Abstract
Accurately identifying Mycobacterium bovis-infected cattle is critical for bovine tuberculosis prevention and control. One method for identifying infected cattle is an ELISA developed by IDEXX laboratories, which detects antibodies to two M. bovis proteins, MPB70 and MPB83. The assay’s sensitivity varies by geographic region, with sensitivities of 77%, 45%, and 9% in bovine serum samples from the United Kingdom (n = 126), the United States (n = 146), and Mexico (n = 128), respectively. We hypothesized that geographically-biased sequence variation in mpb70 and mpb83, or in the genes that regulate their expression (sigK and rskA), may explain these differing sensitivities. This hypothesis was tested by comparing the sequences of these four genes in 455 M. bovis strains isolated from cattle in the aforementioned countries. For each gene, a single, common sequence was identified in most genomes of the M. bovis strains collected in all three countries. Twelve of the 455 strains were isolated from infected cattle for which the IDEXX ELISA was also performed. Five of the seven ELISA-positive genomes and three of the five ELISA-negative genomes contained the most common sequence of all four genes. Thus, sequence variation in mpb70, mpb83, sigK, and rskA does not explain the geographic disparities in IDEXX ELISA sensitivity.
Highlights
The bacterium Mycobacterium bovis is the etiological agent of bovine tuberculosis, a persistent infection that primarily affects the lungs but can spread to other body systems
We present additional data concerning the sensitivity of the IDEXX enzyme-linked immunosorbent assay (ELISA) in different geographic regions, and show that the assay exhibits good sensitivity for serum samples from United Kingdom-derived cattle, moderate sensitivity for serum samples from United States-derived cattle, and low sensitivity for serum samples from Mexico-derived cattle
If a sequence-based explanation exists for the geographic disparity in IDEXX ELISA sensitivity, it would be expected that mutations like those described in Supplementary Discussion S2 would be found with the greatest frequency in M. bovis strains from Mexico, with a lower frequency in strains collected in the United States, and with the lowest frequency in strains from the United Kingdom
Summary
The bacterium Mycobacterium bovis is the etiological agent of bovine tuberculosis, a persistent infection that primarily affects the lungs but can spread to other body systems. Due to the economic consequences associated with M. bovis infections in cattle, as well as its zoonotic potential, methods for quickly and accurately identifying infected cattle are of considerable importance One such method is an enzyme-linked immunosorbent assay (ELISA) developed by IDEXX Laboratories (Westbrook, ME), which allows for the rapid detection of M. bovis-specific antibodies in bovine serum or milk samples[5,6]. (See Supplementary Discussion S1 for further information on MPB70 and MPB83, the genes that encode them, and the proteins involved in regulating their expression) This hypothesis was investigated by obtaining whole genome shotgun (WGS) sequences from a large number of M. bovis strains from infected cattle in the United Kingdom, the United States, and Mexico and comparing their mpb[70], mpb[83], sigK and rskA sequences. If a sequence-based explanation exists for the geographic disparity in IDEXX ELISA sensitivity, it would be expected that mutations like those described in Supplementary Discussion S2 would be found with the greatest frequency in M. bovis strains from Mexico, with a lower frequency in strains collected in the United States, and with the lowest frequency in strains from the United Kingdom
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