Bovine milk fat components inhibit food-borne pathogens

Bovine milk fat may protect against gastrointestinal infections by means of its antimicrobial constituents. This paper summarises our studies performed to test the bactericidal activities of milk fat. In vitro, the fatty acids C(10:0), C(12:0) and unsaturated C18 fatty acids together with digestion products of sphingolipids were effective bactericidal agents. Listeria monocytogenes and Campylobacter jejuni were very sensitive, whereas E. coli O157:H7 and Salmonella enteritidis were less vulnerable. In rats, high intake of milk fat triglycerides protected against orally administered L. monocytogenes but not against S. enteritidis. The enhanced resistance to L. monocytogenes was related to an increased release of gastric bactericidal saturated fatty acids. Since gastric bactericidal activity is predictive for butter fat-mediated resistance to L. monocytogenes in vivo, C. jejuni and E. coli O157:H7 were incubated with gastric contents of rats fed high or low butter fat diets. Ex vivo killing of E. coli was not affected whereas bactericidal activity towards C. jejuni was enhanced in gastric chyme of rats fed high butter fat diets, implying that milk fat triglycerides may also protect against campylobacter infections. Since unsaturated C18 fatty acids were listericidal in vitro, the efficacy of these agents was tested in rats. High corn oil intake did not protect against listeria infection, suggesting that the protective effect of fatty acids in vivo may be limited to C(10:0) and C(12:0). The effectiveness of membrane lipids was also tested in rats. Colonisation of L. monocytogenes was decreased in rats fed diets based on sweet butter milk powder (membrane lipid rich) compared with rats fed skim milk-based diets (low content of membrane lipids). In conclusion, bovine milk fat triglycerides containing C(10:0) and C(12:0), and sphingolipids may enhance the resistance to certain types of food-borne gastrointestinal infections.