1. Prepared by Gabrielle Bailey, MD, and reviewed by Karen Carroll, MD.

An adult patient is admitted with decompensated heart failure. The patient has a past medical history of osteosarcoma (status-post right above knee amputation in 1979), non-ischemic cardiomyopathy secondary to adriamycin treatment, end-stage renal disease secondary to hypertension, and diabetes. After being treated for immune thrombocytopenic purpura (ITP) with IVIG and steroids, the patient receives a simultaneous heart and kidney transplant. The post-transplant course is complicated by right ventricular failure and delayed renal graft function. A few weeks after transplant, the patient develops worsening hypotension and a new oxygen requirement, as well as altered mental status. The patient has leukocytosis (12.4 K/cu mm) and a chest x-ray shows bibasilar infiltrates. A CT scan shows a cavitary lesion in the right lower lobe of the lung.

An expectorated sputum culture grows Klebsiella pneumoniae and Morganella morganii. A bronchoalveolar lavage (BAL) sample is collected and blood cultures are drawn.

After 24 hours, the Gram stain of the BAL shows the following:



The modified acid-fast stain of the BAL shows the following:



The subsequent Gram stain from the blood culture shows this organism:



The modified acid-fast stain from the blood culture shows these structures:



What is the most likely causative organism?