| Abstract|| |
Shewanella alga is a rare gram-negative marine bacterium. Its role as a pathogenic organism is gradually evolving with sporadic cases being reported in humans. We report a case of vascular steal syndrome secondary to a polytetrafluoroethylene (PTFE) graft in the upper extremity of an end-stage renal disease (ESRD) patient on maintenance hemodialysis, which was complicated by infection with S. alga. This resulted in extensive myonecrosis requiring amputation of the limb. To our knowledge this is the fourth case of primary S. alga infection, and the first case in a hemodialysis patient reported in the medical literature from the United States. We also discuss the biochemical tests for identification and differentiation of S. alga from a closely related strain S. putrefaciens.
Keywords: Shewanella alga, Shewanella putrfaciens, End-stage renal disease, Hemodialysis.
|How to cite this article:|
Jammula P, Gupta R, Agraharkar M. Vascular Steal Syndrome and Shewanella alga Infection Requiring Amputation in a Hemodialysis Patient. Saudi J Kidney Dis Transpl 2003;14:511-5
|How to cite this URL:|
Jammula P, Gupta R, Agraharkar M. Vascular Steal Syndrome and Shewanella alga Infection Requiring Amputation in a Hemodialysis Patient. Saudi J Kidney Dis Transpl [serial online] 2003 [cited 2020 Feb 29];14:511-5. Available from: http://www.sjkdt.org/text.asp?2003/14/4/511/32988
| Introduction|| |
Shewanella spp. is widely distributed in nature, with soil and water being its natural habitat.  Shewanella putrefaciens is the major species, and was initially considered to be a colonizer or a saprophyte thriving on previously damaged tissue.  There have been numerous reports associating this bacterium with otitis media, ulcers of the lower extremities and hands, infective endocarditis, arthritis, peritonitis and systemic infections in patients with liver disease, malignancy and severe debility. ,,,,,,,,, Shewanella alga is a newly discovered strain that is being increasingly implicated in human disease. , We report a case of vascular steal syndrome in a hemodialysis (HD) patient complicated by S. alga infection and septicemia that ultimately required amputation of the limb.
| Case Report|| |
A 58-year-old African-American male presented with the complaints of pain in the left forearm and hand. He had end-stage renal disease (ESRD) from hypertensive nephrosclerosis, and was receiving maintenance HD. He had a history of thrombosis of multiple polytetrafluoroethylene (PTFE) grafts placed for vascular access for HD. Another PTFE graft had been placed three months before, in the left arm. He complained of worsening of the pain in the left hand along with nausea, vomiting and abdominal discomfort. The patient was a resident of Galveston Island and enjoyed fishing. His vital signs recorded at the time of admission showed a blood pressure of 132/88 mm Hg; pulse rate of 94/min; respiratory rate of 20/min; and a temperature of 38.6 °C. Physical examination at admission revealed an anxious person in moderate pain. The left hand had a dusky appearance. It was edematous, cold, and tender to touch and the radial artery pulsation was impalpable. A palpable thrill and an audible bruit were recorded over the PTFE graft. Rest of the physical examination was unremarkable.
Initial laboratory data demonstrated an elevated white cell count (WBC) of 35,100/ml with a differential count of 77% neutrophils and 14% lymphocytes; hemoglobin was 11.1 g/dl; and the platelet count was 161,000/ml. Serum chemistry revealed a blood urea nitrogen (BUN) of 21.1 mmol/L and serum creatinine of 1016.6 µmmol/L The liver function tests and radiography of the left forearm was normal. Arteriogram of the left upper extremity showed severe atherosclerosis in the brachial and radial arteries, with occlusion of the ulnar and interosseous arteries. Injection of the dye into the graft caused minimal opacification of the distal vasculature suggesting the presence of a vascular steal syndrome [Figure - 1].
On the third day of admission, necrotic ulcers, bullous lesions, and a foul odor became evident in the left hand and forearm. The PTFE was ligated and surgical exploration of left forearm and hand, and aspiration of the bullous lesions was performed. Blood cultures demonstrated a growth of gram-negative rods, which were subsequently identified as Shewanella alga. The organism was identified using the commercially available API 20 NE system. Standard sensitivity testing was not used for determination of sensitivity for this organism and instead we used the Sensititer® (Trek Diagnostics, UK) system for determining the sensitivity for Shewanella alga. The antibiogram revealed sensitivity to amikacin, gentamicin, tobramycin, ampicillin/sulbactam, piperacillin, ticarcillin/clavunate, cefepime, ceftazidime, ciprofloxacin, imipenem and trimethoprim/sulfamethoxazole [Table - 1].
Aspirate of bullous lesions and tissue culture also demonstrated the growth of S. alga. The gangrene in the left upper extremity worsened and the patient subsequently underwent an amputation of the left forearm. He was treated with cefepime resulting in clinical improvement and subsequent blood cultures were sterile.
| Discussion|| |
Shewanella alga is a recently discovered nonfermentative, motile, gram negative, mesophilic marine bacterium closely related to the more psychrotolerant Shewanella putrefaciens.  It is capable of reducing Fe (III) in anaerobic conditions and may play an important role in the turnover of inorganic material. , S. alga usually does not grow at temperatures below 5°C. A Danish study, however, reported its detection at water temperature above 13°C. They also demonstrated its survival in cold water with regrowth after increase in water temperature. 
Prior to the identification of S. alga, most of the human infections caused by Shewanella species were believed to be caused by S. putrefaciens which was first reported in clinical isolates by King.  In 1990, Simidu et al proposed the name S. alga for a tetrodotoxin producing isolate that was recovered from red algae.  Later, Nozue et al demonstrated that strains of S. putrefaciens with high guanine and cytosine (G+C) content (52-54 mol%) were genetically related to S. alga. Of the 40 clinical isolates of S. putrefaciens reidentified by Nozue et al, 33 (83%) were found to be S. alga based on the DNA homology and phenotypic criteria. Later, Vogel et al found that 16 of the 19 human isolates of Shewanella strains, that were studied by them, belonged to S. alga group, based on the 16S rRNA sequencing, ribotyping and whole cell protein profiles.  Studies on mice by Khashe and Janda have also reported similar results.  The above studies suggest that S. alga may be the predominant human pathogen in this genus.
S. alga can be differentiated from S. putrefaciens by its ability to grow at 42°C and 6% NaCl, and its inability to grow at 4°C. Additionally, it produces acid oxidatively from D-glucose and D-ribose but not from Larabinose or maltose. It grows on Salmonella More Details- Shigella agar and exhibits β-hemolysis on sheep and bovine blood agars. S. alga was also noted to produce tetrodotoxin.  Finally, the percentage of G+C contents differentiate S . alga (52-54 mol %) from S. putrefaciens (43-47 mol %). 
There are very few case reports of primary S.alga infection. Strains identified as S. putrefaciens in the past may have factually belonged to S. alga. Dominguez et al, in 1996, reported the first two Danish patients with S. alga bacteremia and lower extremity ulcers. Extensive myonecrosis was found in one of the patients.  Iwata et al in 1999, reported the first Japanese case of primary septicemia in a patient on HD.  Our patient had primary S. alga induced infection of the skin and soft tissues including the musculature involving the hand and forearm, with septicemia. Skin defects and contact with seawater predisposes to infection with S. alga.  Noticeably, case reports with this organism have been from geographic areas with long shorelines. , We attribute contact with the marine environment during fishing expeditions as the source of infection in our patient. Our case supports the previously expressed notion that this organism may have predilection for tissues with poor circulation.  The myonecrosis in our patient was possibly due to the combined effect of vascular insufficiency and infection. The spread of infection was rapid and our patient had to undergo amputation. To our knowledge, this is the fourth case of primary S. alga septicemia and probably the second case of primary S. alga sepsis in a patient on HD, the first being the case reported by Iwata et al. This may be the first case of primary S. alga septicemia in a HD patient being reported from the United States.
Susceptibility of S. alga to cephalosporins, aminoglycosides, quinolones, ampicillin and tetracyclines was reported by Dominguez.  A good clinical response to levofloxacin, cefpirome and minocycline was observed by Iwata.  S. alga in our patient was sensitive to penicillins, cephalosporins, aminoglycosides, fluoroquinolones and trimethoprim/ sulfame thoxazole [Table - 1]. We treated our patient with cefepime, and clindamycin was added to provide anaerobic coverage. Despite significant morbidity, mortality from S. alga infections has so far not been reported.
There is a growing evidence of S. alga infection in patients in contact with marine environment. Immunocompromised patients such as those with ESRD may be more susceptible. However, further studies regarding bacterial virulence factors and host immune response are required to clarify its pathogenic role in humans.
| Conclusion|| |
We conclude that S. alga is a rare human pathogen acquired through contact with sea water that can cause septicemia and tissue necrosis in immunocompromised hosts in the setting of vascular insufficiency.
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Department of Medicine, Nephrology Division, University of Texas Medical Branch, 4200 John Sealy Annex, 301 University Boulevard, Galveston, Texas 77555-0562
[Figure - 1]
[Table - 1]