The development of Escherichia coli and Listeria monocytogenes variants resistant to high-pressure carbon dioxide inactivation

Aims: The objective of this study was to investigate whether bacterial cells could develop resistance (as a part of their adaptation strategy) to high-pressure CO2 (HPCD) inactivation. Methods and Results: Alternating cycles of exposure to pressurized CO2 (10 center dot 5 MPa, 35 degrees C, 400 min-1, 70% working volume ratio during 10 min) and re-growth of the surviving subpopulation were used to investigate possible increases in the resistance of Escherichia coli and Listeria monocytogenes to HPCD. The results show an increased resistance of both pathogens tested after seven cycles of inactivation. Increase in the resistance after 15 cycles resulted in a difference of 2 center dot 4 log CFU ml-1 in log N-0/N-i when parental (N-0) and treated cultures (N-i) of E. coli and L. monocytogenes were compared. Conclusions: Current findings indicate the ability of micro-organisms to adapt to HPCD preservation technology. Significance and Impact of the Study: The occurrence of HPCD-resistant micro-organisms could pose a new hazard to the safety and stability of HPCD-processed foods.