Abstract
Relative air humidity fluctuations could potentially affect the development and persistence of pathogenic microorganisms in their environments. This study aimed to characterize the impact of relative air humidity (RH) variations on the survival of Listeria monocytogenes, a bacterium persisting on food processing plant surfaces. To assess conditions leading to the lowest survival rate, four strains of L. monocytogenes (EGDe, CCL500, CCL128, and LO28) were exposed to different RH conditions (75%, 68%, 43% and 11%) with different drying kinetics and then rehydrated either progressively or instantaneously. The main factors that affected the survival of L. monocytogenes were RH level and rehydration kinetics. Lowest survival rates between 1% and 0.001% were obtained after 3 hours of treatment under optimal conditions (68% RH and instantaneous rehydration). The survival rate was decreased under 0.001% after prolonged exposure (16h) of cells under optimal conditions. Application of two successive dehydration and rehydration cycles led to an additional decrease in survival rate. This preliminary study, performed in model conditions with L. monocytogenes, showed that controlled ambient RH fluctuations could offer new possibilities to control foodborne pathogens in food processing environments and improve food safety.
Highlights
Listeria monocytogenes, the causative agent of listeriosis, is an ubiquitous Gram-positive bacterium distributed in many environments [1,2,3,4] and is frequently isolated in food processing environments or in raw food products [5,6,7,8,9]
relative air humidity (RH) level and drying kinetics affect the survival of L. monocytogenes
Viability kinetics of CCL500, LO28, EGDe, and CCL128 L. monocytogenes strains at 75%, 68%, 43%, and 11% RH in ventilated hermetic boxes for 180 min at 25°C were studied, and in parallel, evaporation of water was measured by weight loss (Fig 1)
Summary
The causative agent of listeriosis, is an ubiquitous Gram-positive bacterium distributed in many environments [1,2,3,4] and is frequently isolated in food processing environments or in raw food products [5,6,7,8,9]. L. monocytogenes is adapted to many otherwise stressful environmental conditions as reviewed by Gandhi and Chikindas (2007) [15] It can grow in high salt concentrations of up to 10% NaCl [16], tolerates low-pH environments [16], and grows in a wide range of temperatures (2°C to 45°C) [15] [17]. L. monocytogenes can be persistent in food industry environments where it can survive for several months or years [18,19,20]. This ability to persist and multiply makes contamination by L. monocytogenes difficult to control and eradicate. Food-processing facilities must be designed carefully, with an emphasis on effective cleaning and disinfection operations in the production line
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