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Clinical challenges and culture-based diagnostics

Efficient inactivation of clinically relevant antimicrobial drug concentrations by two resin-containing media in simulated paediatric blood cultures

April 20 • P2909

F. Marzia Liotti1, G. Menchinelli1, L. Giordano1, G. De Angelis1, T. Spanu1/2, M. Sanguinetti1/2, B. Posteraro3/4

1) Institute of Microbiology, Università Cattolica del Sacro Cuore, Rome, Italy
2) Dipartimento di Scienze di Laboratorio e Infettivologiche, Fondazione Policlinico Universitario A. Gemelli IRCCS, Rome, Italy
3) Institute of Medical Pathology and Semeiotics, Fondazione Policlinico Universitario A. Gemelli IRCCS, Università Cattolica del Sacro Cuore, Rome, Italy
4) Dipartimento di Scienze Gastroenterologiche, Endocrino-Metaboliche e Nefro-Urologiche, Fondazione Policlinico Universitario A. Gemelli IRCCS, Rome, Italy

Background: Diagnosis of bloodstream infection in paediatric patients is a major challenge for clinical microbiologists. Improvements in blood culture (BC) media and the availability of automated growth detectors enhance the recovery of bloodstream pathogens and decrease the time to detection (TTD) of microbial growth. However, antimicrobial treatment administered before drawing BCs can reduce or delay pathogen recovery, especially in paediatric patient settings where low-level bacteraemias and small blood sample volumes often complicate the situation. The aim of this study was to evaluate the BacT/Alert PF Plus (bioMérieux) or Bactec Peds Plus (Becton Dickinson) resin-containing media for their capability of inactivating clinically relevant antimicrobial drug concentrations in simulated paediatric BCs.

Materials/methods: We tested eight antimicrobial-organism combinations in BacT/Alert PF Plus or BACTEC Peds Plus bottles, which were inoculated with 2 or 10 mL of banked whole blood, 0.5 mL of antimicrobial drugs at peak or trough serum concentrations, and 0.5 mL of bacterial suspensions containing 5 or 30 CFU of per bottle. This resulted in eight conditions (each was tested in triplicate) for each combination. Positive and negative controls were included. All bottles were incubated in both BacT/Alert Virtuo or Bactec FX systems. Results were reported as organism’s recovery rates and mean TTDs, and differences were assessed using the McNemar’s test or the paired t test, as appropriate.

Results: The overall recovery rate of organisms with the BacT/Alert PF Plus medium was 39.1% (75/192 bottles), whereas the rate with the BACTEC Peds Plus medium was 25.0% (48/192 bottles) for all the antimicrobial-organism combinations tested. We found that this difference was statistically significant (P <0.001). The mean TTDs were 14.26 h and 16.37 h for the BacT/Alert PF Plus medium or the BACTEC Peds Plus medium, respectively (P <0.05). Interestingly, there was no recovery at any condition with ceftriaxone tested against Streptococcus pneumoniae for both the media and with vancomycin tested against S. pneumoniae only for the BACTEC Peds Plus medium.

Conclusions: Despite preliminary, our findings show that the BacT/Alert PF Plus medium is more efficient than the BACTEC Peds Plus medium in a simulated paediatric BC setting.

microbiology

BACT/ALERT® VIRTUO™

Paper poster