Serratia marcescens is a one of gram-negative rod-shaped Enterobacteriacease that is involved in nosocomial infections, particularly catheter-associated bacteremia, urinary tract infections, and wound infections [1]. It can cause endocarditis and osteomyelitis, pneumonia, and meningitis. S. marcescens is also a rare cause of peritonitis.

Peritonitis is one of the most significant complications in patients undergoing continuous ambulatory peritoneal dialysis (CAPD). Peritonitis is the leading cause of hospitalization in peritoneal dialysis patients, and the infection is also associated with catheter loss, transfer to hemodialysis, and considerable morbidity in these patients [2]. The initial treatment of peritonitis is empirical, making the effective treatment of cases that are caused by a rare organism a challenge. We report an unusual case of CAPD-related peritonitis caused by S. marcescens.

A 45-year-old male on CAPD with end-stage renal disease (ESRD) secondary to diabetes mellitus presented with abdominal pain and a dialysate WBC count of 9,070/mm³ (97% neutrophils). The patient had a history of hypertension and insulin-dependent diabetes mellitus for over 20 years, and had been maintained on CAPD since 2001. He had experienced two episodes of CAPD-associated peritonitis caused by coagulase-negative staphylococci 10 years earlier. He had not taken immunosuppressive drugs or steroids. The patient's blood sugar had been well controlled, and his hemoglobin A1c was 6.7%.

A 50 mL sample of peritoneal fluid was centrifuged at 3,000 g for 15 minutes, followed by resuspension of the sediment in 5 ml of sterile saline and inoculation on solid culture medium. Immediately after sampling, the patient was treated empirically with intraperitoneal cefazolin (15 mg/kg/day) and ceftazidime (1 g/day). His body weight was 52.0 kg, his creatinine level was 10.0 mg/dL, and his urine output was < 100 mL/day. After 5 days of aerobic incubation on blood agar, the pathogenic organism was identified as S. marcescens. In vitro susceptibility, tested by the disk diffusion method, demonstrated that the organism was resistant to cefoxitin, imipenem, and ampicillin/sulbactam, but susceptible to gentamicin, ciprofloxacin, levofloxacin, and ceftazidime. At the same time, blood cultures that were performed were positive for an organism identified as S. marcescens via bacterial recombinant DNA sequencing. At this point, the patient's clinical symptoms and cloudy dialysate had not shown significant improvement. His peritoneal WBC count was 8,750/mm³ (98% neutrophils), and he continued to complain persistent abdominal distension and pain. On the basis of culture and antibiotic susceptibility results, cefazolin was discontinued and intraperitoneal gentamicin (40 mg/day) was started. Oral ciprofloxacin was also begun at a dose of 500 mg daily, which has been known to be effective in S. marcescens peritonitis [3]. Despite appropriate antibiotic therapy, however, the patient still complained of abdominal pain, and the peritoneal dialysate remained cloudy and continued to demonstrate a high WBC count, consisting mainly of neutrophils. The CAPD catheter was removed 10 days after the initiation of intraperitoneal antibiotic treatment. After removal of the catheter, the patient's abdominal pain was relieved and his C-reactive protein level decreased from 13.80 mg/dL to 8.07 mg/dL. His total hospital stay was 20 days, and oral ciprofloxacin was continuously prescribed for 10 days following removal of the CAPD catheter.

Peritoneal dialysis has been widely accepted as a form of renal replacement therapy for patients with end-stage renal disease (ESRD). Despite increased experience with and advances in the technique, peritonitis remains a major cause of morbidity in peritoneal dialysis patients. The overall rates of peritonitis in these patients have decreased because of advances in connectology and Staphylococcus decolonization protocols [4]. These improvements have primarily made an impact on the incidence of gram-positive peritonitis, however, to such an extent that the prevalence of gram-negative organisms has consequently increased [5]. Infections with gram-negative organisms are often more severe than other forms of peritoneal dialysis-associated peritonitis, and are associated with worse clinical outcomes, including catheter loss, technical failure, and death [6]. Among gram-negative infections, S. marcescens peritonitis is associated with the poorest outcomes and is most commonly refractory to antibiotics [7].

The diabetic patient discussed here experienced severe peritonitis, which was resistant to adequate antibiotic treatment. The causative microorganism was identified as S. marcescens, which has been rarely reported as a cause of invasive peritonitis in diabetic patients undergoing CAPD. The morbidity and mortality rates for S. marcescens infection are generally high, because most patients have serious underlying medical problems and the causative strains usually exhibit multiple drug resistance [8]. S. marcescens was usually resistant to ampicillin, tetracycline, cefazolin, cephalothin, and cefuroxime [9]. Some cases of S. marcescens peritonitis have been managed using fluoroquinolones [3]. Fluoroquinolones offer a promising alternative to standard parenteral treatment in CAPD patients, while their high oral bioavailability makes them attractive and convenient [10]. Nonetheless, peritonitis due to S. marcescens had high non-resolution rate. In a retrospective clinical study, four episodes of Serratia peritonitis were identified among 104 episodes of recurrent CAPD peritonitis. One of them was effectively treated by catheter removal [11]. The poor outcome probably reflects the virulence of the organism.

S. marcescens causes nosocomial infection, and several factors have been associated with the acquisition of this pathogen. Prior administration of antimicrobials, immunosuppression, diabetes, renal failure, steroid use, and malignancy seem to be predisposing factors [12]. Peritoneal dialysis patients with diabetes are known to be at particularly high risk for peritonitis. Importantly, when subgroups of causative organisms were analyzed, incidence and rates of gram-negative peritonitis were remarkably increased among peritoneal dialysis patients with diabetes [13]. Recurrent peritonitis caused by S. marcescens in one diabetic patient receiving CAPD had a fatal course [14]. In each instance of nosocomial infection, an inciting event or risk factor could be identified. The patient in the present case displayed the following risk factors: diabetes, renal failure, and peritoneal catheter insertion.

In summary, we report an unusual case of S. marcescens peritonitis. Considering the increased morbidity and poor resolution rate of S. marcescens infection, clinicians should carefully watch for signs of S. marcescens peritonitis in peritoneal dialysis patients, particularly in high-risk patients.