Factors predisposing to urinary tract infections in children

The normal urinary tract is sterile for many reasons. These include: bacterial eradication by urinary and mucus flow, urothelial bactericidal activity, urinary secretory IgA, and blood group antigens in secretions which interfere with bacterial adherence. Periodic emptying of the bladder should wash bacteria out, but uropathogens grow well in urine and their rapid doubling time might not clear bacteria by voiding at the usual frequency. The ability to colonize the gut, as well as adhere to host squamous and urothelial cells, is due to bacterial adherence, a mechanism by which fluid washout would not be effective. Fimbriae or pili, hair-like surface appendages of Escherichia coli, are the usual adhesins. E. coli with type 1 fimbriae adhere to mucus, and P-fimbriae adhere to glycolipids on mucous membranes and urothelial cells. Other common virulence factors of E. coli include the capsule, which prevents phagocytosis, hemolysin, which damages urothelium, and aerobactin, which sequesters iron. Adherence stimulates the inflammatory response by activation of cytokines such as interleukin-1, -6, and -8. These cytokines stimulate the production of intercellular adhesion molecule, which by leukocyte adhesion causes migration of these cells to the site of infection to counteract it.