Abstract
BackgroundMycobacterium avium subspecies paratuberculosis (Map) is the aetiological agent of Johne’s disease or paratuberculosis and is included within the Mycobacterium avium complex (MAC). Map strains are of two major types often referred to as ‘Sheep’ or ‘S-type’ and ‘Cattle’ or ‘C-type’. With the advent of more discriminatory typing techniques it has been possible to further classify the S-type strains into two groups referred to as Type I and Type III. This study was undertaken to genotype a large panel of S-type small ruminant isolates from different hosts and geographical origins and to compare them with a large panel of well documented C-type isolates to assess the genetic diversity of these strain types. Methods used included Mycobacterial Interspersed Repetitive Units - Variable-Number Tandem Repeat analysis (MIRU-VNTR), analysis of Large Sequence Polymorphisms by PCR (LSP analysis), Single Nucleotide Polymorphism (SNP) analysis of gyr genes, Pulsed-Field Gel Electrophoresis (PFGE) and Restriction Fragment Length Polymorphism analysis coupled with hybridization to IS900 (IS900-RFLP) analysis.ResultsThe presence of LSPA4 and absence of LSPA20 was confirmed in all 24 Map S-type strains analysed. SNPs within the gyr genes divided the S-type strains into types I and III. Twenty four PFGE multiplex profiles and eleven different IS900-RFLP profiles were identified among the S-type isolates, some of them not previously published. Both PFGE and IS900-RFLP segregated the S-type strains into types I and III and the results concurred with those of the gyr SNP analysis. Nine MIRU-VNTR genotypes were identified in these isolates. MIRU-VNTR analysis differentiated Map strains from other members of Mycobacterium avium Complex, and Map S-type from C-type but not type I from III. Pigmented Map isolates were found of type I or III.ConclusionThis is the largest panel of S-type strains investigated to date. The S-type strains could be further divided into two subtypes, I and III by some of the typing techniques (IS900-RFLP, PFGE and SNP analysis of the gyr genes). MIRU-VNTR did not divide the strains into the subtypes I and III but did detect genetic differences between isolates within each of the subtypes. Pigmentation is not exclusively associated with type I strains.
Highlights
Mycobacterium avium subspecies paratuberculosis (Map) is the aetiological agent of Johne’s disease or paratuberculosis and is included within the Mycobacterium avium complex (MAC)
We studied both inter and intra-subtype genotypic strain differences using restriction fragment length polymorphism analysis coupled with hybridization to IS900 (IS900 RFLP), Pulsed-Field Gel Electrophoresis (PFGE) and various PCRs based on variable-number tandem repeat (VNTR) loci and mycobacterial interspersed repetitive units (MIRUs) [9,10] MIRU-VNTR typing [11], the presence or absence of large sequence polymorphisms (LSPs) [12] and the gyrA and B genes [13]
The existence of two major Map lineages was previously supported by the distribution of two LSPs specific for Map as described by Semret et al [12,26,27]: the region corresponding to LSPA20 is absent from strains of the sheep lineage whereas that corresponding to LSPA4 is absent from strains of the cattle lineage
Summary
Mycobacterium avium subspecies paratuberculosis (Map) is the aetiological agent of Johne’s disease or paratuberculosis and is included within the Mycobacterium avium complex (MAC). We undertook the first comprehensive genotyping study of a large representative panel of S-type strains using various typing methods that have been applied to Map strains, individually or in combinations, to draw a portrait of S-type strains We studied both inter and intra-subtype genotypic strain differences using restriction fragment length polymorphism analysis coupled with hybridization to IS900 (IS900 RFLP), PFGE and various PCRs based on variable-number tandem repeat (VNTR) loci and mycobacterial interspersed repetitive units (MIRUs) [9,10] MIRU-VNTR typing [11], the presence or absence of large sequence polymorphisms (LSPs) [12] and the gyrA and B genes [13]. We incorporated typing data obtained for additional Map C-type isolates to represent the all diversity of the genotypes described and Mycobacterium. avium subsp. avium (Maa) Mycobacterium. avium subsp. silvaticum (Mas) and Mycobacterium avium subsp. hominissuis (Mah) for comparison
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