Microcalorimetry: a novel method for detection of microbial contamination in platelet products

Abstract

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. 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. 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. 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.