Inactivation of Vibrio parahaemolyticus in pure culture, whole live and half shell oysters (Crassostrea virginica) by X-ray

To study the inactivation effect of different doses of X-ray on Vibrio parahaemolyticus in pure culture, inoculated whole live and half shell oysters and to evaluate the efficacy of X-ray doses on reduction of inherent microflora on oysters. X-ray was produced using RS 2400 generator system (Rad Source Technologies Inc.). Pure culture of V. parahaemolyticus, inoculated half and whole shell oysters with V. parahaemolyticus were treated with 0.0, 0.1, 0.5, 0.75, 1.0, 1.5, 2.0, 3.0 and 5.0 kGy X-ray. Surviving bacteria in the pure culture and inoculated oysters, before and after treatment, were enumerated using overlay plating (in TSA then TCBS) and most probable number (MPN) methods. A greater than 6.0 log reduction of V. parahaemolyticus was observed with 0.75, 2.0 and 5.0 kGy X-ray for pure culture, half shell and whole shell oysters, respectively. Treatment with 0.75, 2.0 and 5.0 kGy X-ray reduced the MPN to < 3 for pure culture, half and whole shell oysters, respectively. Treatment with 1.0 kGy X-ray significantly (P < 0.05) reduced the inherent micro-organisms on whole shell oysters from 4.7 +/- 0.1 to less than the detectable limit (< 1.0 log CFU g(-1)). X-ray (1-5 kGy) significantly (P < 0.05) reduced V. parahaemolyticus and inherent microflora on oysters to less than detectable limit (< 1.0 log CFU g(-1)). Treatment with X-ray could control pathogenic bacteria and extend the shelf life of oysters.