Growth rates and lag times of Listeria monocytogenes at 4 and 8°C were compared in dairy products (milk, cream, and cheese), minced beef, and smoked salmon. Results showed that an increase in incubation temperature from 4 to 8°C leads to a significant decrease in time required to reach a given bacterial population density. The decreases were about 50% on cheese surfaces, 60 to 65% in milk and cream, and 75 to 80% in minced beef and smoked salmon. Consequences on the shelf life of chilled products are discussed on the basis of a simple and general linear relationship between the relative decrease in shelf life and generation time. This relationship was experimentally highlighted and theoretically demonstrated.

No abstract

The influence of the hatchery and the poultry farm on the contamination of poultry carcases by Salmonella species has been studied by examining samples from different stages of production. The incidence of Salmonella serotypes in the hatchery varied considerably in different broiler flocks and decreased from the beginning to the end of the rearing period. Serotypes originating in the hatchery were less important in the final product than those present in the house, or those introduced into the house by vectors during rearing.

An assay is described for evaluating live-culture treatment material that may be given orally to chicks to prevent intestinal colonization by non-host-specific salmonellae. Both pre-treated and control chicks are challenged with ca 104 salmonellae/chick, using a strain bearing an antibiotic resistance marker. Chicks are examined 5 d after challenge to determine both the proportion of positive birds in treated and control groups and the levels of Salmonella in the caeca of infected individuals. The efficacy of the treatment is determined by calculation of values for Infection Factor and Protection Factor.

An epidemiological survey was made of 5329 samples from 10 poultry operations to determine the relationship between total poultry farm environment and incidences of Salmonella contamination of broiler flocks. Samples were analyzed from walls, drinkers, feeders, litter, insects, water, chicks, broilers, and feed to determine the effect of common sanitary practices on Salmonella contamination of flocks. Results indicated that although similar hygienic practices had been taken on the 10 poultry farms examined, great variation exists in Salmonella contamination among the farms. Among the sources studied, the most important source of contamination was determined to be the resident Salmonella of the flock i.e., the strain isolated on chicks' first day in the poultry house. This source was more important than Salmonella isolated during the rearing period. However, the precise conditions of Salmonella contamination in poultry flocks remain to be elucidated.