Clinical Metagenomic Sequencing for Species Identification and Antimicrobial Resistance Prediction in Orthopaedic Device Infection
Background Diagnosis of orthopaedic device-related infection is challenging, and causative pathogens may be difficult to culture. Metagenomic sequencing can diagnose infections without culture, but attempts to detect antimicrobial resistance (AMR) determinants using metagenomic data have been less successful. Human DNA depletion may maximise the amount of microbial DNA sequence data available for analysis. Methods Human DNA depletion by saponin was tested in 115 sonication fluid samples generated following revision arthroplasty surgery, comprising 67 where pathogens were detected by culture and 48 culture-negative samples. Metagenomic sequencing was performed on the Oxford Nanopore Technologies GridION platform. Filtering thresholds for detection of true species versus contamination or taxonomic misclassification were determined. Mobile and chromosomal genetic AMR determinants were identified in Staphylococcus aureus-positive samples. Results Of 114 samples generating sequence data, species-level sensitivity of metagenomic sequencing was 49/65 (75%; 95%CI 63-85%) and specificity 103/114 (90%; 95%CI 83-95%) compared with culture. Saponin treatment reduced the proportion of human bases sequenced in comparison to 5um filtration from a median (IQR) 98.1% (87.0%-99.9%) to 11.9% (0.4%-67.0%), improving reference genome coverage at 10-fold depth from 18.7% (0.30%-85.7%) to 84.3% (12.9%-93.8%). Metagenomic sequencing predicted 13/15 (87%) resistant and 74/74 (100%) susceptible phenotypes where sufficient data were available for analysis. Conclusions Metagenomic nanopore sequencing coupled with human DNA depletion has the potential to detect AMR in addition to species detection in orthopaedic device-related infection. Further work is required to develop pathogen-agnostic human DNA depletion methods, improving AMR determinant detection and allowing its application to other infection types.