Use of Photobacterium leiognathi in studies of process equipment cleanability

Summary The aim of the EC funded Project AIRI-CT-92 is to develop methods for the cleanability testing of food processing equipment. Photobacterium leiognathi ATCC 33469 has been suggested as an indicator organism in cleanability testing. Here, this bacterium was grown as a biofilm for 5 h or 24 h at room temperature on various surfaces, clean or milk-soiled, by immersing the surfaces in luminous medium inoculated with P. leiognathi. The surfaces were then rinsed or cleaned using a CIP procedure before the hygienic status was determined using conventional plating, bioluminescence output and image analysis. Rinsing did not eliminate the bacterium from the surfaces nor did the CIP procedure when 24-h biofilms were used, as was readily seen after enrichment in luminous medium. In image analysis the biofilm showed a spotlike growth pattern which was most evident on stainless steel. The advantage of P. leiognathi in the cleanability assessment, which is based on the natural light output of the test bacterium, is that the test is easy to perform and can be carried out without use of expensive reagents.