Impacts of anthropogenic contaminants and elevated temperature on prevalence and proliferation of Escherichia coli in the wild-caught American oyster, Crassostrea virginica in the southern Gulf of Mexico coast

ABSTRACT

Escherichia coli is one of the most common indicators of environmental contamination and health risk to aquatic organisms including shellfish. E. coli can adapt to various stress conditions (e.g. heat, pollution, acidification, etc.). American oyster, Crassostrea virginica, a marine bivalve mollusc, is a seafood popular due to its delicacy and high nutritional value. Based on increasing concern about global warming, coastal pollution and microbial contamination in live or raw seafood, the present study focused on the detection and enumeration of the bacterial pathogen E. coli in the American oyster in south Texas waters, and in controlled laboratory heat-exposure conditions. Immunohistochemical, reverse transcription-polymerase chain reaction (RT-PCR) and quantitative real-time PCR (qRT-PCR) analyses showed substantial bacterial pathogen presence in the gills and digestive glands of oysters collected from polluted sites in San Martin Lake and South Padre Island on the southern Gulf coast of Texas. Laboratory heat-exposure studies showed an increasing trend of E. coli protein and mRNA expression in gills and digestive glands in elevated temperatures (28°C and 32°C) compared with control (24°C) and reduced integrated protein density of E. coli in gills at high temperature. Biochemical analyses were also performed to examine the extrapallial fluid (EPF, an integral body fluid) conditions in oysters. EPF glucose levels, pH and protein concentration varied at high temperatures and appeared to be pertinent to pathogen intensity in oysters. Collectively, these results suggest that American oyster is prone to waterborne pathogen contamination in the southern Gulf of Mexico coast, and E. coli proliferation escalates at rising sea surface temperatures.

KEYWORDS:

• Coastal region
• E. coli
• environmental pollution
• global warming
• Gulf of Mexico
• oyster

Acknowledgements

The authors would like to thank Dr Aubrey Converse, Marine Science Institute, University of Texas at Austin, for her suggestions and comments on the manuscript. We greatly acknowledge the support and permission of the Texas Park & Wildlife Department to collect wild oysters.

Author contributions and consent of participations

Md Saydur Rahman gave the research idea and supervised field and lab studies. Md Saydur Rahman and Mohammad Maruf Billah collected oysters from field. Mohammad Maruf Billah conducted laboratory study, collected, and analysed data. Md Saydur Rahman and Mohammad Maruf Billah analysed data and designed figures. Mohammad Maruf Billah drafted manuscript. Md Saydur Rahman and Mohammad Maruf Billah edited and reviewed the manuscript.

Availability of data

The datasets generated and/or analysed of this study are available from the corresponding author on reasonable request.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Ethical approval

Oysters were collected in the South Padre Island and San Martin Lake according to the approved wildlife species capture rules and regulations by the Texas Parks & Wildlife Department (scientific permit number: SPR1018-274). The UTRGV Institutional Animal Care and Use Committee (IACUC) do not require an animal use and/or care protocol for research conducted on invertebrates including marine bivalve molluscs. All oysters, however, were cared and handled following invertebrate standards of Guide for the Care and Use Laboratory Animals in the US National Research Council Committee (https://grants.nih.gov/grants/olaw/guide-for-the-care-and-use-of-laboratory-animals.pdf).

Additional information

Funding

This study was funded in part by the start-up fund and University of Texas Rio Grande Valley College of Science SEED (grant number 210000371) to Md Saydur Rahman.