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Location: Infectious Bacterial Diseases Research

Title: Optimization of methods for the detection of Mycobacterium avium subsp. paratuberculosis in milk and colostrum of naturally infected dairy cows

item Bradner, Laura - Iowa State University
item Stabel, Judith
item Beitz, Donald - Iowa State University
item Robbe-austerman, Suelee - Animal And Plant Health Inspection Service (APHIS)

Submitted to: Iowa State University Animal Industry Report
Publication Type: Proceedings
Publication Acceptance Date: 1/23/2012
Publication Date: 2/8/2012
Citation: Bradner, L., Stabel, J.R., Beitz, D.C., Robbe-Austerman, S. 2012. Optimization of methods for the detection of Mycobacterium avium subsp. paratuberculosis in milk and colostrum of naturally infected dairy cows. Iowa State University Animal Industry Report. A.S. Leaflet No. R2676.

Interpretive Summary: Johne's disease is a chronic, debilitating intestinal disorder in cattle characterized by diarrhea, reduced feed intake, weight loss and death. Cattle usually become infected as young calves by ingesting feces containing the causative bacteria. However, symptoms of disease do not usually present themselves until the animals reach 3 to 5 years of age or even older. During this time the animal is infected and may be shedding the organism in its feces without showing any clinical signs of disease. In addition to reduced production by these animals through reduced milk production, they also present a potential infective threat to the rest of the herd. Shedding of this bacterium into the milk of infected dams is one mode of transmission to young calves. However, there is very little data to determine how much shedding occurs. This is due to the difficulty in culturing the bacterium from milk and colostrum. The present study evaluates the best method for decontamination and culturing of milk for optimal recovery of the bacterium. These results are critical for diagnostic laboratories so that proper methods can be employed to assess exposure of calves on-farm.

Technical Abstract: Two decontamination chemicals, hexadecylpyridinium choride (HPC) and N-acetyl-L-cysteine-sodium hydroxide (NALC-NaOH), were compared for their efficacy of reducing the growth of non-specific microorganisms in milk while minimally affecting the recovery of Mycobacterium avium subsp. paratuberculosis (MAP). In addition three culture mediums, Bactec 12B and Trek-ESP para-JEM, and Herrold’s egg yolk media (HEYM), were compared for the ability to suppress growth of non-specific microorganisms as well as their sensitivity of detection of low levels of MAP in milk. Results indicated that exposing the milk to 1.5% NALC-NaOH for 15 minutes most effectively reduced non-target microorganisms without reducing MAP viability. In addition, the Bactec 12B medium detected the lowest levels of MAP more rapidly and more consistently than the other two mediums.