Blue pigment in fresh cheese produced by Pseudomonas fluorescens

This study describes the process of identifying the causative agent of a blue pigment on the surface of fresh raw cheese. It was studied using traditional microbiological methods and genotypic tests. These techniques identified Pseudomonas fluorescens biovar IV, which produces a blue, non-diffusible pigment, as the likely contaminating agent. The isolates collected from contaminated cheese, milk, water and curd were initially identified by the Analytical Profile Index test as Pseudomonas aeruginosa and later confirmed by 16S rDNA sequencing as P. fluorescens. Pulsed field gel electrophoresis with the enzyme XbaI identified Pseudomonas fluorescens in milk and cheese. Pasteurizer installation and a new cleaning-disinfection program allowed us to control Pseudomonas spp. until all the blue coloration in the cheese had been eliminated.