Summary Seasonal variation in the fecal shedding of Listeria spp. in dairy cattle was examined by collecting a total of 3,878 fecal samples during a period of two years. The prevalences of Listeria spp. and L. monocytogenes were higher during the indoor season (12.7% and 9.2%, respectively) than in samples collected from the animals on pasture (5.3 % and 3.1 %, respectively). The highest frequencies of Listeria spp. (19.4%) and L. monocytogenes (16.1 %) were detected in December. Listeriae were isolated from at least one of the dairy cows from 45.8 % of the 249 herds examined. 2.9% of the 314 milk samples collected from the farm bulk tanks on 80 dairy farms on four different occasions yielded L. monocytogenes. The seasonal occurrence of these bacteria in milk reflected the frequencies of Listeria in the fecal material but not those in the main roughage used; grass silage and pasture grass. Fecal material is considered to be a potential source of contamination of raw milk by L. monocytogenes. Investigation of the numbers of viable Listeria organisms in different animal fodders is considered essential in further epidemiological studies of these bacteria.

Serum and colostrum but not post-colostral milk from non-immunized Friesian cows was found highly bactericidal for Helicobacter pylori NCTC 11637. This bactericidal activity was destroyed by heating at 56 degrees C for 30 min and restored by the addition of fetal calf serum as a source of complement, indicating that the bacterial effect was probably dependent on an antibody-complement system. Systemic, serial immunization of non-lactating, pregnant cows with H. pylori resulted in high specific antibody titres in serum and colostrum. No titres were found in post-colostral milk, even after booster-immunization during lactation. Immunization did not enhance the bactericidal activity of serum and colostrum, but increased it in post-colostral milk. The bactericidal activity was not correlated with titres of specific antibody or with IgG concentrations.

Summary Possible sources of exogenous contamination of raw milk by Listeria monocytogenes were examined on four dairy farms of different size and type of animal housing during morning milking. Feeds, including hay and concentrates, were found to be major sources of both pathogenic and nonpathogenic species of Listeria on the barns. L. innocua was the only species isolated from the grass silage, which was of good quality on all the farms. The numbers of Listeria were below 102/g in all feed samples. Fecal shedding of listeriae was detected in 11.9% of the cows and the prevalences of L. monocytogenes among farms ranged from no detections to 8.7 %. The number of Listeria isolations from constructions inside the barns and from the milking environment varied between the farms. Listeriae were detected almost everywhere on one of the farms whereas on another farm the only isolations were from feed passages and floors. 13.6 % of the swab samples taken from the teats before washing and drying were Listeria positive, whereas no isolations were made after cleaning the udder. Good milking and barn hygiene is considered important for diminishing the risks of exogenous contamination of raw milk by listeriae.

We induced an experimental listeriosis in five goats by oral inoculation of Listeria monocytogenes serovar 1/2a. The resulting generalized bacteremia was reflected by systemic illness in four of the five animals inoculated and by excretion of L. monocytogenes in milk by all five animals. By using an enzyme immunoassay, we recorded a markedly enhanced immunoglobulin G (IgG) antibody response in the two youngest and most seriously ill test animals. In these, the elimination of L. monocytogenes from the gastrointestinal tract occurred simultaneously with the development of the highest antibody levels at 14 to 15 days postinoculation. In the case of the oldest test animal, a preexisting, persistent IgG antibody response was recorded which was associated with the total absence of clinical symptoms and the shortest observed fecal carriage of L. monocytogenes, lasting for only 3 days. Two animals remained practically seronegative, and an IgM antibody response was not recorded for any of the animals. The findings suggest that an association exists between the humoral immune defense against Listeria infections, the clinical course of the infection, and the elimination of the Listeria organisms from the gastrointestinal tract.

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