Case 71

1. Presented by Yembur Ahmad, MD
Reviewed by Patricia Simner, PhD

Clinical Vignette
An adult patient with presented to the hospital with an open wound of the extremity, with increasing size and purulent drainage over the past weeks. The patient previously had multifocal extremity ulcerations and infections, wound cultures showing a polymicrobial infection (Staphylococcus aureus, Streptococcus anginosus, Streptococcus agalactiae and Prevotella bivia).

Physical exam revealed a wound that appears to pass through the extremity, with associated purulent drainage and myiasis. An X-ray revealed acute osteomyelitis with extensive subcutaneous air and osseous erosion/destruction. Tissue was excised, with pathology showing deep soft tissue abscesses and tissue necrosis. Blood cultures are drawn due to concern for sepsis.

Figure 1: Blood agar plates (initial culture and subculture of larger colonies) incubated at 35?C. (Pictures taken approximately 6 days after cultures plates inoculated.)

Figure 2: Subculture of larger colonies from blood agar on MacConkey agar after incubation at 35?C. (Pictures taken approximately 6 days after cultures plates inoculated.)

Laboratory findings:

Blood cultures grew a mixed population of small, ?-hemolytic colonies mixed with large, gray mucoid colonies. These larger colonies were subcultured onto blood agar and MacConkey agar plates. MacConkey agar grew colorless colonies initially and with time started showing a slight purple tinge (likely due to uptake of crystal violet from the media rather than lactose-fermentation). This gram negative organism was found to be oxidase positive.


What is the most likely gram-negative organism that was isolated from this patient's blood that is associated with myiasis?