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 5% more 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.

Controlled evaluation of supplemented peptone and Bactec blood culture broths for the detection of bacteremia and fungemia

“…In this controlled evaluation, the Bactec two-bottle set recovered 11% more bacteria and fungi and did so faster in 18% of samples than a single bottle of SPB with equal volumes of blood in both. This result confirms the early results obtained with the Bactec system (2,5,15,18,22,25). However, one might have expected that acridine orange staining would have matched the speed of radiometric detection, since other studies have shown the utility of early acridine orange screening in the rapid detection of bacteremia (9, 10,12,14,23).…”

“…Few clinical studies have been done to compare Bactec with a conventional broth culture method; none has been published since 1975, although both aerobic and anaerobic Bactec media have been modified since then. In early trials, Bactec detected positive cultures earlier, and had a yield similar to conventional broth cultures (2,5,15,17,22,24), but the volume of blood cultured in these studies was usually not the same; early Gram stains and subcultures of conventional bottles were not performed, so that slower recovery in the conventional system was predictable. Moreover, these studies were done before acridine orange staining had been recognized as a useful early screening method (12,14,23).…”

“…Moreover, these studies were done before acridine orange staining had been recognized as a useful early screening method (12,14,23). Reports that radiometric culture bottles grew baçteria despite negative growth readings (1,3,5,18) and that some radiometric culture bottles had high radiometric readings in the absence of bacteria (2-4, 17,22,25) further suggested that a controlled comparison with conventional media was needed.…”

A Comparison of a Conventional and a Radiometric Examination of Clinical Blood Cultures With Respect to Recovery Rate and Detection Time of Microorganisms

“…The recovery rate in the radiometric system in this study was higher than previously reported. A few investigators reported a recovery rate of about 90% (5,28), but generally a recovery rate of about 80% was demonstrated (8, 23, 25, 31).…”

“…Since DeLand & Wagner (9) in 1969 first described a radiometric method for detection of bacteria in blood, several investigators have reported promising results with the radiometric system, BactecB. This system has been shown to be faster than some of the conventional methods used today and comparable with respect to the detection rate (5, 8, 9, 10, 23, 28, 31).…”