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Improved detection of Mycobacterium bovis infection in bovine lymph node tissue using immunomagnetic separation
Linda D Stewart1, James McNair, Lyanne McCallan
1Institute for Global Food Security, School of Biological Sciences, Queen's University Belfast, Belfast, Northern Ireland, United Kingdom.
Insights
Immunomagnetic separation (IMS) offers a more sensitive and rapid method for detecting Mycobacterium bovis in cattle lymph nodes compared to traditional culture. This advanced technique improves detection rates, especially in non-visibly lesioned samples, aiding bovine tuberculosis eradication efforts.
Area of Science:
- Veterinary Microbiology
- Bovine Tuberculosis Diagnostics
- Infectious Disease Detection
Background:
- Bovine tuberculosis (TB) eradication programs rely on accurate detection of Mycobacterium bovis.
- Traditional culture methods for M. bovis detection can be slow and may yield false negatives, particularly in samples with low bacterial loads.
- Immunomagnetic separation (IMS) offers a potential improvement for isolating M. bovis from complex biological matrices like lymph nodes.
Purpose of the Study:
- To evaluate the diagnostic performance of novel immunomagnetic separation-based methods (IMS-PCR and IMS-MGIT) for detecting Mycobacterium bovis in bovine lymph nodes.
- To compare the sensitivity and speed of IMS-based detection with conventional culture methods in a field survey.
- To assess the utility of IMS for detecting M. bovis in both visibly lesioned (VL) and non-visibly lesioned (NVL) lymph node samples.
Main Methods:
- A survey of 280 bovine lymph nodes from cattle at slaughter was conducted.
- Samples were tested using culture, PCR targeting IS6110 after IMS (IMS-PCR), and MGIT culture after IMS (IMS-MGIT).
- Performance of IMS-based methods was evaluated relative to culture, with analysis of VL and NVL samples.
Main Results:
- Culture detected 62.1% of samples, IMS-PCR 57.8%, and IMS-MGIT 68.2%.
- IMS-based methods identified an additional 79 M. bovis positive samples not detected by culture, particularly in NVL (70.3% of NVL samples).
- IMS-based methods demonstrated greater sensitivity than culture, especially for samples with low M. bovis viability, and were more rapid.
Conclusions:
- Immunomagnetic separation-based methods (IMS-PCR and IMS-MGIT) offer superior sensitivity and speed for Mycobacterium bovis detection in bovine lymph nodes compared to culture alone.
- These methods are particularly advantageous for detecting M. bovis in non-visibly lesioned lymph nodes, where conventional culture may fail due to low bacterial numbers.
- Adoption of IMS-based methods holds significant potential for enhancing the accuracy and efficiency of bovine TB surveillance and eradication programs.
Abstract:
Immunomagnetic separation (IMS) can selectively isolate and concentrate Mycobacterium bovis cells from lymph node tissue to facilitate subsequent detection by PCR (IMS-PCR) or culture (IMS-MGIT). This study describes application of these novel IMS-based methods to test for M. bovis in a survey of 280 bovine lymph nodes (206 visibly lesioned (VL), 74 non-visibly lesioned (NVL)) collected at slaughter as part of the Northern Ireland bovine TB eradication programme. Their performance was evaluated relative to culture. Overall, 174 (62.1%) lymph node samples tested positive by culture, 162 (57.8%) by IMS-PCR (targeting IS6110), and 191 (68.2%) by IMS-MGIT culture. Twelve (6.9%) of the 174 culture positive lymph node samples were not detected by either of the IMS-based methods. However, an additional 79 M. bovis positive lymph node samples (27 (13.1%) VL and 52 (70.3%) NVL) were detected by the IMS-based methods and not by culture. When low numbers of viable M. bovis are present in lymph nodes (e.g. in NVLs of skin test reactor cattle) decontamination prior to culture may adversely affect viability, leading to false negative culture results. In contrast, IMS specifically captures whole M. bovis cells (live, dead or potentially dormant) which are not subject to any deleterious treatment before detection by PCR or MGIT culture. During this study only 2.7% of NVL lymph nodes tested culture positive, whereas 70.3% of the same samples tested M. bovis positive by the IMS-based tests. Results clearly demonstrate that not only are the IMS-based methods more rapid but they have greater detection sensitivity than the culture approach currently used for the detection of M. bovis infection in cattle. Adoption of the IMS-based methods for lymph node testing would have the potential to improve M. bovis detection in clinical samples.
