Effect of High Pressure and Heat on Bacterial Toxins

Dirk Margosch¹, Maximilian Moravek², Michael G. Gänzle¹, Erwin Märtlbauer², Rudi F. Vogel¹ and Matthias A. Ehrmann¹*

¹Technische Universität München, Lehrstuhl Technische Mikrobiologie, Weihenstephaner Steig 16, D-85350 Freising, Germany
²Ludwig-Maximilians Universität München, Lehrstuhl für Hygiene und Technologie der Milch, Tierärztliche Fakultät, Schönleutnerstrasse 8, D-85764 Oberschleißheim, Germany

Article history:
Received December 14, 2004
Accepted June 28, 2005

Key words:
high hydrostatic pressure, bacterial toxins, food safety

Summary:
Even though the inactivation of microorganisms by high pressure treatment is a subject of intense investigations, the effect of high pressure on bacterial toxins has not been studied so far. In this study, the influence of combined pressure/temperature treatment (0.1 to 800 MPa and 5 to 121 °C) on bacterial enterotoxins was determined. Therefore, heat-stable enterotoxin (STa) of cholera toxin (CT) from Vibrio cholerae, staphylococcal enterotoxins A-E, haemolysin BL (HBL) from Bacillus cereus, and Escherichia coli (STa) were subjected to different treatment schemes. Structural alterations were monitored in enzyme immunoassays (EIAs). Cytotoxicity of the pressure treated supernatant of toxigenic B. cereus DSM 4384 was investigated with Vero cells. High pressure of 200 to 800 MPa at 5 °C leads to a slight increase of the reactivity of the STa of E. coli. However, reactivity decreased at 800 MPa and 80 °C to (66±21) % after 30 min and to (44±0.3) % after 128 min. At ambient pressure no decrease in EIA reactivity could be observed after 128 min. Pressurization (0.1 to 800 MPa) of heat stable monomeric staphylococcal toxins at 5 and 20 °C showed no effect. A combined heat (80 °C) and pressure (0.1 to 800 MPa) treatment lead to a decrease in the immuno-reactivity to 20 % of its maximum. For cholera toxin a significant loss in latex agglutination was observable only at 80 °C and 800 MPa for holding times higher than 20 min. Interestingly, the immuno-reactivity of B. cereus HBL toxin increased with the increase of pressure (182 % at 800 MPa, 30 °C), and high pressure showed only minor effects on cytotoxicity to Vero cells. Our results indicate that pressurization can increase inactivation observed by heat treatment, and combined treatments may be effective at lower temperatures and/or shorter incubation time.

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