Management of Listeria monocytogenes on Surfaces via Relative Air Humidity: Key Role of Cell Envelope

Abstract

Although relative air humidity (RH) strongly influences microbial survival, its use for fighting surface pathogens in the food industry has been inadequately considered. We asked whether RH control could destroy Listeria monocytogenes EGDe by envelope damage. The impact of dehydration in phosphate-buffered saline (PBS) at 75%, 68%, 43% and 11% RH on the bacterial envelope was investigated using flow cytometry and atomic force microscopy. Changes after rehydration in the protein secondary structure and peptidoglycan were investigated by infrared spectroscopy. Complementary cultivability measurements were performed by running dehydration–rehydration with combinations of NaCl (3–0.01%), distilled water, city water and PBS. The main results show that cell membrane permeability and cell envelope were greatly altered during dehydration in PBS at 68% RH followed by rapid rehydration. This damage led cells to recover only 67% of their initial volume after rehydration. Moreover, the most efficient way to destroy cells was dehydration and rehydration in city water. Our study indicates that rehydration of dried, sullied foods on surfaces may improve current cleaning procedures in the food industry.

Isolation of Listeria ivanovii from Bulk-Tank Milk of Sheep and Goat Farms—From Clinical Work to Bioinformatics Studies: Prevalence, Association with Milk Quality, Antibiotic Susceptibility, Predictors, Whole Genome Sequence and Phylogenetic Relationships

“…The results of previous studies regarding the potential effects of relative humidity on L. monocytogenes are conflicting, whilst no relevant studies for L. ivanovii are available. In food-related matrices, relative humidity in the range from 43% to 68% was found to adversely affect the viability of the bacteria [ 85 , 86 ] as the result of changes in the permeability of the bacterial membrane [ 86 ]. In contrast, in an experimental study that assessed viability of L. monocytogenes in the environment, this was found to be best at a relative humidity of around 50% (i.e., close to the mean relative humidity of the four farms where L. monocytogenes or L. ivanovii was isolated, which was 55.5%), irrespective of the temperature [ 87 ].…”