Skip to main content

Can Bacteria in the Water Infect Us through Shellfish?


Oysters and Clams Carry Different Levels of Microbes – And Some Are Harmful

Shellfish are filter feeders, meaning they take in water, and from this water, they take in food and nutrients. This means sometimes they also take in water-borne pathogenic bacteria, such as Vibrio vulnificus and Vibrio parahaemolyticus. When we consume raw clams and oysters, these pathogenic bacteria remain alive and, therefore, can infect us.

clams. credit: North Carolina Sea Grant
Credit: North Carolina Sea Grant

Research Need

With a trend in declining water quality, an increasing number of shellfish contain pathogenic bacteria. Therefore, understanding the conditions surrounding the intake of these microbes is a crucial human health need. If the amount of bacteria in the water correlates with the amount present in the shellfish, water sampling could help to better understand the potential risk to shellfish consumers.

What did they study?

Over a period of 2 years, researchers sampled water and collected shellfish from several sites, including some sites in North Carolina.

You can view these sites here.

What did they find?

Concentrations of Vibrio bacteria in the water and in the oysters correlated. However, the concentrations of these microbes in clams and in the water did not correlate. When researchers compared oysters and clams from the same site, oysters had a higher level of Vibrio infection than clams.

What else did they find?

In order to decrease risk of human infection from Vibriosis, modeling can be effective for estimating areas of high concentrations of these microbes.


Froelich, B. A., Phippen, B., Fowler, P., Noble, R. T., & Oliver, J. D. (2016). Differences in Abundances of Total Vibrio spp., V. vulnificus, and V. parahaemolyticus in Clams and Oysters in North Carolina. Applied and Environmental Microbiology, 83(2).

Summary compiled by Anna Greene and Scott Baker
Lead photo by Chuck Weirich  

The text from Hook, Line & Science is available to reprint and republish at no cost with this attribution: Hook, Line & Science, courtesy of Scott Baker and Sara Mirabilio, North Carolina Sea Grant.