Controlled evaluation of the effect of atmosphere of incubation on detection of bacteremia and fungemia in supplemented peptone broth

Abstract

To evaluate the role of atmosphere of incubation in the detection of clinically important bacteremia and fungemia in adults, the yield of microorganisms from 10,541 paired 5 ml samples of blood incubated aerobically and anaerobically was compared. The medium, supplemented peptone broth (SPB) with 0.03% sodium polyanetholesulfonate, and the ratio of blood to broth (1:10) were the same for all cultures. Only cultures with adequate blood samples (.gtoreq. 80% of stated volume) were compared statistically. More fungi (P < 10-7) grew in continuously vented bottles of SPB. Aerobic incubation also favored (P < 0.01) isolation of Neisseria gonorrhoeae and Eubacterium; > 80% of these bacterial organisms were detected only in vented bottles. Anaerobic incubation (plugged venting units) did not significantly favor the isolation of any genus of microorganisms, although an estimated 11% more Bacteroidaceae grew in the unvented bottle of SPB. Evidently, the need for both aerobic and anaerobic incubation of blood cultures is dependent upon the medium used and the microorganisms likely to be encountered. Vented incubation of blood cultured in SPB is crucial for detection of fungi and some bacteria. Routine use of an unvented bottle of SPB may not be worthwhile for patients in whom Bacteroidaceae cause bacteremia infrequently. When Bacteroidaceae are suspected as the cause of sepsis, use of an unvented bottle of SPB is prudent.