Mycobacterium avium subsp. paratuberculosis(MAP) is considered as a highly resistant species among mycobacteria towards various stress factors. The purpose of this study is to assess a resistance profile for MAP towards inactivation factors relevant in food processing, such as an increased temperature, UV-light pulses, chlorine dioxide and lactic acid. Two strains of MAP, a reference strain and a bovine isolate from faeces, have been subjected to the heat treatment (60-90°C at 10s, 20s and 30s intervals), the chlorine dioxide treatment (6-12 ppm, 2 min. interval), and the lactic acid treatment (25, 50, 75 and 100 mg/ml, 2 min. interval). Two repeated cycles of inactivation by UV-light pulses with the same strains have been performed in order to induce resistant variants (number of pulses: 10-120). Controls are included in all experiments. The results of inactivation have been measured by the time to detection in liquid MGIT media and by the log mean CFU/ml on solid HEYM media. A not so clear effect of an increased temperature on MAP has been observed within the time intervals, even some kind of activation has been shown from the curves at 60-80°C. With UV-light pulses, only mild inactivation has been observed for both the first and the second repeated experiments, depending on the strain. On the other hand, when using chlorine dioxide, a strong effect of inactivation for the chosen range of concentrations has been demonstrated. Similarly, a strong effect of lactic acid on MAP has been documented. The reference strain, probably more sensitive than the bovine isolate, does not grow after some treatments on solid HEYM, but it grows in liquid MGIT. Thus, the use of the MGIT culture system may be promising for such studies or perhaps for primary isolation of the etiological agent of paratuberculosis.

This work was supported by the "PathogenCombat" grant No. FOOD-CT-2005-007081 (Brussels, EC).