Mycobacterium bovis strain Ravenel is attenuated in cattle

Authors: HADI, SYEDA - Michigan State University; BRENNER, EVAN - Michigan State University; Palmer, Mitchell; Waters, Wade; THACKER, TYLER - Animal And Plant Health Inspection Service (APHIS); VILCHEZE, CATHERINE - Albert Einstein College Of Medicine; LARSEN, MICHELLE - Albert Einstein College Of Medicine; JACOBS, WILLIAM - Albert Einstein College Of Medicine; SREEVATASAN, SRINAND - Michigan State University

Submitted to: Pathogens
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/23/2022
Publication Date: 11/11/2022
Citation: Hadi, S.A., Brenner, E.P., Palmer, M.V., Waters, W.R., Thacker, T.C., Vilcheze, C., Larsen, M.H., Jacobs, W.R., Sreevatasan, S. 2022. Mycobacterium bovis strain Ravenel is attenuated in cattle. Pathogens. 11(11). Article 1330. https://doi.org/10.3390/pathogens11111330.
DOI: https://doi.org/10.3390/pathogens11111330

Interpretive Summary: Mycobacterium bovis (M. bovis) is the cause of tuberculosis in animals and can cause disease in humans. There are various strains of M. bovis, some of which are held in laboratories and used as reference strains. Other strains recently isolated from animals are known as wild type strains. The M. bovis strain Ravenel is a reference strain, believed to be representative of all disease causing strains of M. bovis. We showed that strain Ravenel produces a robust immune response but little or no disease in cattle compared to wild type strains. As such, strain Ravenel should not be considered representative of all disease causing strains of M. bovis. We further investigated genetic differences between strain Ravenel and 3 wild type strains and found significant differences that likely led to the lack of disease in Ravenel infected cattle. This information is valuable to researchers investigating M. bovis.

Technical Abstract: Mycobacterium tuberculosis variant bovis (MBO) has one of the widest known mammalian host ranges, including humans. Despite characterization of this pathogen in the 1800s, and whole genome sequencing of a UK strain (AF2122) nearly two decades ago, the basis of its host specificity and pathogenicity remains poorly understood. Recent experimental calf infection studies show that MBO strain Ravenel (MBO Ravenel) is attenuated in the cattle host. In the present study, experimental infections were performed to define attenuation, and whole genome sequencing completed to identify regions of differences (RD) and single nucleotide polymorphisms (SNPs) to explain the observed attenuation. Comparative genomic analysis of MBO Ravenel against three pathogenic strains of MBO (strains AF2122-97, 10-7428 and 95-1315) was performed. Experimental infection studies on 5 calves each, with either MBO Ravenel or 95-1315, revealed no visible lesions in all 5 animals in the Ravenel group despite robust IFN-' responses. Out of 486 polymorphisms in the present analysis, 173 were unique to MBO Ravenel among the strains compared. A high-confidence subset of 9 unique SNPs were missense mutations in genes with annotated functions impacting 2 major MBO survival and virulence pathways: 1) Cell wall synthesis & transport [espH (A103T), mmpL8 (V888I), aftB (H484Y), eccC5 (T507M), rpfB (E263G)], and 2) Lipid metabolism & respiration [mycP1(T125I), pks5 (G455S), fadD29 (N231S), fadE29 (V360G)]. These substitutions likely contribute to the observed attenuation. Results from experimental calf infections and the functional attributions of polymorphic loci on the genome of MBO Ravenel provides new insights into the strain’s genotype-disease phenotype associations.