Bacterial inactivation by high-pressure homogenisation and high hydrostatic pressure.
The resistance of five gram-positive bacteria, Enterococcus faecalis, Staphylococcus aureus, Lactobacillus plantarum, Listeria innocua and Leuconostoc dextranicum, and six gram-negative bacteria, Salmonella enterica serovar typhimurium, Shigella flexneri, Yersinia enterocolitica, Pseudomonas fluorescens and two strains of Escherichia coli, to high-pressure homogenisation (100-300 MPa) and to high hydrostatic pressure (200-400 MPa) was compared in this study. Within the group of gram-positive bacteria and within the group of gram-negative bacteria, large differences were observed in resistance to high hydrostatic pressure, but not to high-pressure homogenisation. All gram-positive bacteria were more resistant than any of the gram-negative bacteria to high-pressure homogenisation, while in relative to high hydrostatic pressure resistance both groups overlapped. Within the group of gram-negative bacteria, there also existed another order in resistance to high-pressure homogenisation than to high hydrostatic pressure. Further it appears that the mutant E. coli LMM1010, which is resistant to high hydrostatic pressure is not more resistant to high-pressure homogenisation than its parental strain MG1655. The preceding observations indicate a different response of the test bacteria to high-pressure homogenisation compared to high hydrostatic pressure treatment, which suggests that the underlying inactivation mechanisms for both techniques are different. Further, no sublethal injury could be observed upon high-pressure homogenisation of Y. enterocolitica and S. aureus cell population by using low pH (5.5 7), NaCl (0 6%) or SDS (0-100 mg/l) as selective components in the plating medium. Finally, it was observed that successive rounds of high-pressure homogenisation have an additive effect on viability reduction of Y. enterocolitica and S. aureus.
Wuytack
Elke Y
EY
Laboratory of Food Microbiology, Katholieke Universiteit Leuven, Belgium.
Diels
Ann M J
AM
Michiels
Chris W
CW
D015169:Colony Count, Microbial; D006090:Gram-Negative Bacteria / Q000254:growth & development / Q000502:physiology*; D006094:Gram-Positive Bacteria / Q000254:growth & development / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D006874:Hydrostatic Pressure; D011312:Pressure; D012965:Sodium Chloride / Q000494:pharmacology; D012967:Sodium Dodecyl Sulfate / Q000494:pharmacology
D012967:Sodium Dodecyl Sulfate; D012965:Sodium Chloride