Escherichia coli S fimbriae do not contribute to intestinal colonization or translocation in the gnotobiotic rat.

Escherichia coli S fimbriae, which bind to sialic acid residues, are a virulence factor for extraintestinal infection, but also promote binding to intestinal epithelial cells. In this study, we investigated whether S fimbriae would enhance intestinal colonization by E. coli or promote translocation to extraintestinal sites. A mixture of two E. coli isogenic strains both expressing type-1 fimbriae but differing in the carriage of S fimbriae (Sfim+ and Sfim-) were given perorally to germfree neonatal, infant or adult rats. The Sfim+ bound better to rat intestinal mucus and epithelial cells. However, both strains colonized equally well in both the small and large intestine and their rate of translocation to the mesenteric lymph nodes was similar. Infant rats had higher E. coli levels in the small intestine than adult rats, but their translocation rates were lower. This was at least partly due to their milk diet, since weaned infant rats had more translocating bacteria than infant rats that continued suckling their mother. The results suggest that S fimbriae, despite binding to intestinal epithelial cells and mucus, do not contribute to either colonization or translocation in the gnotobiotic rat.

Breast feeding: overview and breast milk immunology.

The transfer of host defence capacity to the human offspring provides a remarkable model of passive transfer of immunity. In fact it may also provide an example of active immunization. The transfer of mucosal protection via breast feeding offers many additional advantages for the mother and infant. Through its contraceptive effects it increases the spacing between births, thus diminshing the infant mortality and the burden on the mother. It also enhances bonding between mother and child, it seems to increase the IQ and school result of the infant and might decrease the risk of certain malignancies and perhaps of juvenile diabetes. A fully breast-fed infant receives as much as 0.5-1 g of secretory immunoglobulin A (SIgA) antibodies daily, the predominant antibody of human milk. This can be compared to the production of some 2.5 g of SIgA per day for a 60 kg adult. These SIgA antibodies have been shown to protect against Vibrio cholerae, ETEC, Campylobacter, Shigella and Giardia. Furthermore, milk is rich in receptor analogues for certain epithelial structures which microbes need for attachment to host tissues as an initial step in infections. Thus the adherence of Haemophilus influenzae and pneumococci for example to retropharyngeal cells is efficiently inhibited by human milk. This may be one explanation for the fact that breast-fed babies have less otitis media than the non-breast-fed. Other milk factors like lysozyme and lactoferin may contribute to the host defence, but this has not yet been well defined. However, human milk also supports the well-being of the infant by being anti-inflammatory.(ABSTRACT TRUNCATED AT 250 WORDS)