Clinical laboratory comparison of the 10-ml isolator blood culture system with BACTEC radiometric blood culture media

Abstract

The efficiency of the 10-ml Isolator (E. I. du Pont de Nemours & Co., Inc.) for recovery of pathogens from blood was compared with that of BACTEC 6B and 7C media (Johnston Laboratories) by using 4,195 cultures from 1,662 patients. During the first phase of the study, BACTEC bottles were inoculated with 3 ml of blood; in the second phase, bottles were inoculated with 5 ml. The objectives were to compare results with similar blood volumes used for the detection of anaerobes as well as similar overall volumes and to determine the relative sensitivity of BACTEC media inoculated with the minimum and maximum volumes suggested by the manufacturer. From 180 patients, 391 significant isolates were recovered, 354 (91%) with the Isolator and 304 (78%) with the bottles. Isolators recovered 31 (15%) and 19 (18%) more pathogens overall than did the two-bottle system inoculated with 3 and 5 ml of blood, respectively, including 30 (36%) and 10 (34%) more Enterobacteriaceae. Recovery of anaerobes was greater in the BACTEC anaerobic medium, but only when its inoculum was increased to 5 ml. No significant differences existed between the two systems in pathogen detection times or detection of polymicrobic bacteremia. The Isolator contamination rate (8.3%) was approximately 4 times that of the bottles. The number of CFU of pathogen per milliliter of blood, blood volume sampled, and number of Isolators collected were more important than antimicrobial agent pretreatment in contributing to patient bacteremia of fungemia undetected by the Isolator. The Isolator appeared to be a practical alternative for recovery of aerobic and facultatively anaerobic pathogens from the blood.