## 1 Introduction  
Food preservation strategies to which foodborne pathogens are subjected throughout the food chain may result in physiological alterations of varying degrees, i.e., sublethal injury (SI) [1,2]. [PERSON] [3] defined SI as \"a consequence of exposure to a chemical or physical process that damages but does not kill a microorganism\". Since the selective media which are commonly used to detect pathogenic microorganisms are unable to support the growth of sublethally injured target microorganisms, SI causes serious limitations in food diagnostics due to the possible underestimation of contamination and false negative results [2]. Moreover, injured microorganisms might be able to recover and exhibit enhanced resistance to antimicrobial treatments [1]. Cells can become sublethally injured due to the specific food environment, processing or preservation technologies, and the injury can be either structural (i.e., altered membrane permeability), metabolic (i.e., damage to functional cell components), or a combination of both [1].  
Various preservation technologies are used to prevent the outgrowth of pathogens in food products. Nowadays, consumers show an increased interest in natural, nutritious, minimally processed food products, which are still safe to eat. Most traditional food preservation technologies fail to succeed in retaining the nutritional aspects of foods (e.g., loss of vitamins), resulting in a need for novel food preservation technologies [4]. Recently, food researchers are investigating natural antimicrobial compounds like natural plant extracts as possible alternatives [5; 6]. Grape seed extract (GSE) and garlic extract (GE) are examples of natural plant extracts which have shown promising antimicrobial effects [7; 8]. GSE and GE owe their antimicrobial properties to phenolic compounds [9] and allicin (an oxygenated organic sulfur compound) [10], respectively.  
Among the common foodborne pathogens, _Listeria monocytogenes_ is very relevant for the validation of antimicrobial treatments due to its high resistance to various stresses [11]. Furthermore, the bacterium is especially dangerous due to its high fatality rate, e.g., 13.8% of infected people died in Europe in 2017 [12]. Symptoms of the disease range from mild clinical features like fever and diarrhea to severe infections like meningitistis and septicemia [13]. Both GSE and GE are commonly investigated for novel multiple-hurdle applications against _L. monocytogenes_. In this regard, GSE is studied for its antilisterial effect in edible antimicrobial food coatings [14; 15; 16; 17] and as a preservative replacement in food products [18; 19]. An example of a novel application of GE is the encapsulation of the extract in order to overcome common applicability limitations of allicin, e.g., heat sensitivity and strong odor [20; 21; 22].  
Despite the extensive amount of studies that focused on promising novel antibacterial applications of natural plant extracts like GSE and GE, none of these (to the best knowledge of the authors) took into account the effect of those extracts on SI of _Listeria_. Consequently, the antibacterial (i.e., growth inhibition or inactivation) effect of those novel applications could be overestimated, leading to serious food safety issues. In this study, the separate effect of GSE and GE on the occurrence of SI in _L. monocytogenes_ was therefore investigated, both for the pure extracts and the extracts at their minimum inhibitory concentration (MIC). The extracts at their MIC and the pure extracts were used to simulate applications resulting in growth reduction and inactivation (of _L. monocytogenes_), respectively. In order to understand the nature of the sublethal injury caused by the extracts, possible membrane damage was investigated using propidium iodide (PI) staining.