Potential antimicrobial effects of human lactoferrin against oral infection with Listeria monocytogenes in mice

Listeria monocytogenes is a food-borne pathogen that causes serious listeriosis in humans. Antimicrobial effects of human lactoferrin (hLF) against L. monocytogenes have been clearly demonstrated in in vitro studies. However, in vivo studies have not been reported yet. This study investigated whether the oral administration of hLF could inhibit oral infection of listeria in BALB/c mice. The MICs for several strains of L. monocytogenes were determined, and the most sensitive strain was used for the animal work. hLF was administered to BALB/c mice for 7 days, commencing 4 days before oral infection. The effect of hLF was determined by bacterial enumeration and histopathological analysis of the liver and spleen, which are well-known as the major targets of oral listeria infection in mice. In bacterial enumeration, hLF decreased the number of L. monocytogenes cells in the liver. Histopathologically, the size and frequency of necrotic foci in the liver samples decreased with hLF administration. However, these changes were not observed in the spleen samples. The mRNA levels of inflammatory cytokines, such as interleukin (IL)-1 beta, tumour necrosis factor (TNF)-alpha and interferon (IFN)-gamma, decreased in the liver of mice receiving hLF. This study has shown that hLF decreases the hepatic colonization of L. monocytogenes, hepatic necrosis and expression of inflammatory cytokines. It revealed that perorally given hLF could mediate antimicrobial and anti-inflammatory activities remote from the gut (i.e. in the liver) of mice challenged with L. monocytogenes.