Many children who catheterize their bladders because of spina bifida or other neurologic disorders have bacteriuria. This can lead to urinary tract infections by bacteria from the gut which colonize the vagina and are carried into the bladder during catheter passage. We seek to test whether oral administration of probiotic bacteria can "displace" these vagina-derived uropathogens and reduce or prevent bacteriuria in girls with spina bifida who empty their bladders through catheterization.