Case 106

1. Presented by Laetitia Daou, MD and reviewed by Patricia Simner, PhD

A young adult with intravenous substance use disorder, untreated Hepatitis C virus (viral load >10,000 IU/mL), and housing instability is admitted for skin and soft tissue infection with concerns for underlying osteomyelitis. Over the past year, they have had multiple worsening, painful, purulent wounds on the extremities. They do not inject drugs directly into the wounds but around them. X-Ray of one of the extremity wounds shows new periosteal reaction concerning for osteomyelitis. Thus, a magnetic resonance imaging (MRI) is performed to rule out osteomyelitis and does not demonstrate any fluid collections or abscesses. A complete blood count is remarkable for leukocytosis (white blood cell count 12.81 K/cu mm [ref: 4.50 - 11.00 K/cu mm]). The patient remains hemodynamically stable with Tmax 37.7 ?C, so blood cultures are drawn. Cefepime and vancomycin are started. The blood culture comes back positive for gram-variable rods in the aerobic bottle; there is no growth in the anaerobic bottle. Subcultures are performed and colonies grow on Blood agar plate (BAP: TSA + 5% sheep blood), Chocolate Agar (CHOC) and Columbia Naladixic Acid Agar (CNA); there is no growth on MacConkey (MAC).

Figure 1:


Figure 2:

Figure 1: Aerobic blood bottle subculture on (A) blood agar plate (BAP) and (B) chocolate agar (CHOC). Figure 2: Gram stain morphology obtained from the aerobic blood bottle is remarkable for gram variable bacilli with some demonstrating subterminal oval spores (arrows).

Which of the following is the most likely etiologic organism?