Practical Considerations for Reporting Staphylococcus epidermidis Using BioFire FilmArray Blood Culture...

The BioFire FilmArray Blood Culture Identification 2 (BCID2; bioMérieux, Marcy-l'Étoile, France) panel enables the rapid detection of bloodstream pathogens directly from positive blood cultures. However, in polymicrobial cultures involving coagulase-negative staphylococci (CoNS), Staphylococcus epidermidis detection by BCID2 may not always align with standard culture results. We evaluated whether analyzing ΔCp-defined as the difference in crossing point (Cp) values between the Staphylococcus genus target and the S. epidermidis species-specific target in BIOFIRE FIREWORKS software, as a within-system proxy for relative target abundance-along with multicolony subculture could improve result interpretation. Between April and September 2025, the BCID2 results from 20 patients at a tertiary hospital in Korea indicated S. epidermidis. These results were compared with standard culture and multicolony subculture findings. Conventional blood culture confirmed S. epidermidis in 12 cases, whereas eight bottles grew other CoNS. Multicolony identification demonstrated S. epidermidis co-detection in six of these BCID2-culture-discrepant cases. Amplification curve analysis revealed significantly higher ΔCp values in discrepant cases than in concordant cases (+0.5 to +11.5 vs. -0.7 to +0.2 cycles; median 3.55 vs. -0.15 cycles; P =0.0002). Hence, ΔCp analysis, supported by subculture, may help identify potential BCID2-culture discrepancies in mixed CoNS cases.