Antibiotic Resistance Profiling of Hemolytic Shewanella Species in Oysters and Seawater from the Mid-Atlantic Region Journal of Food Protection

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. Only Ertapenem showed a statistically significant difference in resistance 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. Grant no. NA16SEC481007 Grant no. NA21SEC481005