Studies on Mycobacterium avium subsp. Paratuberculosis: Genotypic and phenotypic variations

The objective of the study was to understand the genotypic and phenotypic variations across Mycobacterium avium subsp. paratuberculosis (M. paratuberculosis) isolates form diverse hosts and geographic locations.; Multiplex PCR of IS900 loci (MPIL) fingerprint analysis of M. paratuberculosis isolates recovered from diverse hosts and geographic localities clustered 78% of bovine origin isolates into a major node, while isolates from human and ovine sources showed greater genetic diversity. Amplified fragment length polymorphism (AFLP) analysis clustered 75% of the isolates from bovine sources into 2 major nodes while those recovered from sheep or human clustered on distinct branches. This suggested that the M. paratuberculosis isolates were genotypically homogenous or were converging into a common fingerprint.; To evaluate the alternate possibility that MPIL and AFLP analyses were inadequate for dissecting the M. paratuberculosis genotypes, short sequence repeat (SSR) analysis was performed on mycobacterial isolates obtained from 33 different host species and from environmental sources. Sequence based characterization of the G-repeat locus enabled differentiation of the M. paratuberculosis isolates from the major MPIL cluster into seven distinct alleles. Subsequent analysis of M. paratuberculosis isolates from human Crohn's disease cases using two polymorphic SSR loci (G- and GGT- repeats) identified a limited number of genotypes amongst the human strains indicating an association of a few M. paratuberculosis types with the pathobiology of Crohn's disease. SSR analysis using both polymorphic loci also enabled identification of varying levels of within-farm and between farm diversity and indicated that 7g-4ggt as the most common genotype in animals from Ohio dairy farms.; To explore whether the differences in fingerprint profiles translated to variation in biological function and/or host adaptation, cDNA microarray analysis of a human macrophage cell line exposed to M. paratuberculosis isolated from cattle and human hosts was undertaken. Results indicated that the expression profiles induced by representative cattle and human M. paratuberculosis strains differed in several key inflammatory and apoptotic pathways suggesting that M. paratuberculosis strains with different genotypes induce variant transcriptional regulation.; Taken together, the results of our genotypic and phenotypic analyses demonstrated that SSR analysis enabled the genetic characterization of M. paratuberculosis isolates from different host species, and provided support for a genotype-phenotype association in M. paratuberculosis infection.