Inactivation of Vibrio vulnificus in Shucked Oysters Using Natural Antimicrobials

Introduction: Vibrio vulnificus is a gram-negative bacterium, occurring naturally in the Gulf Coast water where the majority of U.S. oysters are harvested. It is the leading cause of foodborne illness associated with the consumption of raw oysters. It has the highest fatality rate (40–50%) among foodborne pathogens in the United States. The CDC estimates 47 foodborne illnesses of V. vulnificus yearly in the U.S., resulting in 18 deaths.

Purpose: The purpose of this investigation was to study the efficacy of citric acid (CA), grape seed extract (GE) and lactic acid (LA) on the inactivation of V. vulnificus to achieve a 5.0 log reduction.

Methods: The minimum inhibitory concentration (MIC) for CA, GE or LA against V. vulnificus was determined. Furthermore, the shucked oysters were artificially inoculated with V. vulnificus. The inoculated shucked oysters (25 g) were then dipped in 250 ml CA, GE or LA solutions (according to the MIC results) for 10 min. The population of V. vulnificus in shucked oysters was determined. The surviving cell population was expressed as log CFU/g. The effects of the treatment with GE, CA, and LA on the inherent microbiota on oysters during storage at 5°C for 20 days were also studied.

Results: The MICs for CA, GE or LA against V. vulnificus were 5.0, 10.0 or 1.0 mg/ml, respectively. The concentration of 300, 500, or 150 mg/ml CA, GE or LA solutions were needed to reduce the population of V. vulnificus to below the detection level (1.0 log/g). Treatment with 500, 300, 150 mg/ml GE, CA, and LA significantly reduced the initial inherent microbiota on oysters and inherent levels were significantly (P < 0.05) lower than the control sample throughout refrigerated storage for 20 days.

Significance: The results of investigation indicated that LA is a strong natural antimicrobial to eliminate V. vulnificus or spoilage bacteria in shucked oysters.