Food-Associated Stress Primes Foodborne Pathogens for the Gastrointestinal Phase of Infection

Anchorless Bacterial Moonlighting Metabolic Enzymes Modulate the Immune System and Contribute to Pathogenesis

Moonlighting proteins (MPs), characterized by their ability to perform multiple physiologically unrelated functions without alterations to their primary structures, represent a fascinating class of biomolecules with significant implications for host-pathogen interactions. This Review highlights the emerging importance of metabolic moonlighting proteins (MetMPs) in bacterial pathogenesis, focusing on their non-canonical secretion and unconventional surface anchoring mechanisms. Despite lacking typical signal peptides and anchoring motifs, MetMPs such as acetaldehyde alcohol dehydrogenase (AdhE) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) are secreted and localized to the bacterial surface under stress conditions, facilitating host colonization and immune evasion. The secretion of MetMPs, often observed during conditions such as resource scarcity or infection, suggests a complex regulation akin to the overexpression of heat shock proteins in response to environmental stresses. This Review proposes two potential pathways for MetMP secretion: membrane damage-induced permeability and co-transportation with traditionally secreted proteins, highlighting a remarkable bacterial adaptability. Biophysically, surface anchoring of MetMPs is driven by electrostatic interactions, bypassing the need for conventional anchoring sequences. This mechanism is exemplified by the interaction between the bifunctional enzyme AdhE (known as Listeria adhesion protein, LAP) and the internalin B (InlB) in Listeria monocytogenes, which is mediated by charged residues facilitating adhesion to host tissues. Furthermore, MetMPs play critical roles in iron homeostasis, immune modulation, and evasion, underscoring their multifaceted roles in bacterial pathogenicity. The intricate dynamics of MetMP secretion and anchoring underline the need for further research to unravel the molecular mechanisms underpinning these processes, offering potential new targets for therapeutic intervention against bacterial infections.

Acid tolerance response of Salmonella during the squid storage and its amine production capacity analysis

Salmonella exhibits a strong inducible acid tolerance response (ATR) under weak acid conditions, and can also induce high-risk strains that are highly toxic, acid resistant, and osmotic pressure resistant to aquatic products. However, the induction mechanism is not yet clear. Therefore, this study aims to simulate the slightly acidic, low-temperature, and high-protein environment during squid processing and storage. Through λRed gene knockout, exploring the effects of low-acid induction, long-term low-temperature storage, and two-component regulation on Salmonella ATR. In this study, we found the two-component system, PhoP/PhoQ and PmrA/PmrB in Salmonella regulates the amino acid metabolism system and improves bacterial acid tolerance by controlling arginine and lysine. Compared with the two indicators of total biogenic amine and diamine content, biogenic amine index and quality index were more suitable for evaluating the quality of aquatic products. The result showed that low-temperature treatment could inhibit Salmonella-induced ATR, which further explained the ATR mechanism from the amino acid metabolism.

Effects of intrinsic characteristics of Salmonella enterica strains isolated from foods and humans, and their interaction with food matrices during simulated gastric conditions

The stomach's acidic pH is a crucial barrier against foodborne pathogens such as Salmonella enterica. This study investigated the survival of S. enterica under simulated oral and gastric conditions (SGC; pH 2 for 120 min) as a function of intrinsic pathogen characteristics and food matrix. Fifty-seven S. enterica strains isolated from food and human infections (previously characterized by serotype, virulotype, multi-drug resistance, isolation source, and isolation season) were subjected to SGC using water as a vehicle. Population reduction among the 57 isolates ranged from 2.7 to 4.7 log CFU, revealing that human isolates were inactivated less than food isolates (p = 0.0008). Among food strains, strains isolated during the cold season (food sampled from December to February) displayed the highest reduction (p = 0.00002). Six representatives of the 57 S. enterica strains were selected according to their virulotype and antimicrobial profile. They were further used to evaluate their survival under SGC in four food matrices (water, mango, tomato, and chicken), measuring S. enterica at 30 min intervals. The strains in chicken showed the lowest reduction and inactivation rate (1.42 ± 0.35 log CFU; 0.03 ± 0.005 min-1), followed by tomato (3.75 ± 0.57 log CFU; 0.15 ± 0.02 min-1), water (4.23 ± 0.27 log CFU; 0.17 ± 0.02 min-1), and mango (4.49 ± 0.39 log CFU; 0.17 ± 0.03 min-1). These data suggest that not all S. enterica strains have the same ability to survive under SGC, influencing the probability of arriving into the small intestine.

Antimicrobial use and resistance in food animal production: food safety and associated concerns in Sub-Saharan Africa

The use of antimicrobials in food animal (FA) production is a common practice all over the world, with even greater usage and dependence in the developing world, including Sub-Saharan Africa (SSA). However, this practice which serves obvious economic benefits to producers has raised public health concerns over the last decades, thus driving the selection and dissemination of antimicrobial resistance and adversely impacting food safety and environmental health. This review presents the current and comprehensive antimicrobial usage practices in food animal production across SSA. We further highlighted the overall regional drivers as well as the public health, environmental, and economic impact of antimicrobial use in the production of food animals. Antimicrobial use is likely to increase with even exacerbated outcomes unless cost-effective, safe, and sustainable alternatives to antibiotics, especially probiotics, prebiotics, bacteriocins, antimicrobial peptides, bacteriophages, vaccines, etc. are urgently advocated for and used in food animal production in SSA. These, in addition to the implementation of strong legislation on antimicrobial use, and improved hygiene will help mitigate the public health concerns associated with antimicrobial use in food animals and improve the well-being and safety of food animals and their products.

Persistence of microbiological hazards in food and feed production and processing environments

Listeria monocytogenes (in the meat, fish and seafood, dairy and fruit and vegetable sectors), Salmonella enterica (in the feed, meat, egg and low moisture food sectors) and Cronobacter sakazakii (in the low moisture food sector) were identified as the bacterial food safety hazards most relevant to public health that are associated with persistence in the food and feed processing environment (FFPE). There is a wide range of subtypes of these hazards involved in persistence in the FFPE. While some specific subtypes are more commonly reported as persistent, it is currently not possible to identify universal markers (i.e. genetic determinants) for this trait. Common risk factors for persistence in the FFPE are inadequate zoning and hygiene barriers; lack of hygienic design of equipment and machines; and inadequate cleaning and disinfection. A well-designed environmental sampling and testing programme is the most effective strategy to identify contamination sources and detect potentially persistent hazards. The establishment of hygienic barriers and measures within the food safety management system, during implementation of hazard analysis and critical control points, is key to prevent and/or control bacterial persistence in the FFPE. Once persistence is suspected in a plant, a 'seek-and-destroy' approach is frequently recommended, including intensified monitoring, the introduction of control measures and the continuation of the intensified monitoring. Successful actions triggered by persistence of L. monocytogenes are described, as well as interventions with direct bactericidal activity. These interventions could be efficient if properly validated, correctly applied and verified under industrial conditions. Perspectives are provided for performing a risk assessment for relevant combinations of hazard and food sector to assess the relative public health risk that can be associated with persistence, based on bottom-up and top-down approaches. Knowledge gaps related to bacterial food safety hazards associated with persistence in the FFPE and priorities for future research are provided.

Heterogeneous Phenotypic Responses of Antibiotic-Resistant Salmonella Typhimurium to Food Preservative-Related Stresses

This study was designed to evaluate the response of antibiotic-resistant Salmonella Typhimurium to food preservative-related stresses, such as lactic acid and sodium chloride (NaCl). S. Typhimurium cells were exposed to 1 µg/mL of ciprofloxacin (CIP), 0.2% lactic acid (LA), 6% NaCl, CIP followed by LA (CIP-LA), and CIP followed by NaCl (CIP-NaCl). The untreated S. Typhimurium cells were the control (CON). All treatments were as follows: CON, CIP, LA, NaCl, CIP-LA, and CIP-NaCl. The phenotypic heterogeneity was evaluated by measuring the antimicrobial susceptibility, bacterial fluctuation, cell injury, persistence, and cross-resistance. The CIP, CIP-LA, and CIP-NaCl groups were highly resistant to ciprofloxacin, showing MIC values of 0.70, 0.59, and 0.54 µg/mL, respectively, compared to the CON group (0.014 µg/mL). The susceptibility to lactic acid was not changed after exposure to NaCl, while that to NaCl was decreased after exposure to NaCl. The Eagle phenomenon was observed in the CIP, CIP-LA, and CIP-NaCl groups, showing Eagle effect concentrations (EECs) of more than 8 µg/mL. No changes in the MBCs of lactic acid and NaCl were observed in the CIP, LA, and CIP-LA groups, and the EECs of lactic acid and NaCl were not detected in all treatments. The bacterial fluctuation rates of the CIP-LA and CIP-NaCl groups were considerably increased to 33% and 41%, respectively, corresponding to the injured cell proportions of 82% and 89%. CIP-NaCl induced persister cells as high as 2 log cfu/mL. The LA and NaCl treatments decreased the fitness cost. The CIP-NaCl treatment showed positive cross-resistance to erythromycin (ERY) and tetracycline (TET), while the LA and NaCl treatments were collaterally susceptible to chloramphenicol (CHL), ciprofloxacin (CIP), piperacillin (PIP), and TET. The results provide new insight into the fate of antibiotic-resistant S. Typhimurium during food processing and preservation.

Controlling Salmonella: strategies for feed, the farm, and the processing plant

Controlling Salmonella in poultry is an ongoing food safety measure and while significant progress has been made, there is a need to continue to evaluate different strategies that include understanding Salmonella-poultry interaction, Salmonella-microbiota interactions, Salmonella genetics and response to adverse conditions, and preharvest and postharvest parameters that enable persistence. The purpose of this symposium is to discuss different strategies to consider from feed milling to the farm to the processing environment. This Poultry Science Association symposium paper is divided into 5 different sections that covers 1) immunological aspects of Salmonella control, 2) application of Salmonella genetics for targeted control strategies in poultry production, 3) improving poultry feed hygienics: utilizing feed manufacture techniques and equipment to improve feed hygienics, 4) practical on farm interventions for controlling Salmonella-what works and what may not work, and 5) monitoring and mitigating Salmonella in poultry. These topics elucidate the critical need to establish control strategies that will improve poultry gut health and limit conditions that exposes Salmonella to stress causing alterations to virulence and pathogenicity both at preharvest and postharvest poultry production. This information is relevant to the poultry industry's continued efforts to ensure food safety poultry production.

A multidrug-resistant Salmonella enterica Typhimurium DT104 complex lineage circulating among humans and cattle in the USA lost the ability to produce pertussis-like toxin ArtAB

Salmonella enterica subsp. enterica serotype Typhimurium definitive type 104 (DT104) can infect both humans and animals and is often multidrug-resistant (MDR). Previous studies have indicated that, unlike most S . Typhimurium, the overwhelming majority of DT104 strains produce pertussis-like toxin ArtAB via prophage-encoded genes artAB . However, DT104 that lack artAB have been described on occasion. Here, we identify an MDR DT104 complex lineage circulating among humans and cattle in the USA, which lacks artAB (i.e. the ‘U.S. artAB -negative major clade’; n =42 genomes). Unlike most other bovine- and human-associated DT104 complex strains from the USA (n =230 total genomes), which harbour artAB on prophage Gifsy-1 (n =177), members of the U.S. artAB -negative major clade lack Gifsy-1, as well as anti-inflammatory effector gogB . The U.S. artAB -negative major clade encompasses human- and cattle-associated strains isolated from ≥11 USA states over a 20-year period. The clade was predicted to have lost artAB , Gifsy-1 and gogB circa 1985–1987 (95 % highest posterior density interval 1979.0–1992.1). When compared to DT104 genomes from other regions of the world (n =752 total genomes), several additional, sporadic artAB , Gifsy-1 and/or gogB loss events among clades encompassing five or fewer genomes were observed. Using phenotypic assays that simulate conditions encountered during human and/or bovine digestion, members of the U.S. artAB -negative major clade did not differ from closely related Gifsy-1/artAB /gogB -harbouring U.S. DT104 complex strains (ANOVA raw P >0.05); thus, future research is needed to elucidate the roles that artAB , gogB and Gifsy-1 play in DT104 virulence in humans and animals.

Identification of pH-specific protein expression responses by Campylobacter jejuni strain NCTC 11168

In this study a data dependent acquisition label-free based proteomics approach was used to identify pH-dependent proteins that respond in a growth phase independent manner in C. jejuni reference strain NCTC 11168. NCTC 11168 was grown within its pH physiological normal growth range (pH 5.8, 7.0 and 8.0, μ = ∼0.5 h^-1) and exposed to pH 4.0 shock for 2 hours. It was discovered that gluconate 2-dehydrogenase GdhAB, NssR-regulated globins Cgb and Ctb, cupin domain protein Cj0761, cytochrome c protein CccC (Cj0037c), and phosphate-binding transporter protein PstB all show acidic pH dependent abundance increases but are not activated by sub-lethal acid shock. Glutamate synthase (GLtBD) and the MfrABC and NapAGL respiratory complexes were induced in cells grown at pH 8.0. The response to pH stress by C. jejuni is to bolster microaerobic respiration and at pH 8.0 this is assisted by accumulation of glutamate the conversion of which could bolster fumarate respiration. The pH dependent proteins linked to growth in C. jejuni NCTC 11168 aids cellular energy conservation maximising growth rate and thus competitiveness and fitness.

Assessment of phenotypic heterogeneity in Salmonella Typhimurium preadapted to ciprofloxacin and tetracycline

Bacterial population exposed to stressful antibiotic conditions consists of various subpopulations such as tolerant, persister, and resistant cells. The aim of this study was to evaluate the phenotypic heterogeneity of Salmonella Typhimurium preadapted to sublethal concentrations of antibiotics. Salmonella Typhimurium cells were treated with 1/2 × MIC of antibiotics for the first 48 h and successively 1 × MIC for the second 24 h at 37°C, including untreated control (CON), no antibiotic and 1 × MIC ciprofloxacin (NON-CIP), 1/2 × MIC ciprofloxacin and 1 × MIC ciprofloxacin (CIP-CIP), 1/2 × MIC tetracycline and 1 × MIC ciprofloxacin (TET-CIP), no antibiotic and 1 × MIC tetracycline (NON-TET), 1/2 × MIC ciprofloxacin and 1 × MIC tetracycline (CIP-TET), and 1/2 × MIC tetracycline and 1 × MIC tetracycline (TET-TET). All treatments were evaluated by antibiotic susceptibility, ATP level, relative fitness, cross-resistance, and persistence. S. Typhimurium cells were more susceptible to non-adapted NON-CIP and NON-TET (>3-log reduction) than pre-adapted CIP-CIP, TET-CIP, CIP-TET, and TET-TET. CON exhibited the highest ATP level, corresponding to the viable cell number. The relative fitness levels were more than 0.95 for all treatments, except for NON-CIP (0.78). The resistance to ciprofloxacin and tetracycline was increased at all treatments with the exception of NON-TET. The persister cells were noticeably induced at CIP-TET treatment, showing more than 5 log CFU mL-1. The results suggest that the antibiotic preadaptation led to heterogeneous populations including persisters that can develop to resistance. This study provides new insight in the bacterial persistence associated with their potential risk and paves the way to design antibiotic therapy targeting dormant bacteria.

Comparative virulence of the worldwide ST19 and emergent ST213 genotypes of Salmonella enterica serotype Typhimurium strains isolated from food

Salmonella enterica Typhimurium represents one of the most frequent causal agents of food contamination associated to gastroenteritis. The sequence type ST19 is the founder and worldwide prevalent genotype within this serotype, but its replacement by emerging genotypes has been recently reported. Particularly, the ST213 genotype has replaced it as the most prevalent in clinical and contaminated food samples in Mexico and has been recently reported in several countries. In this study, the in vitro and in vivo virulence of ST213 and ST19 strains isolated from food samples in Mexico was evaluated. Three out of the five analyzed ST213 strains, showed a greater internalization capacity and increased secretion of interleukins IL-8 and IL-6 of Caco-2 cells than the ST19 strains. Microbiological counts in feces and tissues showed the ability of all strains tested to establish infection in the rat model. The ST213 strains also caused histopathological damage, characteristic of gastroenteritis in Wistar rats. In contrast to the in vitro result, one of the ST19 strains showed marked damage in the test animals. The ST213 genotype strains showed in vitro and in vivo virulence variability, but significantly higher than the observed in the ST19 genotype strains, thus such emergent genotype represents a public health concern.

Heterogeneity and Evolutionary Tunability of Escherichia coli Resistance against Extreme Acid Stress

Since acidic environments often serve as an important line of defense against bacterial pathogens, it is important to fully understand how the latter manage to mount and evolve acid resistance mechanisms. Escherichia coli, a species harboring many pathovars, is typically equipped with the acid fitness island (AFI), a genomic region encoding the GadE master regulator together with several GadE-controlled functions to counter acid stress. This study reveals that gadE and consequently AFI functions are heterogeneously expressed even in the absence of any prior acid stress, thereby preemptively creating acid-resistant subpopulations within a clonal E. coli population. Directed evolution efforts selecting for modulated gadE expression confirm that a gain-of-function mutation in the EvgS sensor kinase can constitutively upregulate gadE expression and concomitant acid resistance. However, we reveal that such upregulation of EvgS also causes cross-resistance to heat stress because of SafA-mediated cross-activation of the PhoPQ regulon. Surprisingly, loss of function of the serC gene (encoding phosphoserine/phosphohydroxythreonine aminotransferase) can also significantly upregulate gadE expression, acid resistance, and heat cross-resistance, although via a currently cryptic mechanism. As such, our data reveal a noisy expression of gadE in E. coli that is functional for the survival of sudden acid stress and that can readily be genetically tuned. IMPORTANCE Acidic environments constitute one of the most important stresses for enteric bacteria and can be encountered in both natural (e.g., host gastrointestinal tract) and manmade (e.g., food processing) environments. The enteric species Escherichia coli harbors many pathovars and is well known for its ability to cope with acid stress. In this study, we uncover that E. coli's acid fitness island (AFI), a genomic region that encodes important functions to deal with acid stress, is by default expressed in a heterogeneous manner. In fact, using microfluidics-based single-cell approaches, we further demonstrate that this heterogeneity preemptively creates a clonal subpopulation that is much better equipped to survive a sudden acid shock. In addition, we reveal that environments with recurring acid stress can readily select for mutants displaying a higher fraction of AFI-expressing cells. These new insights are important to properly understand and anticipate the survival characteristics of E. coli.

Listeria monocytogenes-How This Pathogen Uses Its Virulence Mechanisms to Infect the Hosts

Listeriosis is a serious food-borne illness, especially in susceptible populations, including children, pregnant women, and elderlies. The disease can occur in two forms: non-invasive febrile gastroenteritis and severe invasive listeriosis with septicemia, meningoencephalitis, perinatal infections, and abortion. Expression of each symptom depends on various bacterial virulence factors, immunological status of the infected person, and the number of ingested bacteria. Internalins, mainly InlA and InlB, invasins (invasin A, LAP), and other surface adhesion proteins (InlP1, InlP4) are responsible for epithelial cell binding, whereas internalin C (InlC) and actin assembly-inducing protein (ActA) are involved in cell-to-cell bacterial spread. L. monocytogenes is able to disseminate through the blood and invade diverse host organs. In persons with impaired immunity, the elderly, and pregnant women, the pathogen can also cross the blood-brain and placental barriers, which results in the invasion of the central nervous system and fetus infection, respectively. The aim of this comprehensive review is to summarize the current knowledge on the epidemiology of listeriosis and L. monocytogenes virulence mechanisms that are involved in host infection, with a special focus on their molecular and cellular aspects. We believe that all this information is crucial for a better understanding of the pathogenesis of L. monocytogenes infection.

Bacteriophage-Based Biosensors: A Platform for Detection of Foodborne Bacterial Pathogens from Food and Environment

Foodborne microorganisms are an important cause of human illness worldwide. Two-thirds of human foodborne diseases are caused by bacterial pathogens throughout the globe, especially in developing nations. Despite enormous developments in conventional foodborne pathogen detection methods, progress is limited by the assay complexity and a prolonged time-to-result. The specificity and sensitivity of assays for live pathogen detection may also depend on the nature of the samples being analyzed and the immunological or molecular reagents used. Bacteriophage-based biosensors offer several benefits, including specificity to their host organism, the detection of only live pathogens, and resistance to extreme environmental factors such as organic solvents, high temperatures, and a wide pH range. Phage-based biosensors are receiving increasing attention owing to their high degree of accuracy, specificity, and reduced assay times. These characteristics, coupled with their abundant supply, make phages a novel bio-recognition molecule in assay development, including biosensors for the detection of foodborne bacterial pathogens to ensure food safety. This review provides comprehensive information about the different types of phage-based biosensor platforms, such as magnetoelastic sensors, quartz crystal microbalance, and electrochemical and surface plasmon resonance for the detection of several foodborne bacterial pathogens from various representative food matrices and environmental samples.

Effect of Thymus vulgaris L. essential oil and thymol on the microbiological properties of meat and meat products: A review

Since foodborne diseases are often considered as one of the biggest public health threats worldwide, effective preservation strategies are needed to inhibit the growth of undesirable microorganisms in food commodities. Up to now, several techniques have been adopted for the production of safe and high-quality products. Although the traditional methods can improve the reliability, safety, and shelf-life of food, some of them cannot be applied without rising health concerns. Thereby, the addition of various phytochemicals has gained much attention during the last decades, especially for meat products that may be contaminated with pathogenic and spoilage organisms. Thyme (Thymus vulgaris L.), as an important medicinal and culinary herb, is a promising source of bioactive compounds that have a great impact on the microbiological stability of meat by suppressing the undesirable microflora. However, the use of these antimicrobials is still facing difficulties due to their aromatic properties and variable efficacy against targeted species. In this paper, we provide an overview on the potential effects of thyme essential oil (EO) and thymol as bio-preservative agents in meat products. Furthermore, this paper provides insights into the limitations and current challenges of the addition of EOs and their constituents to meat commodities and suggests viable solutions that can improve the applicability of these phytochemicals.

Effects of Sublethally Injured Campylobacter jejuni in Mice

Globally, Campylobacter spp. are the most common food-associated bacterial cause of human gastrointestinal disease. Campylobacteriosis is primarily associated with the consumption of contaminated chicken meat. Chemical decontamination of chicken carcasses during processing is one of the most effective interventions to mitigate Campylobacter contamination. Following exposure to sanitizers, however, sublethally injured populations of bacteria may persist. The risk that sublethally injured Campylobacter pose for public health is unknown. Furthermore, the virulence potential of sublethally injured Campylobacter jejuni during prolonged storage in relation to host pathogenesis and the host immune response has not been well established. Therefore, we evaluated the effects of sublethally injured C. jejuni on the host, after storage in chicken meat juice. C57BL/6 mice were infected with two C. jejuni chicken meat isolates or the ATCC 33291 strain that had been stored in the chicken meat juice, after exposure to chlorine or acidified sodium chlorite (ASC). Although chlorine exposure was unable to reduce intestinal colonization by C. jejuni, exposure to ASC significantly reduced the intestinal colonization and tissue translocation in mice. The expression of pro- and anti-inflammatory cytokine genes for interleukin-6 (IL-6), IL23a, and IL-10, Toll-like receptor 2 (TLR2) and TLR4 genes, and host stress response genes (CRP, MBL1, and NF-κB1) were significantly reduced following the exposure to ASC. Our results demonstrated that sublethally injured C. jejuni has reduced virulence potential and colonization in mice. The data contribute toward clarification of the importance of chemical decontamination during processing to minimize human campylobacteriosis.

IMPORTANCECampylobacter is the most common cause of bacterial gastrointestinal disease, and consumption of contaminated poultry is frequently identified as the source of bacteria. The survivability and virulence potential of sublethally injured Campylobacter following exposure to chemicals which are commonly used to eliminate Campylobacter during the poultry meat processing are of concern to the food industry, government health officials, and consumers. Here, we demonstrate that sublethally injured Campylobacter jejuni has reduced bacterial virulence and colonization potential in mice.

Research progress on antibiotic resistance of Salmonella

Antibiotic abuse results in various antibiotic resistance among a number of foodborne bacteria, posing a severe threat to food safety. Antibiotic resistance genes are commonly detected in foodborne pathogens, which has sparked much interest in finding solutions to these issues. Various strategies against these drug-resistant pathogens have been studied, including new antibiotics and phages. Recently, a powerful tool has been introduced in the fight against drug-resistant pathogens, namely, clustered regularly interspaced short palindromic repeats-CRISPR associated (CRISPR-Cas) system aggregated by a prokaryotic defense mechanism. This review summarized the mechanism of antibiotic resistance in Salmonella and resistance to common antibiotics, analysed the relationship between Salmonella CRISPR-Cas and antibiotic resistance, discussed the changes in antibiotic resistance on the structure and function of CRISPR-Cas, and finally predicted the mechanism of CRISPR-Cas intervention in Salmonella antibiotic resistance. In the future, CRISPR-Cas is expected to become an important tool to reduce the threat of antibiotic-resistant pathogens in food safety.

Stress response modulation: the key to survival of pathogenic and spoilage bacteria during poultry processing

The control of bacterial contaminants on meat is a key area of interest in the food industry. Bacteria are exposed to a variety of stresses during broiler processing which challenge bacterial structures and metabolic pathways causing death or sublethal injury. To counter these stresses, bacteria possess robust response systems that can induce shifts in the transcriptome and proteome to enable survival. Effective adaptive responses, such as biofilm formation, shock protein production and metabolic flexibility, require rapid induction and implementation at a cellular and community level to facilitate bacterial survival in adverse conditions. This review aims to provide an overview of the scientific literature pertaining to the regulation of complex adaptive processes used by bacteria to survive the processing environment, with particular focus on species that impact the quality and safety of poultry products like Campylobacter spp., Salmonella enterica and Pseudomonas spp.

Landscape of Stress Response and Virulence Genes Among Listeria monocytogenes Strains

The pathogenic microorganism Listeria monocytogenes is ubiquitous and responsible for listeriosis, a disease with a high mortality rate in susceptible people. It can persist in different habitats, including the farm environment, the food production environments, and in foods. This pathogen can grow under challenging conditions, such as low pH, low temperatures, and high salt concentrations. However, L. monocytogenes has a high degree of strain divergence regarding virulence potential, environmental adaption, and stress response. This review seeks to provide the reader with an up-to-date overview of clonal and serotype-specific differences among L. monocytogenes strains. Emphasis on the genes and genomic islands responsible for virulence and resistance to environmental stresses is given to explain the complex adaptation among L. monocytogenes strains. Moreover, we highlight the use of advanced diagnostic technologies, such as whole-genome sequencing, to fine-tune quantitative microbiological risk assessment for better control of listeriosis.

Bacterial Biofilms and Their Implications in Pathogenesis and Food Safety

Biofilm formation is an integral part of the microbial life cycle in nature. In food processing environments, bacterial transmissions occur primarily through raw or undercooked foods and by cross-contamination during unsanitary food preparation practices. Foodborne pathogens form biofilms as a survival strategy in various unfavorable environments, which also become a frequent source of recurrent contamination and outbreaks of foodborne illness. Instead of focusing on bacterial biofilm formation and their pathogenicity individually, this review discusses on a molecular level how these two physiological processes are connected in several common foodborne pathogens such as Listeria monocytogenes, Staphylococcus aureus, Salmonella enterica and Escherichia coli. In addition, biofilm formation by Pseudomonas aeruginosa is discussed because it aids the persistence of many foodborne pathogens forming polymicrobial biofilms on food contact surfaces, thus significantly elevating food safety and public health concerns. Furthermore, in-depth analyses of several bacterial molecules with dual functions in biofilm formation and pathogenicity are highlighted.

Vibrio vulnificus induces the death of a major bacterial species in the mouse gut via cyclo-Phe-Pro

BACKGROUND

A foodborne pathogen, Vibrio vulnificus, encounters normal microflora inhabiting the gut environments prior to causing fatal septicemia or gastroenteritis and should overcome the barriers derived from the gut commensals for successful infection. Its interactions with gut commensals during the infection process, however, have not yet been understood. In the present study, the effect of V. vulnificus on the community structures of gut microbiota in mice was examined.

RESULTS

Analyses of microbiota in the fecal samples of mice that died due to V. vulnificus infection revealed the decreased abundance of bacteria belonged to Bacteroidetes, notably, the species Bacteroides vulgatus. In vitro coculturing of the two bacterial species resulted in the decreased survival of B. vulgatus. The antagonistic effect of V. vulnificus against B. vulgatus was found to be mediated by cyclo-Phe-Pro (cFP), one of the major compounds secreted by V. vulnificus. cFP-treated B. vulgatus showed collapsed cellular morphology with an undulated cell surface, enlarged periplasmic space, and lysed membranes, suggesting the occurrence of membrane disruption. The degree of membrane disruption caused by cFP was dependent upon the cellular levels of ObgE in B. vulgatus. Recombinant ObgE exhibited a high affinity to cFP at a 1:1 ratio. When mice were orally injected with cFP, their feces contained significantly reduced B. vulgatus levels, and their susceptibility to V. vulnificus infection was considerably increased.

CONCLUSIONS

This study demonstrates that V. vulnificus-derived cFP modulates the abundance of the predominant species among gut commensals, which made V. vulnificus increase its pathogenicity in the hosts. Video abstract.

Antibody- and nucleic acid-based lateral flow immunoassay for Listeria monocytogenes detection

Listeria monocytogenes is an invasive opportunistic foodborne pathogen and its routine surveillance is critical for protecting the food supply and public health. The traditional detection methods are time-consuming and require trained personnel. Lateral flow immunoassay (LFIA), on the other hand, is an easy-to-perform, rapid point-of-care test and has been widely used as an inexpensive surveillance tool. In recent times, nucleic acid-based lateral flow immunoassays (NALFIA) are also developed to improve sensitivity and specificity. A significant improvement in lateral flow-based assays has been reported in recent years, especially the ligands (antibodies, nucleic acids, aptamers, bacteriophage), labeling molecules, and overall assay configurations to improve detection sensitivity, specificity, and automated interpretation of results. In most commercial applications, LFIA has been used with enriched food/environmental samples to ensure detection of live cells thus prolonging the assay time to 24-48 h; however, with the recent improvement in LFIA sensitivity, results can be obtained in less than 8 h with shortened and improved enrichment practices. Incorporation of surface-enhanced Raman spectroscopy and/or immunomagnetic separation could significantly improve LFIA sensitivity for near-real-time point-of-care detection of L. monocytogenes for food safety and public health applications.

Listeria monocytogenes: review of pathogenesis and virulence determinants-targeted immunological assays

Listeria monocytogenes is one of the most invasive foodborne pathogens and is responsible for numerous outbreaks worldwide. Most of the methods to detect this bacterium in food require selective enrichment using traditional bacterial culture techniques that can be time-consuming and labour-intensive. Moreover, molecular methods are expensive and need specific technical knowledge. In contrast, immunological approaches are faster, simpler, and user-friendly alternatives and have been developed for the detection of L. monocytogenes in food, environmental, and clinical samples. These techniques are dependent on the constitutive expression of L. monocytogenes antigens and the specificity of the antibodies used. Here, updated knowledge on pathogenesis and the key immunogenic virulence determinants of L. monocytogenes that are used for the generation of monoclonal and polyclonal antibodies for the serological assay development are summarised. In addition, immunological approaches based on enzyme-linked immunosorbent assay, immunofluorescence, lateral flow immunochromatographic assays, and immunosensors with relevant improvements are highlighted. Though the sensitivity and specificity of the assays were improved significantly, methods still face many challenges that require further validation before use.

Pakistan's backyard poultry farming initiative: impact analysis from a public health perspective

Commercial poultry rearing in Pakistan dates back to the 1960s. Meanwhile, backyard poultry setups have been providing meat and eggs for human consumption and supplementing the livelihood of farmers in many rural setups for ages. Different poultry rearing practices have varied approaches to feed supplementation, administration, biosafety practices, and flock size. All are important factors affecting disease spread and vulnerability. Recently, the Pakistani government announced the prime minister's Backyard Poultry Initiative under the National Agricultural Emergency program to economically develop farmers, especially women. Widespread adoption of this scheme with little to no training of inexperienced farmers may lead to the emergence of zoonotic infections in the population. The focus of the current review is to examine the probable impact of the promotion of backyard poultry farming practices by the government on the spread of zoonotic illnesses, both in the farmers and consumer population.

Biofilm-isolated Listeria monocytogenes exhibits reduced systemic dissemination at the early (12-24 h) stage of infection in a mouse model

Environmental cues promote microbial biofilm formation and physiological and genetic heterogeneity. In food production facilities, biofilms produced by pathogens are a major source for food contamination; however, the pathogenesis of biofilm-isolated sessile cells is not well understood. We investigated the pathogenesis of sessile Listeria monocytogenes (Lm) using cell culture and mouse models. Lm sessile cells express reduced levels of the lap, inlA, hly, prfA, and sigB and show reduced adhesion, invasion, translocation, and cytotoxicity in the cell culture model than the planktonic cells. Oral challenge of C57BL/6 mice with food, clinical, or murinized-InlA (InlAm) strains reveals that at 12 and 24 h post-infection (hpi), Lm burdens are lower in tissues of mice infected with sessile cells than those infected with planktonic cells. However, these differences are negligible at 48 hpi. Besides, the expressions of inlA and lap mRNA in sessile Lm from intestinal content are about 6.0- and 280-fold higher than the sessle inoculum, respectively, suggesting sessile Lm can still upregulate virulence genes shortly after ingestion (12 h). Similarly, exposure to simulated gastric fluid (SGF, pH 3) and intestinal fluid (SIF, pH 7) for 13 h shows equal reduction in sessile and planktonic cell counts, but induces LAP and InlA expression and pathogenic phenotypes. Our data show that the virulence of biofilm-isolated Lm is temporarily attenuated and can be upregulated in mice during the early stage (12-24 hpi) but fully restored at a later stage (48 hpi) of infection. Our study further demonstrates that in vitro cell culture assay is unreliable; therefore, an animal model is essential for studying the pathogenesis of biofilm-isolated bacteria.

Access to thermally robust and abrasion resistant antimicrobial plastics: synthesis of UV-curable phosphonium small molecule coatings and extrudable additives

The threat of antibiotic-resistant, biofilm-forming bacteria necessitates a preventative approach to combat the proliferation of robust, pathogenic strains on "high touch surfaces" in the food packaging, biomedical, and healthcare industries. The development of both biocide-releasing and tethered, immobilized biocide surface coatings has risen to meet this demand. While these surface coatings have demonstrated excellent antimicrobial efficacy, there are few examples of antimicrobial surfaces with long-term durability and performance. To this end, UV-curable phosphoniums bearing benzophenone anchors with either an alkyl, aryl, or fluoroalkyl group were synthesized and their efficacy as thermally stable antimicrobial additives in extruded plastics or as surface attached coatings probed. The surface topology and characteristics of these materials were studied to gain insight into the mechanism of their antimicrobial activity. Efficacy against both Gram negative and Gram positive bacteria as either a coating or additive showed compete reductions of the initial bacterial load. Crucially, the materials maintained the ability to kill biofilm-forming bacteria even after being subject to several cycles of abrasion.

Impact of pH on citric acid antimicrobial activity against Gram-negative bacteria

The antimicrobial activity of citric acid (CA) is often evaluated without pH adjustment or control and its impact on micro‐organisms is better understood in acidic conditions. However, the biocidal action of the fully ionized CA molecule, predominantly available at higher pH, has not been previously investigated. The objective of this study was to evaluate the antimicrobial effect of high (10%) and low (1%) concentrations of CA, each adjusted over a wide range of pH values (4·5, 6·5 and 9·5) relative to the controls exposed to corresponding pH levels alone (no CA). The viability and morphology of Escherichia coli and Klebsiella aerogenes were evaluated using a culture‐based enumeration assay in parallel with direct SEM imaging. Overall, the highest membrane damage and loss in viability were achieved with 10% CA at pH 9·5, which yielded at least 4·6 log₁₀ CFU per ml (P < 0·001) reductions in both organisms. Insight into the superior efficacy of CA at high pH is proposed based on zeta potential measurements which reveal a more negatively charged bacterial surface at higher pH. This pH‐dependent increase in surface charge may have rendered the cells potentially more sensitive towards chelants such as CA³⁻ that interact with membrane‐stabilizing divalent metals.

Virulence assessment of Listeria monocytogenes grown in different foods using a Galleria mellonella model

Various produce including cantaloupe, caramel-coated apples, and packaged salads, have been recognized in recent years as vehicles for listeriosis, a human foodborne disease caused by intracellular pathogen Listeria monocytogenes. Our knowledge regarding the role of these foods in L. monocytogenes virulence, however, is limited. Understanding their role in modulating L. monocytogenes virulence can be useful in risk assessments and for developing control measures. In this study, we employed the Galleria mellonella larvae model to evaluate virulence potential of fifteen clinical, environmental and food isolates of L. monocytogenes, related to three major outbreaks, after growth on different foods. The non-human pathogen Listeria innocua was also included in the panel. Strains were inoculated in parallel in 5ml of brain heart infusion (BHI) broth, and on the surfaces of cantaloupe and apple fragments (5g each) at about 10⁵ colony forming units (CFU)/ml/fragment. One set of inoculated broth and food fragments was incubated at 10°C for 5 days while the second set was kept at 25°C for 3 days. L. monocytogenes cells were recovered from the fruits and BHI, washed twice, re-suspended in saline, and used to inoculate G. mellonella larvae at final concentrations of 10⁶ and 10⁵ CFU/larva. The larvae were incubated at 37°C and monitored for mortality (LT₅₀—time taken to kill 50% of the larvae) and phenotypic changes over seven days. L. monocytogenes grown on cantaloupe and apple flesh surfaces resulted in higher virulence than when grown in BHI. L. monocytogenes infection at 10⁶ CFU/larvae resulted in an average LT₅₀ of ≤ 30, 36 and 47 hours on cantaloupe, apples and BHI, respectively. These results represent a 2.5–4-fold increased mortality compared with an LT₅₀ ≥120 hours in larvae infected with the same doses of L. innocua grown in corresponding matrices. Similar trends were also recorded with doses of about 10⁵ CFU /larvae.

A State-of-Art Review on Multi-Drug Resistant Pathogens in Foods of Animal Origin: Risk Factors and Mitigation Strategies

Most of the foodborne microbial diseases are linked to foods of animal origin such as milk, meat, and poultry. Nowadays, the presence of multi-drug resistant (MDR) pathogens in foods is becoming an increasingly public health concern worldwide due to the overuse of antimicrobial drugs in animal feed. MDR pathogens can enter the food chain by posing a significant risk to both animals and consumers. MDR pathogens causing infections are untreatable due to their resistance to various antibiotics, primarily cephalosporin and carbapenems and to their extended-spectrum beta-lactamase (ESBL)-producing capability. In addition, foods of animal origin and food-related environments can be likely vehicles for spreading of multi-drug resistance genes, which accelerates the thriving of global antibiotic resistance. This paper reviews the role of foods of animal origin as a vehicle for MDR pathogens, stressing the contribution of food processes, environments, and storage conditions in dissemination and reduction of antimicrobial resistances (AMRs). Controlling the growth of MDR microorganisms and limiting the transmission/expression of AMR genes in food ecosystems could be an effective mitigation strategy, putting the focus on food processes as a part of the solution for AMR in foods. Bioprotective cultures are also a promising and environmentally friendly technology to reduce the incidence of MDR pathogens, though caution is taken as microbial starters and probiotics can also carry AMR. Finally, applying Whole Genome Sequencing (WGS) and predictive microbiology, within a Risk Assessment framework, is key to get insight into those mechanisms and conditions along the food chain favoring or reducing AMR.

Internalin AB-expressing recombinant Lactobacillus casei protects Caco-2 cells from Listeria monocytogenes-induced damages under simulated intestinal conditions

Background

Listeria monocytogenes is an intracellular foodborne pathogen that employs a number of strategies to survive challenging gastrointestinal conditions. It proliferates in the gut and subsequently causes listeriosis in high-risk individuals. Therefore, inhibition of its adherence to the intestinal receptors is crucial in controlling its infection. In this study, the effect of our previously developed recombinant Lactobacillus casei strain expressing invasion protein, Internalin AB of L. monocytogenes (Lbc^InlAB) on epithelial infection processes of the latter under simulated intestinal conditions was investigated.

Materials and methods

The confluent Caco-2 cell monolayer was pre-exposed to different L. casei strains at a multiplicity of exposure (MOE) of 10 for various periods before infection with L. monocytogenes at a multiplicity of infection (MOI) of 10 under simulated intestinal conditions. Subsequently, L. monocytogenes adhesion, invasion, and translocation, cytotoxicity and impact on tight junction integrity of the Caco-2 cells were analyzed.

Results

Under the simulated gastrointestinal condition, Lbc^InlAB showed a significant increase (p<0.0001) in adherence to, invasion and translocation through the Caco-2 cells when compared with the wild type strain. Although Lbc^InlAB strain exhibited enhanced inhibition of L. monocytogenes, it was not able to displace L. monocytogenes cells already attached to the monolayer. Additionally, pre-exposure to Lbc^InlAB reduced L. monocytogenes-mediated cytotoxicity and protected the tight junction barrier function.

Conclusion

The recombinant L. casei expressing InlAB shows potential for use as a prophylactic intervention strategy for targeted control of L. monocytogenes during the intestinal phase of infection.