Variability in CO2, O2, and pH levels in blood culture bottles from five different manufacturers

The CO2, O2, and pH levels of commercially available blood culture bottles with tryptic soy broth medium from five different manufacturers were compared. Ranges of 1.3 to 6.9% for CO2, 1.1 to 6.0% for O2, and pH 6.94 to 7.26 were found. Different venting procedures revealed that blood culture bottles from which the rubber diaphragm was removed equilibrated the most rapidly (24 h) to the atmosphere (10, 5, and 2.5% CO2) they were incubated in. In contrast, blood culture bottles vented with cotton-plugged needles required 48 h to achieve similar CO2 levels in the medium. The ability of these venting procedures to support bacterial growth was confirmed by measuring the growth of a CO2-dependent Escherichia coli isolate in such vented bottles; blood culture bottles that showed rapid atmospheric (5 and 10% CO2) equilibration had the fastest growth curves. Our results suggest that the differences in the recovery of certain microorganism from blood culture bottles may be due in part to the large variability seen in CO2 and O2 concentrations and the use of various venting procedures.