The research, conducted by a team at Semmelweis University in Budapest along with collaborators in Romania and Hungary, took the form of a systematic review and meta-analysis published in the journal Gut Pathogens. Rather than relying on any single centre’s experience, the investigators systematically searched the medical literature for studies reporting on the microbiological profile of patients undergoing endoscopic or percutaneous drainage for infected walled-off necrosis or pancreatic pseudocysts. These two types of pancreatic fluid collections represent distinct pathological entities. Walled-off necrosis arises when areas of dead pancreatic or surrounding tissue become encapsulated by a wall of inflammatory tissue, typically four or more weeks after the onset of necrotising pancreatitis. Pancreatic pseudocysts, by contrast, are fluid-filled cavities bounded by fibrous tissue that lack the solid necrotic component. Both can become infected, and both are increasingly managed through minimally invasive drainage rather than open surgery, making the organisms they harbour directly relevant to treatment decisions.

After screening the available literature according to a protocol registered in advance on the PROSPERO international prospective register of systematic reviews, the team identified thirty-one eligible studies encompassing one thousand two hundred and eighty-six patients with culture-positive infections of pancreatic fluid collections. The pooled analysis revealed a microbial ecosystem dominated by organisms that originate in the gastrointestinal tract, which makes anatomical sense given that the pancreas lies adjacent to the duodenum and that pancreatic fluid collections frequently communicate with the gut either through the pancreatic duct or through erosion into adjacent bowel. Escherichia coli emerged as the single most prevalent bacterium in infected walled-off necrosis, detected in twenty-one percent of cases with a ninety-five percent confidence interval spanning thirteen to thirty-one percent. Enterococcus species followed closely at twenty percent, with a wider confidence interval of twelve to thirty-three percent reflecting the heterogeneity of the underlying studies.

Perhaps the most striking finding was the prominence of Candida species, detected in twenty percent of infected walled-off necrosis cases with a confidence interval of eleven to thirty-three percent. The presence of this fungal genus at rates comparable to the leading bacterial pathogens challenges the traditional assumption that bacterial organisms alone drive the majority of these infections. Candida is a normal inhabitant of the gastrointestinal tract, and its appearance in pancreatic collections likely reflects translocation from the gut across compromised mucosal barriers. The finding has important therapeutic implications because standard empiric antibiotic regimens for intra-abdominal infections typically do not cover fungi, meaning that clinicians who rely on broad-spectrum antibacterial agents alone may miss a substantial proportion of causative organisms.

The analysis also quantified the burden of antimicrobial resistance in these collections, finding that multidrug-resistant organisms were present with a pooled prevalence of twenty-four percent among infected patients, with a confidence interval stretching from ten to fifty percent. This wide range reflects significant variability across the included studies, likely driven by differences in local antibiotic prescribing practices, infection control infrastructure, and patient populations. Nevertheless, the central estimate is alarming because it means that approximately one in four patients with an infected pancreatic fluid collection harbours organisms resistant to multiple first-line antimicrobial agents. The authors noted that the spectrum of resistance includes extended-spectrum beta-lactamase producing Enterobacteriaceae, methicillin-resistant Staphylococcus aureus, and vancomycin-resistant Enterococcus, each of which demands specific therapeutic agents that may not be part of standard empiric protocols.

One of the most clinically valuable contributions of the study lies in its regional stratification, which exposed dramatic geographical variation in pathogenic distribution. In European patients, Candida species predominated at thirty-eight percent with a confidence interval of twenty-three to fifty-six percent, followed by Enterococcus species at thirty-five percent. In Asian populations, the picture shifted markedly, with Escherichia coli leading at twenty-nine percent and Klebsiella species rising to twenty-seven percent. This east-west divide has tangible implications for how empiric antibiotic therapy should be selected. A clinician in Budapest or Bucharest facing a patient with suspected infected pancreatic necrosis might reasonably weight antifungal and anti-enterococcal coverage more heavily, while a counterpart in Seoul or Mumbai would need to ensure robust coverage against gram-negative organisms including Klebsiella, which in many Asian centres carries elevated rates of carbapenem resistance.

When the researchers turned their attention specifically to infected pancreatic pseudocysts rather than walled-off necrosis, they found a somewhat different hierarchy. Escherichia coli was again the leading pathogen at twenty-nine percent, though with a very wide confidence interval of eight to sixty-five percent that underscores the smaller number of studies and patients available for this subgroup. Staphylococcus species followed at twenty-five percent, and Klebsiella species came in at eighteen percent. The broader confidence intervals for pseudocyst-associated infections reflect the relative rarity of infected pseudocysts compared with infected necrosis, since pseudocysts are less likely to harbour solid necrotic debris that serves as a nutrient-rich medium for bacterial proliferation. Nevertheless, the finding that Staphylococcus species rank second in pseudocyst infections is noteworthy because it suggests a possible role for skin flora or healthcare-associated contamination in these collections, particularly when interventions such as fine-needle aspiration or drainage have been performed.

The technical challenges of obtaining reliable microbiological data from pancreatic fluid collections deserve careful consideration. Culture results can be influenced by the sampling method employed, whether by endoscopic ultrasound-guided fine-needle aspiration, direct puncture during drainage, or percutaneous catheter placement. Prior antibiotic exposure, which is nearly universal in these patients by the time drainage is attempted, can suppress the growth of susceptible organisms and lead to false-negative cultures or an overrepresentation of resistant species. The heterogeneity of sampling modalities across the thirty-one included studies represents a limitation that the authors acknowledged, noting that marked variation across regions and sampling techniques contributed to the wide confidence intervals observed for many organisms. The researchers also pointed out that the retrospective and observational nature of most included studies means that temporal trends in resistance patterns could not be reliably assessed, and that the findings warrant further prospective evaluation.

The clinical implications of this work extend beyond the choice of individual antibiotics. The authors argue that recognition of regional pathogenic distribution should inform antimicrobial stewardship programmes, which aim to optimise antibiotic use to preserve efficacy and limit the emergence of resistance. In the context of infected pancreatic fluid collections, stewardship involves a delicate balance. Empiric coverage must be broad enough to address the likely pathogens, including consideration of fungal coverage in European settings, yet targeted de-escalation based on culture results is essential to avoid selecting for multidrug-resistant organisms. The finding that nearly a quarter of infections involve multidrug-resistant organisms adds urgency to calls for rapid diagnostic methods that can identify pathogens and their resistance profiles within hours rather than days, allowing clinicians to narrow therapy sooner and spare patients the toxicities and costs of unnecessarily broad regimens.

This study represents a significant step forward in understanding the microbiological underpinnings of one of the most feared complications of acute pancreatitis. By synthesising data from thirty-one studies and over twelve hundred patients across multiple continents, it provides clinicians with evidence-based benchmarks against which to judge their local microbiology results and to calibrate empiric therapy. The dominance of enteric organisms confirms that the gut serves as the primary reservoir for infection in these collections, while the unexpected prominence of Candida species and the substantial burden of antimicrobial resistance highlight gaps in current treatment paradigms. As the authors conclude, a diverse microbial profile with enteric organisms, fungal pathogens, and significant heterogeneity across regions characterises infected pancreatic fluid collections, and integrating this knowledge into clinical practice may ultimately translate into better outcomes for patients facing these life-threatening complications.

Subject of Research: Microbiological profile of infected walled-off pancreatic necrosis and pseudocysts

Article Title: The microbiological landscape of infected walled-off necrosis and pancreatic pseudocysts: a systematic review and meta-analysis

Article References: Brand, T., Marchis, A., Grigorovici, R., Aviv, K., Tóth, R., Bunduc, S., Mihály, E., Obeidat, M., Erőss, B., Hegyi, P., & Hegyi, P. J. (2026). The microbiological landscape of infected walled-off necrosis and pancreatic pseudocysts: a systematic review and meta-analysis. Gut Pathogens. https://doi.org/10.1186/s13099-026-00883-9

Image Credits: AI Generated

DOI: 10.1186/s13099-026-00883-9

Keywords: acute pancreatitis, walled-off necrosis, pancreatic pseudocyst, pancreatic fluid collections, Escherichia coli, Enterococcus, Candida, multidrug resistance, antimicrobial stewardship, endoscopic drainage, meta-analysis, microbiology