Temporal and spatial distribution of Cronobacter isolates in a milk powder processing plant determined by pulsed-field gel electrophoresis.

A milk powder processing line was sampled for the presence of Enterobacteriaceae and the opportunistic neonatal pathogen Cronobacter at six different sampling sites during an 11-month period. The highest number of Enterobacteriaceae-positive samples was recovered from the raw milk concentrate before pasteurization (78.2%) and from nonproduct samples of the processing line (86.5%), which included swabs from the drying tower and screw conveyers, swabs from the explosion chamber, waste water after the automated cleaning-in-place procedure, air filter cut-outs, and floor samples underneath the outlet of the packaging machine. The prepackaged and packaged final product was contaminated at a rate of 6.6% and 7.1%, respectively. The prevalence of Cronobacter in the prefinal product and the prepackaged and packaged final product was 14.3%, 3.8%, and 2.1%, respectively. Pulsed-field gel electrophoresis (PFGE) analysis of 133 Cronobacter isolates yielded 40 different PFGE profiles. Long-term persistence in the processing line of some of these PFGE profiles was observed. Comparison of the PFGE profiles recovered at different sampling sites revealed the supply air as a potential source for extrinsic Cronobacter contamination. In addition, recovery of the same PFGE profiles before and after CIP events followed by heat treatment indicated the inefficiency of these hygiene measures to completely eliminate Cronobacter from all areas of the processing line. This information provides an essential basis for developing control and prevention strategies concerning this opportunistic pathogen.

Finding optimal photosensitisers for the decontamination of foods by the photodynamic effect.

A new method for sanitation based on the photodynamic effect is introduced. Photosensitisers are compounds that generate cytotoxic oxygen species and free radicals after excitation with appropriate visible light. The cell killing efficacy is due to their chemical structure, to the actual environment and therefore also to their degree of aggregation. As has been shown, photosensitisers bound to the cell wall or incorporated into the cells are very effective cytotoxic agents after illumination. Even singlet oxygen generated in the gas phase surrounding the micro-organisms effectively kills cells. Especially membrane components are the targets of the photodynamic effect. Membrane disintegration is observed soon after illumination. The food contaminants under investigation are Bacillus subtilis, Bacillus cereus, forming endospores, Staphylococcus aureus, forming a wide range of agressins, exotoxins and enterotoxins, all gram positive micro-organisms, Escherichia coli, a hygiene indicator, and the yeasts Saccharomyces cerevisiae, Kloeckera javanica, Rhodotorula mucilaginosa, a blue and a pink pigmented isolate from foods. We investigated the capacity of several photosensitisers to induce the phototoxic effect towards those micro-organisms following excitation by visible light.