Abstract

   Listeria monocytogenes (L. monocytogenes) is a serious food-borne
   pathogen that can cause listeriosis, an illness caused by eating food
   contaminated with this pathogen. Currently, the treatment or prevention
   of listeriosis is a global challenge due to the resistance of bacteria
   against multiple commonly used antibiotics, thus necessitating the
   development of novel green antimicrobials. Scientists are increasingly
   interested in microbial surfactants, commonly known as
   “biosurfactants”, due to their antimicrobial properties and
   eco-friendly nature, which make them an ideal candidate to combat a
   variety of bacterial infections. Therefore, the present study was
   designed to use a network pharmacology approach to uncover the active
   biosurfactants and their potential targets, as well as the signaling
   pathway(s) involved in listeriosis treatment. In the framework of this
   study, 15 biosurfactants were screened out for subsequent studies.
   Among 546 putative targets of biosurfactants and 244 targets of
   disease, 37 targets were identified as potential targets for treatment
   of L. monocytogenes infection, and these 37 targets were significantly
   enriched in a Gene Ontology (GO) analysis, which aims to identify those
   biological processes, cellular locations, and molecular functions that
   are impacted in the condition studied. The obtained results revealed
   several important biological processes, such as positive regulation of
   MAP kinase activity, protein kinase B signaling, ERK1 and ERK2 cascade,
   ERBB signaling pathway, positive regulation of protein serine/threonine
   kinase activity, and regulation of caveolin-mediated endocytosis.
   Several important KEGG pathways, such as the ERBBB signaling pathway,
   TH17 cell differentiation, HIF-1 signaling pathway, Yersinia infection,
   Shigellosis, and C-type lectin receptor signaling pathways, were
   identified. The protein–protein interaction analysis yielded 10 core
   targets (IL2, MAPK1, EGFR, PTPRC, TNF, ITGB1, IL1B, ERBB2, SRC, and
   mTOR). Molecular docking was used in the latter part of the study to
   verify the effectiveness of the active biosurfactants against the
   potential targets. Lastly, we found that a few highly active
   biosurfactants, namely lichenysin, iturin, surfactin, rhamnolipid,
   subtilisin, and polymyxin, had high binding affinities towards IL2,
   MAPK1, EGFR, PTPRC, TNF, ITGB1, IL1B, ERBB2, SRC, and mTOR, which may
   act as potential therapeutic targets for listeriosis. Overall, based on
   the integrated network pharmacology and docking analysis, we found that
   biosurfactants possess promising anti-listeriosis properties and
   explored the pharmacological mechanisms behind their effect, laying the
   groundwork for further research and development.

   Keywords: Listeria monocytogenes, listeriosis, network pharmacology,
   biosurfactants, antimicrobial

1. Introduction

   More than 200 diseases can be caused in humans by food-borne
   contaminations, which are caused by a variety of factors that are
   involved with the cause and development of disease related to food
   consumption [[46]1]. In this regard, we can point to the increasing
   population of the world, which has led to the subsequent rise in the
   demand for food, as well as microbial genomic diversification and
   selection pressures, resulting in the emergence of new pathogens as a
   result of the growing popularity of eating outside the home [[47]2]. An
   infection caused by the bacterium Listeria monocytogenes (L.
   monocytogenes) is called “listeriosis” and is usually a result of
   eating food that has been contaminated with this food pathogen. In a
   wide range of food products, such as dairy products, raw vegetables,
   and raw meat, as well as ready-to-eat products, this bacterium has been
   found to be present [[48]3]. The L. monocytogenes are a Gram-positive,
   rod-shaped, non-spore forming, non-capsule forming bacteria, which are
   motile at 10 to 25 °C [[49]4]. They can infect a wide range of human
   and animals cell types. Few populations of humans are reported to carry
   the bacterium without showing symptoms in the intestinal tract [[50]5].
   Following the ingestion of bacterium by the host, L. monocytogenes
   first encounters epithelial cells of the gut lining and then enters the
   host’s monocytes, macrophages, or polymorphonuclear leukocytes. The
   bacterium becomes blood-borne and multiplies both intracellularly and
   extracellularly. In pregnant women, it can migrate through the placenta
   to reach the fetus intracellularly [[51]6]. When L. monocytogenes is
   infected in mice, the bacteria first appear in macrophages before
   spreading to liver hepatocytes [[52]7]. Several outbreaks have been
   associated with the consumption of ready-to-eat food, because L.
   monocytogenes is capable of growing at refrigerated temperatures
   [[53]8].

   There are several high-risk populations that are susceptible to
   listeriosis, including the elderly, pregnant women, newborns, and
   immunocompromised patients due to kidney transplant, cancer, HIV/AIDS,
   and steroid therapy [[54]8]. Around the world, there are approximately
   1600 cases of listeriosis each year, and approximately 260 people die
   from it [[55]9]. Despite the fact that there are a small number of
   cases of listeriosis in the world, the high rate of death associated
   with this infection makes it an important public health concern. Due to
   this, there is a need to implement effective medical management for
   listeriosis. Therefore, alternative measures are needed to control L.
   monocytogenes in the food industry.

   Over the past few years, natural products and their derivatives have
   been gaining more and more attention as insights into research and
   possible drug sources for targeted therapy, owing to their variety of
   structural features, multi-target action, and low toxicity [[56]10].
   There have been a great number of dramatic advances in high-throughput
   screening techniques over the past few decades that have greatly
   contributed to the discovery of novel drugs based on natural products
   [[57]11]. Hence, a new discovery of a potential bioactive compound that
   can affect the pathophysiology of diseases and disorders will be
   considered a thunderbolt of this new era of pharmaceuticals.

   Biological surfactants (biosurfactants) are surface active compounds
   which are synthesized by the microbes (bacteria and fungi) on their
   cell surface or excreted that can reduce surface and interfacial
   tension [[58]12]. There is no doubt that biosurfactants are becoming
   more and more popular among scientists because of their
   eco-friendliness properties, scalability, durability under harsh
   environmental conditions, specificity, and versatility, which make them
   appealing for their application in various fields [[59]13]. There are
   numerous applications for these compounds as antimicrobials,
   anti-adhesives, and anticancer agents, in addition to being extensively
   used for the purposes of recovery of oil, bioremediation, and
   emulsification in industry [[60]14].

   In previous studies, biosurfactants have been demonstrated to have
   antimicrobial, antibiofilm, and anti-listeriosis properties
   [[61]13,[62]14,[63]15], suggesting that they could potentially be
   useful for preventing and treating listeriosis. In spite of this, very
   few studies have been published that have examined the use of
   biosurfactants in the prevention and treatment of listeriosis, and no
   research has examined the mechanisms behind their action [[64]15].
   Insights into the mechanisms of action of biosurfactants against
   listeriosis will be possible if studies focusing on molecular targets
   and their related signal pathways are conducted. To accomplish this
   purpose, we utilized network pharmacology [[65]16,[66]17] and a
   molecular docking methodology [[67]18] approach in the present study to
   construct a multidimensional network of
   “component–target–pathway–disease” that is able to explain the
   biological mechanisms underlying biosurfactants for the prevention and
   treatment of listeriosis. It is intended that the results of the
   present study will provide a scientific foundation for clinical trial
   research and the development of biosurfactant products in the future.
   [68]Figure 1 illustrates the flowchart of this study.

Figure 1.

   [69]Figure 1
   [70]Open in a new tab

   Framework based on an integration strategy of network pharmacology.

2. Results

2.1. Identification of Active Components of Biosurfactants

   In total, 15 biosurfactants were selected, and their detailed
   information was retrieved from the PubChem database in order to be
   analyzed, using the SwissTargetPrediction database ([71]Table 1). We
   predicted the potential protein targets of each biosurfactant by using
   SwissTargetPrediction ([72]Figure 2A–F, [73]Figure 3A–F, [74]Figure
   4A–F, and [75]Figure 5A–C). Following the removal of duplicate targets
   from the target prediction, screening of 546 potential targets was
   conducted for further evaluation. A visual compound–target network was
   subsequently constructed by using Cytoscape 3.9.1 in order to construct
   a visual network with 546 nodes and 545 edges ([76]Figure 6A). The
   nodes represent ingredients and their corresponding targets. The higher
   the degree corresponding to the node, the greater the pharmacological
   effects of this ingredient or target. The calculated average shortest
   path length, betweenness centrality, closeness centrality, and degree
   of nodes in the network are shown in [77]Table 2.

Table 1.

   List of biosurfactants.
   Sr. No. Biosurfactant Microbial Origin References Molecular Formula