Bacterial concentrations were determined using standard plating methods and expressed as the number of viable CFUs per milliliter (CFU/mL). Streptococcus dysgalactiae was cultured on Columbia blood agar (Merck, Darmstadt, Germany). All other bacterial species were plated on CASO agar (Merck, Darmstadt, Germany). Samples with an expected count of >100 CFU/mL were inoculated using a spiral plater. Serial ten-fold dilutions of each sample were transferred to agar plates (2 plates/dilution, 50 μL/plate). Samples with an expected count of <100 CFU/mL were cultured using the pour plate method (2 plates/sample, 0.5–1 mL/plate). All agar plates were incubated at 37°C (except for Serratia marcescens, which was incubated at 30°C) for 1–2 days until colonies could be counted.
PC samples collected on day 7 of storage were tested for sterility with the BACT/ALERT 3D 60 Microbial Detection System (bioMérieux, Nuertingen, Germany). Briefly, after the collection of PC samples (20 mL each) under sterile conditions on day 7 of storage, half (10 mL) was injected into a BACT/ALERT SA (aerobic) and SN (anaerobic) culture bottle, respectively, and cultivated under automated blood culture conditions at 36°C in the BACT/ALERT incubator (bioMérieux) for 7 days.
PC samples collected on day 7 of storage were tested for sterility with the BACT/ALERT 3D 60 Microbial Detection System (bioMérieux, Nuertingen, Germany). Briefly, after the collection of PC samples (20 mL each) under sterile conditions on day 7 of storage, half (10 mL) was injected into a BACT/ALERT SA (aerobic) and SN (anaerobic) culture bottle, respectively, and cultivated under automated blood culture conditions at 36°C in the BACT/ALERT incubator (bioMérieux) for 7 days.