Use of simulated blood cultures for antibiotic effect on time to detection of the two blood culture systems BacT/ALERT and BACTEC 9240.

To avoid the influence of pre-analytical steps, this study was performed using sterile blood spiked with defined loads of microorganisms as inoculum. Time-to-Detection (TTD) was evaluated for the most frequently encountered bacteria comparing two commercially available blood culture systems, BD BACTEC 9240 (Becton Dickinson) and BacT/ALERT (Organon Teknika). The effect of the most widely used antibiotics on TTD was evaluated on both systems. TTD was measured with antibiotics at their trough and at increasing concentrations. The results show that the BACTEC PLUS system recovers more pathogens with shorter time to detection than the BacT/ALERT FAN system when beta-lactam antibiotics (Ampicillin, Cefotaxime) are present at their respective trough concentration corresponding to parenteral therapy. The two systems seem to be equally efficient when Gentamicin, Ciprofloxacin and Trimethoprim/sulfamethoxazole are used; in the case of Vancomycin, BACTEC seems more effective than BacT/ALERT.