Multidrug-resistant Serratia odorifera urinary tract infection with discordant carbapenem susceptibility: A case report

Background : Serratia odorifera is a less prevalent Gram-negative bacillus of the order Enterobacterales and a rare cause of urinary tract infection. It’s intrinsic and acquired antimicrobial resistance limit its empirical treatment options. Case presentation: A 34-year-old woman presented with dysuria, burning micturition, urgency and suprapubic discomfort. Symptoms persisted and fever developed after 3 days of oral norfloxacin; amoxicillin-clavulanate was then started, and urine was sent for culture. Automated urinalysis showed marked pyuria (61.4 WBC/HPF), WBC clumps and bacteriuria, with granular and pathological casts flagged. Urine culture yielded S. odorifera ≥10⁵ CFU/mL in pure growth. The isolate was resistant to fluoroquinolones, ceftriaxone, imipenem and meropenem (MIC 8 µg/mL each), but susceptible to ertapenem (MIC ≤0.12 µg/mL), piperacillin-tazobactam, gentamicin and trimethoprim-sulfamethoxazole. Intravenous ertapenem 1 g once daily for 7 days led to complete clinical recovery, and follow-up urine culture was sterile. Concurrent investigations showed severe vitamin D deficiency (25-hydroxyvitamin D 16.2 ng/mL) and hypocalcaemia (serum calcium 8.2 mg/dL). Conclusion : S. odorifera can cause clinically significant community-onset urinary tract infection. Urine culture should be performed when symptoms persist or worsen despite empirical therapy. The unusual pattern of resistance to imipenem and meropenem with retained susceptibility to ertapenem highlights the need for careful, agent-specific interpretation of carbapenem susceptibility results and, where appropriate, confirmatory testing.