Mycobacterium paratuberculosis detection in cow's milk in Argentina by immunomagnetic separation-PCR

Abstract The aim of this study was to standardize a diagnosis procedure to detect Mycobacterium avium subsp. paratuberculosis (Map) DNA in raw cow milk samples under field conditions. A procedure that combines both immunomagnetic separation and IS900 -PCR detection (IMS-IS1 PCR) was employed on milk samples from 265 lactating Holstein cows from Map infected and uninfected herds in Argentina. IMS-IS1 PCR results were analyzed and compared with those obtained from milk and fecal culture and serum ELISA. The extent of agreement between both tests was determined by the Kappa test. IMS-IS1 PCR showed a detection limit of 101 CFU of Map/mL of milk, when 50:50 mix of monoclonal and polyclonal antibodies were used to coat magnetic beads. All of the 118 samples from the Map uninfected herds were negative for the set of the tests. In Map infected herds, 80 out of 147 cows tested positive by milk IMS-IS1 PCR (55%), of which 2 (1.4%) were also positive by milk culture, 15 (10%) by fecal culture, and 20 (14%) by serum ELISA. Kappa statistics (95% CI) showed a slight agreement between the different tests (<0.20), and the proportions of agreement were ≤0.55. The IMS-IS1 PCR method detected Map in milk of the cows that were not positive in other techniques. This is the first report dealing with the application of IMS-IS1 PCR in the detection of Map in raw milk samples under field conditions in Argentina.

Obtención y evaluación de un derivado proteico purificado de una cepa argentina de Mycobacterium avium subsp. paratuberculosis / Production and evaluation of a purified protein derivative from an Argentine strain of Mycobacterium avium subsp. paratuberculosis (MAP)

Los derivados proteicos purificados (PPD) son mezclas antigénicas no definidas obtenidas de distintas micobacterias. Los PPD bovino (PPDb) y PPD aviar (PPDa) son los antígenos que se emplean para evaluar la respuesta inmunitaria celular en infecciones como tuberculosis y paratuberculosis en el bovino. El PPDa comercial se produce a partir de Mycobacterium avium subsp. avium, y no a partir de la subespecie paratuberculosis. En este trabajo se seleccionó una cepa local de Mycobacterium avium subsp. paratuberculosis cuyo patrón molecular por RFLP es el más frecuente entre los aislamientos de nuestro país que han sido estudiados, y a partir de esta, se obtuvo un derivado proteico purificado: PPDj-IB. Se emplearon tanto el PPDa comercial como el PPDj-IB como antígenos en la prueba de liberación de gamma-interferón en animales de un tambo con paratuberculosis y en animales control. Aun cuando ambos PPD fueron capaces de estimular diferencialmente la liberación de la citoquina en el tambo infectado (respecto de los tambos control), no hubo diferencias significativas en los niveles de estimulación producidos y solo dos animales fueron positivos mediante el empleo de PPDj-IB. A partir del análisis por Western blot se demostró que el contenido de lipoarabinomano y del antígeno Apa/ModD era distinto en los PDD evaluados. Estas diferencias podrían explicar, en parte, las diferencias en los niveles de estimulación en términos individuales. Si bien el empleo de PPDj-IB no mejoró significativamente los resultados de la prueba de liberación de ?IFN, es importante destacar que se logró producir en el laboratorio un PPD apto para su empleo en ensayos in vitro.

Purified Protein Derivatives (PPDs) are non-defined antigens prepared from mycobacteria cultures. They are usually employed to evaluate the specific cellular immune response both in animals and humans. Bovine and avian PPDs are usually employed as antigens in mycobacterial infections such as tuberculosis and paratuberculosis. Nevertheless, PPD from Mycobacterium avium subsp. paratuberculosis, (PPDj) is neither commonly used nor frequently available. However, PPD from Mycobacterium avium subsp. avium is in fact used. We aimed to obtain and evaluate the performance of a PPDj from a local isolate of MAP using the ãInterferon-release assay. The stimulation of ãInterferon-release was significantly different between infected and control cattle when this antigen, named PPDj-IB, was used. Stimulation in the infected animals was similar with both antigens (PPDa and PPDj-IB). However, some animals were positively stimulated with PPDj-IB and not with PPDa. We demonstrated by Western blot that two antigenic molecules, lipoarabinoman and APA/ModD antigen were differentially represented in both PPDs. This could explain the difference in stimulation induction of ?IFN observed at individual level. Although PPDj-IB could not improve PPDa performance, we could easily produce an effective purified protein derivative for in vitro assays.