Spontaneous Bacterial Peritonitis Caused by <i>Campylobacter fetus </i>Identified by MALDI-TOF MS

Campylobacter fetus has rarely been reported as a pathogen of spontaneous bacterial peritonitis (SBP). A 60-year-old man with cirrhosis and diabetic nephropathy developed diarrhea, abdominal pain, and fever. Abdominal paracentesis revealed a significantly increased neutrophil count in the ascites. He was diagnosed as having SBP and treated empirically with ceftriaxone. Five days later, the blood culture performed on the day of admission yielded spiral-shaped gram negative bacilli. Both ascites and stool cultures were negative. Although conventional biochemical methods could not identify the colony, MALDI-TOF MS (Matrix Assisted Laser Desorption Ionization Time Of Flight Mass Spectrometry) identified it as C. fetus. Ceftriaxone was switched to ampicillin and continued for 21 days in total. He was fully recovered. Only 9 such patients have been reported including our patient, and 8 of them had a favorable outcome. SBP caused by C. fetus tends to present with diarrhea frequently and one patient died. Identification of C. fetus is important to select appropriate antimicrobial therapy. Our case suggests MALDI-TOF MS is a useful tool to identify C. fetus.