Avoiding persistent contamination with propionic acid bacteria and Lactobacillus parabuchneri in milking systems Persistent contaminations with propionic acid bacteria and Lactobacillus parabuchneri in milking systems have repeatedly resulted in financial losses in cheese processing. Moreover, histamine in the cheese, caused by Lactobacillus parabuchneri, can also affect consumer health. Biochemical and molecular biological methods have been developed and introduced into practice to enable the quick and reliable identification of these bacteria both in delivered milk as well as in milking systems and milk tanks. By investigating the milk production facilities and sampling various milking system components, sensitive areas as well as the most frequent causes of persistent contamination were successfully identified and eliminated. Means and information are therefore available to help milk-producing farms quickly and sustainably.