Revisiting rhinoscleroma microbiology: a case with concordant dual-specimen bacterial isolation

Background: Rhinoscleroma is a chronic granulomatous infection of the upper airway traditionally considered a monomicrobial disease caused by Klebsiella pneumoniae subsp. rhinoscleromatis. However, limited use of deep-tissue microbiological sampling may have contributed to underrecognition of additional bacterial isolates and microbial complexity. Methods: We report a biopsy-confirmed case of nasal rhinoscleroma in a previously healthy adult. Histopathological evaluation and microbiological analysis were performed on deep intranasal tissue. Bacterial identification was conducted using VITEK 2 and MALDI-TOF mass spectrometry. Antimicrobial susceptibility testing was interpreted according to EUCAST 2025 criteria. Results: Histology demonstrated characteristic Mikulicz cells. Microbiological analysis revealed K. pneumoniae (consistent with subsp. rhinoscleromatis) together with Morganella morganii from deep-tissue biopsy. Importantly, both organisms were also recovered from an independent nasal swab specimen, with concordant antimicrobial susceptibility profiles. M. morganii showed resistance to aminopenicillins and amoxicillin-clavulanate while remaining susceptible to piperacillin-tazobactam, consistent with its intrinsic AmpC β-lactamase profile. Microbiological findings prompted targeted modification of antimicrobial therapy, and targeted therapy with oral levofloxacin was initiated. Conclusion: This case suggests possible microbial complexity in rhinoscleroma and highlights the value of deep-tissue and concordant multi-sample microbiological evaluation. Recognition of co-isolated organisms may have implications for antimicrobial selection and stewardship, although their pathogenic contribution requires further investigation.