The Effect of Water Temperature on Bacteriophage MS-2 Persistence within Live Oysters (C. virginica)

Introduction: Shellfish-borne viruses (i.e., noroviruses) are a challenging problem for raw oyster producers and consumers.  Male-specific (MS) bacteriophages are considered better indicators of fecal impact and potential virus contamination than E. coli.  As such, they are being evaluated by regulatory agencies as a means to access and improve the sanitary quality of raw shellfish.

Purpose: To characterize the ability of viable bacteriophage to persist within oysters as a function of time and holding temperature.

Methods: Oysters were individually exposed to 10⁹ pfu of MS-2 bacteriophage in 500 ml of seawater at 15.5°C for 48 h followed by maintaining oysters within at 7.5, 15.5 or 24°C for up to 6 weeks in 40-liter aquaria containing approximately 25 liters of 28 ppt seawater.  Oysters were evaluated for the presence of viable MS-2 bacteriophage within their meats weekly for 6 weeks.

Results: Log reduction rates of MS-2 bacteriophage within oysters were substantially influenced by water temperature.  Log reductions observed 3 weeks post contamination for oysters were 2.33, 2.90, and 4.55 (N=2; n=6) held at 7.5, 15.5 and 24°C, respectively.  After 6 weeks, observed log reductions were 3.56, 3.99, and non-detected (>5.99) for oysters held at 7.5, 15.5 and 24°C, respectively.

Significance:   Results indicate that water temperature can play an extensive role in retention of MS-2 bacteriophage in seawater.  Water temperatures should be taken into account by regulatory agencies when making management decisions or growing area classifications based on MS bacteriophage.