X-rays may offer benefits to help reduce risk of foodborne illness from oysters

PHILADELPHIA – X-ray irradiation may be beneficial in reducing the rate of foodborne illness associated with the consumption of oysters, according to results of a study presented at the 109th General Meeting of the American Society for Microbiology, held here this week.

Barakat Mahmoud, MD, from Mississippi State University in Pascagoula, and his colleagues, studied the effects of the RS 2400 X-ray irradiator (Rad Source Technologies) on reducing Vibrio vulnificus in half shell and whole shell oysters.

V. vulnificus is associated with the highest fatality rate among foodborne pathogens in the United States, about 40% to 50%, according to CDC data. Mahmoud and his colleagues said this high rate indicates that the current methods to prevent V. vulnificus – including high temperature, freezing, pasteurization, vacuum packaging, UV light, electrolyzed water and hydrostatic high pressure processing – are not adequate to prevent infection.

To test the efficacy of X-rays, the researchers first inoculated both half shell oysters and whole shell live oysters with a mixed culture of three V. vulnificus strains. The pure culture and the inoculated oysters were then treated with 0.1, 0.5, 0.75, 1.0, 1.5, 2.0 and 3.0 kGy X-ray at 22°C and 55% relative humidity. Following this, the researchers measured surviving bacterial populations in the pure culture and the inoculated oysters.

The results demonstrated a reduction of V. vulnificus of more than one million cells per gram with 1.0 kGy X-ray doses in half shell oysters. In whole shell live oysters, this same reduction was achieved with 3.0 kGy X-ray doses. The results also showed that the inherent microflora in the oysters were significantly reduced to less than 10 cells per gram.

The researchers added that X-ray irradiation may offer further benefit because, unlike some other methods to reduce the spread of foodborne illness in oysters, the X-ray treatment did not kill the oysters. – by Jay Lewis

For more information:

Mahmoud B. P-017. Presented at: The 109th General Meeting of the American Society for Microbiology. May 17-21, 2009. Philadelphia