Evaluation of the Microbiological Quality and Identification of Vibrio spp. in Fresh and Fish Sauce Marinated Seafood by 16S rRNA Gene Analysis for Seafood Safety Surveillance

Abstract

Fresh and fish sauce–marinated seafood are popular in many areas of Thailand but are prone to contamination by pathogenic microorganisms. This study aimed to compare total microbial counts in fresh and marinated seafood and to identify Vibrio spp. using 16S rRNA gene analysis. Samples of white shrimp, blue swimming crab, and bloody cockle were collected from a market in Mueang District, Chonburi Province, in fresh condition and after marination in fish sauce for 24 and 48 hours (n = 3). Total microbial counts were determined using the standard plate count method, and bacterial species were identified using TCBS selective agar, Gram staining, and nucleotide sequencing. Results showed that fresh seafood had the highest microbial loads, with bloody cockle at 3.19×10⁶ CFU/g and blue swimming crab at 1.86×10⁵ CFU/g, exceeding the Department of Medical Sciences standards. Marination reduced microbial loads, with the lowest counts found in the 48-hour group; for example, marinated shrimp had 2.85×10² CFU/g. The mean total microbial counts (log₁₀ CFU/g) for fresh, 24-hour, and 48-hour marinated samples were 5.536±0.865, 4.449±0.588 and 3.387±0.876, respectively. Statistical analysis showed that fresh seafood differed significantly from 48-hour marinated seafood (p<0.05). Identified bacteria included V. parahaemolyticus, V. alginolyticus, V. cholerae, Aeromonas sp., and Shewanella sp., all of which are gastrointestinal pathogens. In particular, V. cholerae is of epidemiological importance in environmental health. The presence of these bacteria in seafood indicates a potential risk to consumers. The study demonstrates that marination significantly reduces microbial contamination, but raw material quality and hygienic processing remain essential to minimize microbial risks to consumers.