Case Presentation: An undomiciled 48-year-old man with HIV presented with fever, chills, rigors, and bilateral leg swelling with pain for 1 week. He had developed worsening painful weeping ulceration most prominently over his right leg below the knee after exposure to water during a series of thunderstorms over the week prior. Physical examination revealed fever, tachycardia, lethargy, and bilateral pitting edema to mid thighs, and hyperpigmented thickened skin below his shin. He was initiated on broad spectrum antibiotics after blood cultured were drawn. Labs were notable for CD4 count of 157 cells/µL with HIV viral load of 263,515 copies/µL. Blood cultures showed gram-negative bacilli identified as Shewanella algae and found to be susceptible to third generation cephalosporins, fluoroquinolones, and trimethoprim-sulfamethoxazole. Antibiotics were narrowed to a two week course of ceftriaxone, with subsequent improvement in pain, swelling, and ulceration, and was discharged with outpatient HIV care follow-up.
Discussion: Shewanella species are non-fermentative catalase positive, hydrogen-sulfide producing, gram negative bacilli belonging to the Shewanellaceae family previously classified under the Pseudomonas genus. They are primarily mesophilic bacteria most often found in aquatic environments. Most pathogenic strains including Shewanella putrefaciens and Shewanella algae. The latter of which can be distinguished by growth at 42°C, growth in 6.5% NaCl, mucoid and β-hemolytic colonies on sheep blood agar, and reduction of nitrite. Classically, S. algae infections manifest as skin and soft tissue infections, peritonitis, and bacteremia. Thus far, Shewanella species display susceptibility to 3rd and 4th generation cephalosporins, piperacillin-tazobactam, gentamicin, and fluoroquinolones. The distribution and prevalence of Shewanella species in the environment may be influenced by changes in sea-surface temperatures caused by climate change. Susceptible hosts living along coastlines may be at risk of exposure, raising the possibility of Shewanella species becoming emerging pathogens.
Conclusions: This is to our knowledge the first reported case of Shewanella algae soft tissue infection and bacteremia in a patient with HIV/ AIDS. Our case demonstrates the need to consider environmental gram-negative bacteria such as S. algae as a potential pathogen in patients with skin and soft-tissue infections, especially in the immunocompromised who have exposure to water or marine environments. More studies are needed to investigate these organisms as potential emerging threats in the context of climate change.