Molecular detection and culture of Mycobacterium avium subsp. paratuberculosis in pasteurized and raw retail milk in Kampala, Uganda

Abstract

Background The hypothesis that Mycobacterium avium subsp. paratuberculosis (MAP) is a zoonotic pathogen has gained traction with the repeated isolation of MAP from patients with Crohn’s disease. As consumption of contaminated milk and dairy products represents a primary suspected route for human exposure to MAP, this study was designed to investigate the presence of MAP in retail milk sold in Kampala, Uganda’s Capital and central hub for the nation’s milk distribution. Methods A total of 772 milk samples were collected and analysed sequentially using two molecular assays targeting the IS900 gene sequence, with positive findings validated by DNA sequencing. To determine MAP viability, samples were cultured on Herrold’s egg yolk media (HEYM) slants supplemented with selective antibiotics and mycobactin J. Results MAP DNA was confirmed by nested PCR and subsequent sequencing in 2.3% of the samples, with equal frequencies in pasteurized and unpasteurized milk. Additionally, one raw milk sample demonstrated viable MAP growth by culture. Conclusion The findings of contamination of commercial milk with MAP in the Uganda’s Capital aligns with the reported prevalence of cattle paratuberculosis in the country and underscore the need for rigorous protocols for preparation of milk and dairy products to reduce contaminating viable pathogenic bacteria including MAP. Consequently, more efforts toward control of paratuberculosis in livestock are required to mitigate possible public health risks through foodborne pathogens.