Occurrence, antimicrobial resistance, virulence, and biofilm formation capacity of Vibrio spp. and Aeromonas spp. isolated from raw seafood marketed in Bangkok, Thailand

Abstract

Background and aim: Bacteria of the genera Vibrio and Aeromonas cause seafood-borne zoonoses, which may have a significant impact on food safety, economy, and public health worldwide. The presence of drug-resistant and biofilm-forming phenotypes in the food chain increases the risk for consumers. This study aimed to investigate the characteristics, virulence, biofilm production, and dissemination of antimicrobial-resistant pathogens isolated from seafood markets in Bangkok, Thailand.

Materials and methods: A total of 120 retail seafood samples were collected from 10 local markets in Bangkok and peripheral areas. All samples were cultured and the Vibrio and Aeromonas genera were isolated using selective agar and biochemical tests based on standard protocols (ISO 21872-1: 2017). The antibiotic susceptibility test was conducted using the disk diffusion method. The presence of hemolysis and protease production was also investigated. Polymerase chain reaction (PCR) was used to determine the presence of the hlyA gene. Furthermore, biofilm formation was characterized by microtiter plate assay and scanning electron microscopy.

Results: The bacterial identification test revealed that 35/57 (61.4%) belonged to the Vibrio genus and 22/57 (38.6%) to the Aeromonas genus. The Kirby-Bauer test demonstrated that 61.4% of the isolates were resistant to at least one antibiotic and 45.61% had a high multiple antibiotic resistance index (≥0.2). PCR analysis indicated that 75.44% of the bacteria harbored the hlyA gene. Among them, 63.16% exhibited the hemolysis phenotype and 8.77% showed protease activity. The biofilm formation assay demonstrated that approximately 56.14% of all the isolates had the potential to produce biofilms. The moderate biofilm production was the predominant phenotype.

Conclusion: The results of this study provide evidence of the multiple drug resistance phenotype and biofilm formation capacity of Vibrio and Aeromonas species contaminating raw seafood. Effective control measures and active surveillance of foodborne zoonoses are crucial for food safety and to decrease the occurrence of diseases associated with seafood consumption.

Keywords: Aeromonas spp; biofilm formation; drug resistance; foodborne; seafood; vibriosis.

Figure-1

Heatmap of percent distribution for antimicrobial resistance phenotypes and virulence phenotypes of Vibrio isolates from seafood samples. The color band illustrates the percentages of virulence characteristics with individual drug-resistant phenotype. Generate using GraphPad Prism version 9 (La Jolla, CA, USA).

Figure-2

Biofilm formation potentials of bacterial isolated from different seafood samples using microtiter plate assay.

Figure-3

Representative scanning electron micrographs of biofilm formed by Vibrio isolate no. V19 at 37°C for 12 h (a, d), 24 h (b,e), and 48 h (c,f). Scale bars: 10 μm (upper panels) and 2 μm (lower panels).