Bacterial Localization in the Kidney **

Adult male Sprague-Dawley rats weighing 175 to 250 grams were injected intravenously with 0.5-0.8 ml. of a four-hour culture of Escherichia coli (containing 4-7 x 108 organisms/ml.) in beef heart infusion broth. This particular strain was originally isolated from the urine of a patient with pyelonephritis and has been fully described elsewhere.' It is known that this organism is trapped by the kidneys during the course of bacteremia, remains there several days after the cessation of the bacteremia, and finally disappears without causing progressive infection or visible damage to renal tissues.' At 30 minutes and at 2, 4, 6, 12, 18, 24, 96, and 240 hours following inoculation, animals were anesthetized with 0.01 g. sodium pentobarbital intraperitoneally. An agar pour plate was made with 1.0 ml. of heart blood, and 0.05 ml. of bladder urine was aspirated and streaked on a desoxycholate agar plate. The kidneys were removed, using sterile technique, and each cortex separated from its medulla by sharp dissection. The cortical and medullary tissues were then weighed separately and after the addition of enough 0.85% NaCl to the solution to give a final volume of 10.0 ml., each preparation was ground in a homogenizer obtained from the Tri-R Instrument Company, 144-13 Jamaica Avenue, Jamaica 35, New York. One milliliter of each homogenate was incorporated into an agar pour plate. All cultures of blood, urine, and tissue were incubated for 36 to 48 hours at 370 C. and colony counts were then performed using a Quebec counter.