Solid organ tumors cause anatomic abnormalities as a result of progressive disease, and chemotherapy for these tumors compromises normal anatomic barriers, such as the skin and mucous membranes, disrupting important innate defense mechanisms against pathogens [1]. Most infections in patients with solid tumors are caused by the indigenous flora of the patient, and the causative microorganisms reflect the commensal flora at the site of infection [2,3]. Plesiomonas shigelloides is a gram-negative facultative anaerobic rod that is found primarily in freshwater but may also be recovered from river estuaries, seawater, and various fish and shellfish [4]. P. shigelloides, one of the causative organisms of traveler's diarrhea in developed countries [5], causes self-limited diarrhea; however, reports regarding carriers and bacteremia are rare [[6], [7], [8]]. Reports of P. shigelloides bacteremia, particularly in patients with malignancies, are extremely rare. Most of such cases occur with hematologic malignancies, whereas a small number of cases occur with solid organ tumors [8].

Polymicrobial bacteremia is a condition in which multiple bacterial species, generally nosocomial in origin, are found in older adult patients with multiple underlying diseases, often with an intra-abdominal focus of infection, and is associated with a high mortality rate [9,10]. Here, we report the first case of an intratumoral abscess with bloodstream infection caused by P. shigelloides, Citrobacter freundii, Streptococcus mitis/oralis, Clostridium perfringens, and Candida albicans in a patient with postoperative recurrence of cholangiocarcinoma. Except for P. shigelloides, C. freundii, S. mitis/oralis, C. perfringens, and C. albicans are found in the gastrointestinal tract of healthy humans [[11], [12], [13], [14]].