Esch. coli infections in childhood. Significance of bacterial virulence and immune defence.

The Esch. coli harboured in the gut constitute a reservoir of potential pathogens in the infant and child. The conditions required for these intestinal inhabitants to cause infection are not well understood. The presence of virulence factors such as capsular antigens, especially K1, may be of significance for the ability of Esch. coli to cause neonatal meningitis. The capacity of certain Esch. coli to attach to epithelial cells of mucous membranes may be important for their infective powers in the urinary as well as the intestinal tract. Furthermore, the ability of certain Esch. coli to produce enterotoxins similar to that of V. cholerae is of importance for their capacity to provoke diarrhoea. The importance of the immune defence mechanisms for prevention of these Esch. coli infections is suggested, especially in the form of local immunity provided by secretory IgA antibodies. Such antibodies directed against Esch. coli O and K antigens as well as enterotoxins are present in large amounts in human milk and may be of considerable importance for protection against Esch. coli in the breast-fed baby. Breast feeding may be of special significance until the baby has built up its own local immune defence preventing the micro-organisms from attaching to and invading the intestinal mucous membranes. SIgA antibodies in urine may have a similar protective effect against urinary tract infections. The variable pictures of Esch. coli infections in childhood are striking, ranging from severe sepsis/meningitis or diarrhoea to "asymptomatic" bacteriuria. This variability is obviously closely connected with the presence of various virulence factors and the function of different components of the immune defence.