Antibiotic Resistance in Pathogenic Vibrio Found in Oysters

Pathogenic Vibrio parahaemolyticus and Vibrio vulnificus have shown increasing numbers in oysters in recent years. These bacteria, transmitted through the ingestion of raw oysters, cause significant health issues such as septicemia, gastroenteritis, and soft tissue infection. Antibiotics are the primary treatment method, however, the increase in antibiotic resistant bacteria raises concern regarding this treatment’s effectiveness.  The purpose of this study is to determine if V. parahaemolyticus and V. vulnificus demonstrate resistance to ampicillin and ciprofloxacin, which are commonly used to treat vibriosis. Oysters (Crassostrea virginica) were collected on Sapelo Island, GA in July 2025. Tissues were homogenized in sterile saline and plated on CHROMagar™ Vibrio to isolate Vibrio spp. Selected colonies from these plates were subsequently streaked on CHROMagar to create pure cultures. Colonies from streak plates were resuspended in sterile 3% NaCl and were then inoculated on MHII agar. Ampicillin and ciprofloxacin antibiotic discs were placed on the MHII plates. Following incubation, the antibiotic inhibition zones were measured and compared to antimicrobial susceptibility testing standards to determine if bacteria exhibited resistance to the antibiotics. We analyzed 29 Vibrio samples. Our results showed 59% resistance to ampicillin and 6% resistance to ciprofloxacin in tested bacteria. Understanding the extent of antibiotic resistance seen in the samples can assist in combating food-borne illness associated with oysters carrying these bacteria. From the findings, antibiotic resistance is commonly seen with ampicillin, which prompts further investigation. This research has the potential to be beneficial for influencing safe oyster harvesting practices on the Georgia coast.