Investigation of Biochemical and Genetic Variations in Rapid and Slow Growing Mycobacterium avium subspecies paratuberculosis strains
Authors: Uzoigwe Jacinta Chinwe , Kargbo Robert , Takahashi Yoko , Cook Gregory , Khaitsa Margaret , Gibbs Penelope 
Published: June 2021

Background

Crohn's disease is a chronic inflammatory disease of the intestinal wall in humans, with unknown etiology. Mycobacterium avium subspecies paratuberculosis (MAP) is an organism that causes paratuberculosis (or Johnes disease) in cattle and other ruminants and one purported to have a causal link with Crohn's disease in humans. Previous works have shown that the growth rates for MAP are slow, with generation times of more than 24 hours.

Aim

The purpose of this study was to examine for associations between the biochemical and genetic variability of MAP strains and their growth rate and presence of symptom in the source cattle. Additionally, to obtain insights into the pathogenic mechanisms involving MAP in Crohn's disease, we compared the phenotypic and genotypic characteristics of MAP strains isolated from Crohn's disease patients with those from cattle with Johnes disease.

Methods

Mass spectrometry and pulse field gel electrophoresis (PFGE) of 118 culture‐positive MAP isolates and three human strains of MAP (ATCC 43015, 43544, 49164) were performed. MAP isolates were classified as slow growers if they grew in > 2 weeks and rapid growers if they grew in ≤ 2 weeks. Epi Info version 3.5.1 was used to analyze for associations between the biochemical and genetic variability of MAP strains and their growth rate or presence of symptoms in source cattle using Chi‐square and logistic regression.

Results

Different mass spectra patterns were detected and categorized in two groups: [M1 (short carbon chain lengths) and M2 (long carbon chain lengths)]. We observed PFGE patterns that were unique for each group [rapid growers (P1 and P2) and slow growers (P3–P7)], and also identified some PFGE profiles (P7 and P8) that were shared by both groups. A significant difference (P< 0.05) was observed between growth rate and symptom manifestation with 82.7 % of rapid growers having symptoms in source cattle compared to only 30.3 % of slow growers. Also, univariate logistic regression showed a significant association between growth rate and presence of symptoms in source cattle (OR=11.0, 95% CI= 4.5, 26.8; p <0.0001), as well as between growth rate and presence of long chain length mycolic acid (M2) (OR= 4.4, 95% CI= 2.0, 9.8; p = 0.0002). Comparison of PFGE profiles of bovine MAP isolates with those of humans revealed similarities in their profiles. The human (ATCC 43015 and 43544) isolates possessed the PG8 cattle profile, while the other human isolate (ATCC 43015) possessed PG6 cattle profile.

Conclusion

Data from this study provided an insight into the genetic and biochemical diversity among rapid and slow growing MAP strains and associations with manifestation of symptoms in source cattle. The similarities in PFGE profiles between bovine and human MAP isolates could possibly explain the theory of strain sharing, intra‐species and interspecies transmission, which may further support an association between johnne's disease and Crohn's disease. The association between growth rate of MAP strains and presence of symptoms in source cattle, or between growth rate and lipid profiles provided a better understanding of the differences in disease progression and pathogenicity of MAP isolates. This study provides useful data in future management of animal farmingoperations and possibly in future design of diagnostics and therapeutics for both johnne's disease and Crohn's disease.