Synergism of Mild Heat and High-Pressure Pasteurization Against Listeria monocytogenes and Natural Microflora in Phosphate-Buffered Saline and Raw Milk

Abstract

As many as 99% of illnesses caused by Listeria monocytogenes are foodborne in nature, leading to 94% hospitalizations, and are responsible for the collective annual deaths of 266 American adults. The current study is a summary of microbiological hurdle validation studies to investigate synergism of mild heat (up to 55 °C) and elevated hydrostatic pressure (up to 380 MPa) for decontamination of Listeria monocytogenes and natural background microflora in raw milk and phosphate-buffered saline. At 380 MPa, for treatments of 0 to 12 min, d-values of 3.47, 3.15, and 2.94 were observed for inactivation of the pathogen at 4, 25, and 50 °C. Up to 3.73 and >4.26 log CFU/mL reductions (p < 0.05) of habituated Listeria monocytogenes were achieved using pressure at 380 MPa for 3 and 12 min, respectively. Similarly, background microflora counts were reduced (p < 0.05) by 1.3 and >2.4 log CFU/mL after treatments at 380 MPa for 3 and 12 min, respectively. Treatments below three min were less efficacious (p ≥ 0.05) against the pathogen and background microflora, in the vast majority of time and pressure combinations. Results of this study could be incorporated as part of a risk-based food safety management system and risk assessment analyses for mitigating the public health burden of listeriosis.

Augmenting the Pressure-Based Pasteurization of Listeria monocytogenes by Synergism with Nisin and Mild Heat

“…The log reduction values (TSA + YE counts) associated with 3, 6, and 9 min treated samples at 400 MPa and at 40 • C were 2.5, 3.6, and 5.2, respectively ( Figure 2B,F). This enhancement in decontamination effectiveness of a high-pressure pasteurization unit in the presence of mild heat is similar to that in recent literature, where L. monocytogenes were reduced more effectively via thermal-assisted pressure pasteurization relative to treatments of elevated hydrostatic pressure at 4 • C [25]. Results of the current study are also in harmony with the previous literature, where it has been shown that a pressure treatment at temperatures around 43 • C could lead to reductions of >5 log CFU for L. monocytogenes [18].…”

“…Treatments of hydrostatic pressure lasting for 3 min are of particular importance since currently the private industry utilizes 3-min treatments for the vast majority of commercially available products [19,20,25]. Under the condition of our experiment at 4 • C, exposure to 400 MPa of high-pressure treatments for 3 min resulted in 1.9 log CFU/mL reductions (p < 0.05) of L. monocytogenes (Figure 1A,D).…”

“…Temperature values of the experiments were controlled by a water jacket made from stainless steel, covering the treatment chamber. The jacket was mechanically linked to a refrigerated circulating water bath (VWR International, Radnor, PA, USA, Model refrigerated 1160s), and temperature values were recorded by a t-type thermocouple (Omega Engineering Inc., Norwalk, CT, USA) as further detailed in our open access recent publications [20,21,25]. Pressure treatments occurred inside the PULSE tubes without disk (Pressure BioScience Inc., Easton, MA, USA) that contained 1.5 mL of inoculated PBS with or without presence of the antimicrobial.…”

Fate and Biofilm Formation of Wild-Type and Pressure-Stressed Pathogens of Public Health Concern in Surface Water and on Abiotic Surfaces

“…A four-strain mixture of L. monocytogenes (ATCC®numbers 51772, 51779, BAA-2657, and 13932), six-strain mixture of E. coli O157:H7 (ATCC®numbers BAA-460, 43888, 43894, 35150, 43889, 43890), and five-strain mixture of non-typhoidal Salmonella enterica serovars (ATCC®numbers 13076, 8387, 6962, 9270, 14028) were used in this study. The strains are selected based on preliminary data and their epidemiological and public health significance that are elaborated in detail in our recent open access publications [13][14][15][16]. These strain mixtures were used for inoculation of Cumberland river (Nashville, TN) water samples that were autoclaved for 15 min at 121 • C (MLS3781L-PA model, PHC Corporation of North America, Wood Dale, IL, USA).…”

“…While the effects of an array of stressors are investigated and reviewed in the literature [12], there is currently a knowledge gap for the assimilation of the effects of sub-lethal exposure to elevated hydrostatic pressure on the fate and biofilm formation of an array of microbial pathogens. This is of particular importance since the utilization of elevated hydrostatic pressure is gaining increasing importance and momentum in food manufacturing [13][14][15][16]. Information about the survival and biofilm formation of the pressure-stressed phenotype of the main microbial pathogens is critical to assure existing validation studies conducted using wild-type phenotypes are capable of controlling the pressure-stressed phenotypes of the pathogens as well.…”