Major Bacterial Pathogens Research Articles

Microbiome diversity protects against pathogens by nutrient blocking.

The human gut microbiome plays an important role in resisting colonization of the host by pathogens, but we lack the ability to predict which communities will be protective. We studied how human gut bacteria influence colonization of two major bacterial pathogens, both in vitro and in gnotobiotic mice. Whereas single species alone had negligible effects, colonization resistance greatly increased with community diversity. Moreover, this community-level resistance rested critically upon certain species being present. We explained these ecological patterns through the collective ability of resistant communities to consume nutrients that overlap with those used by the pathogen. Furthermore, we applied our findings to successfully predict communities that resist a novel target strain. Our work provides a reason why microbiome diversity is beneficial and suggests a route for the rational design of pathogen-resistant communities.

Prevalence, Associated Risk Factors and Major Bacterial Pathogens causing Bovine Mastitis on Selected Dairy Farms in and around Harar, Ethiopia

Aim Mastitis, an inflammation of the mammary gland, is a complex and costly disease in dairy herds. The main aim of this study was to estimate the prevalence of mastitis and associated risk factors for bacterial pathogens in lactating dairy cows. Methods A cross-sectional study was carried out. The study was conducted in Harar town and its district from November 2016 to April 2017. A total of 384 (264 crossbreds and 120 Holstein Frisian) milking cows were tested using the California mastitis test (CMT), direct diagnosis of obverse clinical mastitis, and bacterial culture in Harar City and its district. Results The result of the study indicated the prevalence of mastitis at the cow level was 58.60% (225/384), out of which 10.7% (41/384) and 47.9% (184/384) were clinical and subclinical, respectively. The quarter-level prevalence was 34.1% (513/1536); from this, the clinical and subclinical forms were 8.7% (131/1536) and 25.4% (382/1536), respectively, while 2% (31/1536) had blind teats. From 341 culture-positive samples, the following bacteria were isolated: Out of the total, Coagulase-negative Staphylococcus (CNS) (28.5%) was the most prevalent isolate, followed by Streptococcus species (27.5%), Staphylococcus aureus (21.4%), Escherichia coli species (14.4%), Micrococcus species (5.3%) and Corynebacterium species (2.9%). Age, parity, breed, production, and hygiene were significant associated risk factors, whereas management risk factors such as house types, milking systems, farming systems, and treatment history do not have a significant association with the prevalence of mastitis in the study area at this level of significance. Conclusion Based on the findings of this study, a thorough screening of high-producing and aged cows should be needed; optimum space should be required for those cows kept in intensive and closed houses to reduce the risk of contagious mastitis; attention should be paid to the informal use of drugs; and further research should be needed to view other risk factors for mastitis

High genomic plasticity and unique features of Xanthomonas translucens pv. graminis revealed through comparative analysis of complete genome sequences

BackgroundXanthomonas translucens pv. graminis (Xtg) is a major bacterial pathogen of economically important forage grasses, causing severe yield losses. So far, genomic resources for this pathovar consisted mostly of draft genome sequences, and only one complete genome sequence was available, preventing comprehensive comparative genomic analyses. Such comparative analyses are essential in understanding the mechanisms involved in the virulence of pathogens and to identify virulence factors involved in pathogenicity.ResultsIn this study, we produced high-quality, complete genome sequences of four strains of Xtg, complementing the recently obtained complete genome sequence of the Xtg pathotype strain. These genomic resources allowed for a comprehensive comparative analysis, which revealed a high genomic plasticity with many chromosomal rearrangements, although the strains were highly related. A high number of transposases were exclusively found in Xtg and corresponded to 413 to 457 insertion/excision transposable elements per strain. These mobile genetic elements are likely to be involved in the observed genomic plasticity and may play an important role in the adaptation of Xtg. The pathovar was found to lack a type IV secretion system, and it possessed the smallest set of type III effectors in the species. However, three XopE and XopX family effectors were found, while in the other pathovars of the species two or less were present. Additional genes that were specific to the pathovar were identified, including a unique set of minor pilins of the type IV pilus, 17 TonB-dependent receptors (TBDRs), and 11 plant cell wall degradative enzymes.ConclusionThese results suggest a high adaptability of Xtg, conferred by the abundance of mobile genetic elements, which could play a crucial role in pathogen adaptation. The large amount of such elements in Xtg compared to other pathovars of the species could, at least partially, explain its high virulence and broad host range. Conserved features that were specific to Xtg were identified, and further investigation will help to determine genes that are essential to pathogenicity and host adaptation of Xtg.

In Vitro Efficacy of Isobutyl Cyanoacrylate Nanoparticles against Fish Bacterial Pathogens and Selection Preference by Rainbow Trout (Oncorhynchus mykiss).

The upsurge in havoc being wreaked by antibiotic-resistant bacteria has led to an urgent need for efficacious alternatives to antibiotics. This study assessed the antibacterial efficacy of two isobutyl cyanoacrylate nanoparticles (iBCA-NPs), D6O and NP30, against major bacterial pathogens of fish. In vivo tests on rainbow trout were preceded by in vitro tests of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). NP30 exhibited higher efficacy than D60, but both iBCA-NPs demonstrated dose-dependent and species-specific in vitro antibacterial properties against the bacterial isolates. Generally, Gram-negative bacteria were more resistant to the iBCA-NPs. Streptococcus iniae, Tenacibaculum maritimum, and Photobacterium damselae were particularly sensitive to both iBCA-NPs. Administered to rainbow trout at 3571.4 mg (iBCA-NP)/kg feed, the iBCA-NPs produced a relative gain rate and survival rates comparable to the control (p > 0.05). The condition factor and the hepatosomatic and viscerosomatic indices of fish were indifferentiable (p > 0.05) between the iBCA-NP groups and the control. The iBCA-NPs caused no alteration in stress, oxidative stress (superoxide dismutase, SOD), plasma complement titer, or lysozyme activity. This study presents the first report of antibacterial activity of iBCA-NPs against Gram-negative bacteria. The results of this study suggest that D60 and NP30 may contribute to reducing the amounts of antibiotics and chemotherapeutic agents used in aquaculture.

High-depth RNA-Seq data sets to investigate the differences in gene expression mediated by phasevarions in non-typeable Haemophilus influenzae.

Non-typeable Haemophilus influenzae (NTHi) is a major bacterial pathogen of the human airway. We report high-depth coverage RNA-Seq data from prototype NTHi strains 723 and R2866, encoding two of the most common phase-variable ModA alleles found in NTHi strains, ModA2 and ModA10, respectively.

Introduction and benchmarking of pyMLST: open-source software for assessing bacterial clonality using core genome MLST.

Core genome multilocus sequence typing (cgMLST) has gained in popularity for bacterial typing since whole-genome sequencing (WGS) has become affordable. We introduce here pyMLST, a new complete, stand-alone, free and open source pipeline for cgMLST analysis. pyMLST can create or import a core genome database. For each gene, the first allele is aligned against the bacterial genome of interest using BLAT. Incomplete genes are aligned using MAFT. All data are stored in a SQLite database. pyMLST accepts assembly genomes or raw data (with the option pyMLST-KMA) as input. To evaluate our new tool, we selected three genome collections of major bacterial pathogens (Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus) and compared them with pyMLST, pyMLST-KMA, ChewBBACA, SeqSphere and the variant calling approach. We compared the sensitivity, precision and false-positive rate for each method with those of the variant calling approach. Minimal spanning trees were generated with each type of software to evaluate their interest in the context of a bacterial outbreak. We found that pyMLST-KMA is a convenient screening method to avoid assembling large bacterial collections. Our data showed that pyMLST (free, open source, available in Galaxy and pipeline ready) performed similarly to the commercial SeqSphere and performed better than ChewBBACA and pyMLST-KMA.

Pathogen-driven degradation of endogenous and therapeutic antibodies during streptococcal infections

Group A streptococcus (GAS) is a major bacterial pathogen responsible for both local and systemic infections in humans. The molecular mechanisms that contribute to disease heterogeneity remain poorly understood. Here we show that the transition from a local to a systemic GAS infection is paralleled by pathogen-driven alterations in IgG homeostasis. Using animal models and a combination of sensitive proteomics and glycoproteomics readouts, we documented the progressive accumulation of IgG cleavage products in plasma, due to extensive enzymatic degradation triggered by GAS infection in vivo. The level of IgG degradation was modulated by the route of pathogen inoculation, and mechanistically linked to the combined activities of the bacterial protease IdeS and the endoglycosidase EndoS, upregulated during infection. Importantly, we show that these virulence factors can alter the structure and function of exogenous therapeutic IgG in vivo. These results shed light on the role of bacterial virulence factors in shaping GAS pathogenesis, and potentially blunting the efficacy of antimicrobial therapies.

Pathogenic bacteria exploit transferrin receptor transcytosis to penetrate the blood–brain barrier

The human blood-brain barrier (BBB) comprises a single layer of brain microvascular endothelial cells (HBMECs) protecting the brain from bloodborne pathogens. Meningitis is among the most serious diseases, but the mechanisms by which major meningitis-causing bacterial pathogens cross the BBB to reach the brain remain poorly understood. We found that Streptococcus pneumoniae, group B Streptococcus, and neonatal meningitis Escherichia coli commonly exploit a unique vesicle fusion mechanism to hitchhike on transferrin receptor (TfR) transcytosis to cross the BBB and illustrated the details of this process in human BBB model in vitro and mouse model. Toll-like receptor signals emanating from bacteria-containing vesicles (BCVs) trigger K33-linked polyubiquitination at Lys168 and Lys181 of the innate immune regulator TRAF3 and then activate the formation of a protein complex containing the guanine nucleotide exchange factor RCC2, the small GTPase RalA and exocyst subcomplex I (SC I) on BCVs. The distinct function of SEC6 in SC I, interacting directly with RalA on BCVs and the SNARE protein SNAP23 on TfR vesicles, tethers these two vesicles and initiates the fusion. Our results reveal that innate immunity triggers a unique modification of TRAF3 and the formation of the HBMEC-specific protein complex on BCVs to authenticate the precise recognition and selection of TfR vesicles to fuse with and facilitate bacterial penetration of the BBB.

Antibacterial and Antibiofilm Activity of Endophytic Alternaria sp. Isolated from Eremophila longifolia.

The threat to public health resulting from the emergence of antimicrobial resistance (AMR) is ever rising. One of the major bacterial pathogens at the forefront of this problem is methicillin-resistant Staphylococcus aureus, or MRSA, for which there is a great need to find alternative treatments. One of the most promising alternatives is endophytic fungi, which were shown to produce a vast array of bioactive compounds, including many novel antibacterial compounds. In this study, two endophytic Alternaria sp., EL 24 and EL 35, were identified from the leaves of Eremophila longifolia. Ethyl acetate (EtOAc) extracts of their culture filtrates were found to inhibit both methicillin-sensitive S. aureus ATCC 25923 and MRSA strains M173525 and M180920. The activity of each extract was shown to be greatly affected by the growth medium, with considerable reductions in minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) observed when tested in tryptic soy broth with glucose (TSBG) compared with Mueller-Hinton broth (MHB). Both extracts displayed significant (p ≤ 0.05) antibiofilm activity against all three S. aureus strains, the greatest of which was that of EL 35, which reduced biofilm formation by M180920 by 72%, while that of EL 24 resulted in a 57% reduction against ATCC 25923. Both extracts also disrupted established biofilms, of which the most effective was EL 35, which reduced the M180920 biofilm by 64%, while EL 24 also performed best against M180920, reducing biofilm by 54%. Gas chromatography-mass spectrometry (GC-MS) analysis of the EL 24 EtOAc extract revealed five known compounds. This study highlights the promise of endophytic fungi from Australian plants as a potential source of substances effective against important bacterial pathogens. Further understanding of the responsible compounds and their mechanisms could lead to the development of treatments effective against MRSA, as well as novel biofilm-resistant biomedical materials, contributing towards reducing the burden of AMR.

De novo whole transcriptome analysis of Aeromonas hydrophila isolated from the gut of an infected Labeo rohita.

Aeromonas hydrophila is a major generalist bacterial pathogen causing severe infections and mortalities in aquatic animals. Its genome, which was the first to be sequenced from the Aeromonas genus, may serve as a model for studying pathogenic mechanisms. To explore the pathogen-host fitness mechanism of bacterium, a comprehensive comparative transcriptome ecotype analysis of A. hydrophila isolated from the gut of Labeo rohita during infection was performed. Special characteristics in gene expression, gene ontology terms and expression of pathogenesis-associated genes, including genes encoding secreted proteins, candidate effectors, hydrolases, and proteins involved in secondary metabolite production were revealed. Among the database, 6,533 were gene ontology (GO) annotated, while 1,480 were not allocated in any GO terms. Investigation on GO illustrated that the articulated genes were improved with molecular function, cellular components, and biological processes. Further bioinformatics analysis identified the outer membrane protein genes (ompA, ompts, ompw, omp38, and omp48), cytotoxin, amylase, and lipase genes. Overall, this work allowed to designate, for the first time, a global view on the pathogenicity of Aeromonas hydrophila during infection. Furthermore, the study provides information on the fitness of A. hydrophila, a severe pathogen with a wide host range.

Computational generation and characterization of IsdA-binding aptamers with single-molecule FRET analysis.

Staphylococcus aureus is a major foodborne bacterial pathogen. Early detection of S. aureus is crucial to prevent infections and ensure food quality. The iron-regulated surface determinant protein A (IsdA) of S. aureus is a unique surface protein necessary for sourcing vital iron from host cells for the survival and colonization of the bacteria. The function, structure, and location of the IsdA protein make it an important protein for biosensing applications relating to the pathogen. Here, we report an in-silico approach to develop and validate high-affinity binding aptamers for the IsdA protein detection using custom-designed in-silico tools and small-molecule Fluorescence Resonance Energy Transfer (smFRET) measurements. We utilized in-silico oligonucleotide screening methods and metadynamics-based methods to generate 10 aptamer candidates and characterized them based on the Dissociation Free Energy (DFE) of the IsdA-aptamer complexes. Three of the aptamer candidates were shortlisted for smFRET experimental analysis of binding properties. Limits of detection in the low picomolar range were observed for the aptamers, and the results correlated well with the DFE calculations, indicating the potential of the in-silico approach to support aptamer discovery. This study showcasesa computational SELEXmethod in combination with single-molecule binding studies decipheringeffectiveaptamersagainst S. aureusIsdA, protein. Theestablished approach demonstrates the abilityto expediteaptamerdiscovery that has the potential to cutcosts and predict binding efficacy.The application can be extendedto designingaptamersfor various protein targets, enhancing molecular recognition, and facilitating the development of high-affinityaptamersfor multiple uses. This article is protected by copyright. All rights reserved.

An Overview of Antimicrobial Resistance in Saudi Arabia (2013-2023) and the Need for National Surveillance.

Antimicrobial resistance (AMR) is a well-recognized global threat. The World Health Organization (WHO) issued a report ranking the critical types of bacterial resistance that need to be monitored. Several studies from individual institutions in Saudi Arabia have reported rates of antimicrobial resistance using automated methods. However, no national surveillance study has been conducted to date using gold standard methods for antimicrobial susceptibility testing. This review summarizes AMR rates for major bacterial pathogens in Saudi Arabia and provides a justification for the need for a national surveillance project. In Saudi Arabia, AMR rates for both Gram-positive and Gram-negative bacteria are on the rise. Surveillance studies help identify AMR trends and emergence of outbreaks. The WHO has started a program, the Global Antimicrobial Resistance Surveillance System (GLASS), encouraging its member states, including Saudi Arabia, to conduct antimicrobial surveillance studies to estimate AMR rates worldwide. Of the microbiological methods used to test antimicrobial susceptibility, only broth microdilution (BMD) is considered the "gold standard." As AMR studies in Saudi Arabia are sparse, mostly limited to single centers and were conducted using automated methods, a national AMR surveillance project is needed to evaluate the current status and to inform stewardship decisions.

High throughput Luminex beads based multiplex assay for identification of six major bacterial pathogens of mastitis in dairy animals.

Bovine mastitis is caused by over 150 different microorganisms. Specific identification and quantification of multiple bacteria in a single milk sample becomes essential for rapid intervention. In the present study a Luminex beads based multiplex assay emphasizing on the precise identification of six major bacterial pathogens of mastitis was developed. Assay was developed in two triplex sets, triplex 1 comprised of Streptococcus agalactiae, Streptococcus dysgalactiae and Streptococcus uberis while triplex 2 consisted of Staphylococcus aureus, E. coli and Klebsiella pneumoniae. The analytical sensitivity was 10 6 copies per reaction mixture for all the six bacteria. A 100% analytical specificity was observed for simultaneous detection of these bacteria. Clinical milk samples from 100 bovine quarters were tested for validation. The analytical sensitivity was similar to the findings reported earlier in real time PCR multiplex assay targeting the DNA of the 11 most common bacterial species or groups in mastitis. The analytical specificity of the optimized assay was 100% similar to reported earlier for simultaneous detection of Mycoplasma spp. and for seven entric viruses of humans.The developed assay indicates a concept proof of a rapid, cost effective high throughput diagnostic tool for identification of major bacteria causing mastitis.

Molecular Epidemiology of Streptococcus pneumoniae Detected in Hospitalized Pediatric Acute Respiratory Infection Cases in Central Vietnam.

Streptococcus pneumoniae is the major bacterial pathogen causing high pneumonia morbidity and mortality in children <5 years of age. This study aimed to determine the molecular epidemiology of S. pneumoniae detected among hospitalized pediatric ARI cases at Khanh Hoa General Hospital, Nha Trang, Vietnam, from October 2015 to September 2016 (pre-PCV). We performed semi-quantitative culture to isolate S. pneumoniae. Serotyping, antimicrobial susceptibility testing, resistance gene detection and multi-locus sequence typing were also performed. During the study period, 1300 cases were enrolled and 413 (31.8%) S. pneumoniae were isolated. School attendance, age <3 years old and prior antibiotic use before admission were positively associated with S. pneumoniae isolation. Major serotypes were 6A/B (35.9%), 19F (23.7%) and 23F (12.7%), which accounted for 80.3% of vaccine-type pneumococci. High resistance to Clarithromycin, Erythromycin and Clindamycin (86.7%, 85%, 78.2%) and the mutant drug-resistant genes pbp1A (98.1%), pbp2b (98.8%), pbp2x (99.6%) ermB (96.6%) and mefA (30.3%) were detected. MLST data showed high genetic diversity among the isolates with dominant ST 320 (21.2%) and ST 13223 (19.3%), which were mainly found in Vietnam. Non-typeables accounted for most of the new STs found in the study. Vaccine-type pneumococcus and macrolide resistance were commonly detected among hospitalized pediatric ARI cases.

Community-acquired pneumonia in children: updated perspectives on its etiology, diagnosis, and treatment.

Pneumonia is a common pediatric infectious disease that is familiar to pediatricians and a major cause of hospitalization worldwide. Recent well-designed epidemiologic studies in developed countries indicated that respiratory viruses are detected in 30%-70%, atypical bacteria in 7%-17%, and pyogenic bacteria in 2%-8% of children hospitalized with community-acquired pneumonia (CAP). The etiological distribution of CAP varies widely by child age and the epidemiological season of the respiratory pathogen. Moreover, diagnostic tests, particularly for the detection of Streptococcus pneumoniae and Mycoplasma pneumoniae, the 2 major bacterial pathogens involved in pediatric CAP, have several limitations. Therefore, management and empirical antimicrobial therapy for children with CAP should be applied in a stepwise manner based on recent epidemiological, etiological, and microbiological evidence.

The effects of Pandanus tectorius leaf extract on the resistance of White-leg shrimp Penaeus vannamei towards pathogenic Vibrio parahaemolyticus

Pandanus tectorius leaf extract effect on the White-leg shrimp Penaeus vannamei tolerance against Vibrio parahaemolyticus were investigated in this study. Thirty shrimp post-larvae measured at approximately 1 cm were exposed for 24 h to 0.5, 1, 2, 3, 4, 5 and 6 g/L leaf extract and subsequently observed for survival and immune-related genes expression (Hsp70, ProPO, peroxinectin, penaeidin, crustin and transglutaminase), followed by determination of their tolerance and histological tissue profiles upon Vibrio challenge. Survival of shrimps treated with 6 g/L of leaf extract improved by up to 95% to controls. Hsp70, crustin, and prophenoloxidase mRNA levels were observed to be 8.5, 10.4, and 1.5-fold higher, respectively. Histopathological analysis of the hepatopancreas and the muscle tissues revealed major tissue degeneration in Vibrio-challenged shrimps but not in shrimps primed with P. tectorius leaf extract. Of all the dose examined, the best pathogen resistance results were obtained with a 24 h incubation of shrimp in 6 g/L P. tectorius methanolic leaf extract. The tolerance towards V. parahaemolyticus might be associated with the increased regulation of Hsp70, prophenoloxidase and crustin upon exposure to the extract, all immune-related proteins essential for pathogen elimination in Penaeid shrimp. The present study primarily demonstrated that P. tectorius leaf extract is a viable alternative for enhancing P. vannamei post-larvae resistance against V. parahaemolyticus, a major bacterial pathogen in aquaculture.

Development and validation of a bacterial gastrointestinal multiplex RT-PCR assay for use on a fully automated molecular system

PCR-based enteric multiplex panels represent a rapid and reliable alternative to conventional “classical” phenotypic stool diagnostics. The aim of this study was to establish a laboratory-developed non-commercial multiplex Real-Time-PCR panel for the detection of the most important bacterial stool pathogens, Salmonella spp., Shigella spp., Yersinia enterocolitica/ pseudotuberculosis and Campylobacter jejuni/coli. on the “open” cobas omni Utility Channel (UC) of the cobas 6800 system (Roche). The aim was to replace the laborious phenotypical stool diagnostics with a high throughput Real-Time PCR method. The respective primers and probes were designed to cover conserved genomic regions of the pathogens and validated using Ultramer oligonucleotides, positive stool material and reference strains. To further validate the multiplex PCR-assay, the following parameters were evaluated: analytical-sensitivity and -specificity, cross-reactivity, linearity and inter- and intra-assay variance as well as limit of detection (LOD). In addition a retrospective analysis of culture positive and negative samples from daily routine was performed using 745 native stool samples.The Gastro assay was linear over a 5-log-unit and within the expected dynamic range with amplification efficiencies ranging from 94.6% to 120%. In addition, all targets showed excellent coefficients of repeatability (≤ 1.11%), intermediate precision (≤ 1.02%) and total variance (≤ 1.39%). In terms of analytical sensitivity the assay demonstrated detection limits ranging from 7.83 copies per reaction to 14.4 copies per reaction. The assay showed excellent agreement with culture methods (>95%) and a 100% sensitivity and specificity after resolution of discrepant results.The multiplex-PCR assay provides a comprehensive, rapid and sensitive alternative to conventional methods for the detection of the major bacterial stool pathogens in diagnostic laboratories.

Major food-borne zoonotic bacterial pathogens of livestock origin: Review

Animal food-borne microbes are pathogens that jeopardize food safety and cause illness in humans via natural infection or contamination. Most of those microbes are bacteria that have considerable impacts on public health. Their survival and pathogenicity are due to toxin production, biofilm development, spore formation, disinfection resistance, and other traits. However, detailed information about them is scattered across scientific literature.&#x0D; We aimed to compile information about major zoonotic bacteria linked with human food of livestock origin and describe their typical features, transmission modes, detection, and preventative approaches. In particular, we addressed the following pathogens that cause food-borne disease worldwide: Campylobacter, Salmonella, Listeria, Staphylococcus, Brucella, Clostridium, Mycobacterium, Colibacilus, and some others.&#x0D; Many of those bacteria have substantial reservoirs in food animals, and food products of animal origin are the primary vehicles of their transmission. Human beings become affected by food-borne zoonotic bacteria if they consume raw animal products or foods produced by using unstandardized slaughtering methods or unsanitary preparation and handling procedures. These zoonotic bacteria and their toxins can be detected in food by culturing, serological, and molecular diagnostic methods. They are effectively controlled and prevented by good hygiene, good management practices, cooking, and pasteurization protocols. &#x0D; In addition, there is a need for a centralized surveillance and monitoring system, as well as higher awareness in society of the occurrence, prevention, and control of bacterial pathogens related to food animals.

Pectate Lyase from Fusarium sacchari Induces Plant Immune Responses and Contributes to Virulence.

Fusarium sacchari is one of the primary pathogens causing Pokkah Boeng disease (PBD) in sugarcane in China. Pectate lyases (PL), which play a critical role in pectin degradation and fungal virulence, have been extensively studied in major bacterial and fungal pathogens of a wide range of plant species. However, only a few PLs have been functionally investigated. In this study, we analyzed the function of the pectate lyase gene, FsPL, from F. sacchari. FsPL is a key virulence factor of F. sacchari and can induce plant cell death. FsPL also triggers the pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) response in Nicotiana benthamiana, as reflected by increases in reactive oxygen species (ROS) production, electrolyte leakage, and callose accumulation, as well as the upregulation of defense response genes. In addition, our study also found that the signal peptide of FsPL was necessary for induced cell death and PTI responses. Virus-induced gene silencing showed that FsPL-induced cell death in Nicotiana benthamiana was mediated by leucine-rich repeat (LRR) receptor-like kinases BAK1 and SOBIR1. Thus, FsPL may not only be a critical virulence factor for F. sacchari but may also induce plant defense responses. These findings provide new insights into the functions of pectate lyase in host-pathogen interactions. IMPORTANCE Pokkah Boeng disease (PBD) is one of the main diseases affecting sugarcane in China, seriously damaging sugarcane production and economic development. Therefore, it is important to clarify the pathogenic mechanisms of this disease and to provide a theoretical basis for the breeding of PBD-resistant sugarcane strains. The present study aimed to analyze the function of FsPL, a recently identified pectate lyase gene from F. sacchari. FsPL is a key virulence factor of F. sacchari that induces plant cell death. Our results provide new insights into the function of pectate lyase in host-pathogen interactions.

Constitutive secretion of pro-IL-18 allows keratinocytes to initiate inflammation during bacterial infection.

Group A Streptococcus (GAS, Streptococcus pyogenes) is a professional human pathogen that commonly infects the skin. Keratinocytes are one of the first cells to contact GAS, and by inducing inflammation, they can initiate the earliest immune responses to pathogen invasion. Here, we characterized the proinflammatory cytokine repertoire produced by primary human keratinocytes and surrogate cell lines commonly used in vitro. Infection induces several cytokines and chemokines, but keratinocytes constitutively secrete IL-18 in a form that is inert (pro-IL-18) and lacks proinflammatory activity. Canonically, IL-18 activation and secretion are coupled through a single proteolytic event that is regulated intracellularly by the inflammasome protease caspase-1 in myeloid cells. The pool of extracellular pro-IL-18 generated by keratinocytes is poised to sense extracellular proteases. It is directly processed into a mature active form by SpeB, a secreted GAS protease that is a critical virulent factor during skin infection. This mechanism contributes to the proinflammatory response against GAS, resulting in T cell activation and the secretion of IFN-γ. Under these conditions, isolates of several other major bacterial pathogens and microbiota of the skin were found to not have significant IL-18-maturing ability. These results suggest keratinocyte-secreted IL-18 is a sentinel that sounds an early alarm that is highly sensitive to GAS, yet tolerant to non-invasive members of the microbiota.