Real-time investigation of antibiotics-induced oxidative stress and superoxide release in bacteria using an electrochemical biosensor

Real-time monitoring of cellular superoxide anion release in THP-1 cells using a catalytically amplified superoxide dismutase-based microbiosensor

Reactive oxygen species (ROS) including the superoxide anion (O2•-) are typically studied in cell cultures using fluorescent dyes, which provide only discrete single-point measurements. These methods lack the capabilities for assessing O2•- kinetics and release in a quantitative manner over long monitoring times. Herein, we present the fabrication and application of an electrochemical biosensor that enables real-time continuous monitoring of O2•- release in cell cultures for extended periods (> 8 h) using an O2•- specific microelectrode. To achieve the sensitivity and selectivity requirements for cellular sensing, we developed a biohybrid system consisting of superoxide dismutase (SOD) and Ti3C2Tx MXenes, deposited on a gold microwire electrode (AuME) as O2•- specific materials with catalytic amplification through the synergistic action of the enzyme and the biomimetic MXenes-based structure. The biosensor demonstrated a sensitivity of 18.35 nA/μM with a linear range from 147 to 930 nM in a cell culture medium. To demonstrate its robustness and practicality, we applied the biosensor to monitor O2•- levels in human leukemia monocytic THP-1 cells upon stimulation with lipopolysaccharide (LPS). Using this strategy, we successfully monitored LPS-induced O2•- in THP-1 cells, as well as the quenching effect induced by the ROS scavenger N-acetyl-L-cysteine (NAC). The biosensor is generally useful for exploring the role of oxidative stress and longitudinally monitoring O2•- release in cell cultures, enabling studies of biochemical processes and associated oxidative stress mechanisms in cellular and other biological environments.

Listeria monocytogenes in beef: a hidden risk

Listeria monocytogenes in beef receives less attention compared to other pathogens such as Salmonella and Escherichia coli. To address this gap, we conducted a literature review focusing on the presence of L. monocytogenes in beef. This review encompasses the pathogenic mechanisms, routes of contamination, prevalence rates, and the laws and regulations employed in various countries. Our findings reveal a prevalence of L. monocytogenes in beef and beef products ranging from 2.5% to 59.4%. Notably, serotype 4b was most frequently isolated in cases of beef contamination during food processing, with the skinning and evisceration stages identified as critical points of contamination.

Deterministic effect of oxygen level variation on shaping antibiotic resistome

An increase in acquisition of antibiotic resistance genes (ARGs) by pathogens under antibiotic selective pressure poses public health threats. Sub-inhibitory antibiotics induce bacteria to generate reactive oxygen species (ROS) dependent on dissolved oxygen (DO) levels, while molecular connection between ROS-mediated ARG emergence through DNA damage and metabolic changes remains elusive. Thus, the study investigates antibiotic resistome dynamics, microbiome shift, and pathogen distribution in hyperoxic (5-7 mg L-1), normoxic (2-4 mg L-1), and hypoxic (0.5-1 mg L-1) conditions using lab-scale bioreactor. Composite inoculums in the reactor were designed to represent comprehensive microbial community and AR profile from selected activated sludge. RT-qPCR and metagenomic analysis showed an increase in ARG count (100.98 ppm) with enrichment of multidrug efflux pumps (acrAB, mexAB) in hyperoxic condition. Conversely, total ARGs decreased (0.11 ppm) under hypoxic condition marked by a major decline in int1 abundance. Prevalence of global priority pathogens increased in hyperoxic (22.5%), compared to hypoxic (0.9%) wherein major decrease were observed in Pseudomonas, Shigella, and Borrelia. The study observed an increase in superoxide dismutase (sodA, sodB), DNA repair genes (nfo, polA, recA, recB), and ROS (10.4 µmol L-1) in adapted biomass with spiked antibiotics. This suggests oxidative damage that facilitates stress-induced mutagenesis providing evidence for observed hyperoxic enrichment of ARGs. Moreover, predominance of catalase (katE, katG) likely limit oxidative damage that deplete ARG breeding in hypoxic condition. The study proposes a link between oxygen levels and AR development that offers insights into mitigation and intervention of AR by controlling oxygen-related stress and strategic selection of bacterial communities.

Direct real-time measurements of superoxide release from skeletal muscles in rat limbs and human blood platelets using an implantable Cytochrome C microbiosensor

Oxidative stress and excessive accumulation of the superoxide (O2.-) anion are at the genesis of many pathological conditions and the onset of several diseases. The real time monitoring of (O2.-) release is important to assess the extent of oxidative stress in these conditions. Herein, we present the design, fabrication and characterization of a robust (O2.-) biosensor using a simple and straightforward procedure involving deposition of a uniform layer of L-Cysteine on a gold wire electrode to which Cytochrome C (Cyt c) was conjugated. The immobilized layers, studied using conductive Atomic Force Microscopy (c-AFM) revealed a stable and uniformly distributed redox protein on the gold surface, visualized as conductivity and surface topographical plots. The biosensor enabled detection of (O2.-) at an applied potential of 0.15 V with a sensitivity of 42.4 nA/μM and a detection limit of 2.4 nM. Utility of the biosensor was demonstrated in measurements of real time (O2.-) release in activated human blood platelets and skeletal rat limb muscles following ischemia reperfusion injury (IRI), confirming the biosensor's stability and robustness for measurements in complex biological systems. The results demonstrate the ability of these biosensors to monitor real time release of (O2.-) and estimate the extent of oxidative injury in models that could easily be translated to human pathologies.

Electrochemical Sensors for the Detection of Reactive Oxygen Species in Biological Systems: A Critical Review

Reactive oxygen species (ROS) involving superoxide anion, hydrogen peroxide and hydroxyl radical play important role in human health. ROS are known to be the markers of oxidative stress associated with different pathologies including neurodegenerative and cardiovascular diseases, as well as cancer. Accordingly, ROS level detection in biological systems is an essential problem for biomedical and analytical research. Electrochemical methods seem to have promising prospects in ROS determination due to their high sensitivity, rapidity, and simple equipment. This review demonstrates application of modern electrochemical sensors for ROS detection in biological objects (e.g., cell lines and body fluids) over a decade between 2011 and 2021. Particular attention is paid to sensors materials and various types of modifiers for ROS selective detection. Moreover, the sensors comparative characteristics, their main advantages, disadvantages and their possibilities and limitations are discussed.

Effect of a synbiotic supplement as an antibiotic alternative on broiler skeletal, physiological, and oxidative parameters under heat stress

The aim of this study was to examine if synbiotics can function as alternatives to antibiotics in broiler production under heat stress (HS). Day-old broiler chicks (528 birds) were randomly placed in floor pens within 2 identical temperature-controlled rooms (11 birds/pen and 24 pens/room). The pens of each room were evenly divided among 3 treatments (n = 8): basal diet (CON), the basal diet mixed with 50 ppm of bacitracin methylene disalicylate (BMD) or a synbiotic (50 ppm of PoultryStar me^US, SYN). From d 15, room 2 was under thermoneutral (TN) conditions (TN-CON, TN-BMD, and TN-SYN), while HS was applied to room 1 at 32^oC for 9 hrs/d (0800 to 1700) (HS-CON, HS-BMD, and HS-SYN). Treatment effects on footpad dermatitis and gait score were measured on 5 birds/pen, and latency to lie (LTL) test was measured on 2 birds/pen at d 27 and d 41; and 1 broiler/pen was sampled on d 28 and d 42, respectively. Body, liver, and spleen weight were determined. Plasma levels of interleukins (IL), heat shock protein 70, immunoglobulin (Ig)Y, liver superoxide dismutase (SOD) and glutathione peroxidase (GPx) enzyme activities were examined. Heat stress suppressed BW and IgY concentrations on both d 28 and d 42, while suppressed plasma IL-6 concentrations, SOD activities, and LTL duration on d 28 only (P < 0.05). Among all treatments, SYN birds had the best foot and skeletal health scores on both d 27 and d 41 (P < 0.05). On d 42, SYN increased BW, and TN-SYN birds had higher relative spleen weight than both TN-BMD and TN-CON birds (P < 0.05). Antibiotic BMD increased BW (P < 0.05) but decreased SOD activities (P < 0.05) on d 42. These results indicate that the SYN supplementation decreases HS negative effect on broilers by improving BW, foot, and skeletal health, while BMD improves BW but also increases oxidative stress in broilers. The data suggest that synbiotic supplement may function as an alternative to antibiotics in broiler production during summer seasons, especially in the tropical and subtropical regions.

Effects of 4-epianhydrotetracycline on oxidative stress in zebrafish (Danio rerio) embryos

4-Epianhydrotetracycline (4-EATC) is a major intermediate product of tetracycline during its degradation progress in the natural environment, which is frequently detected in aquatic environments and poses a potential threat to aquatic organisms. In the present study, the ecotoxicity of 4-EATC have been studied from the perspective of oxidative stress by using zebrafish embryos. After 96 h exposure, the reactive oxygen species (ROS) levels, malondialdehyde (MDA) concentrations and protein carbonyl (PC) contents in zebrafish embryos in the lower-concentration 4-EATC treatment groups (1.25 mg/L and 2.50 mg/L) showed no significant differences compared with the negative control group. However, the total superoxide dismutase (SOD) activity was increased significantly. After exposed to the higher-concentration of 4-EATC (5.00, 10.0 and 20.0 mg/L) resulted in a significant increase in ROS levels, MDA concentrations and PC contents, in contrast, a significant decrease in SOD activities. The results indicate that exposure to high concentrations of 4-EATC (5.00, 10.0 and 20.0 mg/L) could disrupt the redox equilibrium in zebrafish embryos, leading to the occurrence of oxidative damage. Apoptosis of the embryonic cells could be induced by 4-EATC exposure at different concentration and the rate of apoptosis enhanced with the increase of 4-EATC concentration. The pericardium was the most frequent site of apoptosis. The present study points out that more attention should be paid to the potential ecological risks of antibiotic degradation products.

Mediated electrochemistry for redox-based biological targeting: entangling sensing and actuation for maximizing information transfer

Biology and electronics are both expert at receiving, analyzing, and responding to information, yet they use entirely different information processing paradigms. Biology processes information using networks that are intrinsically molecular while electronics process information through circuits that control the flow of electrons. There is great interest in coupling the molecular logic of biology with the electronic logic of technology, and we suggest that redox (reduction-oxidation) is a uniquely suited modality for interfacing biology with electronics. Specifically, redox is a native biological modality and is accessible to electronics through electrodes. We summarize recent advances in mediated electrochemistry to direct information transfer into biological systems intentionally altering function, exposing it for more advanced interpretation, which can dramatically expand the biotechnological toolbox.

Decreased Antibiotic Susceptibility in Pseudomonas aeruginosa Surviving UV Irradition

Given its excellent performance against the pathogens, UV disinfection has been applied broadly in different fields. However, only limited studies have comprehensively investigated the response of bacteria surviving UV irradiation to the environmental antibiotic stress. Here, we investigated the antibiotic susceptibility of Pseudomonas aeruginosa suffering from the UV irradiation. Our results revealed that UV exposure may decrease the susceptibility to tetracycline, ciprofloxacin, and polymyxin B in the survival P. aeruginosa. Mechanistically, UV exposure causes oxidative stress in P. aeruginosa and consequently induces dysregulation of genes contributed to the related antibiotic resistance genes. These results revealed that the insufficient ultraviolet radiation dose may result in the decreased antibiotic susceptibility in the pathogens, thus posing potential threats to the environment and human health.

Real-time monitoring of cellular oxidative stress during aerosol sampling: a proof of concept study

The Portable In Vitro Exposure Cassette (PIVEC) was developed for on-site air quality testing using lung cells. Here, we describe the incorporation of a sensor within the PIVEC for real time monitoring of cellular oxidative stress during exposure to contaminated air. An electrochemical, enzymatic biosensor based on cytochrome c (cyt c) was selected to measure reactive oxygen species (ROS), including hydrogen peroxide and super oxides, due to the stability of signal over time. Human A549 lung cells were grown at the air-liquid interface and exposed within the PIVEC to dry 40 nm copper nanoparticle aerosols for 10 minutes. The generation of ROS compounds was measured during exposure and post-exposure for one hour using the biosensor and compared to intracellular ROS determined using the 2',7'-dichlorodihydrofluoroscein diacetate (DCFH-DA) assay. A similar increase in oxidative stress upon aerosol exposure was measured using both the cyt c biosensor and DCFH-DA assay. The incorporation of a biosensor within the PIVEC is a unique, first-of-its-kind system designed to monitor the real-time effect of aerosols.

Development of antiseptic adaptation and cross-adapatation in selected oral pathogens in vitro

There is evidence that pathogenic bacteria can adapt to antiseptics upon repeated exposure. More alarming is the concomitant increase in antibiotic resistance that has been described for some pathogens. Unfortunately, effects of adaptation and cross-adaptation are hardly known for oral pathogens, which are very frequently exposed to antiseptics. Therefore, this study aimed to determine the in vitro increase in minimum inhibitory concentrations (MICs) in oral pathogens after repeated exposure to chlorhexidine or cetylpyridinium chloride, to examine if (cross-)adaptation to antiseptics/antibiotics occurs, if (cross-)adaptation is reversible and what the potential underlying mechanisms are. When the pathogens were exposed to antiseptics, their MICs significantly increased. This increase was in general at least partially conserved after regrowth without antiseptics. Some of the adapted species also showed cross-adaptation, as shown by increased MICs of antibiotics and the other antiseptic. In most antiseptic-adapted bacteria, cell-surface hydrophobicity was increased and mass-spectrometry analysis revealed changes in expression of proteins involved in a wide range of functional domains. These in vitro data shows the adaptation and cross-adaptation of oral pathogens to antiseptics and antibiotics. This was related to changes in cell surface hydrophobicity and in expression of proteins involved in membrane transport, virulence, oxidative stress protection and metabolism.

Heterogeneity of ROS levels in antibiotic-exposed mycobacterial subpopulations confers differential susceptibility

Phenotypically heterogeneous but genetically identical mycobacterial subpopulations exist in in vitro cultures, in vitro-infected macrophages, infected animal models and tuberculosis patients. In this regard, we recently reported the presence of two subpopulations of cells, which are phenotypically different in length and buoyant density, in mycobacterial cultures. These are the low-buoyant-density short-sized cells (SCs), which constitute ~10-20 % of the population, and the high-buoyant-density normal/long-sized cells (NCs), which form ~80-90 % of the population. The SCs were found to be significantly more susceptible to rifampicin (RIF), isoniazid (INH), H2O2 and acidified nitrite than the NCs. Here we report that the RIF-/INH-/H2O2-exposed SCs showed significantly higher levels of oxidative stress and therefore higher susceptibility than the equivalent number of exposed NCs. Significantly higher levels of hydroxyl radical and superoxide were found in the antibiotic-exposed SCs than in the equivalently exposed NCs. Different proportions of the subpopulation of SCs were found to have different levels of reactive oxygen species (ROS). The hydroxyl radical quencher, thiourea, and the superoxide dismutase mimic, TEMPOL, significantly reduced hydroxyl radical and superoxide levels, respectively, in the antibiotic-exposed SCs and NCs and thereby decreased their differential susceptibility to antibiotics. Thus, the present study shows that the heterogeneity of the reactive oxygen species (ROS) levels in these mycobacterial subpopulations confers differential susceptibility to antibiotics. We have discussed the possible mechanisms that can generate differential ROS levels in the antibiotic-exposed SCs and NCs. The present study advances our current understanding of the molecular mechanisms underlying antibiotic tolerance in mycobacteria.

Is "nano safe to eat or not"? A review of the state-of-the art in soft engineered nanoparticle (sENP) formulation and delivery in foods

With superior physicochemical properties, soft engineered nanoparticles (sENP) (protein, carbohydrate, lipids and other biomaterials) are widely used in foods. The preparation, functionalities, applications, transformations in gastrointestinal (GI) tract, and effects on gut microbiota of sENP directly incorporated for ingestion are reviewed herein. At the time of this review, there is no notable report of safety concerns of these nanomaterials found in the literature. Meanwhile, various beneficial effects have been demonstrated for the application of sENP. To address public perception and safety concerns of nanoscale materials in food, methodologies for evaluation of physiological effects of nanomaterials are reviewed. The combination of these complementary methods will be useful for the establishment of a comprehensive risk assessment system.

Current Knowledge on Listeria monocytogenes Biofilms in Food-Related Environments: Incidence, Resistance to Biocides, Ecology and Biocontrol

Although many efforts have been made to control Listeria monocytogenes in the food industry, growing pervasiveness amongst the population over the last decades has made this bacterium considered to be one of the most hazardous foodborne pathogens. Its outstanding biocide tolerance capacity and ability to promiscuously associate with other bacterial species forming multispecies communities have permitted this microorganism to survive and persist within the industrial environment. This review is designed to give the reader an overall picture of the current state-of-the-art in L. monocytogenes sessile communities in terms of food safety and legislation, ecological aspects and biocontrol strategies.

Antibiotic efficacy-context matters

Antibiotic lethality is a complex physiological process, sensitive to external cues. Recent advances using systems approaches have revealed how events downstream of primary target inhibition actively participate in antibiotic death processes. In particular, altered metabolism, translational stress and DNA damage each contribute to antibiotic-induced cell death. Moreover, environmental factors such as oxygen availability, extracellular metabolites, population heterogeneity and multidrug contexts alter antibiotic efficacy by impacting bacterial metabolism and stress responses. Here we review recent studies on antibiotic efficacy and highlight insights gained on the involvement of cellular respiration, redox stress and altered metabolism in antibiotic lethality. We discuss the complexity found in natural environments and highlight knowledge gaps in antibiotic lethality that may be addressed using systems approaches.

Potentiating antibiotics in drug-resistant clinical isolates via stimuli-activated superoxide generation

The rise of multidrug-resistant (MDR) bacteria is a growing concern to global health and is exacerbated by the lack of new antibiotics. To treat already pervasive MDR infections, new classes of antibiotics or antibiotic adjuvants are needed. Reactive oxygen species (ROS) have been shown to play a role during antibacterial action; however, it is not yet understood whether ROS contribute directly to or are an outcome of bacterial lethality caused by antibiotics. We show that a light-activated nanoparticle, designed to produce tunable flux of specific ROS, superoxide, potentiates the activity of antibiotics in clinical MDR isolates of Escherichia coli, Salmonella enterica, and Klebsiella pneumoniae. Despite the high degree of antibiotic resistance in these isolates, we observed a synergistic interaction between both bactericidal and bacteriostatic antibiotics with varied mechanisms of action and our superoxide-producing nanoparticles in more than 75% of combinations. As a result of this potentiation, the effective antibiotic concentration of the clinical isolates was reduced up to 1000-fold below their respective sensitive/resistant breakpoint. Further, superoxide-generating nanoparticles in combination with ciprofloxacin reduced bacterial load in epithelial cells infected with S. enterica serovar Typhimurium and increased Caenorhabditis elegans survival upon infection with S. enterica serovar Enteriditis, compared to antibiotic alone. This demonstration highlights the ability to engineer superoxide generation to potentiate antibiotic activity and combat highly drug-resistant bacterial pathogens.

Lethality of MalE-LacZ hybrid protein shares mechanistic attributes with oxidative component of antibiotic lethality

Downstream metabolic events can contribute to the lethality of drugs or agents that interact with a primary cellular target. In bacteria, the production of reactive oxygen species (ROS) has been associated with the lethal effects of a variety of stresses including bactericidal antibiotics, but the relative contribution of this oxidative component to cell death depends on a variety of factors. Experimental evidence has suggested that unresolvable DNA problems caused by incorporation of oxidized nucleotides into nascent DNA followed by incomplete base excision repair contribute to the ROS-dependent component of antibiotic lethality. Expression of the chimeric periplasmic-cytoplasmic MalE-LacZ_72-47 protein is an historically important lethal stress originally identified during seminal genetic experiments that defined the SecY-dependent protein translocation system. Multiple, independent lines of evidence presented here indicate that the predominant mechanism for MalE-LacZ lethality shares attributes with the ROS-dependent component of antibiotic lethality. MalE-LacZ lethality requires molecular oxygen, and its expression induces ROS production. The increased susceptibility of mutants sensitive to oxidative stress to MalE-LacZ lethality indicates that ROS contribute causally to cell death rather than simply being produced by dying cells. Observations that support the proposed mechanism of cell death include MalE-LacZ expression being bacteriostatic rather than bactericidal in cells that overexpress MutT, a nucleotide sanitizer that hydrolyzes 8-oxo-dGTP to the monophosphate, or that lack MutM and MutY, DNA glycosylases that process base pairs involving 8-oxo-dGTP. Our studies suggest stress-induced physiological changes that favor this mode of ROS-dependent death.

Europium-Doped Cerium Oxide Nanoparticles Limit Reactive Oxygen Species Formation and Ameliorate Intestinal Ischemia-Reperfusion Injury

Accumulating evidence suggests that ischemia-reperfusion-induced injury is associated with the formation of reactive oxygen species (ROS). This study demonstrates the therapeutic effectiveness of novel europium-doped cerium oxide nanoparticles (Eu-doped Ceria NPs) as ROS scavengers in a mouse model of intestinal ischemia-reperfusion-induced injury. An increased production of superoxide radicals is detected in the intestine throughout the ischemia stage and again after initiating reperfusion. These changes in superoxide radical formation are associated with the induction of inflammatory cytokines in the intestine. This study further shows that Eu-Ceria NPs exhibit superoxide scavenging activity in vitro. Importantly, administration of Eu-Ceria NPs into the intestinal lumen during the onset of ischemia effectively blocks superoxide accumulation, reduces the expression of IL-1b, and ameliorates the intestinal pathology. These results suggest that early increased production of ROS during the ischemia-reperfusion promotes intestinal pathology and that mucosal delivery of Eu-Ceria NPs may be a potential therapeutic approach to block ROS accumulation and ameliorate the severity of intestinal disease.

Bioapplications of Electrochemical Sensors and Biosensors

Recent progress in the electrochemical field enabled development of miniaturized sensing devices that can be used in biological settings to obtain fundamental and practical biochemically relevant information on physiology, metabolism, and disease states in living systems. Electrochemical sensors and biosensors have demonstrated potential for rapid, real-time measurements of biologically relevant molecules. This chapter provides an overview of the most recent advances in the development of miniaturized sensors for biological investigations in living systems, with focus on the detection of neurotransmitters and oxidative stress markers. The design of electrochemical (bio)sensors, including their detection mechanism and functionality in biological systems, is described as well as their advantages and limitations. Application of these sensors to studies in live cells, embryonic development, and rodent models is discussed.

Chemical Characterization and Antioxidant, Antimicrobial, and Anti-Inflammatory Activities of South Brazilian Organic Propolis

South Brazilian organic propolis (OP), which has never been studied before, was assessed and its chemical composition, scavenging potential of reactive oxygen species, antimicrobial and anti-inflammatory activities are herein presented. Based on the chemical profile obtained using HPLC, OP was grouped into seven variants (OP1–OP7) and all of them exhibited high scavenging activity, mainly against superoxide and hypochlorous acid species. OP1, OP2, and OP3 had the smallest minimal inhibitory concentration (MIC) against Gram-positive bacteria Streptococcus mutans, Streptococcus oralis, and Streptococcus aureus (12.5–100 μg/mL). OP1, OP2, OP3, and OP4 were more effective against Pseudomonas aeruginosa (Gram-negative), with MIC values ranging from 100 to 200 μg/mL. OP6 showed anti-inflammatory activity by decreasing NF-kB activation and TNF-α release in RAW 264.7 macrophages, and expressing the NF-κB-luciferase reporter stable gene. Therefore, south Brazilian OP can be considered an excellent source of bioactive compounds with great potential of application in the pharmaceutical and food industry.

Potential Impact of the Resistance to Quaternary Ammonium Disinfectants on the Persistence of Listeria monocytogenes in Food Processing Environments

The persistence of certain strains of Listeria monocytogenes, even after the food processing environment has been cleaned and disinfected, suggests that this may be related to phenomena that reduce the concentration of the disinfectants to subinhibitory levels. This includes (i) the existence of environmental niches or reservoirs that are difficult for disinfectants to reach, (ii) microorganisms that form biofilms and create microenvironments in which adequate concentrations of disinfectants cannot be attained, and (iii) the acquisition of resistance mechanisms in L. monocytogenes, including those that lead to a reduction in the intracellular concentration of the disinfectants. The only available data with regard to the resistance of L. monocytogenes to disinfectants applied in food production environments refer to genotypic resistance to quaternary ammonium compounds (QACs). Although there are several well-characterized efflux pumps that confer resistance to QACs, it is a low-level resistance that does not generate resistance to QACs at the concentrations applied in the food industry. However, dilution in the environment and biodegradation result in QAC concentration gradients. As a result, the microorganisms are frequently exposed to subinhibitory concentrations of QACs. Therefore, the low-level resistance to QACs in L. monocytogenes may contribute to its environmental adaptation and persistence. In fact, in certain cases, the relationship between low-level resistance and the environmental persistence of L. monocytogenes in different food production chains has been previously established. The resistant strains would have survival advantages in these environments over sensitive strains, such as the ability to form biofilms in the presence of increased biocide concentrations.