Shewanella cellulitis and bacteremia following marine water exposure.

A 51-year-old man presented with pain, swelling, redness and a blister formation over his left leg. He recently visited the Chandeleur Islands in Gulf of Mexico, where he was fishing from a boat near the shore. He was initially seen at a local facility, where he was prescribed oral dicloxacillin, but no improvement was noted. He denied any recent trauma, cuts or bites. Physical examination revealed temperature of 38.1 °C and an erythematous and swollen left leg with fluid filled blisters with no areas of necrosis (Fig. 1A,B). Laboratory findings were significant for elevated WBC count (16 K/mm3) with 86% neutrophils. Blood cultures and fluid aspirate from a blister yielded gram-negative rods. Blood and MacConckey agar grew non-fermenting yellowish mucoid bacterial colonies (Fig. 2) that were later identified as Shewanella putrefaciens by Vitek ®2 (bioMérieux). Susceptibility panel showed resistance only to penicillin. The patient was treated with piperacillin-tazobactam with marked clinical improvement and clearance of bacteremia. Then he was switched to oral levofloxacin to complete a 14-day course of treatment. At 3-week follow-up, examination revealed complete resolution of skin lesions.

Fig. 1

A) Cellulitis on hospital day 1 with erythema, edema and blisters. B) Swelling and blisters on the same leg on hospital day 3.

Fig. 2

Yellowish mucoid colonies of Shewanella putrefaciens in MacConckey (left) and blood agar (right).

Shewanella spp. is a non-fermenter gram-negative rod that is naturally present in marine water and soil. It has been also isolated from fish, sewage and carcasses [1,2]. Initially isolated at the beginning of the past century from putrefied butter, its name has changed throughout the decades from Achromobacter putrefaciens, Pseudomonas putrefaciens, Alteromonas putrefaciens and finally Shewanella spp. Human infection is uncommon; however, it can result in a wide variety of syndromes including bacteremia, cellulitis and pneumonia among others [3]. It has similar spectrum of disease to other marine bacteria known to cause disease (Vibrio spp. and Aeromonas spp.).

Of the 30 species identified, only two have been associated with human disease: S. putrefaciens and S. algae. [1,4]. Major predisposing factors include hepatobiliary disease, peripheral vascular disease, chronic leg ulcers, and immunocompromised states [1,2]. Most infections are treated with surgical drainage and antibacterials. Shewanella spp. has shown resistance to penicillin, but it is usually susceptible to ampicillin-sulbactam, piperacillin-tazobactam, cephalosporins, aminoglycosides and fluoroquinolones [2]. It is important to know that resistance to imipenem by a carbapenem-hydrolyzing Ambler class D beta-lactamase OXA-55 has been found in Shewanella algae [5]. Overall mortality rate can be as high as 20–30% [6]. Although rare, Shewanella infection should be considered in patients with exposure to marine environment.

Conflict of interest

None of the authors reports a conflict of interest, and there were no funding sources.