Prevalence and pathogenic potential of Shewanella species in oysters and seawater collected from the Chesapeake Bay and Maryland Coastal Bays

Authors: JOHNSON, TAHIRAH - University Of Maryland Eastern Shore (UMES); Richards, Gary; JACOBS, JOHN - National Oceanic & Atmospheric Administration (NOAA); TOWNSEND, HOWARD - National Oceanic & Atmospheric Administration (NOAA); ALMUHAIDEB, ESAM - University Of Maryland Eastern Shore (UMES); ROSALES, DETBRA - University Of Maryland Eastern Shore (UMES); CHIGBU, PAULINUS - University Of Maryland Eastern Shore (UMES); DASILVA, LIGIA - University Of Maryland Eastern Shore (UMES); PARVEEN, SALINA - University Of Maryland Eastern Shore (UMES)

Submitted to: Frontiers in Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/10/2025
Publication Date: 1/24/2025
Citation: Johnson, T., Richards, G.P., Jacobs, J., Townsend, H., Almuhaideb, E., Rosales, D., Chigbu, P., Dasilva, L., Parveen, S. 2025. Prevalence and pathogenic potential of Shewanella species in oysters and seawater collected from the Chesapeake Bay and Maryland Coastal Bays. Frontiers in Microbiology. https://doi.org/10.3389/fmicb.2025.1503443.
DOI: https://doi.org/10.3389/fmicb.2025.1503443

Interpretive Summary: Shewanella are marine bacteria which include species associated with seafood spoilage as well as infections in humans, fish, and shellfish. This is the first paper to provide insights into the diversity, abundance, and potential pathogenicity of Shewanella species isolated from oysters and seawater from sites in the Chesapeake Bay and the Maryland Coastal Bays. Total Shewanella counts were as high as 1.8 million per gram of oysters. DNA sequencing of 1344 representative isolates revealed the presence of 890 Shewanella within 16 different species, including species not previously reported in the Chesapeake and Maryland Coastal Bays, such as the shrimp pathogen S. khirikhana. Eight percent of the isolates were S. algae, which can cause serious and life-threatening human infections. Isolates were screened for their ability to lyse red blood cells, which serves as an indicator of potential pathogenicity in humans, and many tested positive. Further monitoring is warranted for these potentially pathogenic strains.

Technical Abstract: Shewanella is a genus of Gram-negative marine bacteria with some species associated with human and shellfish illnesses. This study evaluated the abundance of Shewanella species in oysters and seawater from the Chesapeake and Maryland Coastal Bays at four sites between 2019 and 2021. The highest total Shewanella counts were 1.8 × 10e7 CFU/g in oysters and 4.0 × 10e2 in seawater. 16S rRNA sequencing was performed on 1,344 representative isolates of which 890 (713 oyster, 177 seawater) were confirmed as Shewanella within 16 species. The top four species isolated from oysters and seawater were S. khirikhana a known shrimp pathogen (49%), S. marisflavi (19%), S. loihica (11%), and S. algae (8%). Testing for alpha and beta hemolysis was performed on all confirmed Shewanella isolates. Beta hemolysis was observed in 405 (46%) of the isolates of which 313 were in oysters and 92 in seawater. In oysters, beta-hemolysis was most prevalent in S. khirikhana (233 of 344 isolates, 68%), while in seawater 64 of 92 isolates (70%) were beta-hemolytic strains. Beta-hemolysis suggests that these could be potentially pathogenic strains. Correlations were performed between physicochemical attributes of the seawater and Shewanella counts. Only seawater temperature and dissolved oxygen correlated with Shewanella counts (r = 0.45 and -0.41), respectively. No correlations were observed between the physicochemical parameters and Shewanella abundances in oysters. Results suggest that virulent strains of Shewanella may be present in oysters and seawater from the Chesapeake and Maryland Coastal Bays, perhaps as a consequence of rising seawater temperatures.