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. 2023 Nov 29;89(11):e0060223.
doi: 10.1128/aem.00602-23. Epub 2023 Oct 24.

Acid adaptation increased the resistance of Escherichia coli O157:H7 in bok choy (Brassica rapa subsp. chinensis) juice to high-pressure processing

Andrea Koo  1   2 , Vinayak Ghate  2 , Weibiao Zhou  1   2
Affiliations

Acid adaptation increased the resistance of Escherichia coli O157:H7 in bok choy (Brassica rapa subsp. chinensis) juice to high-pressure processing

Andrea Koo et al. Appl Environ Microbiol. .

Abstract

Based on the U.S. Food and Drug Administration regulations, E. coli O157:H7 is a pertinent pathogen in high acid juices that needs to be inactivated during the pasteurization process. The results of this study suggest that the effect of acid adaptation should be considered in the selection of HPP parameters for E. coli O157:H7 inactivation to ensure that pasteurization objectives are achieved.

Keywords: Escherichia coli O157:H7; acid adaptation; alkaline phosphatase; differential fluorescent staining; flow cytometry; sublethal injury.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig 1
Fig 1
Effect of HPP at 400 MPa for 2 min on three strains of non-adapted and acid-adapted E. coli O157:H7 cells. An asterisk (*) indicates a statistically significant difference between non-adapted and acid-adapted cells for each strain (P < 0.05). Different letters indicate a statistically significant difference among the log reduction values across the three strains and treatments (P < 0.05).
Fig 2
Fig 2
Inactivation curves of non-adapted and acid-adapted E. coli O157:H7 at 400 MPa. Curves were fitted based on first-order kinetics. An asterisk (*) indicates a statistically significant difference between non-adapted and acid-adapted cells at each specific time point (P < 0.05).
Fig 3
Fig 3
Reduction in total survivors during storage at 4°C normalized based on survivor counts immediately post processing. An asterisk (*) indicates a statistically significant difference between non-adapted and acid-adapted cells after treatment at 400 MPa for 1 min at each specific time point (P < 0.05). Log counts of untreated cells did not change during storage (P > 0.05).
Fig 4
Fig 4
Changes in membrane integrity and function of non-adapted and acid-adapted E. coli O157:H7 during treatment at 400 MPa. (a) Loss of membrane integrity measured with SYTO9/PI. (b) Loss of efflux pump activity measured with SYTO9/EtBr. (c) Loss of glucose uptake activity measured with 2-NBDG. Different letters indicate a statistically significant difference across the pressure holding times and treatments (P < 0.05).
Fig 5
Fig 5
Sublethal injury in non-adapted and acid-adapted cells after treatment at 400 MPa for 1 min in the presence of metabolic inhibitors. An asterisk (*) indicates a statistically significant difference between non-adapted and acid-adapted cells (P < 0.05). NS indicates that no significant differences were observed between plate counts on selective and non-selective media (P > 0.05).
Fig 6
Fig 6
Loss of alkaline phosphatase activity in non-adapted and acid-adapted E. coli O157:H7 during treatment at 400 MPa. Different letters indicate a statistically significant difference across the pressure holding times and treatments (P < 0.05).
Fig 7
Fig 7
Schematic summarizing the possible mechanisms on how the acid adaptive response may confer cross-resistance against HPP.
See this image and copyright information in PMC

References

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