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.

In comparison with standard methods, enrichment in halfFraser broth for 24 h at 30 C, followed by plating out onto Listeria monocytogenes blood agar (LMBA) and PALCAM medium combined with an additional streak proved to be the most rapid and speci®c method for the detection of indigenous L. monocytogenes populations from soft mould-ripened cheese. This procedure, with a high sensitivity (93%) and a low detection limit (1±10 cfu 25 g À1 ), provided negative and presumptive positive results within 2±3 d. Differences between LMBA, PALCAM and Oxford medium turned out to be highly signi®cant (at 99% signi®cance level); plating on LMBA after standard enrichment protocols giving the best overall results. An improvement in detection was also obtained by modifying the con®rmation procedure. A loopful of culture (an additional streak) from PALCAM or Oxford medium was streaked on non-selective medium in addition to streaking only separate colonies as speci®ed in the standards.