EMERGING ENTEROBACTERIACEAE IN FOODBORNE OUTBREAKS: EVIDENCE FROM CITROBACTER YOUNGAE AND ENTEROBACTER HORMAECHEI CONTAMINATION IN INSTITUTIONAL FOOD SERVICES

Foodborne outbreaks caused by nontraditional Enterobacteriaceae remain insufficiently characterized within collective catering systems, despite increasing evidence of their environmental persistence and potential for post-processing contamination. This study aimed to investigate a foodborne outbreak that occurred in a university restaurant located in northeastern Brazil in February 2025. For this an integrated approach was adopted, encompassing epidemiological, microbiological, and sanitary assessments. Epidemiological data were obtained from diners who developed gastrointestinal symptoms after consuming meals at the university restaurant. Food samples prepared during the implicated period were analyzed by a state public health laboratory using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), in compliance with the Brazilian microbiological regulations (RDC No. 724/2022; IN No. 161/2022). Sanitary inspections were conducted on-site in accordance with Good Manufacturing Practices and the requirements established by the Brazilian Health Regulatory Agency (ANVISA) under RDC No. 216/2004. A total of 439 diners reported gastrointestinal illness, with a median incubation period of 9 h 15 min (approximate range, 20 min–54 h). Predominant symptoms were nausea (84.3%), abdominal cramps (73.6%), vomiting (70.2%), and diarrhea (63.6%). Nineteen food samples collected during the exposure period met all legal microbiological standards; however, two non-regulated Enterobacterales species were isolated from ready-to-eat foods: Citrobacter youngae from cooked beef with sauce and Enterobacter hormaechei from frozen cajá pulp. Although these species are not listed among the regulatory target microorganisms, their detection in ready-to-eat foods is epidemiologically meaningful and indicates post-processing contamination. Sanitary inspections identified deficiencies in time and temperature control during hot holding and conditions that could facilitate recontamination at the distribution/portioning stage. In the case of the acidic frozen fruit pulp, the contamination most likely originated at the industrial processing facility, and the contaminated pulp subsequently affected the juice served to diners. The convergence of epidemiological evidence, microbiological analyses, and sanitary inspection findings supports a scenario of post-processing contamination rather than a failure within the food production workflow or regulatory noncompliance. To the best of our knowledge, this represents the first documented outbreak in Brazil involving Citrobacter youngae and Enterobacter hormaechei. These results emphasize that legal compliance with microbiological standards does not necessarily preclude public health risks when opportunistic Enterobacteriaceae are implicated. Strengthening process control measures, supplier verification systems, and routine surveillance for nontraditional Enterobacteriaceae in ready-to-eat foods is essential to prevent similar events in institutional food service operations.