Mycobacterium avium subsp. paratuberculosis in muscle, lymphatic and organ tissues from cows with advanced Johneʹs disease

Blood, liver, kidney, lymph nodes and muscle tissue were obtained from the carcasses of five cows with advanced Johneʹs disease. Samples from the raw tissues, from cooked muscle tissues and from cooked hamburger patties that contained chopped mesenteric lymph nodes were collected aseptically. Each sample was divided into two portions, one of which was decontaminated. Both portions were homogenized. Homogenates were spread on selective agar for the recovery of Mycobacterium avium subsp. paratuberculosis (Map) and inoculated into a Map growth medium with the organism being detected in the cultures by PCR procedures and Ziehl–Neelsen staining. Map were recovered at numbers > 103 cfu/g from 7 of 15 liver and mesenteric and ileocaecal lymph node samples; and at lesser numbers from 5 of 15 kidney and superficial inguinal and prescapular lymph node samples. The numbers recovered from decontaminated and not decontaminated portions of each sample were generally similar. Map was recovered from 1 and detected in 6 of 50 not decontaminated portions of samples of raw, chilled or frozen meat; and detected in 1 of 15 not decontaminated samples of meat cooked to 61 °C, and in 1 of 40 samples of meat cooked to ≥ 70 °C. Map was detected in 2 of 4 samples of mesenteric lymph nodes cooked to 61 °C, but not in samples cooked to ≥ 70 °C. The findings indicate that Map may be present in meat from infected animals at low numbers, but that any such organisms are likely to be inactivated when meat is cooked to a well done condition.