Shewanella putrefaciens: A Rare Cause of Refractory Peritonsillar Abscess in an Immunocompetent Adult

Shewanella species are motile, oxidase-positive, non-fermenting Gram-negative bacilli widely distributed in marine and aquatic environments. Although primarily environmental organisms, Shewanella spp. are rare human pathogens, most often associated with skin and soft tissue infections. Involvement of the head and neck region is exceptional. We report the case of a 28-year-old immunocompetent male with no history of seawater exposure who presented with a one-week history of odynophagia, fever, trismus, and dysphagia. Clinical examination revealed a unilateral peritonsillar abscess. Needle aspiration yielded hemopurulent material. Direct microscopy showed numerous neutrophils and Gram-negative bacilli. Culture on standard media grew monomorphic, non-lactose-fermenting colonies. Identification by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) (Bruker Daltonics, Bremen, Germany) confirmed Shewanella putrefaciens with a high-confidence score. Antimicrobial susceptibility testing demonstrated resistance to penicillins, β-lactam/β-lactamase inhibitor combinations, and cephalosporins, with preserved susceptibility to fluoroquinolones, aminoglycosides, and carbapenems. Empiric therapy with amoxicillin-clavulanate was ineffective, whereas targeted treatment with levofloxacin resulted in complete clinical recovery. This case highlights S. putrefaciens as an uncommon but clinically relevant cause of refractory peritonsillar abscess and underscores the importance of accurate microbiological identification, particularly in patients not responding to standard empiric therapy.