Abstract
A laboratory-based study testing 9 Listeria innocua strains independently and a cocktail of 11 Listeria monocytogenes strains was carried out. The aim was to identify suitable L. innocua strain(s) to model L. monocytogenes in inactivation experiments. Three separate inactivation procedures and a hurdle combination of the three were employed: thermal inactivation (55°C), UV-C irradiation (245 nm), and chemical sanitizer (TsunamiTM 100, a mixture of acetic acid, peroxyacetic acid, and hydrogen peroxide). The responses were strain dependent in the case of L. innocua with different strains responding differently to different regimes and L. innocua isolates generally responded differently to the L. monocytogenes cocktail. In the thermal inactivation treatment, inactivation of all strains including the L. monocytogenes cocktail plateaued after 120 min. In the case of chemical sanitizer, inactivation could be achieved at concentrations of 10 and 20 ppm with inactivation increasing with contact time up to 8 min, beyond which there was no significant benefit. All L. innocua strains except PFR16D08 were more sensitive than the L. monocytogenes cocktail to the hurdle treatment. PFR16D08 almost matched the resistance of the L. monocytogenes cocktail but was much more resistant to the individual treatments. A cocktail of two L. innocua strains (PFR 05A07 and PFR 05A10) had the closest responses to the hurdle treatment to those of the L. monocytogenes cocktail and is therefore recommended for hurdle experiments.
Highlights
Listeria monocytogenes is a Gram-positive facultative anaerobe that is found in a range of natural environments, in food-processing environments and in ready-to-eat (RTE) food products
Increasing the dose of UV-C exposure resulted in an increase in killing effect reductions in counts were minor for some strains (e.g., Plant & Food Research Ltd. (PFR) 17G901 and PFR 17F10)
The aim of the present study was to select suitable strain(s) of L. innocua to be used as non-pathogenic surrogates for Listeria innocua strains showing similar responses (p < 0.05) to those of the LM cocktail
Summary
Listeria monocytogenes is a Gram-positive facultative anaerobe that is found in a range of natural environments (including soil, water, and vegetation), in food-processing environments and in ready-to-eat (RTE) food products. The human disease incidence rate has not decreased over the past decades (Lebreton et al, 2016; Buchanan et al, 2017). The incidence of human listeriosis cases caused by L. monocytogenes averages at around 1 per 200,000 people in New Zealand, with an estimated 84.9% of cases being food related (MPI, 2013). Food safety criteria for Listeria monocytogenes in RTE foods was implemented in 2006 in Europe; an increasing trend was noticed in human invasive listeriosis over the period 2009–2013 in the European Union and European Economic Area (EU/EEA). Fresh produce is often eaten raw so the high temperatures that are used to eliminate pathogens from other food products cannot be used, meaning that other control strategies must be found
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