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Microcalorimetry – a novel method for rapid diagnosis of bloodstream infections

Abstract number: 1732_66

Antheaume J., Salzmann S., Steinhuber A., Frei R., Daniels A., Trampuz A.

Background: Early detection of microorganisms in blood is essential for early diagnosis and treatment of bloodstream infections. Calorimetric detection of microbial growth may be more sensitive and rapid than blood culture systems. We compared microbial detection in spiked blood specimens using a commercial system (CO2 detection by colour change) and an isothermal microcalorimeter.

Methods:Escherichia coli (ATCC 25922) or Staphylococcus aureus (ATCC 29213) were added at 3 different concentrations to anticoagulated blood obtained from healthy volunteers. Aliquots of 7.5 ml spiked blood were added into aerobic blood culture bottles containing 40 ml growth medium and incubated in the blood culture instrument (BacT/ALERT, bioMérieux, Durham, NC, USA). Before incubation, 1 ml of the bottle content was inoculated in glass ampoules containing 2 ml sterile trypticase soy broth for calorimetry (TAM III, Thermometric AB, Järfälla, Sweden). Blood cultures and calorimetry ampoules were simultaneously loaded in corresponding instruments and incubated at 37°C for 72 hours. Time to positivity was defined as the interval from incubation start until positive signal (BacT/ALERT) or until the heat flow rate increased ≥10 mW above baseline (calorimeter detection limit = ~0.3 mW).

Results: Time to positivity was considerably shorter using calorimetry (Table). Blood without added pathogens produced no heat signal above baseline. Spiked specimen heat signals rose to >100 mW as the pathogens multiplied during the incubation period.

Pathogen (cfu/mL blood)Time to positivity for BacT/ALERT (h)Time to positivity for calorimeter (h)Peak heat flow (mW)
E. coli (105)83.2761
E. coli (103)11.85.4733
E. coli (101)12.27.3741
S. aureus (105)10.54.4278
S. aureus (103)177.8244
S. aureus (101)20.812.9114

Conclusion: Microcalorimetry has the potential to detect bloodstream infections earlier with a smaller volume of blood than commercial blood culture systems and for routine use in microbial screening of blood cultures.

Session Details

Date: 31/03/2007
Time: 00:00-00:00
Session name: European Society of Clinical Microbiology and Infectious Diseases
Subject:
Location: ICC, Munich, Germany
Presentation type:
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