Shigella species cause bacillary dysentery in humans by invasion, intracellular multiplication, spread to adjacent cells, and induction of brisk inflammatory responses in the intestinal epithelium. In vitro data suggest that lactoferrin, a glycoprotein present in human mucosal secretions, has a role in protection from bacterial enteric infections. We sought to determine the activity of lactoferrin in vivo, using the concentration present in human colostrum, to investigate its effect on the development of clinical and pathological evidence of inflammation in a rabbit model of enteritis. Lactoferrin protected rabbits infected with Shigella flexneri from developing inflammatory intestinal disease. Typical histological changes in ill animals included villous blunting with sloughing of epithelial cells, submucosal edema, infiltration of leukocytes, venous congestion, and hemorrhage. Lactoferrin at a concentration normally found in human colostrum blocks development of S. flexneri-induced inflammatory enteritis.Dysentery due to Shigella spp. is among the most communicable and severe forms of bacterial gastroenteritis in humans (43). The virulence of Shigella is due to its ability to invade, multiply, spread intracellularly, and induce inflammation within the intestinal epithelium (33). Most of the genes responsible for invasion of eukaryotic cells are located on a 230-kb virulence plasmid (1). Entry into mammalian cells is regulated by a plasmid-encoded type III secretory system located on a 31-kb locus that codes for the invasion plasmid antigens IpaA, IpaB, IpaC, and IpaD. This secretory mechanism is activated upon contact with epithelial cells (49). Upon entry into host cells, bacteria gain access to the cytoplasm by lysing the phagocytic vacuole and rapidly multiplying and spreading (26,32,41) Epidemiologic studies have shown that breast-feeding decreases the severity of Shigella sp. infection in infants who become colonized early in life (2,12,13,20,22,25). Immune and nonimmune components of milk may be relevant to this protection. Among the nonantibody factors is lactoferrin, an iron-binding glycoprotein of 78 kDa that is resistant to proteolytic enzymes (10). However, epidemiologic data cannot separate the effect of lactoferrin from those of other potentially protective human milk factors. Lactoferrin, antilipopolysaccharide (anti-LPS) and anti-invasion plasmid antigen secretory immunoglobulin A (IgA), lysozyme, and oligosaccharides may each play a role in protection of infants from shigellosis. Although multiple effects of lactoferrin have been demonstrated in vitro, there are no animal model studies demonstrating a role in the gut in vivo. The objective of these studies was to determine whether lactoferrin at concentrations found in human colostrum (0.125 mM) could prevent the development of clinical and pathological changes in an in vivo rabbit model of inflammatory enteritis. MATERIALS AND METHODSLactoferrin was obtained from Agennix Inc. Lactoferrin is expressed in Aspergillus awamori as a glucoamylase fus...

Secretory immunoglobulin A (sIgA) is a primary factor responsible for preventing attachment of enteropathogens to gut epithelium in breastfeeding infants. We compared the frequency of sIgA to major surface antigens of enterohemorrhagic Escherichia coli (EHEC) in milk of 123 women from the United States and Mexico to determine whether regional differences existed in the frequency of antibodies to these surface antigens. In both groups of women, milk commonly has sIgA against various EHEC lipopolysaccharides, EspA, EspB, intimin, and less frequently against Shiga toxin. The study suggests that persons living in the U.S. are exposed to attaching/effacing enteropathogens more frequently than is generally assumed. The low frequency of antibodies to Stx1 (in 12% of Mexican and in 22% of U.S. samples) suggests that the rare appearance of hemolytic uremic syndrome in adults is not due to neutralization of toxin at the gut level. Only anti-EspA is found in most milk samples from both populations of women. EspA may represent a useful target for an immunization strategy to prevent EHEC disease in humans.

RP 59500, a combination of the streptogramins quinupristin and dalfopristin, and sparfloxacin are new antibiotics with good in vitro activities against Enterococcus faecium, which is an increasingly important nosocomial pathogen with resistance to multiple antimicrobials. Since fluoroquinolones and related macrolides have displayed high intracellular concentrations inside host cells, we evaluated the intracellular activities of these agents inside neutrophils against three strains each of vancomycin-susceptible E. faecium (VSEF) and vancomycin-resistant E. faecium (VREF). At concentrations equal to four times the MIC, RP 59500 and sparfloxacin decreased the number of intracellular VSEF organisms, while both antibiotics were at best bacteriostatic against intracellular VREF strains. At concentrations equal to one-fourth of the MIC, both antibiotics were bacteriostatic against intracellular VSEF strains but were ineffective in inhibiting the growth of VREF strains. Despite their anticipated markedly higher intracellular human neutrophil (PMN) concentrations, RP 59500 and sparfloxacin activities in medium alone were equal to or greater than those inside PMNs against almost all strains. We conclude that the intracellular PMN concentrations of these antibiotics may not be directly related to their intracellular activities in our assay. The reason for the differences in their activities against VSEF versus VREF remains undefined.

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Many macrolides have been shown to affect the interaction between bacteria and various immune defense mechanisms, such as chemotaxis, accumulation, and bioactivity within phagocytic cells. The interaction of azithromycin with human polymorphonuclear leukocytes (PMNs) was studied in vitro and compared with the interactions between other macrolides and PMNs. The opsonophagocytic killing of Staphylococcus aureus was synergistically enhanced by azithromycin at concentrations below and above the minimal inhibitory concentration, with a reduction of up to 2.82 log10 cfu/ml with 2 mg/ml of azithromycin. Other macrolides were effective only at subinhibitory concentrations. The beneficial azithromycin-leukocyte interaction may explain azithromycin's efficacy against intracellular pathogens.