Microbial contamination and antimicrobial resistance in seafood-contacted ice: a study from Shanghai wholesale and retail markets

Abstract Objectives This study aimed to investigate microbial contamination in seafood-contacted ice, with a particular focus on the prevalence of pathogenic bacteria, antimicrobial resistance of isolates, and bacterial diversity. Materials and Methods Seafood-contacted ice samples were collected from 12 districts in Shanghai, China, during August and September 2023. The sanitary conditions were assessed using Plate Count Agar (PCA) and Violet Red Bile Agar (VRBA) plates for serial dilution and plating. Microbial prevalence was determined by streaking on selective agar plates. Antimicrobial susceptibility of the isolates was evaluated using the disk diffusion method. Bacterial diversity was analyzed using the Illumina high-throughput sequencing platform. Results The results revealed that the total plate count in the samples ranged from 1.89 to 5.94 log colony-forming units (CFU)/mL, with an average of 4.15 log CFU/mL. Coliform counts were present in 98.50% of the samples, with counts ranging from 0.70 to 4.06 log CFU/mL, with an average of 2.05 log CFU/mL. Pathogenic bacteria detected included Vibrio parahaemolyticus in 31 samples (31/200, 15.50%), Escherichia coli in 16 samples (16/200, 8.00%), and Staphylococcus aureus in nine samples (9/200, 4.50%). V. parahaemolyticus showed a high ampicillin resistance rate of 96.8% (30/31). E. coli exhibited general resistance to most antibiotics. S. aureus isolates demonstrated greater resistance to ampicillin (6/9, 66.7%), but remained sensitive to other antibiotics. High-throughput sequencing has demonstrated that certain microorganisms exhibit resistance to low temperature through mechanisms such as biofilm formation, contributing to their pathogenicity and posing a threat to the safety of seafood-contacted ice. Specifically, Pseudomonas, Aeromonas, and Shewanella should be prioritized in future preventive and control measures. Conclusions The sanitary conditions of seafood-contacted ice in Shanghai are concerned. Certain bacteria exhibit high detection rates and significant antimicrobial resistance, while some microorganisms capable of surviving at low temperature pose a serious threat to the safety of these products.