High pressure-induced inactivation of Qβ coliphage and c2 phage in oysters and in culture media

High pressure (HP) treatment inactivates bacteria in shellfish, but its effects on viruses in shellfish have not yet been determined, although viral illness is frequently associated with shellfish consumption. The aim of this study was to investigate the baroresistance of two bacteriophage viruses, Qβ coliphage and c2 phage, in oysters and in culture media. High numbers (≥ 10⁷ ml^{- 1} or g^{- 1}) of both phages were obtained in culture media and in oysters. Samples were HP treated at 200-800 MPa at 20°C for up to 30 min. Little or no inactivation of either phage was observed in oysters or in culture media after treatment at ≤ 400 MPa. High levels of inactivation of both phages in oysters and in culture medium were observed following treatment at 500-700 MPa. Titres of both phages were reduced to non-detectable levels (up to 8 log inactivation) in oysters and in GM17 broth (for c2 phage) after treatment at 800 MPa. The level of Qβ coliphage in tryptone soya broth with yeast extract (10¹⁰ PFU ml^-1) was reduced by ∼ 7 log units following treatment of 800 MPa. Levels of inactivation of both phages in oysters were similar to those in culture media. Increasing the duration of treatment at 550 or 600 MPa increased the level of inactivation of both phages in oysters. HP treatment may effectively inactivate phage in shellfish but HP-induced inactivation of human enteric viruses in oysters needs to be studied directly, to more accurately assess the ability of this technology to inactivate these viruses.