In this study, Citrobacter freundii was detected in a sample obtained by EUS-FNA of a patient with pancreatic pseudocyst after an acute necrotizing pancreatitis.
EUS-FNA has emerged as an excellent tool to both image and sample pancreatic lesions . It is considered the most sensitive and specific method of identifying pancreatic masses. The American Joint Commission on Cancer recommends EUS-FNA as the preferred diagnostic modality for pancreatic masses . The presence of an on-site cytologist for immediate interpretation is a common practice in most high volume EUS centers . On-site cytologic evaluation has been shown to increase the diagnostic yield by 10 to 15% [4–6] and can decrease procedure time and potential complications through avoidance of unnecessary needle passes once diagnostic tissue is obtained.
Most pathogens in pancreatic infection are gastrointestinal Gram negative bacteria; the colon seems to be the main source of pancreatitis related infections. Therefore, it is possible that bacterial translocation (BT) is the most important mechanism for contamination of pancreatic necrosis.
Pancreatic pseudocysts are more frequently polymicrobial (57%) than monomicrobial (43%). This fact contrasts with infected necrosis, where monomicrobial infections are usually found. Up to now anaerobes and fungi have rarely been reported; however, the bacterial spectrum may change in the near future due to the use of specific antibiotics leading to an increase in different microorganisms, especially fungi .
The diagnosis of pancreatic pseudocyst is based on clinical suspicion, imaging techniques, and demonstration of infection. Since clinical presentation may be very variable, pancreatic infection should be suspected in any patient with fever or suggestive signs or symptoms of sepsis within the context of AP. Once pancreatic pseudocysts have been diagnosed the treatment is complete drainage. Pancreatic pseudocysts do not resolve spontaneously and, if untreated, the prognosis for a patient is almost invariably death. Currently, two different approaches can be considered for primary drainage of a pancreatic pseudocyst: surgical and percutaneous.
Appropriate antibiotic therapy depends on the identification of the causative microorganisms and sensitivity testing. Meanwhile, several options have been recommended: a combination of ceftazidime and clindamycin; a combination of ciprofloxacin and metronidazole; or carbapenems as a single agent due to its extremely broad spectrum of activity .
Several trials have assessed the frequency of bacterial infection of necrotic areas in the natural course of severe AP without antibiotic intervention . Results indicated an overall contamination rate of 24% within the first week of the onset of AP, increasing to 46 and 71%, respectively, in the second and third week.
Escherichia fergusonii was isolated from pancreatic carcinoma and cholangiosepsis  in a patient with a history of weight loss, jaundice, and acholic stools. After one day, E. fergusonii was grown as a single organism from the gallbladder fluid as well as from blood culture. Many other bacteria have been involved in AP . A case of AP associated with brucellosis was reported in a 56-year-old patient with a seven-day history of fever, generalized myalgia and arthralgia, lower back pain, anorexia, and sweating. He experienced a sudden onset of abdominal pain accompanied by nausea and vomiting. He lived in an area of northwestern Greece where brucellosis is endemic. The CT scan revealed the presence of mild swelling of the pancreas without additional abnormality. The Brucella agglutinins were present in a titer and the blood culture grew B. maletiensis after eight days of incubation.
Also, Mycobacterium tuberculosis was isolated from a woman with a pancreatic mass. She was subsequently diagnosed with pancreatic tuberculosis via EUS-FNA. Intraprocedural immediate cytologic evaluation prompted samples to be sent for appropriate microbiological culture .
Studies evaluating the presence of bactDNA in biological fluids of patients with AP and other pathologies have rarely been reported in the literature. Madaria, et al.  reported the presence of Citrobacter freundii DNA and other pathogens (Pseudomona aeruginosa and E. coli) in four blood samples from patients with pancreatitis in Spain. There is no information in the literature regarding the pathogenic role of C. freundii in the development of infections in patients with AP; this bacterium has been shown to translocate in different experimental and clinical situations and is related to both biliary and intra-abdominal infections [12–14].
Enteric bacterial pathogens including Vibrio cholerae and enterotoxigenic Escheriachia coli often produce ADP-ribosylating enterotoxins that are mainly responsible for diarrheal diseases. Two well-characterized enterotoxins, cholera toxins produced by toxigenic strains of Vibrio cholerae and the heat-labile toxin (LT) produced by enterotoxigenic E. coli (ETEC) strains, have been detected to be virulence-like factors in Citrobacter freundii using immunological methods and PCR [15–17]. This suggests a possible gene transfer between C. freundii and this species .
One of the virulence factors attributed to Citrobacter spp. is the activation of transcription factors, kappa beta (NFκβ), concretely in C. rodentium (previously C. freundii biotype 4280). The NFκβ is a nuclear transcription which regulates the expression of a large number of genes that are critical for the regulation of apoptosis, viral replication, tumorigenesis, inflammation, and various autoimmune diseases. The NFκβ can be activated via different pathways. The most common, called the classical pathway, is triggered in response to microbial or pro-inflammatory cytokine injury, leading to a recruitment and activation of the Iκβ-kinase (IκK) complex which includes the scaffold protein NFκβ essential modulator, NEMO, also named, IκKγ [19–21].
It is possible that in pancreatic infections, NFκβ may have an additional role to perform, for example, in the expression and production of pro-inflammatory cytoquines during C. freundii infection and possibly in bacterial clearance.