Diagnosis and epidemiology of bovine tuberculosis using molecular biological approaches

Mycobacterium tuberculosis complex in wildlife: Review of current applications of antemortem and postmortem diagnosis

Tuberculosis (TB) is a chronic inflammatory and zoonotic disease caused by Mycobacterium tuberculosis complex (MTBC) members, which affects various domestic animals, wildlife, and humans. Some wild animals serve as reservoir hosts in the transmission and epidemiology of the disease. Therefore, the monitoring and surveillance of both wild and domestic hosts are critical for prevention and control strategies. For TB diagnosis, the single intradermal tuberculin test or the single comparative intradermal tuberculin test, and the gamma-interferon test, which is regarded as an ancillary test, are used. Postmortem examination can identify granulomatous lesions compatible with a diagnosis of TB. In contrast, smears of the lesions can be stained for acid-fast bacilli, and samples of the affected organs can be subjected to histopathological analyses. Culture is the gold standard test for isolating mycobacterial bacilli because it has high sensitivity and specificity compared with other methods. Serology for antibody detection allows the testing of many samples simply, rapidly, and inexpensively, and the protocol can be standardized in different laboratories. Molecular biological analyses are also applicable to trace the epidemiology of the disease. In conclusion, reviewing the various techniques used in MTBC diagnosis can help establish guidelines for researchers when choosing a particular diagnostic method depending on the situation at hand, be it disease outbreaks in wildlife or for epidemiological studies. This is because a good understanding of various diagnostic techniques will aid in monitoring and managing emerging pandemic threats of infectious diseases from wildlife and also preventing the potential spread of zoonotic TB to livestock and humans. This review aimed to provide up-to-date information on different techniques used for diagnosing TB at the interfaces between wildlife, livestock, and humans.

Development and evaluation of LAMP-coupled lateral flow device for the detection of MAP in livestock at point of care resource-limited areas

The Mycobacterium avium subspecies paratuberculosis (MAP) causes paratuberculosis (Johne's disease), a systemic and chronic inflammation of intestine that affects bovine, small ruminants like goat and sheep. The disease has a greater economic importance in cattle and in small ruminants. But its effective control is impeded due to lack of rapid and accurate diagnostics. The present study is aimed at developing a LAMP-coupled lateral flow device (LFD) for rapid detection of paratuberculosis in livestock animal species such as cattle and in small ruminants at resource-limited areas. LAMP primers with biotin and FITC end tags were designed for IS900 gene specific for MAP. To determine sensitivity of LAMP assay, 10-fold serial dilutions were made from 10 ng/μl MAP stock DNA and were compared with PCR. The detection limits of LAMP-coupled LFD were defined and reactions were repeated for reproducibility. The specificity was evaluated using other infectious bacteria such as M. bovis, M. tuberculosis, Brucella abortus, Leptospira interrogan, Yersinia enterocolitica, Salmonella typhimurium, Listeria monocytogens, and Staphylococcus aureus. A total of 95 samples turned positive for LAMP-coupled LFD out of 389 fecal samples. All the cultural-positive and PCR-positive samples showed positive in LAMP-coupled LFD. Nine samples with negative cultures turned positive in LAMP assay. The overall sensitivity and specificity of the LAMP-coupled LFD assays were 100% and 97.02% respectively in comparison with the culture as the gold standard method. The sensitivity detection limit of developed assay was 10 fg/μl and specificity was 100%. This assay successfully detected MAP not only by using bacterial DNA but also in clinical fecal samples. The clear band formation at control and test positions was observed on LAMP-coupled LFD. The developed assay is a simple, rapid, easy to perform, and is very useful in early diagnosis of Mycobacterium avium subsp. paratuberculosis at point of care resource-limited areas.

Diagnosis of bovine tuberculosis: review of main techniques

Abstract Bovine tuberculosis (BTB) remains an important economic and zoonotic problem in Latin America. Traditionally, the fight against BTB is initiated by the implementation of routine diagnostic tests for certification of free properties. The diagnosis of BTB can be made by direct and indirect methods, in which we can mention clinical, post mortem, histopathological, immunological, bacteriological and molecular methods. The renewal of scientific interest in tuberculosis in recent year has led to develop and improve methods of diagnosis, prevention, control and eradication of BTB. The aim of this review is to present and discuss different diagnosis methods of BTB.

Frequência de lesões macroscópicas em carcaças de bovinos reagentes ao teste tuberculínico

O objetivo deste trabalho foi analisar a frequência de lesões macroscópicas sugestivas de tuberculose em carcaças de bovinos reagentes ao teste intradérmico de tuberculose. Os animais do estudo foram provenientes de rebanhos de exploração leiteira, localizados nos municípios de Perdizes, Patos de Minas, Lagoa Formosa e Uberlândia, Minas Gerais. Foram avaliadas 140 carcaças de bovinos positivos no teste cervical comparativo. Durante o abate sanitário foi realizada inspeção post mortem das carcaças, e as lesões macroscópicas sugestivas de tuberculose foram registradas. Foram avaliados os linfonodos mediastínicos, fígado, pulmão e carcaça. Dos 140 bovinos examinados, 78 (55%) apresentaram algum tipo de lesão macroscópica sugestiva de tuberculose, 38 (49%) ocorreram exclusivamente nos linfonodos mediastínicos, 22 (28%) no fígado e 11 (14%) no pulmão; 5 (6%) carcaças apresentaram lesões no fígado, pulmão e linfonodo mediastínico, e 2 (4%) tiveram lesões no pulmão e linfonodo. Concluem-se que as lesões não visualizadas em bovinos reagentes ao teste tuberculínico podem ocorrer e estariam relacionadas principalmente ao estágio de evolução da doença, tempo insuficiente na inspeção post mortempara detecção, bem como reações inespecíficas para outras micobactérias.

Molecular typing of Mycobacterium bovis isolates: a review

Mycobacterium bovis is the main causative agent of animal tuberculosis (TB) and it may cause TB in humans. Molecular typing of M. bovis isolates provides precise epidemiological data on issues of inter- or intra-herd transmission and wildlife reservoirs. Techniques used for typing M. bovis have evolved over the last 2 decades, and PCR-based methods such as spoligotyping and mycobacterial interspersed repetitive unit-variable number tandem repeat (MIRU-VNTR) have been extensively used. These techniques can provide epidemiological information about isolates of M. Bovis that may help control bovine TB by indicating possible links between diseased animals, detecting and sampling outbreaks, and even demonstrating cases of laboratory cross-contamination between samples. This review will focus on techniques used for the molecular typing of M. bovis and discuss their general aspects and applications.

Thin layer microcolony culture associated with PCR for early identification of Mycobacterium bovis

The initial growth of mycobacteria from 49 samples of cattle and buffalo organs collected in commercial slaughterhouses was compared between modified Middlebrook 7H11 thin layer microcolony culture and Stonebrink medium used in the isolation of Mycobacterium bovis. Aliquots were decontaminated by Petroff's method, processed and cultured in both media. The identity of the acid-fast bacilli stained by Ziehl-Neelsen was confirmed by PCR. Optical microscopy showed that results of the early observation of Mycobacterium bovis colonies in thin layer culture were similar to those obtained in macroscopic observation of the colonies in Stonebrink medium. However, early observation of the colonies enabled early confirmation by PCR, given the shorter time to the visualization of colonies when thin layer culture was used (between the 12(nd) and 25(th) day of culture).

Genome-Wide Sequence Variation among Mycobacterium avium Subspecies paratuberculosis Isolates: A Better Understanding of Johne's Disease Transmission Dynamics

Mycobacterium avium subspecies paratuberculosis (M. ap), the causative agent of Johne’s disease, infects many farmed ruminants, wild-life animals, and recently isolated from humans. To better understand the molecular pathogenesis of these infections, we analyzed the whole-genome sequences of several M. ap and M. avium subspecies avium (M. avium) isolates to gain insights into genomic diversity associated with variable hosts and environments. Using Next-generation sequencing technology, all six M. ap isolates showed a high percentage of similarity (98%) to the reference genome sequence of M. ap K-10 isolated from cattle. However, two M. avium isolates (DT 78 and Env 77) showed significant sequence diversity (only 87 and 40% similarity, respectively) compared to the reference strain M. avium 104, a reflection of the wide environmental niches of this group of mycobacteria. Within the M. ap isolates, genomic rearrangements (insertions/deletions) were not detected, and only unique single nucleotide polymorphisms (SNPs) were observed among M. ap isolates. While more of the SNPs (~100) in M. ap genomes were non-synonymous, a total of ~6,000 SNPs were detected among M. avium genomes, most of them were synonymous suggesting a differential selective pressure between M. ap and M. avium isolates. In addition, SNPs-based phylo-genomics had a enough discriminatory power to differentiate between isolates from different hosts but yet suggesting a bovine source of infection to other animals examined in this study. Interestingly, the human isolate (M. ap 4B) was closely related to a M. ap isolate from a dairy facility, suggesting a common source of infection. Overall, the identified phylo-genomes further supported the idea of a common ancestor to both M. ap and M. avium isolates. Genome-wide analysis described here could provide a strong foundation for a population genetic structure that could be useful for the analysis of mycobacterial evolution and for the tracking of Johne’s disease transmission among animals.

Advances in molecular diagnostics for Mycobacterium bovis

The two most important molecular diagnostic techniques for bovine tuberculosis are the polymerase chain reaction (PCR) because of its rapid determination of infection, and DNA strain typing because of its ability to answer important epidemiological questions. PCR tests for Mycobacterium bovis have been improved through recent advances in PCR technology, but still lack the sensitivity of good culture methods, and in some situations are susceptible to giving both false negative and false positive results. Therefore, PCR does not usually replace the need for culture, but is used to provide fast preliminary results. DNA typing of M. bovis isolates by restriction endonuclease analysis (REA) was developed 25 years ago in New Zealand, and remains an important tool in the New Zealand control scheme, where the typing results are combined with other information to determine large and expensive possum poisoning operations. A range of other DNA typing systems developed for M. bovis in the 1990 s have assisted epidemiological investigations in some countries but are now less commonly used. Variable number tandem repeat (VNTR) typing and spoligotyping, either alone or together, have now become the preferred approaches as they are robust and amenable to electronic analysis and comparison. Spoligotyping gives only moderate discrimination but can be easily applied to large numbers of isolates, and VNTR typing provides better discrimination than all other methods except for REA. While the current typing techniques are sufficient for most epidemiological purposes, more discriminating methods are likely to become available in the near future.

Comparison of 45 variable number tandem repeat (VNTR) and two direct repeat (DR) assays to restriction endonuclease analysis for typing isolates of Mycobacterium bovis

Restriction endonuclease analysis (REA), developed 25 years ago for genotyping Mycobacterium bovis strains, is an important tool for bovine tuberculosis control in New Zealand. While REA gives excellent discrimination, it is technically difficult to perform compared to PCR-based typing systems which are faster and simpler to operate. Genotyping of M. bovis by the use of variable number tandem repeat loci (VNTR) and spoligotyping, either alone or together, has now become the preferred approach for typing M. bovis. Here, we evaluated the widest range of VNTR loci yet investigated for M. bovis, including two VNTR loci not previously studied, one of which (4155) had particular utility for characterizing New Zealand isolates. VNTR typing provided substantial geographical resolution of 26 of the most commonly found REA types and this was improved by the addition of two PCR assays based on parts of the direct repeat (DR) locus. Overall, 68 REA types of M. bovis common in New Zealand were discriminated into 33 VNTR/DR groups by using a minimum of nine VNTR and two DR assays. These 11 VNTR/DR assays concorded for three isolates each of 45 of the REA types but showed some variation with at least one of the VNTR/DR assays for the remaining 23 REA types. Major differences were found in allelic variation of some VNTRs between isolates from New Zealand and other countries, emphasizing the importance of adapting M. bovis typing systems to suit individual countries.

Potential application of new diagnostic methods for controlling bovine tuberculosis in Brazil

Bovine tuberculosis, a chronic infection in cattle caused by Mycobacterium bovis, remains an economic and public health problem for several countries. Due to its economic impact on international trade, contagious nature, and implications for human health, global programs to eradicate the disease were implemented worldwide. Those programs are based on slaughtering PPD-reactive animals. Despite the National Programs in Brazil, complete eradication has not been achieved, and the disease remains, albeit at a lower prevalence. The central purpose of this review is to address diagnostic tests for tuberculosis. Considering the course of the infection in cattle, at least two tests, ideally complementary to one another, may be necessary for an adequate diagnosis: the first based on the cellular response, and the second capable of identifying anergic animals by detection of specific anti-M.bovis antibodies.

Evaluation of adenosine deaminase seric activity in the diagnosis of bovine tuberculosis

Determination of seric levels of adenosine deaminase (ADA), an enzyme produced by monocytes/macrophages and lymphocytes, has been used in the diagnosis of human tuberculosis (TB). In the present study, ADA seric activity was evaluated comparatively to the comparative tuberculin test in the diagnosis of bovine tuberculosis. Two hundred fifty-six cattle were classified by origin and by the comparative tuberculin test as TB-positive animals (n = 52, from herds where the Mycobacterium bovis had previously been isolated), and TB-negative animals (n = 204, TB-free herds). The mean ADA seric value from the TB-positive group (4.45 +/- 2.33 U/L) was significantly lower (p = 0.008) than that observed in sera from the TB-negative group (6.12 +/- 4.47 U/L). When animals from a herd with clinical cases of enzootic bovine leukosis of TB-negative group were withdrawn from analysis, the mean ADA seric values of TB-negative group (5.12 +/- 3.75 U/L) was not significantly different anymore from that of the TB-positive group (p = 0.28). There was no agreement in the diagnosis of bovine TB between comparative tuberculin test and determination of ADA seric values, using two different cutoff points, being 6.12 U/L and 15.0 U/L, (kappa = -0.086 and kappa = -0.082, respectively). In conclusion, the determination of ADA seric activity was not a good auxiliary test for bovine TB, because it was not able to distinguish between TB-positive and TB-negative animals.

TUBERCULOSE BOVINA: ALTERNATIVAS PARA O DIAGNÓSTICO

RESUMO A tuberculose é uma das principais preocupações da Organização Mundial da Saúde, especialmente após o surgimento da AIDS e do aumento da multidroga resistência, sendo considerada a principal causa de morte por um único agente. Além do Mycobaterium tuberculosis, principal responsável pela doença em humanos, outra manifestação de importância epidemiológica é a infecção causada pelo Mycobaterium bovis, devido à transmissão ao homem, especialmente, pela ingestão de alimentos contaminados, e à escassez de dados relacionados a sua prevalência na população. Em várias partes do mundo existem programas de controle da doença nos bovinos, fundamentados na identificação por teste tuberculínico e na eliminação dos animais positivos. As lesões encontradas em exames post-mortem podem ser confirmadas através do isolamento e identificação do agente, porém esse procedimento pode demandar meses para a sua conclusão, razão pela qual, para reduzir o tempo de diagnóstico, novos métodos moleculares são propostos. Para proporcionar uma visão atualizada sobre os esforços no combate da tuberculose bovina, sobre os resultados das campanhas de controle e erradicação e sobre os métodos recentes disponíveis para diagnóstico da tuberculose bovina, como o PCR, neste trabalho é apresentada uma revisão bibliográfica, ressaltando as vantagens e dificuldades para o emprego dos ensaios para diagnóstico e a possibilidade de sua utilização em escala. Concluímos que apesar dos avanços alcançados, ainda não se tem disponível, para a rotina laboratorial, um ensaio sensível, reprodutível e rápido para o diagnóstico da tuberculose em bovinos, sendo essencial esforço e investimento em pesquisas para a solução desse ponto crítico no combate à enfermidade.

DNA typing of Mycobacterium bovis strains from the Castlepoint area of the Wairarapa

AIM

To investigate isolates of Mycobacterium bovis from the Castlepoint area of the Wairarapa using three different methods of DNA typing.

METHODS

Isolates of M. bovis, obtained from animals in the Castlepoint area between 1982-l 998, were characterised by restriction endonuclease analysis. An isolate representing each restriction type was characterised by two newer DNA typing methods based on the polymorphic GC-rich repetitive sequence (PGRS) and spoligotyping.

RESULTS

Over 300 isolates were distinguished into 26 restriction types. The 24 available restriction types were differentiated into 11 PGRS types and 7 spoligotypes. The three most common restriction types had the same PGRS type and the same spoligotype.

CONCLUSIONS

The relatively large number of restriction types found, indicated that restriction endonuclease analysis was well suited for detailed epidemiological studies at Castlepoint. Spoligotyping was less discriminatory than PGRS typing but both methods could be used to group isolates with different restriction types.

Drug susceptibility of Brazilian strains of Mycobacterium bovis using traditional and molecular techniques

Transmission of Mycobacterium bovis from cattle to humans has been reported and can cause tuberculosis (Tb) and a problem in certain risk populations. Therefore, knowledge of resistance of M. bovis towards antibiotics used for therapy of human Tb could help avoiding cure delay and treatment cost increase when dealing with drug resistant organisms. We therefore evaluated the susceptibility of M. bovis isolates towards streptomycin, isoniazide, rifampicin, ethambutol, and ethionamide, the first line antibiotics for human Tb. Therefore, 185 clinical samples from cattle with clinical signs of tuberculosis were processed and submitted to culturing and bacterial isolates to identification and drug susceptibility testing using the proportion method. Among 89 mycobacterial strains, 65 were identified as M. bovis and none were resistant to any of the antibiotics used. Confirmation of present results by future studies, enrolling a large number of isolates and designed to properly represent Brazilian regions, may favor the idea of using isoniazide preventive therapy as part of a Tb control strategy in special situations. Also, nucleic acids from bacterial isolates were submitted to rifoligotyping, a recently described reverse hybridization assay for detection of mutations causing resistance towards rifampicin. Concordance between the conventional and the molecular test was 100%, demonstrating the use of such methodology for rapid evaluation of drug susceptibility in M. bovis.

Molecular epidemiology of Mycobacterium bovis: exploiting molecular data

'Molecular epidemiology' is defined as the integration of conventional epidemiological approaches with molecular techniques to track specific strains of pathogens in order to understand the distribution of disease in populations. It has become a very powerful tool in the study of Mycobacterium tuberculosis and human tuberculosis, where it has been exploited to provide 'added value' to conventional epidemiological approaches (contact tracing) and has often challenged accepted dogmas. It has been used to confirm epidemiologically suspected transmission, to detect epidemiologically unsuspected transmission, to identify risk factors and environments where transmission is occurring, to detect laboratory errors and to monitor the efficacy of tuberculosis control programmes. For Mycobacterium bovis and bovine tuberculosis, molecular epidemiology has a key role to play in providing more precise epidemiological data on the issues of interbovine transmission and the role of wildlife reservoirs in disease maintenance and transmission. M. bovis strains may also differ in key biological properties, such as virulence, transmissibility, stability and antigenic variation, which may help to explain field observations. There may be correlation between strain type and 'herd level' factors such as breakdown size etc. Molecular 'strain typing' studies have provided useful information in several countries, notably New Zealand, where strain typing data is used as an integral part of M. bovis control schemes, to influence the level of herd testing or wildlife control and to define the extent and spread of infected wildlife. This presentation will review the methods and approaches currently appropriate for M. bovis strain typing and will review selected applications as well as discussing future perspectives and challenges for the application of molecular epidemiology to bovine tuberculosis.

Simultaneous detection and strain differentiation of Mycobacterium bovis directly from bovine tissue specimens by spoligotyping

Culture of Mycobacterium bovis is used routinely to support field diagnosis of bovine tuberculosis; however, this method is slow. Rapid detection and strain-typing of M. bovis directly from 37 lesioned bovine lymph node specimens was performed by the polymerase chain reaction (PCR) based method, spoligotyping. Mycobacterial DNA was extracted from the specimens using a nucleic acid sequence capture technique. Two sets of specimens were tested, the first set comprising 16 decontaminated tissue homogenates from lesioned lymph node specimens which had been processed for BACTEC culture and a second set of 21 non-decontaminated lesioned lymph node specimens. Both sets of specimens had been frozen before analysis. Sequence capture PCR enabled detection and strain-typing of M. bovis directly from 15 of the 16 decontaminated homogenates and all 21 of the non-decontaminated tissues. Four spoligotype (ST) patterns were obtained from each set; ST1, ST2, ST3 and ST16 were detected in the decontaminated specimens and ST1, ST2, ST11 and ST14 in the non-decontaminated specimens. For both sets of specimens, ST1 was the predominant strain type detected. ST patterns obtained from the BACTEC cultures of the decontaminated specimens were in agreement with those obtained directly from the tissue. The sensitivity of detection by sequence capture-PCR compared very favourably with that of BACTEC culture. ST patterns were obtained directly from tissues of 34 of the 35 culture positive specimens and the two culture negative specimens. DNA extraction from the 21 non-decontaminated specimens involved an initial stomaching treatment. An assessment of sequence capture on both liquid alone and liquid and tissue homogenate combined, following stomaching, indicated that PCR was less successful on the liquid component alone.

Vaccine protocols to optimise the protective efficacy of BCG

SETTING

A deer model has been developed to study protection produced with BCG vaccination, against infection and the development of pathology, following experimental intratonsilar infection with virulent Mycobacterium bovis.

OBJECTIVE

To determine how the dose of vaccine, the route of vaccination, the viability of the vaccine and exposure to glucocorticoids at the time of vaccination, may affect the protective efficacy of BCG vaccines.

DESIGN

Deer were vaccinated with BCG and later challenged with virulent M. bovis via the tonsilar route. Protection against infection and development of disease was evaluated at necropsy six months after challenge with M. bovis, by histological examination and microbial culture.

RESULTS

Significant protection against infection and disease were obtained following boosting with two low doses (5 x 10(4) cfu) or moderate doses (5 x 10(7) cfu) of live (freshly cultured and lyophilized) BCG. Inferior levels of protection were obtained with high dose (5 x 10(8) cfu) of live BCG. Similar levels of protection were found with vaccines given subcutaneously or via the tonsilar route. Killed vaccine in a mineral-oil adjuvant did not evoke protective immunity and treatment with dexamethasone prior to vaccination with live BCG ablated its efficacy. Protection against infection did not correlate with skin test delayed type hypersensitivity (DTH) or lymphocyte transformation to tuberculin.

CONCLUSIONS

Two doses of live BCG gave significant protection against experimental infection and disease caused by virulent M. bovis. Single dose vaccine protected against disease but not infection. Vaccines administered at a dosage which did not evoke DTH, provided protection against tuberculosis infection and disease.

Molecular epidemiologic analysis of Mycobacterium bovis isolates from Mexico

OBJECTIVE

To assess phylogenetic relationships among Mycobacterium bovis isolates by use of random amplified polymorphic DNA polymerase chain reaction (RAPD-PCR) fingerprinting and to relate genetic profiles of isolates to epidemiologic characteristics.

ANIMALS

400 cattle with tuberculosis.

PROCEDURE

Mycobacterium bovis was isolated from various organs of cattle slaughtered in 6 geographic regions of Mexico. Most cattle were adult Holsteins from large herds that did not participate in a tuberculosis control program. Four random primers and 2 selected primers were used in RAPD-PCR fingerprinting of 88 isolates. Pairwise genetic distance between isolates was obtained and subjected to cluster analysis with bootstrapping to test for levels of support.

RESULTS

98 different fragments were obtained; there was broad genetic diversity among isolates, and each isolate had a unique RAPD-genotype, including those originating from the same herd. Clustering by geographic location, affected organ, or severity of lesion was not detected. Linkage disequilibrium analysis suggested that M. bovis was highly clonal and that mutations develop at a rapid rate among isolates.

CONCLUSIONS AND CLINICAL RELEVANCE

Use of RAPD-PCR could not differentiate M. bovis isolates by epidemiologic characteristics or identify common sources of infection.

Monitoring of transmission of tuberculosis between wild boars and cattle: genotypical analysis of strains by molecular epidemiology techniques

An epidemiological survey for the monitoring of bovine tuberculosis transmission was carried out in western Liguria, a region in northern Italy. Fifteen Mycobacterium bovis strains were isolated from 63 wild boar samples (62 from mandibular lymph nodes and 1 from a liver specimen). Sixteen mediastinal lymph nodes of 16 head of cattle were collected, and 15 Mycobacterium bovis strains were subsequently cultured. All M. bovis strains isolated from cattle and wild boars were genotyped by spoligotyping and by restriction fragment length polymorphism (RFLP) analysis with the IS6110 and IS1081 probes. All M. bovis strains showed the typical spoligotype characterized by the absence of the 39 to 43 spacers in comparison with the number in M. tuberculosis. A total of nine different clusters were identified by spoligotyping. The largest cluster included 9 strains isolated from wild boars and 11 strains isolated from cattle, thus confirming the possibility of transmission between the two animal species. Fingerprinting by RFLP analysis with the IS6110 probe showed an identical single-band pattern for 29 of 30 strains analyzed, and only 1 strain presented a five-band pattern. The use of IS1081 as a second probe was useful for differentiation of M. bovis from M. bovis BCG but not for differentiation among M. bovis strains, which presented the same undifferentiated genomic profile. In relation to the epidemiological investigation, we hypothesized that the feeding in pastures contaminated by cattle discharges could represent the most probable route of transmission of M. bovis between the two animal species. In conclusion, our results confirmed the higher discriminatory power of spoligotyping in relation to that of RFLP analysis for the differentiation of M. bovis genomic profiles. Our data showed the presence of a common M. bovis genotype in both cattle and wild boars, confirming the possible interspecies transmission of M. bovis.

Rapid detection of Mycobacterium bovis on its lipid profile by thin layer chromatography

Sixteen Mycobacterium bovis (M. bovis) strains isolated from bovine tissues and one standard reference strain of M. bovis AN5 alongwith other species of mycobacteria for comparison were investigated for the presence of phenolic glycolipid (PGL) and phthiocerol dimycocerosate (PDIM) for rapid identification of M. bovis by thin-layer chromatography (TLC). The study indicated presence of PGL with an Rf value of 0.75 in chloroform-methanol solvent in all 17 M. bovis strains. The dimycocerostate A corresponding to spot A was the major constituent among all the three spots in M. bovis strains. TLC appeared to be a promising alternative to conventional biochemical methods for identification of M. bovis taking into consideration both PGL and PDIM lipids.

Expression of the Mycobacterium bovis P36 gene in Mycobacterium smegmatis and the baculovirus/insect cell system

In the present study we evaluated different systems for the expression of mycobacterial antigen P36 secreted by Mycobacterium bovis. P36 was detected by Western blot using a specific antiserum. The P36 gene was initially expressed in E. coli, under the control of the T7 promoter, but severe proteolysis prevented its purification. We then tried to express P36 in M. smegmatis and insect cells. For M. smegmatis, we used three different plasmid vectors differing in copy number and in the presence of a promoter for expression of heterologous proteins. P36 was detected in the cell extract and culture supernatant in both expression systems and was recognized by sera from M. bovis-infected cattle. To compare the expression level and compartmentalization, the MPB70 antigen was also expressed. The highest production was reached in insect cell supernatants. In conclusion, M. smegmatis and especially the baculovirus expression system are good choices for the production of proteins from pathogenic mycobacteria for the development of mycobacterial vaccines and diagnostic reagents.

Rapid diagnosis and strain differentiation of Mycobacterium bovis in radiometric culture by spoligotyping

An assessment of spoligotyping for rapid detection and strain typing of Mycobacterium bovis isolates in radiometric culture was made. Spoligotyping was applied to BACTEC 12B broth cultures of 54 lesioned bovine lymph node specimens from 44 herds in Northern Ireland. A nucleic acid sequence capture technique was performed on BACTEC cultures at growth index points of approximately (approximately) 60, approximately 200, and 999. Definitive spoligotype patterns were obtained for 90.4% and 94.2% of all 52 BACTEC culture-positives at growth indexes approximately 60 and approximately 200, respectively. Within 10 days, definitive spoligotype patterns were obtained for 84.6% of the culture-positives. This technique, therefore, allowed earlier and more accurate diagnosis of M. bovis than traditional methodologies, as well as simultaneous strain differentiation. Application of this molecular tool to BACTEC cultures would be a significant advance in bovine tuberculosis eradication programmes. Seven distinct spoligotype patterns were identified in this study, 2 of which (ST21 and ST25), had not been identified previously in cattle from Northern Ireland. Two spoligotype patterns (ST1 and ST2) accounted for 80.7% of the culture-positives. These were found to have widespread geographic distribution, whereas 1 spoligotype pattern (ST14) had limited geographical distribution.

T cell responses to Mycobacterium bovis in red deer, a large animal model for tuberculosis

Red deer (Cervus elaphus) represent an appropriate large animal model to study the immunology of tuberculosis, being naturally susceptible to Mycobacterium bovis infection. Cell-mediated immune responses were investigated in deer displaying protective- or disease-type reactions, following immunization with M. bovis bacille Calmette-Guerin (BCG) or infection with virulent M. bovis, respectively. T cell responses were measured as antigen-dependent cell proliferation and production of T cell growth factor (TCGF) following in vitro stimulation with M. bovis antigens (live or heat-killed BCG, or PPD). T cells from immunized deer proliferated less in response to soluble denatured culture antigen (purified protein derivative, PPD) than to particulate BCG, although there were no differences in the magnitude of these responses between the two groups of animals. Cells derived from immunized deer produced less TCGF than cells from infected deer when stimulated with PPD in vitro, although responses to BCG antigens were similar between the two groups. The majority of TCGF activity was neutralized by anti-IL-2 antibodies, regardless of the animal group or source of antigen used for in vitro stimulation. After 7 days in vitro culture with antigen, blast cells staining positively for alpha beta (CD4, CD8) and gamma delta T cell receptors were recorded. The majority of blasts were CD4+, although in immunized deer fewer CD4+ blasts were produced following in vitro stimulation with PPD than with BCG antigens. These results, together with previous reports from our laboratory, represent the only detailed examinations of T cell responses to M. bovis in this naturally-susceptible ruminant species.

Post mortem diagnosis of Mycobacterium bovis infection in cattle

A tentative diagnosis of bovine tuberculosis can be made following the macroscopic detection at necropsy of typical lesions. Histo-pathological examination of the lesion may increase the confidence of the diagnosis but bacteriological isolation of Mycobacterium bovis from the lesion is the only way to make a definitive diagnosis. The sensitivity of gross post mortem examination is affected by the method employed and the anatomical sites examined. Careful examination of as few as 6 pairs of lymph nodes, the lungs and the mesenteric lymph nodes can result in 95% of cattle with macroscopic lesions being identified. Although during post mortem inspection of carcases at abattoir all the principle sites where lesions are to be found were examined, this procedure was found to be insensitive for the detection of lesions. To determine the significance of cattle that give a positive reaction in diagnostic tests but do not have visible lesions (NVL), a bacteriological examination is necessary. NVLs may be due to early infection, poor necropsy technique or infection with mycobacteria other than M. bovis. M. bovis was found to survive best in frozen tissue and the tissue preservative, sodium tetraborate, was found to have adverse effects on viability. It was found desirable to use two different culture media for the primary isolation of M. bovis; agar media for rapid growth and egg media for control of contamination. Additional control of contamination was achieved without adversely affecting the viability by treating the specimen before culture with 0.075% hexadecylpyridinium chloride. The addition of CO2 to the incubation atmosphere did not enhance the recovery of M. bovis. Conventional identification of isolates of M. bovis is by biochemical tests and cultural characteristics, but methods employing monoclonal antibodies and DNA probes may be used to obtain a rapid identification.