Antibiotic resistance profiling of hemolytic Shewanella species in oysters and seawater from the Mid-Atlantic Region

Authors: JOHNSON, TAHIRAH - University Of Maryland Eastern Shore (UMES); COLLINS, TRENTON - Roger Williams University; Richards, Gary; PARVEEN, SALINA - University Of Maryland Eastern Shore (UMES)

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/2/2025
Publication Date: 8/5/2025
Citation: Johnson, T., Collins, T., Richards, G.P., Parveen, S. 2025. Antibiotic resistance profiling of hemolytic Shewanella species in oysters and seawater from the Mid-Atlantic Region. Journal of Food Protection. https://doi.org/10.1016/j.jfp.2025.100596.
DOI: https://doi.org/10.1016/j.jfp.2025.100596

Interpretive Summary: This study provides important insights into the antibiotic resistance profiles of marine bacteria known as Shewanella species, which can be readily isolated from fish, shellfish, sediment, and seawater. Shewanella are responsible for severe soft tissue and bloodstream infections, especially in individuals with weakened immune systems. Species isolated from the Chesapeake and Maryland Coastal Bays included the potential disease-causing species Shewanella algae and Shewanella xiamenensis. A total of 166 Shewanella isolates from oysters and seawater were tested for sensitivity toward 21 antibiotics. Widespread resistance was observed to clinically-relevant antibiotics, including carbapenems, colistin, and beta-lactams, raising concerns about the persistence of these pathogens in estuarine environments and their potential impact on public health. This data offers valuable guidance for determining potential treatment scenarios by identifying antibiotics that remain effective against key Shewanella species. This study also underscores the need for continued surveillance for antimicrobial resistance in marine ecosystems and supports the development of targeted antibiotic treatment strategies. Moreover, the indiscriminate use of antibiotics in aquaculture and livestock production may accelerate resistance among environmental bacteria like Shewanella, further complicating treatment options. These results highlight the importance of integrated multidisciplinary approaches to monitor resistance, inform policy, and safeguard both environmental and human health.

Technical Abstract: Shewanella species are opportunistic pathogens and food spoilage bacteria that can be transmitted through contaminated seawater and seafood. Immunocompromised individuals are at greater risk when consuming raw fish and shellfish or when open wounds are exposed to contaminated marine environments. The emergence of antibiotic-resistant bacteria has raised concerns over public health and animal health globally. Infections involving resistant hemolytic bacteria can be life-threatening due to limited treatment options. This study aimed to evaluate the resistance profiles of hemolytic Shewanella species against 21 antibiotics commonly used to treat Gram-negative bacterial infections. A total of 166 hemolytic isolates recovered from oyster (n = 107) and seawater (n = 59) samples obtained from the Mid-Atlantic sampling sites between 2019 and 2021 were tested using Sensititre GNX2F antimicrobial susceptibility plates. Overall, 16.27% of oyster isolates and 18.94% of seawater isolates were resistant to one or more antibiotics. While no statistically significant difference in resistance were found between alpha and beta hemolytic groups, resistance levels varied across species. Shewanella algae and S. khirikhana exhibited the highest resistance to 10 and 14 antibiotics, respectively, followed by S. marisflavi (11 antibiotics) and S. indica (9 antibiotics). Doxycycline, Levofloxacin, Minocycline, and Tigecycline were the most effective antibiotics, with low or no resistance observed among Shewanella isolates from both seawater and oysters. This is the first study to provide detailed insights into the antibiotic resistance profiles of hemolytic Shewanella species in the Chesapeake Bay and the Maryland Coastal Bays.