No abstract

Background: Feed contaminated with Salmonella spp. constitutes a risk of Salmonella infections in animals, and subsequently in the consumers of animal products. Salmonella are occasionally isolated from the feed factory environment and some clones of Salmonella persist in the factory environment for several years. One hypothesis is that biofilm formation facilitates persistence by protecting bacteria against environmental stress, e.g. disinfection. The aim of this study was to investigate the biofilm forming potential of Salmonella strains from feed-and fishmeal factories. The study included 111 Salmonella strains isolated from Norwegian feed and fish meal factories in the period 1991-2006 of serovar Agona, serovar Montevideo, serovar Senftenberg and serovar Typhimurium.

Listeria monocytogenes is ubiquitous in nature and a major concern for the food industry, since it is the causal agent of the serious foodborne illness listeriosis. This organism can be introduced through many routes to food-processing environments and may become established on food-processing equipment. Subsequently, food products may become contaminated during processing. In addition, the bacterium can grow at refrigeration temperatures. Biofilms are regarded as important with respect to the survival and growth of microorganisms in the food industry. Microorganisms growing in biofilms are protected against cleaning and disinfection and are difficult to eradicate. Listeria monocytogenes may grow in biofilms that protect them against environmental stress and can be isolated from surfaces after cleaning and disinfection. For each individual food-processing plant, a limited number of clones of L. monocytogenes may become established and persist for years. Persistent strains adhere to surfaces and form biofilms more readily compared to sporadically found strains, suggesting that adherence to surfaces is important for survival and persistence of L. monocytogenes in food-processing environments. Listeria monocytogenes can adhere to all the materials commonly used in the food industry. In biofilms L. monocytogenes is significantly more resistant to disinfection than its free-living counterparts and thick, complex biofilms are more difficult to remove than adherent single cells of L. monocytogenes. Several novel approaches to avoid adhesion of L. monocytogenes have been proposed, but high costs, practical difficulties or resistance problems limit their practical use. Despite considerable research on the adhesive properties and resistance of L. monocytogenes enabling its survival in the food production environment, a final solution for avoiding establishment of the bacterium has not yet been found.

The effects of process conditions and growth kinetics on the production of the bacteriocin sakacin P by Lactobacillus sakei CCUG 42687 have been studied in pH-controlled fermentations. The fermentations could be divided into phases based on the growth kinetics, phase one being a short period of exponential growth, and three subsequent ones being phases of with decreasing specific growth rate. Sakacin P production was maximal at 20 degrees C. At higher temperatures (25-30 degrees C) the production ceased at lower cell masses, when less glucose was consumed, resulting in much lower sakacin P concentrations. With similar media and pH, the maximum sakacin P concentration at 20 degrees C was seven times higher than that at 30 degrees C. The growth rate increased with increasing concentrations of yeast extract, and the maximum concentration and specific production rate of sakacin P increased concomitantly. Increasing tryptone concentrations also had a positive influence upon sakacin P production, though the effect was significantly lower than that of yeast extract. The maximum sakacin P concentration obtained in this study was 20.5 mg l(-1). On the basis of the growth and production kinetics, possible metabolic regulation of bacteriocin synthesis is discussed, e.g. the effects of availability of essential amino acids, other nutrients, and energy.