Evaluation of methods for Mycobacterium avium ssp. paratuberculosis detection in milk samples from the cattle herd showing low seroprevalence of Johne's disease

Short communication: Occurrence and differentiation of Mycobacterium avium ssp. paratuberculosis (MAP) strains from milk of cows from herd with low prevalence of MAP

Mycobacterium avium ssp. paratuberculosis (MAP) is an important pathogen responsible for the chronic progressive granulomatous enteritis known as paratuberculosis. None of the detection methods of MAP infection based on isolation of the bacterium is 100% sensitive or specific. In this article, we describe the comparison of 2 MAP detection methods: direct isolation of genetic material and culture, in individual and pooled milk samples. The genetic types of MAP detected in the samples were also identified. The study was performed in a herd of 321 cows; apparent herd seroprevalence was 3.43%. Seven of 11 individual milk samples from seropositive cows were positive by culture (and confirmed by PCR), whereas all 11 were positive by direct PCR. Of the 62 milk pools from seronegative animals, 15 were positive by culture (and confirmed by PCR) and 13 were positive by direct PCR. Using multiplex PCR and PCR-restriction enzyme analysis (PCR-REA) methods, C (cattle) and S (sheep)-types of mycobacteria were identified. Most of the genetic material tested belonged to C-type. Detection of the MAP type occurring in an infected herd can help track the source of infection. We suggest using genetic material isolated directly from pooled milk samples for quick diagnosis, identification of MAP type, and tracking of infection, without the need to sequence the entire genome.

Management of Mycobacterium avium subsp. paratuberculosis in dairy farms: Selection and evaluation of different DNA extraction methods from bovine and buffaloes milk and colostrum for the establishment of a safe colostrum farm bank

The aim of this study was to develop and validate different innovative DNA extraction methods to detect Mycobacterium avium subsp. paratuberculosis (MAP) DNA from bovine and buffalo colostrum. Paratuberculosis is a chronic inflammatory infection of domestic and wild animals, especially ruminants, caused by MAP. The primary route of disease transmission is feces, but MAP can also be excreted in milk and colostrum. In 2015, the Italian Ministry of Health has issued a voluntary control plan of MAP in order to allow risk‐based certification of bovine and buffaloes farms. In addition to the annual diagnostic screening and to the clinical surveillance of animals the plan includes the adoption of biosecurity and management measures to progressively mitigate the incidence of MAP. To achieve this goal it is crucial to ensure the accuracy of the methods used to detect the presence of MAP in bovine and buffaloes milk and colostrum, in order to: (1) support a "safe colostrum farm‐bank" set‐up and thus prevent the main within‐farm MAP transmission route and (2) to allow the MAP‐free certification of milk products for export purposes. To achieve these goals, seven different DNA extraction protocols were identified from bibliography, out of which three methods were finally selected after the adoption of an evaluation procedure aimed at assessing the efficiency of extraction of DNA, the purity of DNA and the adaptability of the DNA amplification: NucleoSpin^® Food Kit (Macherey‐Nagel), NucleoSpin^® Food Kit (Macherey‐Nagel) combined with the magnetic beads, and QIAamp Cador Pathogen Mini kit (QIAGEN). In particular, the NucleoSpin^® Food Kit (Macherey‐Nagel) and the QIAamp Cador Pathogen Mini kit (QIAGEN) were tested on bovine and buffalo colostrum, showing a LOD between 4 × 10⁴ (2.6 × 10⁶ cfu/ml) and 4.08 (26.7 cfu/ml) IS900 target copies and a LOD between 5.3 × 10⁵ (4.1 × 10⁶ cfu/ml) and 53 (4.1 × 10³ cfu/ml) IS900 target copies, respectively.