BACKGROUND Severe pneumonia requiring admission to an intensive care unit carries high morbidity and mortality. Evidence-based management includes early administration of empiric antibiotics against plausible bacterial pathogens while awaiting results of microbiologic cultures. However, in over 60% of pneumonia cases, no causative pathogen is identified with conventional diagnostic techniques. In this case report, we demonstrate how direct-from-sample sequencing of bacterial DNA could have identified the multiple culprit pathogens early in the disease course to guide appropriate antibiotic management. CASE REPORT A previously healthy, 21-year-old man presented with neck pain and fever and rapidly developed acute respiratory distress syndrome (ARDS) requiring mechanical ventilation. He was started on broad-spectrum antibiotics and was found to have septic thrombophlebitis of the left internal jugular vein (Lemierre syndrome), with blood cultures growing Fusobacterium necrophorum. While his antibiotics were narrowed to piperacillin-tazobactam monotherapy, his clinical condition worsened, but repeated efforts to define an additional/alternative respiratory pathogen resulted in negative cultures. He eventually developed bilateral empyemas growing Mycoplasma hominis. Once azithromycin was added to the patient's regimen, he improved dramatically. Retrospective sequencing of consecutive endotracheal aspirates showed Fusobacterium as the dominant pathogen early in the course, but with significant and increasing Mycoplasma abundance several days prior to clinical detection. CONCLUSIONS Had sequencing information been available to the treating clinicians, the causative pathogens could have been detected earlier, guiding appropriate antibiotic therapy and perhaps preventing his clinical complications. Real-time bacterial DNA sequencing has the potential to shift the diagnostic paradigm in severe pneumonia.