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.

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.

Effect of Ca2+ ions on plasmid transformation of Streptococcus lactis protoplasts.

The effects of Mg2+ and Ca2+ ions on the efficiency of the plasmid transformation of lysozyme-treated Streptococcus lactis protoplasts were compared. A 33-megadalton plasmid, pLP712, coding for lactose fermentation and a 6.5-megadalton plasmid, pGB301, coding for erythromycin and chloramphenicol resistance were used as model plasmids, and S. lactis MG1614 was the recipient. Replacing Mg2+ with Ca2+ in the transformation buffer was found to increase transformant frequency more than 10-fold with both plasmids.