Analysis of the growth pattern, survival and proteome of Mycobacteriumavium subsp. paratuberculosis following exposure to heat

Mycobacterium avium subsp. paratuberculosis (MAP) causes Johne's disease in ruminants and may be involved in Crohn's disease in humans. The aim of this study was to evaluate the in vitro growth pattern and proteome of MAP after heat stress following prior observations that MAP may exist in a dormant state in the environment when protected from extreme temperature flux and may survive pasteurization. Data were obtained for two genomically distinct strains of MAP, sheep (S) and cattle (C), from 50 °C to 80 °C. When assessed by comparing accumulated time at a given high temperature, cycles of heating and cooling resulted in shorter survival than holding at the high temperature, for example MAP survived exposure to 60 °C for only 9 min during repeated cycles of 12–60 °C flux but survived to 28 min when continuously exposed at 60 °C. This helps to explain the observed die off of MAP in natural environments. A prolonged lag phase was observed following sub-lethal exposure to heat, specifically repeated temperature flux in the range 10–50 °C, and this was suggestive of dormancy. 2-D PAGE analysis and identification of differentially expressed spots detected 23 proteins in the C strain and 10 in the S strain associated with heat stress. These proteins represented a range of metabolic pathways, including 12 previously identified in M. tuberculosis during heat stress. These proteins may be required for the survival of MAP both in the environment and within the host.