Bactericidal effect of bovine normal and immune serum, colostrum and milk against Helicobacter pylori.

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.

Production of hyperimmune bovine colostrum against Campylobacter jejuni.

Serial immunization of dairy cows with Campylobacter jejuni resulted in an enhanced serum antibody response and production of hyperimmune colostrum in all vaccinated animals. An approximate 10-fold decrease in the Camp. jejuni-specific antibody titres in colostrum was observed within 2 d post-partum. The lyophilized colostral concentrate fed to newborn calves resulted in a rapid increase in serum antibody response. Specific Camp. jejuni immunoglobulins could be detected in these animals for a further 10 weeks. The lyophilized hyperimmunized colostrum was very stable in vitro at different storage temperatures. It could be used for passive immunization to campylobacteriosis.

Antibodies to listeriolysin O reflect the acquired resistance to Listeria monocytogenes in experimentally infected goats.

We induced experimental listeriosis in goats by two sequential oral inoculations of Listeria monocytogenes serovar 1/2a at 8 months' interval. Immunoblot analysis with the goat sera demonstrated listeriolysin O (LLO) as the principal protein antigen of L. monocytogenes. Pre-existing antibodies to LLO were, depending on their initial level, associated with either mild clinical symptoms of short duration or the total absence of clinical symptoms. Similarly, the presence and development of such antibodies corresponded with the disappearance pattern of L. monocytogenes from the gastrointestinal tract. These findings suggest that an association exists between antibodies to LLO and acquired resistance to Listeria infections.

Fate of Listeria monocytogenes in orally dosed chicks.

The fate of Listeria monocytogenes in chicks perorally dosed with these bacteria at 2 days of age was determined by bacterial enumeration, immunoperoxidase staining and histological examination of the liver, muscle and gastrointestinal tract. Results revealed listerial egress from the digestive tract and elimination of the organism from the body in most of the chicks within 9 days post-inoculation. L. monocytogenes was isolated from the caecum of only one of 10 chicks examined at 4 weeks post-inoculation. Results indicate that chickens are not likely to be common reservoirs of L. monocytogenes. Intestinal carriage of L. monocytogenes by poultry may frequently be transient, resulting from ingestion of Listeria-contaminated feed and soil.

Contamination of raw milk by Listeria monocytogenes on dairy farms.

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 10(2)/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.

Epidemiological studies on the occurrence of Listeria monocytogenes in the feces of dairy cattle.

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 antibody response to Listeria monocytogenes, listerial excretion, and clinical characteristics in experimentally infected goats.

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.