The role of flagella and chemotaxis genes in host pathogen interaction of the host adapted Salmonella enterica serovar Dublin compared to the broad host range serovar S. Typhimurium

Unveiling the synergistic potency of chlorhexidine and azithromycin in combined action

The growing challenge of antibiotic resistance necessitates novel approaches for combating bacterial infections. This study explores the distinctive synergy between chlorhexidine, an antiseptic and disinfectant agent, and azithromycin, a macrolide antibiotic, in their impact on bacterial growth and virulence factors using Escherichia coli strain Crooks (ATCC 8739) as a model. Our findings reveal that the chlorhexidine and azithromycin combination demonstrates enhanced anti-bacterial effects compared to individual treatments. Intriguingly, the combination induced oxidative stress, decreased flagellin expression, impaired bacterial motility, and enhanced bacterial autoaggregation. Notably, the combined treatment also demonstrated a substantial reduction in bacterial adherence to colon epithelial cells and downregulated NF-κB in the epithelial cells. In conclusion, these results shed light on the potential of the chlorhexidine and azithromycin synergy as a compelling strategy to address the rising challenge of antibiotic resistance and may pave the way for innovative therapeutic interventions in tackling bacterial infections.

Advancements in bacterial chemotaxis: Utilizing the navigational intelligence of bacteria and its practical applications

The fascinating world of microscopic life unveils a captivating spectacle as bacteria effortlessly maneuver through their surroundings with astonishing accuracy, guided by the intricate mechanism of chemotaxis. This review explores the complex mechanisms behind this behavior, analyzing the flagellum as the driving force and unraveling the intricate signaling pathways that govern its movement. We delve into the hidden costs and benefits of this intricate skill, analyzing its potential to propagate antibiotic resistance gene while shedding light on its vital role in plant colonization and beneficial symbiosis. We explore the realm of human intervention, considering strategies to manipulate bacterial chemotaxis for various applications, including nutrient cycling, algal bloom and biofilm formation. This review explores the wide range of applications for bacterial capabilities, from targeted drug delivery in medicine to bioremediation and disease control in the environment. Ultimately, through unraveling the intricacies of bacterial movement, we can enhance our comprehension of the intricate web of life on our planet. This knowledge opens up avenues for progress in fields such as medicine, agriculture, and environmental conservation.

Dynamic microbiome disassembly and evolution induced by antimicrobial methylisothiazolinone in sludge anaerobic fermentation for volatile fatty acids generation

In the post-COVID-19 pandemic era, various antimicrobials have emerged and concentrated in waste-activated sludge (WAS), affecting the biological treatment of WAS. However, there is still a knowledge gap in the dynamic response and adaptive mechanism of anaerobic microbiome under exogenous antimicrobial stress. This study found that methylisothiazolinone (MIT, as a typic antimicrobial) caused an interesting lag effect on the volatile fatty acids (VFAs) promotion in the WAS anaerobic fermentation process. MIT was effective to disintegrate the extracellular polymeric substances (EPS), and those functional anaerobic microorganisms were easily exposed and negatively impacted by the MIT interference after the loss of protective barriers. Correspondingly, the ecological interactions and microbial metabolic functions related to VFA biosynthesis (e.g., pyruvate metabolism) were downregulated at the initial stage. The syntrophic consortia gradually adapted to the interference and attenuated the MIT stress by activating chemotaxis and resistance genes (e.g., excreting, binding, and inactivating). Due to the increased bioavailable substrates in the fermentation systems, the dominant microorganisms (i.e., Clostridium and Caloramator) with both VFAs production and MIT-tolerance functions have been domesticated. Moreover, MIT disrupted the syntrophic interaction between acetogens and methanogens and totally suppressed methanogens' metabolic activities. The VFA production derived from WAS anaerobic fermentation was therefore enhanced due to the interference of antimicrobial MIT stress. This work deciphered dynamic changes and adaptive evolution of anaerobic syntrophic consortia in response to antimicrobial stress and provided guidance on the evaluation and control of the ecological risks of exogenous pollutants in WAS treatment.

Review: Salmonella Dublin in dairy cattle

Salmonella enterica serovar Dublin (S. Dublin) is a bacterium host-adapted to cattle with increasing prevalence in dairy facilities. It can severely affect cattle health, producing high morbidity and mortality in young calves and reducing the performance of mature animals. Salmonella Dublin is difficult to control and eradicate from herds, as it can be shed from clinically normal animals. In addition, S. Dublin is a zoonotic bacterium that can be lethal for humans and pose a risk for human and animal health due to its multi-drug resistant characteristics. This review provides an overview of S. Dublin as a pathogen in dairy facilities, the risk factors associated with infection, and current strategies for preventing and controlling this disease. Furthermore, current gaps in knowledge are also discussed.

Machine learning-based motion tracking reveals an inverse correlation between adhesivity and surface motility of the leptospirosis spirochete

Bacterial motility is often a crucial virulence factor for pathogenic species. A common approach to study bacterial motility is fluorescent labeling, which allows detection of individual bacterial cells in a population or in host tissues. However, the use of fluorescent labeling can be hampered by protein expression stability and/or interference with bacterial physiology. Here, we apply machine learning to microscopic image analysis for label-free motion tracking of the zoonotic bacterium Leptospira interrogans on cultured animal cells. We use various leptospiral strains isolated from a human patient or animals, as well as mutant strains. Strains associated with severe disease, and mutant strains lacking outer membrane proteins (OMPs), tend to display fast mobility and reduced adherence on cultured kidney cells. Our method does not require fluorescent labeling or genetic manipulation, and thus could be applied to study motility of many other bacterial species.

Transcriptional Profiling of the Effect of Coleus amboinicus L. Essential Oil against Salmonella Typhimurium Biofilm Formation

Salmonella enterica serovar Typhimurium cause infections primarily through foodborne transmission and remains a significant public health concern. The biofilm formation of this bacteria also contributes to their multidrug-resistant nature. Essential oils from medicinal plants are considered potential alternatives to conventional antibiotics. Therefore, this study assessed the antimicrobial and antibiofilm activities of Coleus amboinicus essential oil (EO-CA) against S. Typhimurium ATCC 14028. Seventeen chemical compounds of EO-CA were identified, and carvacrol (38.26%) was found to be the main constituent. The minimum inhibitory concentration (MIC) of EO-CA for S. Typhimurium planktonic growth was 1024 µg/mL while the minimum bactericidal concentration was 1024 µg/mL. EO-CA at sub-MIC (≥1/16× MIC) exhibited antibiofilm activity against the prebiofilm formation of S. Typhimurium at 24 h. Furthermore, EO-CA (≥1/4× MIC) inhibited postbiofilm formation at 24 and 48 h (p < 0.05). Transcriptional profiling revealed that the EO-CA-treated group at 1/2× MIC had 375 differentially expressed genes (DEGs), 106 of which were upregulated and 269 were downregulated. Five significantly downregulated virulent DEGs responsible for motility (flhD, fljB, and fimD), curli fimbriae (csgD), and invasion (hilA) were screened via quantitative reverse transcription PCR (qRT-PCR). This study suggests the potential of EO-CA as an effective antimicrobial agent for combating planktonic and biofilm formation of Salmonella.

Engineer a double team of short-lived and glucose-sensing bacteria for cancer eradication

Rationally designed and engineered bacteria represent an emerging unique approach for cancer treatment. Here, we engineer a short-lived bacterium, mp105, that is effective against diverse cancer types and safe for intravenous administration. We reveal that mp105 combats cancer by direct oncolysis, depletion of tumor-associated macrophages, and elicitation of CD4⁺ T cell immunity. We further engineer a glucose-sensing bacterium named m6001 that selectively colonizes solid tumors. When intratumorally injected, m6001 clears tumors more efficiently than mp105 due to its post-delivery replication in tumors and potent oncolytic capacity. Finally, we combine intravenous injection of mp105 and intratumoral injection of m6001, forming a double team against cancer. The double team enhances cancer therapy compared with single treatment for subjects carrying both intratumorally injectable and uninjectable tumors. The two anticancer bacteria and their combination are applicable to different scenarios, turning bacterial therapy for cancer into a feasible solution.

Host control and the evolution of cooperation in host microbiomes

Humans, and many other species, are host to diverse symbionts. It is often suggested that the mutual benefits of host-microbe relationships can alone explain cooperative evolution. Here, we evaluate this hypothesis with evolutionary modelling. Our model predicts that mutual benefits are insufficient to drive cooperation in systems like the human microbiome, because of competition between symbionts. However, cooperation can emerge if hosts can exert control over symbionts, so long as there are constraints that limit symbiont counter evolution. We test our model with genomic data of two bacterial traits monitored by animal immune systems. In both cases, bacteria have evolved as predicted under host control, tending to lose flagella and maintain butyrate production when host-associated. Moreover, an analysis of bacteria that retain flagella supports the evolution of host control, via toll-like receptor 5, which limits symbiont counter evolution. Our work puts host control mechanisms, including the immune system, at the centre of microbiome evolution.

Multiple functions of flagellar motility and chemotaxis in bacterial physiology

Most swimming bacteria are capable of following gradients of nutrients, signaling molecules and other environmental factors that affect bacterial physiology. This tactic behavior became one of the most-studied model systems for signal transduction and quantitative biology, and underlying molecular mechanisms are well characterized in Escherichia coli and several other model bacteria. In this review, we focus primarily on less understood aspect of bacterial chemotaxis, namely its physiological relevance for individual bacterial cells and for bacterial populations. As evident from multiple recent studies, even for the same bacterial species flagellar motility and chemotaxis might serve multiple roles, depending on the physiological and environmental conditions. Among these, finding sources of nutrients and more generally locating niches that are optimal for growth appear to be one of the major functions of bacterial chemotaxis, which could explain many chemoeffector preferences as well as flagellar gene regulation. Chemotaxis might also generally enhance efficiency of environmental colonization by motile bacteria, which involves intricate interplay between individual and collective behaviors and trade-offs between growth and motility. Finally, motility and chemotaxis play multiple roles in collective behaviors of bacteria including swarming, biofilm formation and autoaggregation, as well as in their interactions with animal and plant hosts.

Molecular Basis for the Activation of Human Innate Immune Response by the Flagellin Derived from Plant-Pathogenic Bacterium, Acidovorax avenae

Acidovorax avenae is a flagellated, pathogenic bacterium to various plant crops that has also been found in human patients with haematological malignancy, fever, and sepsis; however, the exact mechanism for infection in humans is not known. We hypothesized that the human innate immune system could be responsive to the purified flagellin isolated from A. avenae, named FLA-AA. We observed the secretion of inflammatory cytokines such as tumor necrosis factor-alpha (TNF-α), interleukin (IL)-6, and IL-8 by treating FLA-AA to human dermal fibroblasts, as well as macrophages. This response was exclusively through TLR5, which was confirmed by using TLR5-overexpression cell line, 293/hTLR5, as well as TLR5-specific inhibitor, TH1020. We also observed the secretion of inflammatory cytokine, IL-1β, by the activation of NLRC4 with FLA-AA. Overall, our results provide a molecular basis for the inflammatory response caused by FLA-AA in cell-based assays.

Salmonella enterica Subsp. houtenae Associated with an Abscess in Young Roe Deer (Capreolus capreolus)

BACKGROUND

S. enterica subsp. houtenae has been rarely documented, and very limited genomic information is available. This report describes a rare case of primary extraintestinal salmonellosis in a young roe deer, associated with Salmonella enterica subsp. houtenae.&nbsp;Methods: A traditional cultural-based analysis was carried out from the contents of a neck abscess; biochemical identification and PCR assay were performed to isolate and identify the pathogen. Through whole-genome sequencing (WGS), multilocus sequence typing (MLST), core genome MLST (cgMLST), and the Salmonella pathogenicity islands (SPIs) survey, resistome and virulome genes were investigated to gain insight into the virulence and antimicrobial resistance of S. houtenae.

RESULTS

Biochemical identification and PCR confirmed the presence of Salmonella spp. in the swelling. The WGS analysis identified Salmonella enterica subspecies houtenae serovar 43:z4,z23:- and ST 958. The virulence study predicted a multidrug resistance pattern with resistance shown against aminoglycosides, tetracycline, beta-lactamase, fluoroquinolones, fosfomycin, nitroimidazole, aminocoumarin, and peptide. Fifty-three antibiotic-resistant genes were identified. No plasmids were detected.

CONCLUSION

This study demonstrates the importance of continuous surveillance of pathogenic salmonellae. Biomolecular analyses combined with epidemiological data can provide important information about poorly described Salmonella strains and can help to improve animal welfare.

Cluster II che genes of Pseudomonas syringae pv. tabaci 6605, orthologs of cluster I in Pseudomonas aeruginosa, are required for chemotaxis and virulence

Pseudomonas syringae pv. tabaci 6605 (Pta6605) is a causal agent of wildfire disease in host tobacco plants and is highly motile. Pta6605 has multiple clusters of chemotaxis genes including cheA, a gene encoding a histidine kinase, cheY, a gene encoding a response regulator, mcp, a gene for a methyl-accepting chemotaxis protein, as well as flagellar and pili biogenesis genes. However, only two major chemotaxis gene clusters, cluster I and cluster II, possess cheA and cheY. Deletion mutants of cheA or cheY were constructed to evaluate their possible role in Pta6605 chemotaxis and virulence. Motility tests and a chemotaxis assay to known attractant demonstrated that cheA2 and cheY2 mutants were unable to swarm and to perform chemotaxis, whereas cheA1 and cheY1 mutants retained chemotaxis ability almost equal to that of the wild-type (WT) strain. Although WT and cheY1 mutants of Pta6605 caused severe disease symptoms on host tobacco leaves, the cheA2 and cheY2 mutants did not, and symptom development with cheA1 depended on the inoculation method. These results indicate that chemotaxis genes located in cluster II are required for optimal chemotaxis and host plant infection by Pta6605 and that cluster I may partially contribute to these phenotypes.

Single Cell Analysis of Bistable Expression of Pathogenicity Island 1 and the Flagellar Regulon in Salmonella enterica

Bistable expression of the Salmonella enterica pathogenicity island 1 (SPI-1) and the flagellar network (Flag) has been described previously. In this study, simultaneous monitoring of OFF and ON states in SPI-1 and in the flagellar regulon reveals independent switching, with concomitant formation of four subpopulations: SPI-1^OFF Flag^OFF, SPI-1^OFF Flag^ON, SPI-1^ON Flag^OFF, and SPI-1^ON Flag^ON. Invasion assays upon cell sorting show that none of the four subpopulations is highly invasive, thus raising the possibility that Flag^OFF cells might contribute to optimal invasion as previously proposed for SPI-1^OFF cells. Time lapse microscopy observation indicates that expression of the flagellar regulon contributes to the growth impairment previously described in SPI-1^ON cells. As a consequence, growth resumption in SPI-1^ON Flag^ON cells requires switching to both SPI-1^OFF and Flag^OFF states.

Immunogenicity and protection efficacy of a Salmonella enterica serovar Typhimurium fnr, arcA and fliC mutant

Salmonella enterica serovar Typhimurium is a major food-borne pathogen that can cause self-limited gastroenteritis or life-threatening invasive diseases in humans. There is no licensed S. Typhimurium vaccine for humans to date. In this study, we attempted to construct a live attenuated vaccine strain of S. Typhimurium based on three genes, namely, the two global regulator genes fnr and arcA and the flagellin subunit gene fliC. The S. Typhimurium three-gene mutant, named SLT39 (ΔfnrΔarcAΔfliC), exhibited a high level of attenuation with a colonization defect in mouse tissues and approximately 10⁴-fold decreased virulence compared with that of the wild-type strain. To evaluate the immunogenicity and protection efficacy of STL39, mice were inoculated twice with a dose of 10⁷ CFU or 10⁸ CFU at a 28-day interval, and the immunized mice were challenged with a lethal dose of the wild-type S. Typhimurium strain one month post second immunization. Compared with mock immunization, SLT39 immunization with either dose elicited significant serum total IgG, IgG1 and IgG2a and faecal IgA responses against inactivated S. Typhimurium antigens at a comparable level post second immunization, whereas the 10⁸ CFU group induced higher levels of duodenal and caecal IgA than the 10⁷ CFU group. Furthermore, the bacterial loads in mouse tissues, including Peyer's patches, spleen and liver, significantly decreased in the two SLT39 immunization groups compared to those in the control group post challenge. Additionally, all mice in the SLT39 (10⁸ CFU) group and 80% of the mice in the SLT39 (10⁷ CFU) group survived the lethal challenge, suggesting full protection and 80% protection efficacy, respectively. Thus, the S. Typhimurium fnr, arcA and fliC mutant proved to be a potential attenuated live vaccine candidate for prevention of homologous infection.

The interaction of Escherichia coli O157 :H7 and Salmonella Typhimurium flagella with host cell membranes and cytoskeletal components

Bacterial flagella have many established roles beyond swimming motility. Despite clear evidence of flagella-dependent adherence, the specificity of the ligands and mechanisms of binding are still debated. In this study, the molecular basis of Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium flagella binding to epithelial cell cultures was investigated. Flagella interactions with host cell surfaces were intimate and crossed cellular boundaries as demarcated by actin and membrane labelling. Scanning electron microscopy revealed flagella disappearing into cellular surfaces and transmission electron microscopy of S. Typhiumurium indicated host membrane deformation and disruption in proximity to flagella. Motor mutants of E. coli O157:H7 and S. Typhimurium caused reduced haemolysis compared to wild-type, indicating that membrane disruption was in part due to flagella rotation. Flagella from E. coli O157 (H7), EPEC O127 (H6) and S. Typhimurium (P1 and P2 flagella) were shown to bind to purified intracellular components of the actin cytoskeleton and directly increase in vitro actin polymerization rates. We propose that flagella interactions with host cell membranes and cytoskeletal components may help prime intimate attachment and invasion for E. coli O157:H7 and S. Typhimurium, respectively.

Implications of back-and-forth motion and powerful propulsion for spirochetal invasion

The spirochete Leptospira spp. can move in liquid and on a solid surface using two periplasmic flagella (PFs), and its motility is an essential virulence factor for the pathogenic species. Mammals are infected with the spirochete through the wounded dermis, which implies the importance of behaviors on the boundary with such viscoelastic milieu; however, the leptospiral pathogenicity involving motility remains unclear. We used a glass chamber containing a gel area adjoining the leptospiral suspension to resemble host dermis exposed to contaminated water and analyzed the motility of individual cells at the liquid-gel border. Insertion of one end of the cell body to the gel increased switching of the swimming direction. Moreover, the swimming force of Leptospira was also measured by trapping single cells using an optical tweezer. It was found that they can generate [Formula: see text] 17 pN of force, which is [Formula: see text] 30 times of the swimming force of Escherichia coli. The force-speed relationship suggested the load-dependent force enhancement and showed that the power (the work per unit time) for the propulsion is [Formula: see text] 3.1 × 10-16 W, which is two-order of magnitudes larger than the propulsive power of E. coli. The powerful and efficient propulsion of Leptospira using back-and-forth movements could facilitate their invasion.

Crawling Motility on the Host Tissue Surfaces Is Associated With the Pathogenicity of the Zoonotic Spirochete Leptospira

Bacterial motility is crucial for many pathogenic species in the process of invasion and/or dissemination. The spirochete bacteria Leptospira spp. cause symptoms, such as hemorrhage, jaundice, and nephritis, in diverse mammals including humans. Although loss-of-motility attenuate the spirochete's virulence, the mechanism of the motility-dependent pathogenicity is unknown. Here, focusing on that Leptospira spp. swim in liquid and crawl on solid surfaces, we investigated the spirochetal dynamics on the host tissues by infecting cultured kidney cells from various species with pathogenic and non-pathogenic leptospires. We found that, in the case of the pathogenic leptospires, a larger fraction of bacteria attached to the host cells and persistently traveled long distances using the crawling mechanism. Our results associate the kinetics and kinematic features of the spirochetal pathogens with their virulence.

Involvement of Heme in Colony Spreading of Staphylococcus aureus

Staphylococcus aureus spreads rapidly on the surface of soft agar medium. The spreading depends on the synthesis of biosurfactants, i.e., phenol soluble modulins (PSMs), which facilitate colony spreading of S. aureus. Our earlier study demonstrated that water accumulates in a colony is important to modulate colony spreading of S. aureus. The current study screened a transposon-based mutant library of S. aureus HG001 and obtained four non-spreading mutants with mutations in hemY and ctaA, which are involved in heme synthesis. The spreading ability of these mutants was restored when the mutants are transformed with a plasmid encoding hemY or ctaA, respectively. HemY mutants, which do not synthesize heme B, were able to spread on agar medium supplemented with hemin, a heme B derivative. By contrast, hemin supplementation did not rescue the spreading of the ctaA mutant, which lacks heme B and heme A, indicating that heme A is also critical for colony spreading. Moreover, mutations in hemY and ctaA had little effect on PSMs production but affect ATP production and water accumulation in the colony. In conclusion, this study sheds light on the role of heme synthesis and energy production in the regulation of S. aureus colony spreading, which is important for understanding the movement mechanisms of bacteria lacking a motor apparatus.

Salmonella Typhi, Paratyphi A, Enteritidis and Typhimurium core proteomes reveal differentially expressed proteins linked to the cell surface and pathogenicity

Background

Salmonella enterica subsp. enterica contains more than 2,600 serovars of which four are of major medical relevance for humans. While the typhoidal serovars (Typhi and Paratyphi A) are human-restricted and cause enteric fever, non-typhoidal Salmonella serovars (Typhimurium and Enteritidis) have a broad host range and predominantly cause gastroenteritis.

Methodology/Principle findings

We compared the core proteomes of Salmonella Typhi, Paratyphi A, Typhimurium and Enteritidis using contemporary proteomics. For each serovar, five clinical isolates (covering different geographical origins) and one reference strain were grown in vitro to the exponential phase. Levels of orthologous proteins quantified in all four serovars and within the typhoidal and non-typhoidal groups were compared and subjected to gene ontology term enrichment and inferred regulatory interactions. Differential expression of the core proteomes of the typhoidal serovars appears mainly related to cell surface components and, for the non-typhoidal serovars, to pathogenicity.

Conclusions/Significance

Our comparative proteome analysis indicated differences in the expression of surface proteins between Salmonella Typhi and Paratyphi A, and in pathogenesis-related proteins between Salmonella Typhimurium and Enteritidis. Our findings may guide future development of novel diagnostics and vaccines, as well as understanding of disease progression.

With an estimated 20 million typhoid cases and an even higher number of non-typhoid cases the health burden caused by salmonellosis is huge. Salmonellosis is caused by the bacterial species Salmonella enterica and over 2500 different serovars exist, of which four are of major medical relevance for humans: Typhi and Paratyphi A cause typhoid fever while Typhimurium and Enteritidis are the dominant cause of non-typhoidal Salmonella infections. The proteome is the entire set of proteins that is expressed by a genome and the core proteome are all orthologous proteins detected in a given sample set. In this study we have investigated differential expression of the core proteomes of the Salmonella serovars Typhi, Paratyphi A, Typhimurium and Enteritidis, as well as the regulating molecules. Our comparative proteome analysis indicated differences in the expression of surface proteins between the serovars Typhi and Paratyphi A, and in pathogenesis-related proteins between Typhimurium and Enteritidis. Our findings in proteome-wide expression may guide the development of novel diagnostics and vaccines for Salmonella, as well as understanding of disease.

Comparative Genome Analysis of Uropathogenic Morganella morganii Strains

Morganella morganii is an opportunistic bacterial pathogen shown to cause a wide range of clinical and community-acquired infections. This study was aimed at sequencing and comparing the genomes of three M. morganii strains isolated from the urine samples of patients with community-acquired urinary tract infections. Draft genome sequencing was conducted using the Illumina HiSeq platform. The genomes of MM 1, MM 4, and MM 190 strains have a size of 3.82–3.97 Mb and a GC content of 50.9–51%. Protein-coding sequences (CDS) represent 96.1% of the genomes, RNAs are encoded by 2.7% of genes and pseudogenes account for 1.2% of the genomes. The pan-genome containes 4,038 CDS, of which 3,279 represent core genes. Six to ten prophages and 21–33 genomic islands were identified in the genomes of MM 1, MM 4, and MM 190. More than 30 genes encode capsular biosynthesis proteins, an average of 60 genes encode motility and chemotaxis proteins, and about 70 genes are associated with fimbrial biogenesis and adhesion. We determined that all strains contained urease gene cluster ureABCEFGD and had a urease activity. Both MM 4 and MM 190 strains are capable of hemolysis and their activity correlates well with a cytotoxicity level on T-24 bladder carcinoma cells. These activities were associated with expression of RTX toxin gene hlyA, which was introduced into the genomes by a phage similar to Salmonella phage 118970_sal4.

Effects of fermentation products of the commensal bacterium Clostridium ramosum on motility, intracellular pH, and flagellar synthesis of enterohemorrhagic Escherichia coli

The flagellum and motility are crucial virulence factors for many pathogenic bacteria. In general, pathogens invade and translocate through motility and adhere to specific tissue via flagella. Therefore, the motility and flagella of pathogens are effectual targets for attenuation. Here, we show that the fermentation products of Clostridium ramosum, a commensal intestinal bacterium, decrease the intracellular pH of enterohemorrhagic Escherichia coli (EHEC) and influence its swimming motility. Quantifications of flagellar rotation in individual EHEC cells showed an increase in reversal frequency and a decrease in rotation rate in the presence of C. ramosum fermentation products. Furthermore, the C. ramosum fermentation products affected synthesis of flagellar filaments. The results were reproduced by a combination of organic acids under acidic conditions. Short-chain fatty acids produced by microbes in the gut flora are beneficial for the host, e.g. they prevent infection. Thus, C. ramosum could affect the physiologies of other enteric microbes and host tissues.

[Mechanism of bacterial motility]

Bacteria, life living at microscale, can spread only by thermal fluctuation. However, the ability of directional movement, such as swimming by rotating flagella, gliding over surfaces via mobile cell-surface adhesins, and actin-dependent movement, could be useful for thriving through searching more favorable environments, and such motility is known to be related to pathogenicity. Among diverse migration mechanisms, perhaps flagella-dependent motility would be used by most species. The bacterial flagellum is a molecular nanomachine comprising a helical filament and a basal motor, which is fueled by an electrochemical gradient of cation across the cell membrane (ion motive force). Many species, such as Escherichia coli, possess flagella on the outside of the cell body, whereas flagella of spirochetes reside within the periplasmic space. Flagellar filaments or helical spirochete bodies rotate like a screw propeller, generating propulsive force. This review article describes the current knowledge of the structure and operation mechanism of the bacterial flagellum, and flagella-dependent motility in highly viscous environments.

Discovery of a Novel Periodontal Disease-Associated Bacterium

One of the world's most common infectious disease, periodontitis (PD), derives from largely uncharacterized communities of oral bacteria growing as biofilms (a.k.a. plaque) on teeth and gum surfaces in periodontal pockets. Bacteria associated with periodontal disease trigger inflammatory responses in immune cells, which in later stages of the disease cause loss of both soft and hard tissue structures supporting teeth. Thus far, only a handful of bacteria have been characterized as infectious agents of PD. Although deep sequencing technologies, such as whole community shotgun sequencing have the potential to capture a detailed picture of highly complex bacterial communities in any given environment, we still lack major reference genomes for the oral microbiome associated with PD and other diseases. In recent work, by using a combination of supervised machine learning and genome assembly, we identified a genome from a novel member of the Bacteroidetes phylum in periodontal samples. Here, by applying a comparative metagenomics read-classification approach, including 272 metagenomes from various human body sites, and our previously assembled draft genome of the uncultivated Candidatus Bacteroides periocalifornicus (CBP) bacterium, we show CBP's ubiquitous distribution in dental plaque, as well as its strong association with the well-known pathogenic "red complex" that resides in deep periodontal pockets.

Stress-induced host membrane remodeling protects from infection by non-motile bacterial pathogens

While mucosal inflammation is a major source of stress during enteropathogen infection, it remains to be fully elucidated how the host benefits from this environment to clear the pathogen. Here, we show that host stress induced by different stimuli mimicking inflammatory conditions strongly reduces the binding of Shigella flexneri to epithelial cells. Mechanistically, stress activates acid sphingomyelinase leading to host membrane remodeling. Consequently, knockdown or pharmacological inhibition of the acid sphingomyelinase blunts the stress-dependent inhibition of Shigella binding to host cells. Interestingly, stress caused by intracellular Shigella replication also results in remodeling of the host cell membrane, in vitro and in vivo, which precludes re-infection by this and other non-motile pathogens. In contrast, Salmonella Typhimurium overcomes the shortage of permissive entry sites by gathering effectively at the remaining platforms through its flagellar motility. Overall, our findings reveal host membrane remodeling as a novel stress-responsive cell-autonomous defense mechanism that protects epithelial cells from infection by non-motile bacterial pathogens.

The effect of bacterial chemotaxis on host infection and pathogenicity

Chemotaxis enables microorganisms to move according to chemical gradients. Although this process requires substantial cellular energy, it also affords key physiological benefits, including enhanced access to growth substrates. Another important implication of chemotaxis is that it also plays an important role in infection and disease, as chemotaxis signalling pathways are broadly distributed across a variety of pathogenic bacteria. Furthermore, current research indicates that chemotaxis is essential for the initial stages of infection in different human, animal and plant pathogens. This review focuses on recent findings that have identified specific bacterial chemoreceptors and corresponding chemoeffectors associated with pathogenicity. Pathogenicity-related chemoeffectors are either host and niche-specific signals or intermediates of the host general metabolism. Plant pathogens were found to contain an elevated number of chemotaxis signalling genes and functional studies demonstrate that these genes are critical for their ability to enter the host. The expanding body of knowledge of the mechanisms underlying chemotaxis in pathogens provides a foundation for the development of new therapeutic strategies capable of blocking infection and preventing disease by interfering with chemotactic signalling pathways.

The Homolog of the Gene bstA of the BTP1 Phage from Salmonella enterica Serovar Typhimurium ST313 Is an Antivirulence Gene in Salmonella enterica Serovar Dublin

In a previous study, a novel virulence gene, bstA, identified in a Salmonella enterica serovar Typhimurium sequence type 313 (ST313) strain was found to be conserved in all published Salmonella enterica serovar Dublin genomes. In order to analyze the role of this gene in the host-pathogen interaction in S Dublin, a mutant where this gene was deleted (S Dublin ΔbstA) and a mutant which was further genetically complemented with bstA (S Dublin 3246-C) were constructed and tested in models of in vitro and in vivo infection as well as during growth competition assays in M9 medium, Luria-Bertani broth, and cattle blood. In contrast to the results obtained for a strain of S Typhimurium ST313, the lack of bstA was found to be associated with increased virulence in S Dublin. Thus, S Dublin ΔbstA showed higher levels of uptake than the wild-type strain during infection of mouse and cattle macrophages and higher net replication within human THP-1 cells. Furthermore, during mouse infections, S Dublin ΔbstA was more virulent than the wild type following a single intraperitoneal infection and showed an increased competitive index during competitive infection assays. Deletion of bstA did not affect either the amount of cytokines released by THP-1 macrophages or the cytotoxicity toward these cells. The histology of the livers and spleens of mice infected with the wild-type strain and the S Dublin ΔbstA mutant revealed similar levels of inflammation between the two groups. The gene was not important for adherence to or invasion of human epithelial cells and did not influence bacterial growth in rich medium, minimal medium, or cattle blood. In conclusion, a lack of bstA affects the pathogenicity of S Dublin by decreasing its virulence. Therefore, it might be regarded as an antivirulence gene in this serovar.

mcp, aer, cheB, and cheV contribute to the regulation of Vibrio alginolyticus (ND-01) adhesion under gradients of environmental factors

Adhesion is a key virulence factor of pathogens and can be affected by the environment. Our previously research with RNA-seq indicated that mcp, aer, cheB, and cheV might play roles in the regulation of adhesion in Vibrio alginolyticus (ND-01). In order to determine whether and how environmental factors affect adhesion through these genes, gene silencing was performed followed by quantitative real-time PCR (qRT-PCR), RNAi, transmission electron microscopy, and adhesion, capillary, and motility assays to verify how these genes influence adhesion. Silencing these genes led to deficiencies in adhesion, chemotaxis, flagellar assembly, and motility. The expression levels of cheA, cheW, and cheY, which are important genes closely related to the functions of mcp, aer, cheV, and cheB, were significantly downregulated in all of the RNAi groups. The expression of mcp, aer, cheV, and cheB under different gradients of temperature, pH, and salinity and after starvation for various durations was also detected, which showed that these genes were sensitive to certain environmental stresses, particularly pH and starvation. Our results indicated that mcp, aer, cheB, and cheV: (1) are necessary for ND-01 adhesion; (2) play key roles in the bacterial chemotaxis pathway by controlling the expression of downstream genes; (3) might affect adhesion by impacting motility, though motility is not the only route through which adhesion is affected; and (4) contribute to the regulation of ND-01 adhesion in natural environments with different temperatures, pH levels, and salinities as well as after various starvation periods.

Engineered Salmonella enterica serovar Typhimurium overcomes limitations of anti-bacterial immunity in bacteria-mediated tumor therapy

Cancer is one of the leading causes of death in the industrialized world and represents a tremendous social and economic burden. As conventional therapies fail to provide a sustainable cure for most cancer patients, the emerging unique immune therapeutic approach of bacteria-mediated tumor therapy (BMTT) is marching towards a feasible solution. Although promising results have been obtained with BMTT using various preclinical tumor models, for advancement a major concern is immunity against the bacterial vector itself. Pre-exposure to the therapeutic agent under field conditions is a reasonable expectation and may limit the therapeutic efficacy of BMTT. In the present study, we investigated the therapeutic potential of Salmonella and E. coli vector strains in naïve and immunized tumor bearing mice. Pre-exposure to the therapeutic agent caused a significant aberrant phenotype of the microenvironment of colonized tumors and limited the in vivo efficacy of established BMTT vector strains Salmonella SL7207 and E. coli Symbioflor-2. Using targeted genetic engineering, we generated the optimized auxotrophic Salmonella vector strain SF200 (ΔlpxR9 ΔpagL7 ΔpagP8 ΔaroA ΔydiV ΔfliF) harboring modifications in Lipid A and flagella synthesis. This combination of mutations resulted in an increased immune-stimulatory capacity and as such the strain was able to overcome the efficacy-limiting effects of pre-exposure. Thus, we conclude that any limitations of BMTT concerning anti-bacterial immunity may be countered by strategies that optimize the immune-stimulatory capacity of the attenuated vector strains.

Survival of Helicobacter pylori in gastric acidic territory

BACKGROUND

Helicobacter pylori is well adapted to colonize the epithelial surface of the human gastric mucosa and can cause persistent infections. In order to infect the gastric mucosa, it has to survive in the gastric acidic pH. This organism has well developed mechanisms to neutralize the effects of acidic pH.

OBJECTIVE

This review article was designed to summarize the various functional and molecular aspects by which the bacterium can combat and survive the gastric acidic pH in order to establish the persistent infections.

METHODS

We used the keywords (acid acclimation, gastric acidic environment, H. pylori and survival) in combination or alone for pubmed search of recent scientific literatures. One hundred and forty one papers published between 1989 and 2016 were sorted out. The articles published with only abstracts, other than in English language, case reports and reviews were excluded.

RESULTS

Many literatures describing the role of several factors in acid survival were found. Recently, the role of several other factors has been claimed to participate in acid survival.

CONCLUSION

In conclusion, this organism has well characterized mechanisms for acid survival.

RNA target profiles direct the discovery of virulence functions for the cold-shock proteins CspC and CspE

The functions of many bacterial RNA-binding proteins remain obscure because of a lack of knowledge of their cellular ligands. Although well-studied cold-shock protein A (CspA) family members are induced and function at low temperature, others are highly expressed in infection-relevant conditions. Here, we have profiled transcripts bound in vivo by the CspA family members of Salmonella enterica serovar Typhimurium to link the constitutively expressed CspC and CspE proteins with virulence pathways. Phenotypic assays in vitro demonstrated a crucial role for these proteins in membrane stress, motility, and biofilm formation. Moreover, double deletion of cspC and cspE fully attenuates Salmonella in systemic mouse infection. In other words, the RNA ligand-centric approach taken here overcomes a problematic molecular redundancy of CspC and CspE that likely explains why these proteins have evaded selection in previous virulence factor screens in animals. Our results highlight RNA-binding proteins as regulators of pathogenicity and potential targets of antimicrobial therapy. They also suggest that globally acting RNA-binding proteins are more common in bacteria than currently appreciated.

A review on host-pathogen interactions: classification and prediction

The research on host-pathogen interactions is an ever-emerging and evolving field. Every other day a new pathogen gets discovered, along with comes the challenge of its prevention and cure. As the intelligent human always vies for prevention, which is better than cure, understanding the mechanisms of host-pathogen interactions gets prior importance. There are many mechanisms involved from the pathogen as well as the host sides while an interaction happens. It is a vis-a-vis fight of the counter genes and proteins from both sides. Who wins depends on whether a host gets an infection or not. Moreover, a higher level of complexity arises when the pathogens evolve and become resistant to a host's defense mechanisms. Such pathogens pose serious challenges for treatment. The entire human population is in danger of such long-lasting persistent infections. Some of these infections even increase the rate of mortality. Hence there is an immediate emergency to understand how the pathogens interact with their host for successful invasion. It may lead to discovery of appropriate preventive measures, and the development of rational therapeutic measures and medication against such infections and diseases. This review, a state-of-the-art updated scenario of host-pathogen interaction research, has been done by keeping in mind this urgency. It covers the biological and computational aspects of host-pathogen interactions, classification of the methods by which the pathogens interact with their hosts, different machine learning techniques for prediction of host-pathogen interactions, and future scopes of this research field.

Bacteria in Cancer Therapy: Renaissance of an Old Concept

The rising incidence of cancer cases worldwide generates an urgent need of novel treatment options. Applying bacteria may represent a valuable therapeutic variant that is intensively investigated nowadays. Interestingly, the idea to apply bacteria wittingly or unwittingly dates back to ancient times and was revived in the 19th century mainly by the pioneer William Coley. This review summarizes and compares the results of the past 150 years in bacteria mediated tumor therapy from preclinical to clinical studies. Lessons we have learned from the past provide a solid foundation on which to base future efforts. In this regard, several perspectives are discussed by which bacteria in addition to their intrinsic antitumor effect can be used as vector systems that shuttle therapeutic compounds into the tumor. Strategic solutions like these provide a sound and more apt exploitation of bacteria that may overcome limitations of conventional therapies.

Characterization of the Invasive, Multidrug Resistant Non-typhoidal Salmonella Strain D23580 in a Murine Model of Infection

A distinct pathovar of Salmonella enterica serovar Typhimurium, ST313, has emerged in sub-Saharan Africa as a major cause of fatal bacteremia in young children and HIV-infected adults. D23580, a multidrug resistant clinical isolate of ST313, was previously shown to have undergone genome reduction in a manner that resembles that of the more human-restricted pathogen, Salmonella enterica serovar Typhi. It has since been shown through tissue distribution studies that D23580 is able to establish an invasive infection in chickens. However, it remains unclear whether ST313 can cause lethal disease in a non-human host following a natural course of infection. Herein we report that D23580 causes lethal and invasive disease in a murine model of infection following peroral challenge. The LD₅₀ of D23580 in female BALB/c mice was 4.7 x 10⁵ CFU. Tissue distribution studies performed 3 and 5 days post-infection confirmed that D23580 was able to more rapidly colonize the spleen, mesenteric lymph nodes and gall bladder in mice when compared to the well-characterized S. Typhimurium strain SL1344. D23580 exhibited enhanced resistance to acid stress relative to SL1344, which may lend towards increased capability to survive passage through the gastrointestinal tract as well as during its intracellular lifecycle. Interestingly, D23580 also displayed higher swimming motility relative to SL1344, S. Typhi strain Ty2, and the ST313 strain A130. Biochemical tests revealed that D23580 shares many similar metabolic features with SL1344, with several notable differences in the Voges-Proskauer and catalase tests, as well alterations in melibiose, and inositol utilization. These results represent the first full duration infection study using an ST313 strain following the entire natural course of disease progression, and serve as a benchmark for ongoing and future studies into the pathogenesis of D23580.

A deadly form of non-typhoidal Salmonella has emerged as a major cause of invasive disease in sub-Saharan Africa. Initial genomic profiling of this novel Salmonella sequence type, ST313, indicated that although it is technically classified as S. Typhimurium (a serovar characterized by a broad host range), it may be evolving towards becoming a more human-specific, ‘typhoid-like’ pathogen. However, it was recently demonstrated that ST313 strains were indeed able to establish an invasive and damaging infection in chickens. Despite these important findings, it remains unclear whether ST313 is able to cause lethal disease in a non-human host, since no study has yet followed the entire natural course of disease progression. As such, there are no data available concerning the median lethal dose (LD₅₀) of any ST313 strain. This is an important metric, as the LD₅₀ value will serve as a benchmark for mechanistic studies focused on understanding the relationship between virulence and the phenotypic and molecular genetic attributes associated with ST313 infections. Here we report that D23580 causes lethal disease in BALB/c mice and determined the LD₅₀ following peroral challenge. Phenotypic characterization revealed distinct differences in tissue distribution, acid stress resistance, and biochemical utilization between D23580 and the ‘classic’ Typhimurium strain SL1344.

Flagellin Is Required for Host Cell Invasion and Normal Salmonella Pathogenicity Island 1 Expression by Salmonella enterica Serovar Paratyphi A

Salmonella enterica serovar Paratyphi A is a human-specific serovar that, together with Salmonella enterica serovar Typhi and Salmonella enterica serovar Sendai, causes enteric fever. Unlike the nontyphoidal Salmonella enterica serovar Typhimurium, the genomes of S. Typhi and S. Paratyphi A are characterized by inactivation of multiple genes, including in the flagellum-chemotaxis pathway. Here, we explored the motility phenotype of S. Paratyphi A and the role of flagellin in key virulence-associated phenotypes. Motility studies established that the human-adapted typhoidal S. Typhi, S. Paratyphi A, and S. Sendai are all noticeably less motile than S. Typhimurium, and comparative transcriptome sequencing (RNA-Seq) showed that in S. Paratyphi A, the entire motility-chemotaxis regulon is expressed at significantly lowers levels than in S. Typhimurium. Nevertheless, S. Paratyphi A, like S. Typhimurium, requires a functional flagellum for epithelial cell invasion and macrophage uptake, probably in a motility-independent mechanism. In contrast, flagella were found to be dispensable for host cell adhesion. Moreover, we demonstrate that in S. Paratyphi A, but not in S. Typhimurium, the lack of flagellin results in increased transcription of the flagellar and the Salmonella pathogenicity island 1 (SPI-1) regulons in a FliZ-dependent manner and in oversecretion of SPI-1 effectors via type three secretion system 1. Collectively, these results suggest a novel regulatory linkage between flagellin and SPI-1 in S. Paratyphi A that does not occur in S. Typhimurium and demonstrate curious distinctions in motility and the expression of the flagellum-chemotaxis regulon between these clinically relevant pathogens.

The Type VI Secretion System Modulates Flagellar Gene Expression and Secretion in Citrobacter freundii and Contributes to Adhesion and Cytotoxicity to Host Cells

The type VI secretion system (T6SS) as a virulence factor-releasing system contributes to virulence development of various pathogens and is often activated upon contact with target cells. Citrobacter freundii strain CF74 has a complete T6SS genomic island (GI) that contains clpV, hcp-2, and vgr T6SS genes. We constructed clpV, hcp-2, vgr, and T6SS GI deletion mutants in CF74 and analyzed their effects on the transcriptome overall and, specifically, on the flagellar system at the levels of transcription and translation. Deletion of the T6SS GI affected the transcription of 84 genes, with 15 and 69 genes exhibiting higher and lower levels of transcription, respectively. Members of the cell motility class of downregulated genes of the CF74ΔT6SS mutant were mainly flagellar genes, including effector proteins, chaperones, and regulators. Moreover, the production and secretion of FliC were also decreased in clpV, hcp-2, vgr, or T6SS GI deletion mutants in CF74 and were restored upon complementation. In swimming motility assays, the mutant strains were found to be less motile than the wild type, and motility was restored by complementation. The mutant strains were defective in adhesion to HEp-2 cells and were restored partially upon complementation. Further, the CF74ΔT6SS, CF74ΔclpV, and CF74Δhcp-2 mutants induced lower cytotoxicity to HEp-2 cells than the wild type. These results suggested that the T6SS GI in CF74 regulates the flagellar system, enhances motility, is involved in adherence to host cells, and induces cytotoxicity to host cells. Thus, the T6SS plays a wide-ranging role in C. freundii.

Bacterial flagella: twist and stick, or dodge across the kingdoms

The flagellum organelle is an intricate multiprotein assembly best known for its rotational propulsion of bacteria. However, recent studies have expanded our knowledge of other functions in pathogenic contexts, particularly adherence and immune modulation, e.g., for Salmonella enterica, Campylobacter jejuni, Pseudomonas aeruginosa, and Escherichia coli. Flagella-mediated adherence is important in host colonisation for several plant and animal pathogens, but the specific interactions that promote flagella binding to such diverse host tissues has remained elusive. Recent work has shown that the organelles act like probes that find favourable surface topologies to initiate binding. An emerging theme is that more general properties, such as ionic charge of repetitive binding epitopes and rotational force, allow interactions with plasma membrane components. At the same time, flagellin monomers are important inducers of plant and animal innate immunity: variation in their recognition impacts the course and outcome of infections in hosts from both kingdoms. Bacteria have evolved different strategies to evade or even promote this specific recognition, with some important differences shown for phytopathogens. These studies have provided a wider appreciation of the functions of bacterial flagella in the context of both plant and animal reservoirs.

Chemotactic signal transduction and phosphate metabolism as adaptive strategies during citrus canker induction by Xanthomonas citri

The genome of Xanthomonas citri subsp. Citri strain 306 pathotype A (Xac) was completely sequenced more than 10 years; to date, few studies involving functional genomics Xac and its host compatible have been developed, specially related to adaptive events that allow the survival of Xac within the plant. Proteomic analysis of Xac showed that the processes of chemotactic signal transduction and phosphate metabolism are key adaptive strategies during the interaction of a pathogenic bacterium with its plant host. The results also indicate the importance of a group of proteins that may not be directly related to the classical virulence factors, but that are likely fundamental to the success of the initial stages of the infection, such as methyl-accepting chemotaxis protein (Mcp) and phosphate specific transport (Pst). Furthermore, the analysis of the mutant of the gene pstB which codifies to an ABC phosphate transporter subunit revealed a complete absence of citrus canker symptoms when inoculated in compatible hosts. We also conducted an in silico analysis which established the possible network of genes regulated by two-component systems PhoPQ and PhoBR (related to phosphate metabolism), and possible transcriptional factor binding site (TFBS) motifs of regulatory proteins PhoB and PhoP, detaching high degree of conservation of PhoB TFBS in 84 genes of Xac genome. This is the first time that chemotaxis signal transduction and phosphate metabolism were therefore indicated to be fundamental to the process of colonization of plant tissue during the induction of disease associated with Xanthomonas genus bacteria.

Pseudomonas aeruginosa flagellar motility activates the phagocyte PI3K/Akt pathway to induce phagocytic engulfment

Phagocytosis of the bacterial pathogen Pseudomonas aeruginosa is the primary means by which the host controls bacterially induced pneumonia during lung infection. Previous studies have identified flagellar swimming motility as a key pathogen-associated molecular pattern (PAMP) recognized by phagocytes to initiate engulfment. Correspondingly, loss of flagellar motility is observed during chronic pulmonary infection with P. aeruginosa, and this likely reflects a selection for bacteria resistant to phagocytic clearance. However, the mechanism underlying the preferential phagocytic response to motile bacteria is unknown. Here we have identified a cellular signaling pathway in alveolar macrophages and other phagocytes that is specifically activated by flagellar motility. Genetic and biochemical methods were employed to identify that phagocyte PI3K/Akt activation is required for bacterial uptake and, importantly, it is specifically activated in response to P. aeruginosa flagellar motility. Based on these observations, the second important finding that emerged from these studies is that titration of the bacterial flagellar motility results in a proportional activation state of Akt. Therefore, the Akt pathway is responsive to, and corresponds with, the degree of bacterial flagellar motility, is independent of the actin polymerization that facilitates phagocytosis, and determines the phagocytic fate of P. aeruginosa. These findings elucidate the mechanism behind motility-dependent phagocytosis of extracellular bacteria and support a model whereby phagocytic clearance exerts a selective pressure on P. aeruginosa populations in vivo, which contributes to changes in pathogenesis during infections.

Role of the flagellar basal-body protein, FlgC, in the binding of Salmonella enterica serovar Enteritidis to host cells

Salmonella enterica serovar Enteritidis (SE) infection in humans is often associated with the consumption of contaminated poultry products. Binding of the bacterium to the intestinal mucosa is a major pathogenic mechanism of Salmonella in poultry. Transposon mutagenesis identified flgC as a potential binding mutant of SE. Therefore, we hypothesize FlgC which plays a significant role in the binding ability of SE to the intestinal mucosa of poultry. To test our hypothesis, we created a mutant of SE in which flgC was deleted. We then tested the in vitro and in vivo binding ability of ∆flgC when compared to the wild-type SE strain. Our data showed a significant decrease in the binding ability of ∆flgC to intestinal epithelial cells as well as in the small intestine and cecum of poultry. Furthermore, the decrease in binding correlated to a defect in invasion as shown by a cell culture model using intestinal epithelial cells and bacterial recovery from the livers and spleens of chickens. Overall, these studies indicate FlgC is a major factor in the binding ability of Salmonella to the intestinal mucosa of poultry.

Repression of flagella is a common trait in field isolates of Salmonella enterica serovar Dublin and is associated with invasive human infections

The nontyphoidal Salmonella enterica serovar Dublin is adapted to cattle but infrequently infects humans, very often resulting in invasive infections with high levels of morbidity and mortality. A Salmonella-induced intestinal acute inflammatory response is postulated as a mechanism to prevent bacterial dissemination to systemic sites. In S. enterica serovar Typhimurium, flagella contribute to this response by providing motility and FliC-mediated activation of pattern recognition receptors. In this study, we found 4 Salmonella enterica isolates, with the antigenic formula 9,12:-:-, that, based on fliC sequence and multilocus sequence type (MLST) analyses, are aflagellate S. Dublin isolates. Interestingly, all were obtained from human bloodstream infections. Thus, we investigated the potential role of flagella in the unusual invasiveness exhibited by S. Dublin in humans by analyzing flagellation and proinflammatory properties of a collection of 10 S. Dublin human clinical isolates. We found that 4 of 7 blood isolates were aflagellate due to significantly reduced levels of fliC expression, whereas all 3 isolates from other sources were flagellated. Lack of flagella correlated with a reduced ability of triggering interleukin-8 (IL-8) and CCL20 chemokine expression in human intestinal Caco-2 cells and with reduced early inflammation in the ceca of streptomycin-pretreated C57/BL6 mice. These results indicate that flagella contribute to the host intestinal inflammatory response to Salmonella serovar Dublin and suggest that their absence may contribute to its systemic dissemination through dampening of the gut immune response. Analysis of FliC production in a collection of cattle isolates indicated that the aflagellate phenotype is widely distributed in field isolates of S. Dublin.

Role of StdA in adhesion of Salmonella enterica serovar Enteritidis phage type 8 to host intestinal epithelial cells

Background

Salmonella is often implicated in foodborne outbreaks, and is a major public health concern in the United States and throughout the world. Salmonella enterica serovar Enteritidis (SE) infection in humans is often associated with the consumption of contaminated poultry products. Adhesion to epithelial cells in the intestinal mucosa is a major pathogenic mechanism of Salmonella in poultry. Transposon mutagenesis identified stdA as a potential adhesion mutant of SE. Therefore, we hypothesize StdA plays a significant role in adhesion of SE to the intestinal mucosa of poultry.

Methods and results

To test our hypothesis, we created a mutant of SE in which stdA was deleted. Growth and motility were assayed along with the in vitro and in vivo adhesion ability of the ∆stdA when compared to the wild-type SE strain. Our data showed a significant decrease in motility in ∆stdA when compared to the wild-type and complemented strain. A decrease in adhesion to intestinal epithelial cells as well as in the small intestine and cecum of poultry was observed in ∆stdA. Furthermore, the lack of adhesion correlated to a defect in invasion as shown by a cell culture model using intestinal epithelial cells and bacterial recovery from the livers and spleens of chickens.

Conclusions

These studies suggest StdA is a major contributor to the adhesion of Salmonella to the intestinal mucosa of poultry.

The role of the bacterial flagellum in adhesion and virulence

The bacterial flagellum is a complex apparatus assembled of more than 20 different proteins. The flagellar basal body traverses the cell wall, whereas the curved hook connects the basal body to the whip-like flagellar filament that protrudes several µm from the bacterial cell. The flagellum has traditionally been regarded only as a motility organelle, but more recently it has become evident that flagella have a number of other biological functions. The major subunit, flagellin or FliC, of the flagellum plays a well-documented role in innate immunity and as a dominant antigen of the adaptive immune response. Importantly, flagella have also been reported to function as adhesins. Whole flagella have been indicated as significant in bacterial adhesion to and invasion into host cells. In various pathogens, e.g., Escherichia coli, Pseudomonas aeruginosa and Clostridium difficile, flagellin and/or the distally located flagellar cap protein have been reported to function as adhesins. Recently, FliC of Shiga-toxigenic E. coli was shown to be involved in cellular invasion via lipid rafts. Here, we examine the latest or most important findings regarding flagellar adhesive and invasive properties, especially focusing on the flagellum as a potential virulence factor.