In Vitro Investigation of the Colonization of Microplastic Surfaces by Vibrio parahaemolyticus in Shrimp Litopenaeus vannamei

Microplastics (MPs) are smaller plastics that have become prevalent in aquatic environments. Previous studies have reported MP occurrence in the gastrointestinal tracts of shrimp species collected from public markets and shrimp farms. There are reports that biofilm communities, including potentially pathogenic bacteria, can adhere to the MP surfaces. MPs, when ingested, pose significant health and economic risks, including potential exposure to Vibrio parahaemolyticus (Vp) – a prominent shrimp pathogen found in high concentrations on MP surfaces – increasing disease risks in shrimp and potentially entering the human food chain. In this study, the shrimp Litopenaeus vannamei from a shrimp farm and different wet markets in Bulacan, the Philippines, were tested for MP contamination and the attachment and colonization of Vp to MP surfaces and tested in vitro. The isolated MPs underwent chemical digestion and floatation separation, followed by imaging with a stereomicroscope and characterization based on their morphological features. The isolated putative MPs are frequently observed in fragments of irregular shape. Attenuated total reflectance–Fourier transform infrared spectroscopy results validated that only L. vannamei from Hagonoy and Meycauayan wet markets acquired MPs that exhibited characteristic absorption bands corresponding to the C-H stretching vibrations typical of polyethylene (PE) based plastics. A set of pristine PE-based plastics – one with a smoother surface (PE1) and one with a rougher surface (PE2) – were observed for the attachment of Vp. Scanning electron microscopy images confirmed the attachment of Vp on these MP surfaces and revealed that the colonization could be seen as early as 1 h of incubation. PE2 resulted in a higher abundance of adhered bacteria than PE1, suggesting that surface roughness plays a role in bacterial colonization on MP. However, this observed difference was not statistically significant, suggesting that other parameters such as temperature, pH, salinity, and nutrient availability should also be considered. This study shows that shrimps from the sampling sites are contaminated with MPs, and that PE-based MPs can be colonization sites for Vp.