Effect of aerobic and anaerobic atmosphere on the detection of micro-organisms from blood cultures.

Blood from patients with suspected bacteraemia was simultaneously cultured in two Vacutainer blood culture bottles containing 45 ml of supplemented peptone broth (Becton Dickinson), five ml of blood in each bottle. The cultures were incubated at 37 degrees C for seven days. One of the bottles was vented and the other unvented. A total of 3958 blood culture sets were processed during the 20-month period of the study. Altogether 438 (11%) of the blood culture sets were positive. Of the 438 isolates, 317 (72%) were detected in both bottles, 61 (14%) in the vented bottle and 60 (14%) in the unvented bottle. A total of 60 (14%) isolates would not have been detected if only five ml of blood had been cultured. Only minor differences in the isolation rates of different bacterial and fungal species from the vented and unvented bottles were found. The results indicate that aerobic incubation of Vacutainer bottles with supplemented peptone broth is sufficient in routine diagnostic work.