Background: Measuring heat from replicating microorganisms in culture may be a rapid, accurate, and simple screening method for platelets (PLTs). Microcalorimetry for detection of microorganisms in in vitro contaminated PLT products was evaluated.

Study design and methods: Staphylococcus epidermidis, Staphylococcus aureus, Streptococcus sanguinis, Escherichia coli, Propionibacterium acnes, and Candida albicans were inoculated in single-donor apheresis PLTs to achieve target concentrations of 10(5), 10(3), 10, or 1 colony-forming units (CFU) per mL of PLTs. Contaminated PLTs in growth medium were incubated at 37 degrees C for 5 days in a calorimeter. Positivity was defined as heat flow of at least 10 microW above the lowest value of the power-time curve.

Results: With microcalorimetry, inocula of 10 CFUs per mL PLTs could be detected with the following detection times: S. epidermidis (31.65 hr), S. aureus (24.24 hr), S. sanguinis (7.82 hr), E. coli (7.53 hr), P. acnes (73.57 hr), and C. albicans (43.77 hr). The detection time was less than 4 hr at 10(5) CFUs per mL PLTs for S. aureus, S. sanguinis, and E. coli. Noncontaminated PLTs remained negative. The total heat ranged from 2.8 (S. sanguinis) to 8.3 J (E. coli). The shape of the power-time curve was species-specific and independent from the initial concentration of microorganisms.

Conclusion: The detection limit of microcalorimetry was 1 to 10 CFUs per mL PLTs. Microcalorimetry is a promising novel method for detection of contaminated PLTs. Applying this method to all PLT products could reduce the frequency of transfusion-related sepsis and prolong the shelf life of PLTs.