Contamination routes of Gram-negative spoilage bacteria in the production of pasteurised milk, evaluated by randomly amplified polymorphic DNA (RAPD)

The sources of contamination for Gram-negative psychrotrophic bacteria (GNP), have been traced in three dairies by using the PCR-based method randomly amplified polymorphic DNA (RAPD). GNP isolated from raw and pasteurised milk, air, water and empty packages were RAPD-typed Pasteurised milk was found to be recontaminated by a wide spectrum of different RAPD-types. Several of the milk contaminating RAPD-types were also found in condensed water on the filling nozzles, in waste-water at the bottom of the filling machine, and in the air in the immediate surroundings of the machine. Most of the RAPD-typed bacteria were categorised as pseudomonads. The majority of these belonged to Pseudomonas fluorescens, but also Pseudomonas putida, Pseudomonas corrugata, and Janthinobacterium lividum were identified. Indications of specific RAPD-types associated with the same filling machine over a time period of 6-15 months were found in two of the dairies. (C) 2000 Elsevier Science Ltd. All rights reserved.