## 7 Discussion and Future Perspectives
Indeed, some studies reported that immediately after HPP with different combinations of pressure values (200-600 MPa), times of exposure (3-30 min), temperatures (4-45 \({}^{\circ}\)C), and storage duration and temperature (14-75 days; 4-37 \({}^{\circ}\)C), culturable _L. monocytogenes_ was not detected but grew during storage, suggesting a possible VBNC state induction. However, none of those studies utilized appropriate methods to demonstrate this hypothesis [60]. Other physical treatment methods, e.g., radiofrequency and microwave applied to control microorganisms in a variety of products, must still be evaluated for the ability to induce the VBNC status [59]. A few studies reviewed here regarded the detection of VBNC cells of _L. monocytogenes_ directly in food and on contact surfaces in food production plants after cleaning and disinfection, highlighting the presence of VBNC cells of the pathogen [17; 36; 45; 48]. The findings strongly suggested that many more food categories and processes still need to be evaluated for the induction of VBNC _L. monocytogenes_ and the levels of these forms of the pathogen. Indeed, it is important to note that in a study regarding RTE salad, the number of VBNC cells was higher than the law limit of acceptability for the pathogen at the end of the shelf-life period fixed on the basis of the standard culture method [17]. This result, together with different confirmations that food matrices such as fresh-cut carrots can favor _L. monocytogenes_ VBNC formation [52; 53], clearly indicated the necessity to use methods alternative to the culture-dependent ones to determine the presence of viable _L. monocytogenes_. An example is given by apples with or without wax coating, on which a decrease in count for three major disease-causing serotypes, 1/2a, 1/2b, and 4b of _L. monocytogenes_, was observed at 1 \({}^{\circ}\)C and at room temperature, but it was not elucidated if the reduction was due to death or to the transition to the VBNC state [61]. The strong capacity to form biofilms is a characteristic of some _L. monocytogenes_ strains such as _L. monocytogenes_ EGD-e, and it is favored by endotoxin proteins for initial adhesion and the SecA2 protein export pathway for structure formation and cell-cell interactions. In food processing environments, _L. monocytogenes_ can form mixed biofilms with _E. coli_, _Pseudomonas aeruginosa_, _Staphylococcus aureus_, _Lactiplantibacillus plantarum_, and _Vibrio parahaemolyticus_ that cause food spoilage and cross-contamination. Biofilm formation is one of the main mechanisms for _L. monocytogenes_ persistence in food production plants; so, applying effective cleaning and disinfection treatments to destroy and prevent biofilm formation in food manufacturing plants is a necessity. In addition, the presence of VBNC cells in the biofilm was reported [49]. These insidious persistent forms of _L. monocytogenes_ can be efficiently contrasted only by adopting multiple hurdles, since physical treatments provide insufficient sterilization effects on biofilms, biological techniques are expensive and poorly stable, and chemical sanitizers induce pathogen tolerance and leave residues [33]. Baicalin, the 7-O-glucuronide flavonoid derived from the roots of _Scutellaria bialensis_ and an inhibitor of AI-2 in biofilm-forming bacteria, and postbiotics, which are metabolites derived from probiotics and showed great potential against biofilm-forming bacteria [62], bacteriophages, or their recombinant endolysins [59], should be tested also against _L. monocytogenes_ biofilms and in the prevention of VBNC formation. The studies analyzing resuscitation came to different conclusions on the regain of culturability by VBNC _L. monocytogenes_ even when the same non-selective culture media were used [19; 47]. The discrepancies could be due to the different stages of the VBNC state for the cells tested, the different lengths of incubation time, and differences in the medium composition that can depend on the preparation procedures and ingredient quality.