to bacterial dissemination in other target tissues. This is the first report of bacterial dissemination to these mucosal surfaces in a non-human primate model of brucellosis.

Loop-mediated isothermal amplification (LAMP) test for specific and rapid detection of Brucella abortus in cattle

BACKGROUND

Brucella abortus, the major causative agent of abortion in cattle and a zoonotic pathogen, needs to be diagnosed at an early stage. Loop-mediated isothermal amplification (LAMP) test is easy to perform and also promising to be adapted at field level.

OBJECTIVE

To develop a LAMP assay for specific and rapid detection of B. abortus from clinical samples of cattle.

METHODS

LAMP primers were designed targeting BruAb2_0168 region using specific software tool and LAMP was optimized. The developed LAMP was tested for its specificity with 3 Brucella spp. and 11 other non-Brucella spp. Sensitivity of the developed LAMP was also carried out with known quantity of DNA. Cattle whole blood samples and aborted fetal stomach contents were collected and used for testing with developed LAMP assay and results were compared with polymerase chain reaction (PCR).

RESULTS

The developed LAMP assay works at 61 °C for 60 min and the detection limit was observed to be 100-fold more than the conventional PCR that is commonly used for diagnosis of B. abortus. Clinical sensitivity and specificity of the developed LAMP assay was 100% when compared with Rose Bengal plate test and standard tube agglutination test. SYB® green dye I was used to visualize the result with naked eye.

CONCLUSION

The novelty of the developed LAMP assay for specifically detecting B. abortus infection in cattle along with its inherent rapidness and high sensitivity can be employed for detecting this economically important pathogen of cattle at field level as well be exploited for screening of human infections.

A protein-conjugate approach to develop a monoclonal antibody-based antigen detection test for the diagnosis of human brucellosis

Human brucellosis is most commonly diagnosed by serology based on agglutination of fixed Brucella abortus as antigen. Nucleic acid amplification techniques have not proven capable of reproducibly and sensitively demonstrating the presence of Brucella DNA in clinical specimens. We sought to optimize a monoclonal antibody-based assay to detect Brucella melitensis lipopolysaccharide in blood by conjugating B. melitensis LPS to keyhole limpet hemocyanin, an immunogenic protein carrier to maximize IgG affinity of monoclonal antibodies. A panel of specific of monoclonal antibodies was obtained that recognized both B. melitensis and B. abortus lipopolysaccharide epitopes. An antigen capture assay was developed that detected B. melitensis in the blood of experimentally infected mice and, in a pilot study, in naturally infected Peruvian subjects. As a proof of principle, a majority (7/10) of the patients with positive blood cultures had B. melitensis lipopolysaccharide detected in the initial blood specimen obtained. One of 10 patients with relapsed brucellosis and negative blood culture had a positive serum antigen test. No seronegative/blood culture negative patients had a positive serum antigen test. Analysis of the pair of monoclonal antibodies (2D1, 2E8) used in the capture ELISA for potential cross-reactivity in the detection of lipopolysaccharides of E. coli O157:H7 and Yersinia enterocolitica O9 showed specificity for Brucella lipopolysaccharide. This new approach to develop antigen-detection monoclonal antibodies against a T cell-independent polysaccharide antigen based on immunogenic protein conjugation may lead to the production of improved rapid point-of-care-deployable assays for the diagnosis of brucellosis and other infectious diseases.

Developing a real-time quantitative loop-mediated isothermal amplification assay as a rapid and accurate method for detection of Brucellosis

AIM

The aim of this study was designing a LAMP method for the rapid detection of Brucella and development of a sensitive quantitative-LAMP (Q-LAMP) assay for quantification of brucellosis.

METHODS AND RESULTS

In this study for the LAMP detection of the causative agent of brucellosis, we used specifically designed primers to target the omp25 conserved gene of Brucella spp. The sensitivity of the LAMP method was evaluated by preparing serial tenfold dilution of omp25 gene containing plasmid followed by performing the LAMP reaction. To improve the assay as a quantitative test, LAMP products in the serial dilution were evaluated by Loopamp real-time turbidimeter system and then standard curve was generated by plotting time threshold values against log of copy number. The assay specificity was evaluated using Brucella genomic DNA and a panel containing genomes of 11 gram-positive and gram-negative organisms. The LAMP assay was highly specific and no amplification products were observed from the non-Brucella organisms. The test sensitivity for visual detection of turbidity or fluorescent colour change and also agarose gel electrophoresis was 560 ng and 5·6 ng, respectively. The lower limit of detection was 17 copies of the gene that could be detected in 50 min.

CONCLUSIONS

The results of this study indicated that the LAMP assay is a simple, rapid, sensitive and specific technique for detection of Brucella spp. that may improve diagnostic potential in clinical laboratories.

SIGNIFICANCE AND IMPACT OF THE STUDY

The LAMP assay because of the simplicity and low cost can be preferred to other molecular methods in the diagnosis of infectious diseases.

Evaluation of the recombinant 10-kilodalton immunodominant region of the BP26 protein of Brucella abortus for specific diagnosis of bovine brucellosis

Brucellosis is a disease with worldwide distribution affecting animals and human beings. Brucella abortus is the causative agent of bovine brucellosis. The cross-reactions of currently available diagnostic procedures for B. abortus infection result in false-positive reactions, which make the procedures unreliable. These tests are also unable to differentiate Brucella-infected and -vaccinated animals. The present work is focused on the use of a nonlipopolysaccharide (LPS) diagnostic antigen, a recombinant 10-kDa (r10-kDa) protein of B. abortus, for specific diagnosis of brucellosis. The purified recombinant protein was used as a diagnostic antigen in plate enzyme-linked immunosorbent assay (p-ELISA) format to screen 408 bovine serum samples (70 presumptively negative, 308 random, and 30 vaccinated), and the results were compared with those of the Rose Bengal plate agglutination test (RBPT) and the standard tube agglutination test (STAT). Statistical analysis in presumptive negative samples revealed 100 and 98.41% specificity of p-ELISA with RBPT and STAT, and an agreement of 91.43% with the tests using Cohen's kappa statistics. In random samples, the agreement of p-ELISA was 77.92% and 80.52% with RBPT and STAT, respectively. p-ELISA investigation of vaccinated samples reported no false-positive results, whereas RBPT and STAT reported 30% and 96.6% false-positive results, respectively. The data suggest that p-ELISA with r10-kDa protein may be a useful method for diagnosis of bovine brucellosis. Furthermore, p-ELISA may also be used as a tool for differentiating Brucella-vaccinated and naturally infected animals.

Development of an Individual Rapid Test Based on Enzymatic Immunofiltration Assay for Detection of Anti–Brucella Abortus Antibody in Bovine Sera

To detect bovine antibody directed to smooth lipopolysaccharide (LPS), cell lysate (LYS), O-polysaccharide (OPS), and LPS-deprived chromatographic fractions (ChF) of Brucella abortus, 2 bi-antigenic diagnostic models based on the enzymatic rapid immunofiltration assay (ERIFA), ERIFALPS/LYS and ERIFAOPS/ChF, were developed. Their diagnostic performance was compared with complement fixation test (CFT), Rose Bengal test (RBT), indirect in-house and commercial enzyme-linked immunosorbent assays (iELISA and com-ELISA, respectively), based on the smooth LPS antigen, by using a total of 420 cattle sera collected from aborted-unvaccinated, aborted-unvaccinated and culture-positive, healthy-unvaccinated, and healthy-vaccinated cattle. The results demonstrated excellent agreement and no statistical difference between iELISAs and LPS-, LYS-, OPS-based ERIFA models. However, diagnostic performance of CFT, RBT, and ChF-based ERIFA was less significant than that of LPS-, LYS-, and OPS-based ERIFA models, and iELISAs. The results demonstrated a successful adaptation of the multi-antigenic ERIFA model to anti– B. abortus antibody in bovine sera and suggest that the ERIFA model can be considered as an “individual rapid ELISA” due to its similarity with ELISA, individual applicability, and rapidity in determining reactor animals within 5 minutes. In conclusion, the potential of multi-antigenic applications can make the rapid ERIFA model not only an alternative screening method but also a confirmatory test for bovine brucellosis diagnosis.

Detection of Brucella canis from inguinal lymph nodes of naturally infected dogs by PCR

The aim of this study was to standardize and evaluate a PCR assay for the detection of Brucella canis (B. canis) in lymph node samples of naturally infected dogs. The performance of the PCR was compared with the results of bacteriological culture as reference method. Forty-eight inguinal lymph node samples were collected from 48 dogs (18 males and 30 females) that died in the city's pound in the years 2007-2008 and were examined by microbiological culture and the PCR assay. B. canis was isolated from 4 (8.3%) of 48 lymph node samples. Forty-four (91.7%) of the samples were bacteriological culture negative. B. canis DNA was directly detected from all culture positive lymph node samples (n = 4) by PCR. All of the culture negative samples were confirmed as negative by PCR. When the culture method was used as a gold standard, sensitivity and specificity of the PCR assay were found to be 100%. The limit of PCR detection of B. canis DNA was 1.4 x 10(1) CFU/g at least. In conclusion, the PCR assay has been shown to have a diagnostic performance equal to bacteriological culture for detection of B. canis. By a non-hazardous protocol for laboratory workers, the assay can be performed in one day.

IS711-based real-time PCR assay as a tool for detection of Brucella spp. in wild boars and comparison with bacterial isolation and serology

BACKGROUND

Control of brucellosis in livestock, wildlife and humans depends on the reliability of the methods used for detection and identification of bacteria. In the present study, we describe the evaluation of the recently established real-time PCR assay based on the Brucella-specific insertion sequence IS711 with blood samples from 199 wild boars (first group of animals) and tissue samples from 53 wild boars (second group of animals) collected in Switzerland. Results from IS711 real-time PCR were compared to those obtained by bacterial isolation, Rose Bengal Test (RBT), competitive ELISA (c-ELISA) and indirect ELISA (i-ELISA).

RESULTS

In the first group of animals, IS711 real-time PCR detected infection in 11.1% (16/144) of wild boars that were serologically negative. Serological tests showed different sensitivities [RBT 15.6%, c-ELISA 7.5% and i-ELISA 5.5%] and only 2% of blood samples were positive with all three tests, which makes interpretation of the serological results very difficult. Regarding the second group of animals, the IS711 real-time PCR detected infection in 26% of animals, while Brucella spp. could be isolated from tissues of only 9.4% of the animals.

CONCLUSION

The results presented here indicate that IS711 real-time PCR assay is a specific and sensitive tool for detection of Brucella spp. infections in wild boars. For this reason, we propose the employment of IS711 real-time PCR as a complementary tool in brucellosis screening programs and for confirmation of diagnosis in doubtful cases.