Laboratory experience with a radiometric method for detecting bacteremia

Abstract

Two bacteriologic systems for detecting bacteria in blood were compared; the automated radiometric BACTEC and the conventional method used in our laboratory for many years. BACTEC consisted of two bottles with 30 ml and the conventional method with 50 ml of media for aerobes and anaerobes. The BACTEC bottles were inoculated with 2 to 3 ml and the conventional with 4 to 5 ml of blood at the patient's bedside. Out of the 3,045 blood specimens cultured (804 patients), 262 (117 patients) were positive by one or both methods. The conventional system detected 5more cultures. The explanation of the differences is discussed. Positive blood cultures were detected by the BACTEC procedure as early as 6 h after the blood collection. In the first 24 h, on the average, 77% of aerobic organisms were detected by the BACTEC as compared to 48% by the conventional system. All anaerobic BACTEC cultures were positive within 4 days, whereas the conventional system detected at that time 74%. At day 4, 67% of fungi were detected by the BACTEC and only 27% by the conventional system. Of the 3,045 blood cultures examined by the BACTEC, 208 were recorded as false positive with growth index readings ranging from 30 to 59.