Growth dynamics of Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa as a function of time to detection in BacT/alert 3D blood culture bottles with various preincubation conditions

Abstract

Background: Delayed entry of blood culture bottles is inevitable when microbiological laboratories do not operate for 24 hr. There are few studies reported for prestorage of these bottles. The growth dynamics of Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa were investigated with respect to various preincubation conditions.

Methods: Fifteen or 150 colony-forming units (CFU) of bacteria were inoculated into standard aerobic or anaerobic blood culture bottles. Bottles were preincubated at 25℃ or 37℃ for 0, 2, 4, 8, 12, 24, or 48 hr. The time to detection (TTD) then was monitored using the BacT/Alert 3D system (bioMerieux Inc., USA).

Results: Significant difference in TTD was observed following preincubation for 8 hr at 25℃ vs. 4 hr at 37℃ for S. aureus, 4 hr at 25℃ vs. 4 hr at 37℃ for E. coli, 12 hr at 25℃ vs. 4 hr at 37℃ for P. aeruginosa, compared to no preincubation (P<0.005). TTD values did not vary significantly with bacterial CFU or with aerobic or anaerobic bottle type. The BacT/Alert 3D system returned false negatives following preincubation of P. aeruginosa for 48 hr at 25℃ or 24 hr at 37℃.

Conclusions: TTD was mainly affected by preincubation temperature and duration rather than by input CFU quantity or bottle type for the 3 experimental bacteria.

Keywords: Blood culture; Detection; Preincubation; Storage.

Fig. 1

TTD values for (A) Staphylococcus aureus, (B) Escherichia coli, and (C) Pseudomonas aeruginosa preincubated in aerobic and anaerobic blood culture bottles at 25℃ or 37℃ prior to insertion into the BacT/Alert 3D system. False negatives were detected after 48 hr of prestorage at 25℃ and after 24 hr of preincubation at 37℃ for P. aeruginosa. Bacterial input concentration was 15 colony-forming units/mL. Abbreviation: TTD, time to detection.