Submitted to: Journal of Clinical Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 13, 2005
Publication Date: September 20, 2005
Citation: Stabel, J.R., Bannantine, J.P. 2005. Development of a Nested PCR Method Targeting a Unique Multicopy Element, ISMap02, for Detection of Mycobacterium avium subsp. paratuberculosis in Fecal Samples. Journal of Clinical Microbiology. 43(9):4744-4750. 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. Johne’s disease is difficult to diagnose and therefore to control. Development of accurate and sensitive diagnostic tests is dependent upon understanding how the host animal handles the infection and at what age do signs of infection, such as fecal shedding, become obvious. This study examined the efficacy of a new fecal PCR test for detection of the causative agent of Johne's disease. The current test should be a useful tool in efforts to control paratuberculosis within herds and to reduce the spread of Mycobacterium paratuberculosis among herds.
Technical Abstract: This study describes the development of a nested PCR assay that uses a unique element (ISMap02) for Mycobacterium avium subsp. paratuberculosis that is present at six copies within the genome. In addition, the sensitivity of the assay with this element was compared to the sensitivity of detection of the IS900 element in both conventional and real-time PCR assays. The specificity of the ISMap02 element was evaluated by PCR of the DNA extracted from isolates of M. avium subsp. paratuberculosis and M. avium subsp. avium, as well as DNA from M. fortuitum, M. scofulaceum, M. phlei, M. smegmatis, and M. gordonae. Only M. avium subsp paratuberculosis DNA was detectable after amplification with the ISMap02 primers. The sensitivity of detection for the ISMap02 element in either a conventional or a real-time PCR format was less than 100 fg DNA or 102 CFU/ml in serial titration curves with pure bacteria. These results were comparable to those obtained for the IS900 element. Experimental spiking of a negative fecal sample followed by M. avium subsp. paratuberculosis DNA extraction resulted in detection thresholds of 102 CFU/g for the IS900 element and 103 CFU/g for the ISMap02 element by using a real-time PCR format, but this sensitivity dropped 10-fold for both elements in a conventional PCR format. Analyses of fecal samples obtained from naturally infected animals demonstrated a sensitivity for the detection of M. avium subsp. paratuberculosis DNA by use of the ISMap02 element similar to that achieved by use of the IS900 element when it was used in a conventional PCR format. The real-time PCR format improved the levels of detection of both elements, but not to a significant degree. In conclusion, the ISMap02 element provides a very sensitive and specific alternative as a diagnostic reagent for use in PCR assays for the detection of paratuberculosis.