P092

1:Instituto de Biomedicina de Valencia (IBV-CSIC); 2:Duke University School of Medicine

A 71-year-old male presented 6 years after orthotopic heart transplantation with 4 months of fatigue and night sweats accompanied by a 30-pound weight loss and acute renal failure due to hypercalcemia.  PET/CT demonstrated diffuse, hypermetabolic lymphadenopathy and splenomegaly.  Excisional biopsy of a cervical lymph node demonstrated abundant non-necrotizing granulomas containing acid-fast bacilli. Blood cultures grew an organism initially identified as Mycobacterium nebraskense by 16S rRNA sequencing; 16S PCR of lymph node tissue demonstrated the same organism.  The patient had persistent bacteraemia with this organism over 2.5-years and clarithromycin resistance emerged (MIC ≤0.06 to ˃64 µg/mL) after 8.5 months of azithromycin-based therapy. Whole genome sequencing later revealed that the mycobacterial isolate was not M. nebraskense (90.0% average nucleotide identity despite 99.8% nucleotide match by 16S), matching an isolate designated as SMC-2 (99.95% average nucleotide identity).  This organism, most closely related to M. paraseoulense, has not been previously reported in human disease.  Long-read sequencing of the initial isolate with short-read sequencing of the initial and subsequent isolates revealed several differences from the reference strain including the lack of a plasmid and absence of several prophage sequences.  Preliminary results did not reveal emergence of the expected mutation in 23S rRNA gene after emergence of phenotypic clarithromycin resistance, suggesting a potentially novel resistance mechanism.  One low-frequency, nonsynonymous mutation of unclear significance emerged and persisted in isolates obtained after emergence of clarithromycin resistance.  Whole genome sequencing provided more accurate species identification and provided insight into within-host mycobacterial evolution under antibiotic and immune pressure.