Image analysis based quantification of bacterial volume change with high hydrostatic pressure.

Area of Science:

• Microbiology
• Biophysics
• Food Science

Background:

• High pressure processing (HPP) is a non-thermal technology used for microbial inactivation.
• Understanding the effects of HPP on bacterial cell structure is crucial for optimizing food safety.
• Staphylococcus aureus and Escherichia coli are common foodborne pathogens with different pressure sensitivities.

Purpose of the Study:

• To investigate the morphological changes in Staphylococcus aureus and Escherichia coli following high pressure treatments.
• To quantify the impact of varying pressure levels on bacterial cell volume and surface area.
• To correlate observed morphological changes with potential alterations in cell membrane properties.

Main Methods:

• Scanning electron microscopy (SEM) was employed to visualize bacterial cells.
• Specific strains of Staphylococcus aureus (485) and Escherichia coli (O157:H7 933) were subjected to pressure treatments ranging from 200 to 400 MPa.
• Custom software was utilized to analyze SEM images and calculate changes in cell view area and volume.

Main Results:

• Significant increases in average cell view area and volume were observed for Staphylococcus aureus at 400 MPa.
• Escherichia coli O157:H7 showed significant increases in cell view area and volume at 325 MPa.
• Notably, Escherichia coli O157:H7 exhibited significant morphological changes at a lower pressure (200 MPa) compared to Staphylococcus aureus.

Conclusions:

• High pressure processing induces significant morphological alterations in Staphylococcus aureus and Escherichia coli.
• The observed increase in cell volume and area suggests pressure-induced damage to the bacterial cell membrane.
• Differences in pressure sensitivity between the two bacterial species may be linked to variations in membrane composition and protein structure.