P08 | Environmental monitoring and identification of Shewanella spp. at a seafood processing plant: preliminary results

T. Cardellicchio¹, M. Egidio², A. Mancusi¹, Y.T.R. Proroga¹, S. Capo¹, L. Casalino³, R. Marrone², M. A. Casbarra¹, O. Di Maro¹. | ¹Istituto Zooprofilattico Sperimentale del Mezzogiorno, Dip. Coordinamento di Sicurezza Alimentare; ²Università Federico II di Napoli – DMVPA Dip. Medicina Veterinaria e Produzioni Animali; ³Universitas Mercatorum - Sostenibilità e Agenda ESG, Roma, Italy

Purpose. The genus Shewanella spp. includes Gram-negative bacteria known for their ability to reduce heavy metal compounds and nitrates, a quality that makes them relevant in both ecological and biotechnological fields. This emerging bacterium has been isolated from various environmental matrices, including freshwater and marine waters, sediments, and contaminated surfaces, highlighting its high adaptability and remarkable resistance under varying environmental conditions. In the food sector, Shewanella spp. has been found in seafood products (fish, bivalve mollusks, crustaceans), fresh meats, and, less commonly, in irrigated vegetables, suggesting that the main routes of contamination are the environment and inadequate hygiene practices. In this context, the objective of the present study was to isolate Shewanella spp. from environmental surfaces and food contact equipment within a seafood processing plant, with the aim of conducting microbiological monitoring to assess the extent of biocontamination and verify the effectiveness of the company's sanitation procedures. Methods. The investigation was conducted in the two-year period 2024-2025 at a facility located in Campania, through microbiological sampling performed in three operational areas: environmental surfaces, utensils, and equipment. Sampling was performed according to ISO 18593:2018, using sterile cellulose sponge bags (Whirl-Pak, WI, USA) pre-hydrated with Buffered Peptone Water (BPW; Thermo Fisher Scientific, UK). Two serial dilutions were made from the sponges and spread-plated onto Baird-Parker agar (Thermo Fisher Scientific, UK). The plates were subsequently incubated at 37°C for 24 hours. Suspicious colonies, selected based on morphological characteristics, were finally identified using MALDI-TOF mass spectrometry (Bruker, Germany). During the environmental monitoring conducted between 2024 and 2025, a total of 74 samples were collected using sponge bags, distributed across three operational areas: 27 on environmental surfaces, 20 on utensils, and 27 on equipment. Results. From the microbiological analysis, the genus Shewanella was isolated in 31 out of 74 samples, with an overall positivity rate of 41.9%. Specifically, a clear increase in the number of positive samples was observed between the two years of monitoring, highlighting a significant growth in the frequency of bacterial isolation in the second year of the investigation. The distribution of positive samples across the different operational areas showed some significant differences: 7 out of 27 environmental surface samples tested positive (25.9%); in the tools, 13 out of 20 samples were positive (65%); Finally, in the equipment area, 11 out of 27 samples were positive (40.7%). Conclusions. The microbiological investigation conducted highlighted that utensils and equipment are a significant reservoir of contamination by Shewanella spp., showing a positivity rate almost double that found on environmental surfaces. This result indicates that materials and surfaces in direct contact with the fish product represent a critical point for the spread of the microorganism. These findings highlight the need to strengthen and optimize sanitation procedures by introducing targeted and more rigorous strategies to significantly reduce the risk of cross-contamination and ensure the microbiological safety of the finished product.