High pressure inactivates V. parahaemolyticus and B. cereus.

High-pressure treatment, also known as high-hydrostatic-pressure processing or ultra-high-pressure processing, involves treating food at elevated pressures of 30,000 psi to 130,000 psi at a specific temperature and for a specified time. This approach inhibits microorganisms by inactivating key enzymes and by making modifications in microbial cell walls and membranes. The pressure has a marked killing effect on foodborne pathogens.

Scientists in Spain evaluated the pressure-induced inactivation and sublethal injury of V. parahaemolyticus CECT 588 and B. cereus vegetative cells CECT 148 in buffered suspensions. They used three different media: nonselective, selective and thin agar layer media (TAL). Bacteria-inoculated (4 logs CFU per mL) 0.1 % buffered peptone water at pH 7.4 was treated at 100 MPa, 200 MPa and 300 MPa for both 1 minute and 5 minutes at 20 C, using a discontinuous isostatic system.

Plate counts were determined on tryptic soy agar (TSA), selective media (thiosulfate-citrate-bile-sucrose [TCBS] agar for V. parahaemolyticus and B. cereus selective medium for B. cereus vegetative cells), and TAL (selective medium overlaid with TSA). The researchers used an additional enrichment step with brain-heart infusion broth at 37 C for 24 hours to confirm the complete inactivation of bacteria.

The scientists added sodium chloride to the media used for V. parahaemolyticus so that the final content was 1%. They found that V. parahaemolyticus counts declined from 4 logs CFU per mL to 0.5 log CFU per mL when treated at 200 MPa for 5 minutes. The counts were nondetectable when using 300 MPa. The organism was totally inactivated when it was treated at 300 MPa for 5 minutes. B. cereus vegetative cells were reduced to 2.5 logs CFU per mL when treated at 300 MPa for 1 minute. They were completely inactivated when they were treated at 300 MPa for 5 minutes.

Plate counts on TAL were generally similar to those on TSA and were greater than those on selective media, especially for V. parahaemolyticus treated at 100 MPa for 1 minute and at 200 MPa for 5 minutes. TSA counts were about 0.5 log CFU per mL higher than TCBS agar counts.

Further information. J. Yuste, Departamento de Ciencia Animal y de los Alimentos, Universitat Autonoma de Barcelona, CER Planta de Tecnologia dels Aliments (CeRTA, XIT), Facultat de Veterinaria, Bellaterra, Barcelona 08193, Spain; phone: [phone]; fax: [phone]; email: [e-mail].