Rapid Detection of Pseudomonads in Dairy Products and Process Water

Introduction: Pseudomonad organisms are a major cause of bacterial spoilage of pasteurized milk and dairy products due to post process contamination. Early detection of pseudomonads can be a predictor of product shelf-life as they are the predominant psychotropic bacteria present. The BioLumix system is an optical system that detects growth of pseudomonads using a CO₂ sensor in selective growth media.

Purpose: To evaluate the ability of the optical system to detect pseudomonads in dairy products and process water, and to,determine the speed to results, sensitivity, selectivity and ability to predict shelf-life.

Methods: The optical system was directly compared to the plate count methodology for milk samples stored at refrigerated temperatures and held overnight at room temperatures. Testing of process water was also accomplished.

Results: Commercial milk products were used to measure the presence of pseudomonads during refrigeration and storage at elevated temperatures. Pseudomonads were present at varying levels in dairy samples and were detected within 16-24 hours using BioLumix vials. All process water samples tested were free of Pseudomonads by both methods. Process water samples inoculated with different Pseudomonads strains were detectable by the optical system. The vials were selective by not allowing for growth of unrelated gram positive and gram negative bacteria, mold or yeast. The combination of the Pseudomonas vial with overnight pre-incubation of the sample could serve as an indicator of shelf-life of products.

Significance: The data in this study suggested that the BioLumix Pseudomonas vials are capable of early detection of pseudomonads in dairy products and in process water. The system offered a reduction in time to results as compared to the plate methodology.