In order to reduce the risk of infection several preventive measures have been adopted. Fundamentally, all of these measures were designed to prevent either acquisition of Gram negative rods or fungal pathogens from the environment, or the translocation of these potential pathogens across the mucosal barrier of the gut. These measures include protective (or reverse) isolation, antibiotic prophylaxis with antibiotics which selectively eradicate the aerobic Gram negative rods and yeasts from the gut flora, and finally the use of low-bacterial diets.