Peritoneal dialysis (PD) is a cornerstone of renal replacement therapy for patients with end-stage kidney disease, with its use expanding due to advancements such as automated PD systems.1 However, peritonitis remains a frequent and serious complication, accounting for 25–30% of hospitalizations among PD patients and often leading to technique failure.2–4 Microbiologically, gram-positive organisms predominate (40–50%), followed by gram-negative bacteria (20–30%), fungi (2–4%), mycobacteria (1%), polymicrobial infections (10%), and culture-negative cases (15%).5

Citrobacter species are gram-negative, oxidase-negative bacilli of the Enterobacteriaceae family and are infrequently pathogenic in humans. Typically isolated from urine, soft tissue, or sputum, they have been rarely associated with neonatal meningitis, sepsis, and abscesses.6–10 Within the Citrobacter genus, Citrobacter sedlakii is an uncommon isolate, with limited reports of serious infections.11,12

This case report presents the first documented instance of C. sedlakii-induced PD peritonitis, offering insights into its clinical course and management.

A 31-year-old female patient, in her 120th month of PD, presented with abdominal pain and cloudy peritoneal effluent. The patient had no known immunosuppressive condition other than end-stage kidney disease. Her PD history included two prior episodes of culture-negative peritonitis at 26 and 38 months. On examination, she was alert and oriented, with a temperature of 37°C, blood pressure of 110/70mmHg, and pulse of 90 beats per minute. Abdominal findings included voluntary guarding and rebound tenderness, with no evidence of catheter exit-site infection.

Laboratory results revealed a peripheral leukocyte count of 5780/mm3 and a C-reactive protein (CRP) level of 8.3mg/dL. Peritoneal fluid analysis demonstrated 1600cells/mm3 with 90% neutrophils. Empirical intraperitoneal therapy with ceftazidime (1g every 48h) and vancomycin (0.5g every 48h) was initiated. Cultures of the peritoneal fluid identified C. sedlakii, with susceptibility testing confirming sensitivity to the regimen. Tuberculosis cultures were negative.

By day 7, the peritoneal fluid cell count normalized, and symptoms resolved after 14 days of therapy, prompting discharge. However, 6 days later, the patient returned with recurrent abdominal pain and cloudy effluent. Laboratory findings showed leukocytosis (5970/mm3), elevated CRP (19.9mg/dL), and peritoneal fluid with 3560cells/mm3 (96% neutrophils). Repeat cultures confirmed persistent C. sedlakii growth. During recurrence, no additional pathology other than peritonitis was identified on evaluation Due to refractory infection, the PD catheter was removed, and treatment continued, resulting in clinical resolution. The favorable response to ongoing antibacterial therapy supported the accuracy of the initial microbiological diagnosis. Antifungal prophylaxis was not administered during the treatment period. The patient was transitioned to hemodialysis and discharged in stable condition.

The SPICE group (Serratia, Pseudomonas, indole-positive bacteria, Citrobacter, and Enterobacter) comprises a cluster of gram-negative pathogens associated with severe and recurrent peritoneal dialysis (PD)-related peritonitis.13,14

C. sedlakii, a facultative anaerobic and motile bacillus, is rarely implicated in human infections, although it has been reported in conditions such as neonatal meningitis and brain abscesses.6

To better contextualize the present case, previously reported cases of Citrobacter peritonitis in PD patients are summarized in Table 1.

The available literature remains limited and consists mainly of isolated case reports and small case series, including infections caused by different Citrobacter species such as C. freundii and C. youngae. The largest series by Chao et al. demonstrated that Citrobacter-related peritonitis is associated with high rates of recurrence, technique failure, and mortality.12

Similarly, individual case reports have shown variable clinical outcomes, ranging from complete recovery with antibiotic therapy to refractory infections requiring catheter removal and transition to hemodialysis.

This report represents the first documented association of C. sedlakii with PD-related peritonitis. The recurrence of infection despite initial clinical and microbiological improvement suggests potential pathogenic mechanisms such as biofilm formation on the PD catheter or transmural migration of gastrointestinal flora, findings that are consistent with previous reports of Citrobacter peritonitis.15,16

In addition, organisms within the SPICE group are known to exhibit inducible beta-lactam resistance, which may contribute to relapse despite apparent initial treatment success.

Overall, Citrobacter peritonitis appears to be associated with considerable morbidity, including increased hospitalization rates, catheter loss, and, in some series, significant mortality. In the present case, although initial therapy led to clinical improvement, recurrence occurred shortly after treatment completion. This clinical course highlights the importance of careful follow-up and suggests that prolonged or more aggressive treatment strategies may be required in selected cases.

In our patient, catheter removal was ultimately necessary to achieve definitive resolution, which is consistent with previously reported refractory cases of gram-negative peritonitis.13

Notably, no intra-abdominal source of infection or additional immunosuppressive condition was identified, and persistent isolation of the same organism supports the role of the pathogen itself in disease persistence.

This case adds to the limited body of literature on C. sedlakii infections and underscores its potential as an emerging pathogen in PD patients. Clinicians should be aware that even rare Citrobacter species may lead to recurrent and treatment-resistant peritonitis. Early consideration of catheter removal should be kept in mind in refractory or relapsing cases.

Further studies are needed to better define the epidemiology, risk factors, and optimal management strategies for Citrobacter-associated peritonitis in PD patients.

The study protocol was approved by the Clinical Research Ethics Committee of University of Health Sciences Gazi Yaşargil Training and Research Hospital (approval date: October 3, 2025; approval number: 662). The study was conducted in accordance with the principles of the Declaration of Helsinki.

This study did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

The authors declare that they have no conflict of interest.

The datasets generated and/or analyzed during the current study are available from the corresponding author on reasonable request.