Location: Infectious Bacterial Diseases ResearchTitle: Screening of Mycobacterium avium subsp. paratuberculosis mutants for attenuation in a bovine monocyte-derived macrophage model Author
Submitted to: Frontiers in Cellular and Infection Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/11/2014
Publication Date: 6/30/2014
Publication URL: http://handle.nal.usda.gov/10113/59510
Citation: Lamont, E.A., Talaat, A.M., Coussens, P.M., Bannantine, J.P., Grohn, Y.T., Katanai, R., Li, L., Kapur, V., Sreevatsan, S. 2014. Screening of Mycobacterium avium subsp. paratuberculosis mutants for attenuation in a bovine monocyte-derived macrophage model. Frontiers in Cellular and Infection Microbiology. 4(87)1-7. Interpretive Summary: Johne’s disease in livestock such as dairy cattle and sheep is caused by the bacterium Mycobacterium avium subspecies paratuberculosis (MAP). Perhaps the hallmark of pathogenesis of this bacterium is its ability to survive inside macrophages, which are cells designed to kill bacteria. In this study, we examined 17 crippling mutations in MAP that inhibit its ability to survive in macrophages. The approach was to culture MAP from infect macrophages to measure how many bacteria were present at different time points. If bacterial number decreased with time, then killing occurred. These mutant strains of bacteria may be good candidates for a live, attenuated vaccine against Johne’s disease. This research is of primary interest to veterinarians, stakeholders and other researchers in the field.
Technical Abstract: Vaccination remains a major tool for prevention and progression of Johne’s disease, a chronic enteritis of ruminants worldwide. Currently there is only one licensed vaccine within the United States and two vaccines licensed internationally against Johne’s disease. All licensed vaccines reduce fecal shedding of Mycobacterium avium subsp. paratuberculosis (MAP) and delay disease progression. However, there are no available vaccines that prevent disease onset. A joint effort by the Johne’s Disease Integrated Program (JDIP) Core and USDA-APHIS/VS sought to identify vaccine candidates as part of a three phase study. The focus of the Phase I study was to evaluate MAP mutant attenuation in a well-defined in vitro bovine monocyte-derived macrophage model. Attenuation was determined by colony forming unit (CFUs) counts and slope estimates. Based on CFU counts alone, the MDM model did not identify any mutant that significantly differed from the standard type control, MAP K-10. Slope estimates identified six mutants that were transferred to the Phase II study. CFU data alone correlated with failure to prevent infection in the Phase III study. These results suggest the need for alternative strategies for Johne’s disease vaccine candidate screening and highlight the use of a bovine MDM model for vaccine candidate identification.