Recovery and time to growth of isolates in blood culture bottles: Comparison of BD bactec plus aerobic/F and BD bactec plus anaerobic/F bottles

Background: This study was done to compare the growth of pathogens in paired aerobic/anaerobic blood culture bottles versus the use of only aerobic bottles, and to analyze the time to growth in both atmospheres. Methods: We retrospectively evaluated the results of all blood cultures collected over a 2-y period for the diagnosis of central venous catheter-related bloodstream infections or other severe infections in oncology patients. Results: Among the 487 isolates, 174 (35.7%), all aerobic, grew only in the aerobic bottle; 250 (51.3%), all aerobic, grew in both bottles; and 63 (12.9%) grew only in the anaerobic bottle, of which 24 were anaerobic and 39 were aerobic microorganisms (8% of positive blood cultures). Of these 39 aerobic microorganisms, 12 were Gram-negative, 17 staphylococci (4 were Staphylococcus aureus), 5 streptococci, 2 Gram-positive bacilli, and 3 mixed growth. Though the mean time to positivity of pathogens grown in both atmospheres was significantly lower in the aerobic bottle than in the anaerobic bottle, in 71 cases (28.4%) the pathogens developed earlier in the anaerobic bottle than in the aerobic bottle-in 36 of these cases at least 1 h earlier, which is significant for starting targeted therapy. Conclusions: The use of paired aerobic/anaerobic blood culture bottles allowed the diagnosis of a percentage of bacteraemia due to either anaerobic or aerobic pathogens that would have been missed, as they grew only in the anaerobic atmosphere. Moreover in 8% of bacteraemia we identified a significant decrease in the time to detection, resulting in the opportunity to better manage the infections without an increase in costs.