Introduction

Shewanella species are opportunistic, motile, gram-negative, facultative anaerobic bacteria that are part of the marine environment. It was initially named Achromobacter putrefaciens when isolated for the first time in the early 1930s and later renamed following gene sequencing. Human pathogens out of the 62 species of Shewanella are Shewanella putrefaciens, Shewanella haliotis, and Shewanella algae [1]. Shewanella algae have been reported to cause soft tissue infections, bacteremia, and chronic otitis media. Skin abrasions and traumas exposed to seawater or seafood consumption have been noted to be the risk factors for the infection. Patients with comorbidities such as diabetes, vascular diseases, malignancy, hepatobiliary disease, and immunocompromised individuals are predisposed to Shewanella algae infection [1]. A substantial potential of Shewanella algae to cause skin tissue infections in immunocompetent hosts due to various virulence factors must be noted [2]. Reported cases in India due to this pathogen are scarce in the literature. Here, we present a case of septicemia arising from cellulitis by Shewanella algae in a patient with no comorbidities.

Case Presentation

A 58-year-old fisherman with no known comorbidities presented to our emergency department with a history of right lower limb swelling for two weeks, fever for one week, and right-sided weakness of one-day duration. No history of trauma. He was drowsy but arousable to call and vitals were as follows: heart rate of 120 beats per minute, blood pressure of 90/60 mm Hg, peripheral oxygen saturation of 90% on room air, respiratory rate of 32 cycles/min. Respiratory examination revealed bilateral crepitations. The central nervous system showed a Glasgow coma scale score of E4V2M5, bilateral pupils sluggishly reactive to light, right upper and lower limb power 3/5 with right extensor plantar. Other system examinations were within normal limits. Local examination of the right lower limb showed, oedema extending from the foot to below the knee with multiple blebs. It was erythematous with local rise of temperature, skin peeling, and absent anterior, posterior tibial artery, and dorsalis pedis arterial pulsations. Relevant laboratory investigations are listed in Table 1.

Suspecting acute cerebrovascular accident, plain computed tomography (CT) brain was done which showed features of early acute infarct in the left frontoparietal area. The laboratory investigations suggested severe sepsis, acute kidney injury with partially compensated metabolic acidosis (Table). Chest x-ray showed features of acute respiratory distress (ARDS). He was started on inotropes, oxygen supplementation initially via a non-rebreathing mask (NRBM), and later on non-invasive ventilation when tachypnoea worsened and initiated on empirical intravenous antibiotic – piperacillin/tazobactam. Surgical consultation regarding the right lower limb cellulitis with features of compartment syndrome was sought, fasciotomy was done on the same day. The serous discharge from the fasciotomy site along with peripheral blood was sent to the microbiology laboratory for culture and sensitivity. 2 D echocardiogram showed features of myocarditis with an ejection fraction of 45%.

Microbiological Analysis

The samples were processed by standard laboratory operating procedure. Gram staining of the pus showed the presence of numerous pus cells and gram-negative bacilli. The blood culture system BacT/Alert 3D (bioMérieux, France) had flagged for growth in 18 hours with gram staining indicative of Gram-negative bacilli. Both specimens were inoculated onto MacConkey agar and 5% sheep blood agar and incubated at 37°C for overnight. Beta-hemolytic mucoid colonies on sheep blood agar and non-lactose fermenting colonies on MacConkey agar were noted. (Figure 1a) The Oxidase test was positive for both isolates. Further identification and antibiotic susceptibility testing were carried out by Vitek 2 (bioMérieux, France). The isolates were identified as Shewanella algae. The identification was reconfirmed by Vitek 2 and biochemical reactions. (Figure 1b,1c) Antibiotic susceptibility testing determined the isolate to be sensitive to piperacillin/tazobactam, ceftazidime, meropenem, and gentamicin.

Figure 1: Mucoid beta-haemolytic colonies on sheep blood agar

Figure 2: Biochemical reactions: Lysine decarboxylase negative, ornithine decarboxylase positive, arginine dihydrolase negative.

Figure 3: Biochemical reactions: Indole not produced, citrate utilized, triple sugar iron agar shows alkaline slant/alkaline butt with hydrogen sulphide produced, urea not hydrolysed, mannitol not fermented.

Outcome and Follow-up

The patient's condition continued to deteriorate despite immediate intervention and appropriate treatment, there was worsening sepsis with recurrent hypoglycaemia and persistent metabolic acidosis. In the wee hours of the subsequent day, he desaturated, went into cardiac arrest, and could not be revived.

Discussion

Shewanella spp. are gram-negative, facultatively anaerobic bacteria and predominantly part of marine flora. The species found in clinical isolates are Shewanella putrefaciens and Shewanella algae [2], where the latter has been associated with soft tissue infections and sepsis [3]. The source of infection is through the exposure of breach in the skin to seawater [2]. Most infections have been observed during warm summers in countries with temperate climates [3]. Sharma et al. had noted that four of the five cases in their study on Shewanella spp were suffering from skin and soft tissue infections [4]. Similarly, a study in India investigating the clinical characteristics of Shewanella infection found all the patients to have skin or mucosa as a portal of entry, with 56.25% of patients having a history of seawater contact [5]. Haemolysin production and exotoxin production, which destroys the macrophages prior to phagocytosis by Shewanella algae, could attribute to its virulence [2].

Sepsis has been identified as a predisposing factor for stroke. The mechanism could be due to the activation of inflammatory responses and the hemostatic system during sepsis leading to hemodynamic instability, coagulopathy, and potential embolism [6,7]. Our patient despite having no comorbidities developed the infection, progressed to sepsis, and presented with stroke likely due to the above-mentioned virulence factors and disease pathogenesis.

Conclusion

Treatment of the infection includes combinations of surgical intervention and antibiotics, leading to a favourable outcome. As no specific antibiotic therapy guidelines for Shewanella infection is available, broad-spectrum antibiotics can be tested for susceptibility. Studies have found the isolate sensitive to third-generation cephalosporin, piperacillin/tazobactam, ciprofloxacin, and gentamicin. Associated disease conditions like renal failure, liver disease, septicemia is associated with poor outcome. This can be extrapolated to the mortality in our patient as he had presented with sepsis, acute kidney injury, and partially compensated metabolic acidosis.

References

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