IS6110 Copy Number in Multi-Host Mycobacterium bovis Strains Circulating in Bovine Tuberculosis Endemic French Regions

Genomic Characterization of IS6110 Insertions in Mycobacterium orygis

Mycobacterium orygis, a subspecies of the Mycobacterium tuberculosis complex (MTBC), has emerged as a significant concern in the context of One Health, with implications for zoonosis or zooanthroponosis or both. MTBC strains are characterized by the unique insertion element IS6110, which is widely used as a diagnostic marker. IS6110 transposition drives genetic modifications in MTBC, imparting genome plasticity and profound biological consequences. While IS6110 insertions are customarily found in the MTBC genomes, the evolutionary trajectory of strains seems to correlate with the number of IS6110 copies, indicating enhanced adaptability with increasing copy numbers. Here, we present a comprehensive analysis of IS6110 insertions in the M. orygis genome, utilizing ISMapper, and elucidate their genetic consequences in promoting successful host adaptation. Our study encompasses a panel of 67 paired-end reads, comprising 11 isolates from our laboratory and 56 sequences downloaded from public databases. Among these sequences, 91% exhibited high-copy, 4.5% low-copy, and 4.5% lacked IS6110 insertions. We identified 255 insertion loci, including 141 intragenic and 114 intergenic insertions. Most of these loci were either unique or shared among a limited number of isolates, potentially influencing strain behavior. Furthermore, we conducted gene ontology and pathway analysis, using eggNOG-mapper 5.0, on the protein sequences disrupted by IS6110 insertions, revealing 63 genes involved in diverse functions of Gene Ontology and 45 genes participating in various KEGG pathways. Our findings offer novel insights into IS6110 insertions, their preferential insertion regions, and their impact on metabolic processes and pathways, providing valuable knowledge on the genetic changes underpinning IS6110 transposition in M. orygis.

Droplet digital PCR as alternative to microbiological culture for Mycobacterium tuberculosis complex detection in bovine lymph node tissue samples

Introduction

Bovine tuberculosis (bTB) caused by Mycobacterium tuberculosis complex (MTC) remains a significant concern for public health. Direct real-time PCR and droplet digital PCR (ddPCR) are proposed as alternative tools to enhance diagnostic precision and efficiency. This study aims to assess the diagnostic performance of a ddPCR assay targeting IS6110 for the detection of MTC DNA in both microbiological culture and fresh lymph node (LN) tissue samples obtained from cattle, in comparison with the established reference standard, the microbiological culture followed by real-time PCR.

Methods

The fresh LNs (N=100) were collected each from a different cattle carcass at the slaughterhouse. The limit of detection of ddPCR-IS6110 was set to 101 copies per 20 μl reaction.

Results

DdPCR-IS6110 detected 44 out of 49 reference-standard positive samples and yielded negative results in 47 out of 51 reference-standard negative samples, resulting in adjusted sensitivity (Se) and specificity (Sp) of 90.76% [95% confidence interval (CI): 82.58 - 98.96%)], and 100% (95% CI: 100%) respectively. The estimated adjusted false negative rate (FNR) was 9.23% (95% CI: 1.04 - 17.42%) and the false positive rate (FPR) was 0% (95% CI: 0%). When directly applied from fresh bovine LN tissues, ddPCR-IS6110 identified 47 out of 49 reference-standard positive samples as ddPCR-IS6110-positive and 42 out of 51 reference-standard negative samples as ddPCR-IS6110-negative, resulting in adjusted Se and Sp values of 94.80% [95% (CI): 88.52 - 100%] and 100% (95% CI: 100%), respectively. The adjusted FNR was 5.20% (95% CI: 0 - 11.50%) and the FPR was 0% (95% CI: 0%). Noteworthy, ddPCR-IS6110 disclosed as positive 9 samples negative to reference-standard.

Discussion

DdPCR-IS6110 proved to be a rapid, highly sensitive, and specific diagnostic tool as an alternative to reference-standard method.

Features of Mycobacterium bovis Complete Genomes Belonging to 5 Different Lineages

Mammalian tuberculosis (TB) is a zoonotic disease mainly due to Mycobacterium bovis (M. bovis). A current challenge for its eradication is understanding its transmission within multi-host systems. Improvements in long-read sequencing technologies have made it possible to obtain complete bacterial genomes that provide a comprehensive view of species-specific genomic features. In the context of TB, new genomic references based on complete genomes genetically close to field strains are also essential to perform precise field molecular epidemiological studies. A total of 10 M. bovis strains representing each genetic lineage identified in France and in other countries were selected for performing complete assembly of their genomes. Pangenome analysis revealed a "closed" pangenome composed of 3900 core genes and only 96 accessory genes. Whole genomes-based alignment using progressive Mauve showed remarkable conservation of the genomic synteny except that the genomes have a variable number of copies of IS6110. Characteristic genomic traits of each lineage were identified through the discovery of specific indels. Altogether, these results provide new genetic features that improve the description of M. bovis lineages. The availability of new complete representative genomes of M. bovis will be useful to epidemiological studies and better understand the transmission of this clonal-evolving pathogen.