Salmonella Extracellular Polymeric Substances Modulate Innate Phagocyte Activity and Enhance Tolerance of Biofilm-Associated Bacteria to Oxidative Stress

Combining multiple stressors unexpectedly blocks bacterial migration and growth

In nature, organisms experience combinations of stressors. However, laboratory studies typically simplify reality and focus on the effects of an individual stressor. Here, we use a microfluidic approach to simultaneously provide a physical stressor (shear flow) and a chemical stressor (H 2 O 2 ) to the human pathogen Pseudomonas aeruginosa . By treating cells with levels of flow and H 2 O 2 that commonly co-occur in nature, we discover that previous reports significantly overestimate the H 2 O 2 levels required to block bacterial growth. Specifically, we establish that flow increases H 2 O 2 effectiveness 50-fold, explaining why previous studies lacking flow required much higher concentrations. Using natural H 2 O 2 levels, we identify the core H 2 O 2 regulon, characterize OxyR-mediated dynamic regulation, and dissect the redundant roles of multiple H 2 O 2 scavenging systems. By examining single-cell behavior, we serendipitously discover that the combined effects of H 2 O 2 and flow block pilus-driven surface migration. Thus, our results counter previous studies and reveal that natural levels of H 2 O 2 and flow synergize to restrict bacterial colonization and survival. By studying two stressors at once, our research highlights the limitations of oversimplifying nature and demonstrates that physical and chemical stress can combine to yield unpredictable effects.

The footprint of gut microbiota in gallbladder cancer: a mechanistic review

Gallbladder cancer (GBC) is the most common malignant tumor of the biliary system with the worst prognosis. Even after radical surgery, the majority of patients with GBC have difficulty achieving a clinical cure. The risk of tumor recurrence remains more than 65%, and the overall 5-year survival rate is less than 5%. The gut microbiota refers to a variety of microorganisms living in the human intestine, including bacteria, viruses and fungi, which profoundly affect the host state of general health, disease and even cancer. Over the past few decades, substantial evidence has supported that gut microbiota plays a critical role in promoting the progression of GBC. In this review, we summarize the functions, molecular mechanisms and recent advances of the intestinal microbiota in GBC. We focus on the driving role of bacteria in pivotal pathways, such as virulence factors, metabolites derived from intestinal bacteria, chronic inflammatory responses and ecological niche remodeling. Additionally, we emphasize the high level of correlation between viruses and fungi, especially EBV and Candida spp., with GBC. In general, this review not only provides a solid theoretical basis for the close relationship between gut microbiota and GBC but also highlights more potential research directions for further research in the future.

Defying the odds: Determinants of the antimicrobial response of Salmonella Typhi and their interplay

Salmonella Typhi, the invasive serovar of S. enterica subspecies enterica, causes typhoid fever in healthy human hosts. The emergence of antibiotic-resistant strains has consistently challenged the successful treatment of typhoid fever with conventional antibiotics. Antimicrobial resistance (AMR) in Salmonella is acquired either by mutations in the genomic DNA or by acquiring extrachromosomal DNA via horizontal gene transfer. In addition, Salmonella can form a subpopulation of antibiotic persistent (AP) cells that can survive at high concentrations of antibiotics. These have reduced the effectiveness of the first and second lines of antibiotics used to treat Salmonella infection. The recurrent and chronic carriage of S. Typhi in human hosts further complicates the treatment process, as a remarkable shift in the immune response from pro-inflammatory Th1 to anti-inflammatory Th2 is observed. Recent studies have also highlighted the overlap between AP, persistent infection (PI) and AMR. These incidents have revealed several areas of research. In this review, we have put forward a timeline for the evolution of antibiotic resistance in Salmonella and discussed the different mechanisms of the same availed by the pathogen at the genotypic and phenotypic levels. Further, we have presented a detailed discussion on Salmonella antibiotic persistence (AP), PI, the host and bacterial virulence factors that can influence PI, and how both AP and PI can lead to AMR.

The role of bacteria in gallstone formation

Gallstones are a prevalent biliary system disorder that is particularly common in women. They can lead to various complications, such as biliary colic, infection, cholecystitis, and even gallbladder cancer. However, the etiology of gallstones remains incompletely understood. The significant role of bacteria in gallstone formation has been demonstrated in recent studies. Certain bacteria not only influence bile composition and the gallbladder environment but also actively participate in stone formation by producing enzymes such as β-glucuronidase and mucus. Therefore, this review aimed to analyze the mechanisms involving the types and quantities of bacteria involved in gallstone formation, providing valuable references for understanding the etiology and clinical treatment of gallstones.

The One-Stop Integrated Nanoagent Based on Photothermal Therapy for Deep Infection Healing and Inflammation Inhibition

Chronic wounds caused by bacterial infections are a major challenge in medical fields. The hypoxia condition extremely induces reactive oxygen species (ROS) generation and upregulates the expression of hypoxia-inducible factor, both of which can increase the pro-inflammatory M1 subtype macrophages production while reducing the anti-inflammatory M2 subtype macrophages. Besides, bacteria-formed biofilms can hinder the penetration of therapeutic agents. Encouraged by natural motors automatically executing tasks, hypothesized that supplying sufficient oxygen (O2 ) would simultaneously drive therapeutic agent movement, rescue the hypoxic microenvironment, and disrupt the vicious cycle of inflammation. Here, small organic molecule-based nanoparticles (2TT-mC6B@Cu5.4 O NPs) that possess high photothermal conversion efficiency and enzymatic activities are developed, including superoxide dismutase-, catalase-, and glutathione peroxidase-like activity. 2TT-mC6B@Cu5.4 O NPs exhibit superior ROS-scavenging and O2 production abilities that synergistically relieve inflammation, alleviate hypoxia conditions, and promote their deep penetration in chronic wound tissues. Transcriptome analysis further demonstrates that 2TT-mC6B@Cu5.4O NPs inhibit biological activities inside bacteria. Furthermore, in vivo experiments prove that 2TT-mC6B@Cu5.4 O NPs-based hyperthermia can effectively eliminate bacteria in biofilms to promote wound healing.

Epinephrine Stimulates Mycobacterium tuberculosis Growth and Biofilm Formation

The human stress hormones catecholamines play a critical role in communication between human microbiota and their hosts and influence the outcomes of bacterial infections. However, it is unclear how M. tuberculosis senses and responds to certain types of human stress hormones. In this study, we screened several human catecholamine stress hormones (epinephrine, norepinephrine, and dopamine) for their effects on Mycobacterium growth. Our results showed that epinephrine significantly stimulated the growth of M. tuberculosis in the serum-based medium as well as macrophages. In silico analysis and molecular docking suggested that the extra-cytoplasmic domain of the MprB might be the putative adrenergic sensor. Furthermore, we showed that epinephrine significantly enhances M. tuberculosis biofilm formation, which has distinct texture composition, antibiotic resistance, and stress tolerance. Together, our data revealed the effect and mechanism of epinephrine on the growth and biofilm formation of M. tuberculosis, which contributes to the understanding of the environmental perception and antibiotic resistance of M. tuberculosis and provides important clues for the understanding of bacterial pathogenesis and the development of novel antibacterial therapeutics.

Advancing understanding of microbial biofilms through machine learning-powered studies

Microbial biofilms are prevalent in various environments and pose significant challenges to food safety and public health. The biofilms formed by pathogens can cause food spoilage, foodborne illness, and infectious diseases, which are difficult to treat due to their enhanced antimicrobial resistance. While the composition and development of biofilms have been widely studied, their profound impact on food, the food industry, and public health has not been sufficiently recapitulated. This review aims to provide a comprehensive overview of microbial biofilms in the food industry and their implication on public health. It highlights the existence of biofilms along the food-producing chains and the underlying mechanisms of biofilm-associated diseases. Furthermore, this review thoroughly summarizes the enhanced understanding of microbial biofilms achieved through machine learning approaches in biofilm research. By consolidating existing knowledge, this review intends to facilitate developing effective strategies to combat biofilm-associated infections in both the food industry and public health.

Screening of lipid-A related genes and development of low-endotoxicity live-attenuated Salmonella gallinarum by arnT deletion that elicits immune responses and protection against fowl typhoid in chickens

In the present study, lipid-A gene mutants of Salmonella gallinarum (SG) were screened, and the arnT mutant exhibited optimal acidic and oxidative-stress and macrophage-survival. Modifying lipid-A by arnT-deletion resulted in significantly reduced endotoxicity, virulence, and mortality. Therefore, the arnT-deleted vaccine-candidate strain JOL2841 was constructed and demonstrated to be safe due to appropriate clearance by the chicken immune system. The reduced-endotoxicity of JOL2841 was evident from the downregulation of TNFα and IL-1β inflammatory cytokines, no inflammatory signs in organ gross-examination, and histopathological analysis. The IgY and IgA antibody titres, CD4, and CD8 T-cell population improvements, and IL-4, IL-2, and INFγ expression decipher the profound Th2 and Th1 immunogenicity. Consequently, JOL2841 exhibited prominent protection against wild-type SG challenge, as revealed by organ pathogen-load determination, organ gross-examination, and histopathological examination. Overall, the study represented the first report of arnT deficient SG resulted in negligible endotoxicity, low-virulence, safety and coordinated elicitation of humoral and cell-mediated immune response in chickens.

From Eberthella typhi to Salmonella Typhi: The Fascinating Journey of the Virulence and Pathogenicity of Salmonella Typhi

Salmonella Typhi (S. Typhi), the invasive typhoidal serovar of Salmonella enterica that causes typhoid fever in humans, is a severe threat to global health. It is one of the major causes of high morbidity and mortality in developing countries. According to recent WHO estimates, approximately 11-21 million typhoid fever illnesses occur annually worldwide, accounting for 0.12-0.16 million deaths. Salmonella infection can spread to healthy individuals by the consumption of contaminated food and water. Typhoid fever in humans sometimes is accompanied by several other critical extraintestinal complications related to the central nervous system, cardiovascular system, pulmonary system, and hepatobiliary system. Salmonella Pathogenicity Island-1 and Salmonella Pathogenicity Island-2 are the two genomic segments containing genes encoding virulent factors that regulate its invasion and systemic pathogenesis. This Review aims to shed light on a comparative analysis of the virulence and pathogenesis of the typhoidal and nontyphoidal serovars of S. enterica.

Collective protection against the type VI secretion system in bacteria

Bacteria commonly face attacks from other strains using the type VI secretion system (T6SS), which acts like a molecular speargun to stab and intoxicate competitors. Here we show how bacteria can work together to collectively defend themselves against these attacks. This project began with an outreach activity: while developing an online computer game of bacterial warfare, we noticed that one strategist ("Slimy") that made extracellular polymeric substances (EPS) was able to resist attacks from another strategist that employed the T6SS ("Stabby"). This observation motivated us to model this scenario more formally, using dedicated agent-based simulations. The model predicts that EPS production can serve as a collective defence mechanism, which protects both producing cells and neighbouring cells that do not make EPS. We then tested our model with a synthetic community that contains a T6SS-wielding attacker (Acinetobacter baylyi), and two T6SS-sensitive target strains (Escherichia coli) that either secrete EPS, or not. As predicted by our modelling, we find that the production of EPS leads to collective protection against T6SS attacks, where EPS producers protect each other and nearby non-producers. We identify two processes that explain this protection: EPS sharing between cells and a second general mechanism whereby groups of resistant cells shield susceptible cells, which we call "flank protection". Our work shows how EPS-producing bacteria can work together to defend themselves from the type VI secretion system.

The progress in titanium alloys used as biomedical implants: From the view of reactive oxygen species

Titanium and Titanium alloys are widely used as biomedical implants in oral and maxillofacial surgery, due to superior mechanical properties and biocompatibility. In specific clinical populations such as the elderly, diabetics and patients with metabolic diseases, the failure rate of medical metal implants is increased significantly, putting them at increased risk of revision surgery. Many studies show that the content of reactive oxygen species (ROS) in the microenvironment of bone tissue surrounding implant materials is increased in patients undergoing revision surgery. In addition, the size and shape of materials, the morphology, wettability, mechanical properties, and other properties play significant roles in the production of ROS. The accumulated ROS break the original balance of oxidation and anti-oxidation, resulting in host oxidative stress. It may accelerate implant degradation mainly by activating inflammatory cells. Peri-implantitis usually leads to a loss of bone mass around the implant, which tends to affect the long-term stability and longevity of implant. Therefore, a great deal of research is urgently needed to focus on developing antibacterial technologies. The addition of active elements to biomedical titanium and titanium alloys greatly reduce the risk of postoperative infection in patients. Besides, innovative technologies are developing new biomaterials surfaces conferring anti-infective properties that rely on the production of ROS. It can be considered that ROS may act as a messenger substance for the communication between the host and the implanted material, which run through the entire wound repair process and play a role that cannot be ignored. It is necessary to understand the interaction between oxidative stress and materials, the effects of oxidative stress products on osseointegration and implant life as well as ROS-induced bactericidal activity. This helps to facilitate the development of a new generation of well-biocompatible implant materials with ROS responsiveness, and ultimately prolong the lifespan of implants.

Identification of a Host-Targeted Compound to Control Typhoid Fever

Typhoid fever is caused primarily by the enteric microbe Salmonella enterica serovar Typhi and remains a major global health problem with approximately 14 million new infections and 136,000 fatalities annually. While there are antibiotic options available to treat the disease, the global increase in multidrug-resistant strains necessitates alternative therapeutic options. Host-targeted therapeutics present a promising anti-infective strategy against intracellular bacterial pathogens. A cell-based assay identified a compound that inhibits Salmonella proliferation in infected cells, 2-(3-hydroxypropyl)-1-(3-phenoxyphenyl)-1,2-dihydrochromeno[2,3-c]pyrrole-3,9-dione (KH-1), which is devoid of direct activity against Salmonella. The compound inhibits the growth of both antibiotic-sensitive and -resistant Salmonella strains inside macrophages and reduces lactate dehydrogenase (LDH) release from Salmonella-infected cells. Subsequent screening of KH-1 commercial analogs identified 2-(4-fluorobenzyl)-1-(3-phenoxyphenyl)-1,2-dihydrochromeno[2,3-c] pyrrole-3,9-dione (KH-1-2), which is more effective in controlling Salmonella growth inside macrophages. In vitro KH-1-2 treatment of Salmonella infection resulted in an 8- to 10-fold reduction in bacterial load in infected macrophages. In combination with suboptimal ciprofloxacin treatment, KH-1-2 further reduces Salmonella growth inside macrophages. The toxicity and efficacy of KH-1-2 in controlling Salmonella infection were examined in vivo using a mouse model of typhoid fever. No significant compound-related clinical signs and histological findings of the liver, spleen, or kidney were observed from uninfected mice that were intraperitoneally treated with KH-1-2. KH-1-2 significantly protected mice from a lethal dose of infection by an antibiotic-resistant Salmonella strain. Thus, our study provides support that this is a promising lead compound for the development of a novel host-targeted therapeutic agent to control typhoid fever.

IMPORTANCESalmonella spp. cause significant morbidity and mortality worldwide. Typhoidal spp. (e.g., S. Typhi) cause a systemic disease typically treated with antibiotics. However, growing antibiotic resistance is resulting in increased treatment failures. We screened a compound library for those that would reduce Salmonella-induced macrophage toxicity, identifying compound KH-1. KH-1 has no direct effects on the bacteria but limits Salmonella survival in macrophages and protects against lethal infection in a mouse model of typhoid fever. A suboptimal concentration of ciprofloxacin worked in conjunction with the compound to further decrease Salmonella survival in macrophages. An analog (KH-1-2) was identified that possessed increased activity in vitro in macrophages and in vivo against both antibiotic-sensitive and -resistant strains. Thus, we report the identification of a lead compound that may be a useful scaffold as a host-directed antimicrobial against typhoid fever.

Capsules and Extracellular Polysaccharides in Escherichia coli and Salmonella

Escherichia coli and Salmonella isolates produce a range of different polysaccharide structures that play important roles in their biology. E. coli isolates often possess capsular polysaccharides (K antigens), which form a surface structural layer. These possess a wide range of repeat-unit structures. In contrast, only one capsular polymer (Vi antigen) is found in Salmonella, and it is confined to typhoidal serovars. In both genera, capsules are vital virulence determinants and are associated with the avoidance of host immune defenses. Some isolates of these species also produce a largely secreted exopolysaccharide called colanic acid as part of their complex Rcs-regulated phenotypes, but the precise function of this polysaccharide in microbial cell biology is not fully understood. E. coli isolates produce two additional secreted polysaccharides, bacterial cellulose and poly-N-acetylglucosamine, which play important roles in biofilm formation. Cellulose is also produced by Salmonella isolates, but the genes for poly-N-acetylglucosamine synthesis appear to have been lost during its evolution toward enhanced virulence. Here, we discuss the structures, functions, relationships, and sophisticated assembly mechanisms for these important biopolymers.

Salmonella Biofilms Tolerate Hydrogen Peroxide by a Combination of Extracellular Polymeric Substance Barrier Function and Catalase Enzymes

The ability of Salmonella enterica subspecies enterica serovar Typhi (S. Typhi) to cause chronic gallbladder infections is dependent on biofilm growth on cholesterol gallstones. Non-typhoidal Salmonella (e.g. S. Typhimurium) also utilize the biofilm state to persist in the host and the environment. How the pathogen maintains recalcitrance to the host response, and oxidative stress in particular, during chronic infection is poorly understood. Previous experiments demonstrated that S. Typhi and S. Typhimurium biofilms are tolerant to hydrogen peroxide (H₂O₂), but that mutations in the biofilm extracellular polymeric substances (EPSs) O antigen capsule, colanic acid, or Vi antigen reduce tolerance. Here, biofilm-mediated tolerance to oxidative stress was investigated using a combination of EPS and catalase mutants, as catalases are important detoxifiers of H₂O₂. Using co-cultured biofilms of wild-type (WT) bacteria with EPS mutants, it was demonstrated that colanic acid in S. Typhimurium and Vi antigen in S. Typhi have a community function and protect all biofilm-resident bacteria rather than to only protect the individual cells producing the EPSs. However, the H₂O₂ tolerance deficiency of a O antigen capsule mutant was unable to be compensated for by co-culture with WT bacteria. For curli fimbriae, both WT and mutant strains are tolerant to H₂O₂ though unexpectedly, co-cultured WT/mutant biofilms challenged with H₂O₂ resulted in sensitization of both strains, suggesting a more nuanced oxidative resistance alteration in these co-cultures. Three catalase mutant (katE, katG and a putative catalase) biofilms were also examined, demonstrating significant reductions in biofilm H₂O₂ tolerance for the katE and katG mutants. Biofilm co-culture experiments demonstrated that catalases exhibit a community function. We further hypothesized that biofilms are tolerant to H₂O₂ because the physical barrier formed by EPSs slows penetration of H₂O₂ into the biofilm to a rate that can be mitigated by intra-biofilm catalases. Compared to WT, EPS-deficient biofilms have a heighted response even to low-dose (2.5 mM) H₂O₂ challenge, confirming that resident bacteria of EPS-deficient biofilms are under greater stress and have limited protection from H₂O₂. Thus, these data provide an explanation for how Salmonella achieves tolerance to H₂O₂ by a combination of an EPS-mediated barrier and enzymatic detoxification.

Sulfate Import in Salmonella Typhimurium Impacts Bacterial Aggregation and the Respiratory Burst in Human Neutrophils

During enteric salmonellosis, neutrophil-generated reactive oxygen species alter the gut microenvironment, favoring survival of Salmonella Typhimurium. While type 3 secretion system 1 (T3SS-1) and flagellar motility are potent Salmonella Typhimurium agonists of the neutrophil respiratory burst in vitro, neither of these pathways alone is responsible for stimulation of a maximal respiratory burst. To identify Salmonella Typhimurium genes that impact the magnitude of the neutrophil respiratory burst, we performed a two-step screen of defined mutant libraries in coculture with human neutrophils. We first screened Salmonella Typhimurium mutants lacking defined genomic regions and then tested single-gene deletion mutants representing particular regions under selection. A subset of single-gene deletion mutants was selected for further investigation. Mutants in four genes, STM1696 (sapF), STM2201 (yeiE), STM2112 (wcaD), and STM2441 (cysA), induced an attenuated respiratory burst. We linked the altered respiratory burst to reduced T3SS-1 expression and/or altered flagellar motility for two mutants (ΔSTM1696 and ΔSTM2201). The ΔSTM2441 mutant, defective for sulfate transport, formed aggregates in minimal medium and adhered to surfaces in rich medium, suggesting a role for sulfur homeostasis in the regulation of aggregation/adherence. We linked the aggregation/adherence phenotype of the ΔSTM2441 mutant to biofilm-associated protein A and flagellins and hypothesize that aggregation caused the observed reduction in the magnitude of the neutrophil respiratory burst. Our data demonstrate that Salmonella Typhimurium has numerous mechanisms to limit the magnitude of the neutrophil respiratory burst. These data further inform our understanding of how Salmonella may alter human neutrophil antimicrobial defenses.

Salmonella Biofilm Formation, Chronic Infection, and Immunity Within the Intestine and Hepatobiliary Tract

Within the species of Salmonella enterica, there is significant diversity represented among the numerous subspecies and serovars. Collectively, these account for microbes with variable host ranges, from common plant and animal colonizers to extremely pathogenic and human-specific serovars. Despite these differences, many Salmonella species find commonality in the ability to form biofilms and the ability to cause acute, latent, or chronic disease. The exact outcome of infection depends on many factors such as the growth state of Salmonella, the environmental conditions encountered at the time of infection, as well as the infected host and immune response elicited. Here, we review the numerous biofilm lifestyles of Salmonella (on biotic and abiotic surfaces) and how the production of extracellular polymeric substances not only enhances long-term persistence outside the host but also is an essential function in chronic human infections. Furthermore, careful consideration is made for the events during initial infection that allow for gut transcytosis which, in conjunction with host immune functions, often determine the progression of disease. Both typhoidal and non-typhoidal salmonellae can cause chronic and/or secondary infections, thus the adaptive immune responses to both types of bacteria are discussed with particular attention to the differences between Salmonella Typhi, Salmonella Typhimurium, and invasive non-typhoidal Salmonella that can result in differential immune responses. Finally, while strides have been made in our understanding of immunity to Salmonella in the lymphoid organs, fewer definitive studies exist for intestinal and hepatobiliary immunity. By examining our current knowledge and what remains to be determined, we provide insight into new directions in the field of Salmonella immunity, particularly as it relates to chronic infection.

Antibiofilm peptides: overcoming biofilm-related treatment failure

Health leaders and scientists worldwide consider antibiotic resistance among the world's most dangerous pathogens as one of the biggest threats to global health. Antibiotic resistance has largely been attributed to genetic changes, but the role and recalcitrance of biofilms, largely due to growth state dependent adaptive resistance, is becoming increasingly appreciated. Biofilms are mono- and multi-species microbial communities embedded in an extracellular, protective matrix. In this growth state, bacteria are transcriptionally primed to survive extracellular stresses. Adaptations, affecting metabolism, regulation, surface charge, immune recognition and clearance, allow bacteria to thrive in the human body and withstand antibiotics and the host immune system. Biofilms resist clearance by multiple antibiotics and have a major role in chronic infections, causing more than 65% of all infections. No specific antibiofilm agents have been developed. Thus, there is a pressing need for alternatives to traditional antibiotics that directly inhibit and/or eradicate biofilms. Host defence peptides (HDPs) are small cationic peptides that are part of the innate immune system to both directly kill microbes but also function to modulate the immune response. Specific HDPs and their derivatives demonstrate broad-spectrum activity against biofilms. In vivo biofilm assays show efficacy in abscess, respiratory, in-dwelling device, contact lens and skin infection models. Further progress has been made through the study of ex vivo organoid and air-liquid interface models to better understand human infections and treatment while relieving the burden and complex nature of animal models. These avenues pave the way for a better understanding and treatment of the underlying cause of chronic infections that challenge the healthcare system.