Application of Chitosan Microparticles for the Reduction of Vibrio Species

Introduction: Vibrios are Gram-negative bacteria that commonly occur in costal estuarine environments. V. vulnificus (Vv), V. parahaemolyticus (Vp), and V. cholerae (Vc) are the principle pathogens and cause at least 75% bacterial seafood-borne disease in the U.S. Consumption of undercooked seafood, especially raw oysters, can result in a severe systemic vibriosis. The primary response by the seafood industry to reduce Vibrios relies on the implementation of postharvest processing (PHP), including thermal treatments and high hydrostatic pressure. Although effective, currently approved PHP will also kill the oysters and is not suitable for the live “half shell” market.

Purpose: This study investigated the efficacy of chitosan microparticles (CM) for reduction of Vv, Vp and Vc both in vitro and in live oysters.

Methods: The three Vibrio species were inoculated (ca. 10⁴ CFU/ml) into nutrient medium with different concentrations of CM (0, 0.1, 0.3, and 0.5%) to determine effects on growth over 12 h. Artificial seawater (ASW) was also inoculated (ca. 10⁷ CFU/ml) to examine vibrio survival over 48 h when exposed to the above concentrations of CM. Live oysters maintained in ASW (16ppt) at room temperature and were similarly exposed to CM for 48 h. All samples were processed, serially diluted and spread plated to culture media to enumerate viable bacteria.

Results: Growth of all species was completely inhibited within 3 hours of treatment with 0.3% and 0.5% CM. Furthermore, treatment with 0.5% CM successfully reduced all species by 7.5 log CFU/ml in ASW by 48h. Vv was the most sensitive to CM treatment, while Vc was the most resistant. Numbers of Vibrios also significantly declined (P = 0.012) in treated oyster samples (0.1, 0.3 and 0.5% CM) compared with untreated controls.

Significance: These results show that CM treatment might be an effective postharvest process to reduce spoilage or pathogenic microbial risks in seafood industry.