Objective: To determine whether preincubation would influence the detection capacity of the BacT/Alert blood culture system. Methods: The suspensions of the organisms to be tested (Escherichia coli

Salmonella typhi

Pseudomonas aeruginosa

Stenotrophomonas maltophilia and Acinetobacter baumannii) were added to the ℃FAN aerobic blood culture bottles. They were loaded into the BacT/Alert system after incubation at 36 for 0h

4h

8h 16h and 24h. The computer system would monitor the reflection units to signal positive to determine the detection time for the bottles. Results: All bottles seeded with E.Coli and S.typhi signaled positive during the next 6.8 h after loading into the BacT/Alert system. Organisms in bottles seeded with P. aeruginosa and A.baumannii were not detected by the system

even with shorter preincubation times

down to 4h.Organisms in bottles seeded with S.maltophilia were undetected with preincubation times longer than 8h

bottles failed to signal ℃positive for these species for 7 days. With an incubation time of 8h at 36

the bottles seeded with E.Coli signaled positive at each colony number tested. An inoculum of 1200 cfu/ml of P. aeruginosa

3400 cfu/ml of A. baumannii remained undetected by the system for 7 days. Conclusion: Bottles which have been preincubated for 4h or longer should be subculture prior to loading to avoid false negatives.