Interrelationship between type three secretion system and metabolism in pathogenic bacteria

Unleashing the Influence of cAMP Receptor Protein: The Master Switch of Bacteriocin Export in Pectobacterium carotovorum subsp. carotovorum

Pectobacterium carotovorum subsp. carotovorum (Pcc) is a Gram-negative phytopathogenic bacterium that produces carocin, a low-molecular-weight bacteriocin that can kill related strains in response to factors in the environment such as UV exposure or nutritional deficiency. The function of the catabolite activator protein (CAP), also known as the cyclic AMP receptor protein (CRP), as a regulator of carocin synthesis was examined. The crp gene was knocked out as part of the investigation, and the outcomes were assessed both in vivo and in vitro. Analysis of the DNA sequence upstream of the translation initiation site of carocin S3 revealed two putative binding sites for CRP that were confirmed using a biotinylated probe pull-down experiment. This study revealed that the deletion of crp inhibited genes involved in extracellular bacteriocin export via the flagellar type III secretion system and impacted the production of many low-molecular-weight bacteriocins. The biotinylated probe pull-down test demonstrated that when UV induction was missing, CRP preferentially attached to one of the two CAP sites while binding to both when UV induction was present. In conclusion, our research aimed to simulate the signal transduction system that controls the expression of the carocin gene in response to UV induction.

Role of Two-Component System Networks in Pseudomonas aeruginosa Pathogenesis

Two-component systems (TCS) are the largest family of signaling systems in the bacterial kingdom. They enable bacteria to cope with a wide range of environmental conditions via the sensing of stimuli and the transduction of the signal into an appropriate cellular adaptation response. Pseudomonas aeruginosa possesses one of the richest arrays of TCSs in bacteria and they have been the subject of intense investigation for more than 20 years. Most of the P. aeruginosa TCSs characterized to date affect its pathogenesis, via the regulation of virulence factors expression, modulation of the synthesis of antibiotic/antimicrobial resistance mechanisms, and/or via linking virulence to energy metabolism. Here, we give an overview of the current knowledge on P. aeruginosa TCSs, citing key examples for each of the above-mentioned regulatory actions. We then conclude by mentioning few small molecule inhibitors of P. aeruginosa TCSs that have shown an antimicrobial action in vitro.

Pseudomonas aeruginosa core metabolism exerts a widespread growth-independent control on virulence

To assess the role of core metabolism genes in bacterial virulence - independently of their effect on growth - we correlated the genome, the transcriptome and the pathogenicity in flies and mice of 30 fully sequenced Pseudomonas strains. Gene presence correlates robustly with pathogenicity differences among all Pseudomonas species, but not among the P. aeruginosa strains. However, gene expression differences are evident between highly and lowly pathogenic P. aeruginosa strains in multiple virulence factors and a few metabolism genes. Moreover, 16.5%, a noticeable fraction of the core metabolism genes of P. aeruginosa strain PA14 (compared to 8.5% of the non-metabolic genes tested), appear necessary for full virulence when mutated. Most of these virulence-defective core metabolism mutants are compromised in at least one key virulence mechanism independently of auxotrophy. A pathway level analysis of PA14 core metabolism, uncovers beta-oxidation and the biosynthesis of amino-acids, succinate, citramalate, and chorismate to be important for full virulence. Strikingly, the relative expression among P. aeruginosa strains of genes belonging in these metabolic pathways is indicative of their pathogenicity. Thus, P. aeruginosa strain-to-strain virulence variation, remains largely obscure at the genome level, but can be dissected at the pathway level via functional transcriptomics of core metabolism.

ptsI gene in the phosphotransfer system is a potential target for developing a live attenuated Salmonella vaccine

Salmonella enterica serovar Typhimurium causes invasive non-typhoidal Salmonella diseases in animals and humans, resulting in a high mortality rate and huge economic losses globally. As the prevalence of antibiotic-resistant Salmonella has been increasing, vaccination is thought to be the most effective and economical strategy to manage salmonellosis. The present study aimed to investigate whether dysfunction in the phosphoenolpyruvate:carbohydrate phosphotransferase system (PTS), which is critical for carbon uptake and survival in macrophages, may be adequate to generate Salmonella-attenuated vaccine strains. A Salmonella strain (KST0555) was generated by deleting the ptsI gene from the PTS and it was revealed that this auxotrophic mutant was unable to efficiently utilize predominant carbon sources during infection (glucose and glycerol), reduced its invasion and replication capacity in macrophages, and significantly (P=0.0065) lowered its virulence in the setting of a mouse colitis model, along with a substantially decreased intestinal colonization and invasiveness compared with its parent strain. The reverse transcription-quantitative PCR results demonstrated that the virulence genes in Salmonella pathogenicity island-1 (SPI-1) and -2 (SPI-2) and the motility of KST0555 were all downregulated compared with its parent strain. Finally, it was revealed that when mice were immunized orally with live KST0555, Salmonella-specific humoral and cellular immune responses were effectively elicited, providing protection against Salmonella infection. Thus, the present promising data provides a strong rationale for the advancement of KST0555 as a live Salmonella vaccine candidate and ptsI as a potential target for developing a live attenuated bacterial vaccine strain.

Life After Secretion-Yersinia enterocolitica Rapidly Toggles Effector Secretion and Can Resume Cell Division in Response to Changing External Conditions

Many pathogenic bacteria use the type III secretion system (T3SS) injectisome to manipulate host cells by injecting virulence-promoting effector proteins into the host cytosol. The T3SS is activated upon host cell contact, and its activation is accompanied by an arrest of cell division; hence, many species maintain a T3SS-inactive sibling population to propagate efficiently within the host. The enteric pathogen Yersinia enterocolitica utilizes the T3SS to prevent phagocytosis and inhibit inflammatory responses. Unlike other species, almost all Y. enterocolitica are T3SS-positive at 37°C, which raises the question, how these bacteria are able to propagate within the host, that is, when and how they stop secretion and restart cell division after a burst of secretion. Using a fast and quantitative in vitro secretion assay, we have examined the initiation and termination of type III secretion. We found that effector secretion begins immediately once the activating signal is present, and instantly stops when this signal is removed. Following effector secretion, the bacteria resume division within minutes after being introduced to a non-secreting environment, and the same bacteria are able to re-initiate effector secretion at later time points. Our results indicate that Y. enterocolitica use their type III secretion system to promote their individual survival when necessary, and are able to quickly switch their behavior toward replication afterwards, possibly gaining an advantage during infection.

Molecular analysis of virulence genes of Salmonella Infantis isolated from chickens and turkeys

In this study, virulence genes of S. Infantis strains, which are commonly isolated from chickens and turkeys in Turkey, were analyzed, and the virulence genes of S. Infantis and other common serovars aside from S. Infantis were compared. In this study, 200 S. Infantis strains isolated from litter, powder, environmental sources, rodent samples and broiler chicken carcasses from a chicken slaughterhouse obtained from chickens (broiler chickens, breeders, laying hens) and 24 S. Infantis strains isolated and identified from litter, powder, environmental and rodent samples obtained from turkeys were analyzed. A total of 40 strains, comprising 10 strains from each Salmonella serovar (S. Typhimurium, S. Enteritidis, S. Kentucky and S. Hadar) (chicken-origin) were also selected from the collection of strains for comparison with S. Infantis strains. The virulence genes of 264, comprising 224 S. Infantis strains and 40 strains from common serovars other than S. Infantis were analyzed. A conventional polymerase chain reaction (PCR) was used to analyze the 11 genes associated with the virulence (sipA, sipD, sopD, sopB, sopE, sopE2, sitC, ssaR, sifA, spvC and pefA) in these strains. SipA, ssaR and sopE genes were found in the 209 S. Infantis strains (93.3%), sipD in 208 (92.85%), sopB in 207 (92.41%), sitC in 206 (91.96%), sifA in 203 (90.62%), sopD in 198 (88.39%), sopE2 in 166 (74.1%), spvC in 20 (8.92%) and the pefA virulence gene in one strain (0.44%). It was found that 74.55% of S. Infantis strains were distributed in gene patterns 1 and 2. In this study, the sopE2 virulence gene in S. Infantis strains was analyzed for the first time. The involvement of the dominant gene patterns of the S. Infantis strains isolated from broiler chicken and broiler chicken carcasses, and the fact that none of S. Infantis strains belonging to the breeders and laying hens were included in these patterns, indicated that S. Infantis entered the broilers not through the breeders, but through environmental factors. The presence of sipA, sipD, sopD, ssaR, sopB, sopE, sifA and sitC virulence genes in S. Infantis strains were found to be similar, but remarkable differences were found compared to the S. Typhimurium and S. Enteritidis strains in the presence of sopE2, spvC and pefA virulence genes. This study examining the virulence genes of S. Infantis strains provides detailed information aimed at providing an understanding of the pathogenesis and epidemiology of Salmonella in poultry.

Umbrella Sampling and X-ray Crystallographic Analysis Unveil an Arg-Asp Gate Facilitating Inhibitor Binding Inside Phosphopantetheine Adenylyltransferase Allosteric Cleft

Phosphopantetheine adenylyltransferase (PPAT) is a rate-limiting enzyme essential for biosynthesis of coenzyme A (CoA), which in turn is responsible to regulate the secretion of exotoxins via type III secretion system in Pseudomonas aeruginosa, causing severe health concerns ranging from nosocomial infections to respiratory failure. Acetyl coenzyme A (AcCoA) is a newly reported inhibitor of PPAT, believed to regulate the cellular levels of CoA and thereby the pathogenesis. Very little is known so far regarding the mechanistic details of AcCoA binding inside PPAT-binding cleft. Herein, we have used extensive umbrella sampling simulations to decipher mechanistic insight into the inhibitor accommodation inside the binding cavity. We found that R90 and D94 residues act like a gate near the binding cavity to accommodate and stabilize the incoming ligand. Mutational models concerning these residues also show considerable difference in AcCoA-binding thermodynamics. To substantiate our findings, we have solved the first crystal structure of apo-PPAT from P. aeruginosa, which also found to agree with the simulation results. Collectively, these results describe the mechanistic details of accommodation of inhibitor molecule inside PPAT-binding cavity and also offer valuable insight into regulating cellular levels of CoA/AcCoA and thus controlling the pathogenicity.

The NAG Sensor NagC Regulates LEE Gene Expression and Contributes to Gut Colonization by Escherichia coli O157:H7

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 are human pathogens responsible for bloody diarrhea and renal failures. EHEC employ a type 3 secretion system to attach directly to the human colonic epithelium. This structure is encoded by the locus of enterocyte effacement (LEE) whose expression is regulated in response to specific nutrients. In this study, we show that the mucin-derived sugars N-acetylglucosamine (NAG) and N-acetylneuraminic acid (NANA) inhibit EHEC adhesion to epithelial cells through down-regulation of LEE expression. The effect of NAG and NANA is dependent on NagC, a transcriptional repressor of the NAG catabolism in E. coli. We show that NagC is an activator of the LEE1 operon and a critical regulator for the colonization of mice intestine by EHEC. Finally, we demonstrate that NAG and NANA as well as the metabolic activity of Bacteroides thetaiotaomicron affect the in vivo fitness of EHEC in a NagC-dependent manner. This study highlights the role of NagC in coordinating metabolism and LEE expression in EHEC and in promoting EHEC colonization in vivo.

Plasma metabolomics for the diagnosis and prognosis of H1N1 influenza pneumonia

Background

Metabolomics is a tool that has been used for the diagnosis and prognosis of specific diseases. The purpose of this study was to examine if metabolomics could be used as a potential diagnostic and prognostic tool for H1N1 pneumonia. Our hypothesis was that metabolomics can potentially be used early for the diagnosis and prognosis of H1N1 influenza pneumonia.

Methods

¹H nuclear magnetic resonance spectroscopy and gas chromatography-mass spectrometry were used to profile the metabolome in 42 patients with H1N1 pneumonia, 31 ventilated control subjects in the intensive care unit (ICU), and 30 culture-positive plasma samples from patients with bacterial community-acquired pneumonia drawn within the first 24 h of hospital admission for diagnosis and prognosis of disease.

Results

We found that plasma-based metabolomics from samples taken within 24 h of hospital admission can be used to discriminate H1N1 pneumonia from bacterial pneumonia and nonsurvivors from survivors of H1N1 pneumonia. Moreover, metabolomics is a highly sensitive and specific tool for the 90-day prognosis of mortality in H1N1 pneumonia.

Conclusions

This study demonstrates that H1N1 pneumonia can create a quite different plasma metabolic profile from bacterial culture-positive pneumonia and ventilated control subjects in the ICU on the basis of plasma samples taken within 24 h of hospital/ICU admission, early in the course of disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-017-1672-7) contains supplementary material, which is available to authorized users.

Metabolic flux analyses of Pseudomonas aeruginosa cystic fibrosis isolates

Pseudomonas aeruginosa is a metabolically versatile wide-ranging opportunistic pathogen. In humans P. aeruginosa causes infections of the skin, urinary tract, blood, and the lungs of Cystic Fibrosis patients. In addition, P. aeruginosa's broad environmental distribution, relatedness to biotechnologically useful species, and ability to form biofilms have made it the focus of considerable interest. We used ¹³C metabolic flux analysis (MFA) and flux balance analysis to understand energy and redox production and consumption and to explore the metabolic phenotypes of one reference strain and five strains isolated from the lungs of cystic fibrosis patients. Our results highlight the importance of the oxidative pentose phosphate and Entner-Doudoroff pathways in P. aeruginosa growth. Among clinical strains we report two divergent metabolic strategies and identify changes between genetically related strains that have emerged during a chronic infection of the same patient. MFA revealed that the magnitude of fluxes through the glyoxylate cycle correlates with growth rates.

Environmental Regulation of Yersinia Pathophysiology

Hallmarks of Yersinia pathogenesis include the ability to form biofilms on surfaces, the ability to establish close contact with eukaryotic target cells and the ability to hijack eukaryotic cell signaling and take over control of strategic cellular processes. Many of these virulence traits are already well-described. However, of equal importance is knowledge of both confined and global regulatory networks that collaborate together to dictate spatial and temporal control of virulence gene expression. This review has the purpose to incorporate historical observations with new discoveries to provide molecular insight into how some of these regulatory mechanisms respond rapidly to environmental flux to govern tight control of virulence gene expression by pathogenic Yersinia.

A small-molecule compound belonging to a class of 2,4-disubstituted 1,3,4-thiadiazine-5-ones suppresses Salmonella infection in vivo

Therapeutic strategies that target bacterial virulence have received considerable attention. The type III secretion system (T3SS) is important for bacterial virulence and represents an attractive therapeutic target. A novel compound with a predicted T3SS inhibitory activity named CL-55 (N-(2,4-difluorophenyl)-4-(3-ethoxy-4-hydroxybenzyl)-5-oxo-5,6-dihydro-4H-[1,3,4]-thiadiazine-2-carboxamide) was previously characterized by low toxicity, high levels of solubility, stability and specific efficiency toward Chlamydia trachomatis in vitro and in vivo. In this study, we describe the action of CL-55 on Salmonella enterica serovar Typhimurium. We found that CL-55 does not affect Salmonella growth in vitro but suppresses Salmonella infection in vivo. The i.p. injection of CL-55 at a dose of 10 mg kg(-1) for 4 days significantly (500-fold) decreased the numbers of Salmonella in the spleen and peritoneal lavages and increased the survival rates in susceptible (BALB/c, I/St) and resistant (A/Sn) mice. Twelve days of therapy led to complete eradication of Salmonella in mice. Moreover, no pathogen was found 4-6 weeks post treatment. CL-55 was not carcinogenic or mutagenic, did not increase the level of chromosomal aberrations in bone marrow cells and had low toxicity in mice, rats and rabbits. Pharmacokinetic studies have shown that CL-55 rapidly disappears from systemic blood circulation and is distributed in the organs. Our data demonstrates that CL-55 affects S. enterica serovar Typhimurium in vivo and could be used as a substance in the design of antibacterial inhibitors for pharmaceutical intervention of bacterial virulence for infection.