Case Presentation: An 80-year-old man native to the Rio Grande Valley with chronic obstructive pulmonary disease (COPD) and obesity presented with bilateral lower extremity pain and erythema that had been worsening over the last six months. Prior to admission the patient had been diagnosed with bilateral lower extremity cellulitis and completed multiple courses of oral antibiotics without resolution of his symptoms. On presentation the patient had a temperature of 98.9F, HR 115, and BP 109/66. Physical exam was notable for erythema of both lower extremities with foul-smelling purulent drainage coming from open wounds on both legs. Laboratory tests were significant for leukocytosis to 32.2 (94% neutrophils) and an elevated lactate of 3.77. Imaging of the lower extremities did not show any signs of osteomyelitis. The patient was started on IV Vancomycin and Piperacillin/tazobactam. Wound cultures from the legs grew mixed aerobic flora with no predominant organism identified. Blood cultures came back positive for Shewanella algae two weeks after admission. An echocardiogram was negative for any valvular vegetations. The patient was treated for Shewanella algae bacteremia with fourteen days of IV Meropenem and had resolution of his lower extremity cellulitis and was ultimately discharged.
Discussion: Shewanella algae is a Gram-negative, motile bacillus found ubiquitously in saltwater reservoirs of warmer climates. Even though Shewanella spp. infections in humans are rare, the number of reports has significantly increased over the last decade, suggesting that species within the Shewanella genus, in particular S. algae, have a pathogenic potential. The most common manifestations of acute Shewanella algae infection are skin and soft tissue infections, otitis media, or bacteremia. Many infections, especially skin infections, are polymicrobial and occur in people with a history of chronic leg wounds—a finding reflected in our patient. Its pathogenicity is presumed secondary to virulence factors such as siderophores and biofilm production. Furthermore, Shewanella spp. are also considered a possible reservoir for antimicrobial resistance. Although they are typically susceptible to aminoglycosides, carbapenems, and fluoroquinolones, they have variable resistance to ampicillin and cephalosporins, and carbapenem resistance has been reported. Traditionally, those at risk for infection include men over 50 with malignancies or underlying cardiovascular, hepatobiliary, renal, or respiratory disease who have been exposed to marine environments or had recent seafood consumption. However, there are some case reports of Shewanella algae infections in individuals without any exposure to marine environments or seafood consumption. This correlates to our patient who had the risk factors consisting of residing in a warm climate, sex, age, and underlying COPD, however he denied a history of exposure to saltwater or recent seafood consumption.
Conclusions: Shewanella algae particularly in warm coastal areas, can be considered an emerging pathogen. Infections with this bacterium should be considered in individuals who present with limb infections such as cellulitis, ulcers, or necrotizing wounds that are resistant to standard oral antibiotic regimens. A high index of suspicion is required to diagnose and treat such infections particularly when a patient denies exposure to traditional risk factors.