The Phosphocarrier Protein HPr Contributes to Meningococcal Survival during Infection

Determinants of bacterial survival and proliferation in blood

Bloodstream infection is a major public health concern associated with high mortality and high healthcare costs worldwide. Bacteremia can trigger fatal sepsis whose prevention, diagnosis, and management have been recognized as a global health priority by the World Health Organization. Additionally, infection control is increasingly threatened by antimicrobial resistance, which is the focus of global action plans in the framework of a One Health response. In-depth knowledge of the infection process is needed to develop efficient preventive and therapeutic measures. The pathogenesis of bloodstream infection is a dynamic process resulting from the invasion of the vascular system by bacteria, which finely regulate their metabolic pathways and virulence factors to overcome the blood immune defenses and proliferate. In this review, we highlight our current understanding of determinants of bacterial survival and proliferation in the bloodstream and discuss their interactions with the molecular and cellular components of blood.

An RNA modification enzyme directly senses reactive oxygen species for translational regulation in Enterococcus faecalis

Bacteria possess elaborate systems to manage reactive oxygen and nitrogen species (ROS) arising from exposure to the mammalian immune system and environmental stresses. Here we report the discovery of an ROS-sensing RNA-modifying enzyme that regulates translation of stress-response proteins in the gut commensal and opportunistic pathogen Enterococcus faecalis. We analyze the tRNA epitranscriptome of E. faecalis in response to reactive oxygen species (ROS) or sublethal doses of ROS-inducing antibiotics and identify large decreases in N²-methyladenosine (m²A) in both 23 S ribosomal RNA and transfer RNA. This we determine to be due to ROS-mediated inactivation of the Fe-S cluster-containing methyltransferase, RlmN. Genetic knockout of RlmN gives rise to a proteome that mimics the oxidative stress response, with an increase in levels of superoxide dismutase and decrease in virulence proteins. While tRNA modifications were established to be dynamic for fine-tuning translation, here we report the discovery of a dynamically regulated, environmentally responsive rRNA modification. These studies lead to a model in which RlmN serves as a redox-sensitive molecular switch, directly relaying oxidative stress to modulating translation through the rRNA and the tRNA epitranscriptome, adding a different paradigm in which RNA modifications can directly regulate the proteome.

The Role of ptsH in Stress Adaptation and Virulence in Cronobacter sakazakii BAA-894

Cronobacter sakazakii, an emerging foodborne pathogen that was isolated primarily from powdered infant formula, poses an important issue in food safety due to its high stress tolerance and pathogenicity. The Hpr (encoded by ptsH gene) has been shown to regulate carbon metabolism as well as stress response and virulence. However, the functional properties of ptsH in C. sakzakii have not been investigated. In this study, we clarified the role of ptsH in the C. sakzakii stress response and virulence, and explored its possible regulatory mechanism by RNA-seq. Compared with wild-type, the ΔptsH mutant showed a slower growth rate in the log phase but no difference in the stationary phase. Moreover, the resistance to heat stress (65 °C, 55 °C), simulated gastric fluid (pH = 2.5), biofilm formation and adhesion to HT-29 cells of ΔptsH mutant were significantly decreased, whereas the oxidative resistance (1, 5, 10 mM H₂O₂), osmotic resistance (10%, 15%, 20% NaCl), and superoxide dismutase activity were enhanced. Finally, RNA-seq analysis revealed the sulfur metabolism pathway is significantly upregulated in the ΔptsH mutant, but the bacterial secretion system pathway is dramatically downregulated. The qRT-PCR assay further demonstrated that the ΔptsH mutant has elevated levels of genes that are related to oxidative and osmotic stress (sodA, rpoS, cpxA/R, osmY). This study provides a great understanding of the role of ptsH in diverse stress responses and virulence in C. sakazakii, and it contributes to our understanding of the genetic determinant of stress resistance and pathogenicity of this important foodborne pathogen.

Comparative proteomics and secretomics revealed virulence, and coresistance-related factors in non O1/O139 Vibrio cholerae recovered from 16 species of consumable aquatic animals

Vibrio cholerae can cause pandemic cholera in humans. The bacterium resides in aquatic environments worldwide. Identification of risk factors of V. cholerae in aquatic products is imperative for assuming food safety. In this study, we determined virulence-associated genes, cross-resistance between antibiotics and heavy metals, and genome fingerprinting profiles of non O1/O139 V. cholerae isolates (n = 20) recovered from 16 species of consumable aquatic animals. Secretomes and proteomes of V. cholerae with distinct genotypes and phenotypes were obtained by using two-dimensional gel electrophoresis (2D-GE) and/or liquid chromatography-tandem mass spectrometry (LC-MS/MS) techniques. Comparative secretomic analysis revealed 4 common and 45 differential extracellular proteins among 20 V. cholerae strains, including 13 virulence- and 8 resistance-associated proteins. A total of 21,972 intracellular proteins were identified, and comparative proteomic analysis revealed 215 common and 913 differential intracellular proteins, including 22 virulence- and 8 resistance-associated proteins. Additionally, different secretomes and proteomes were observed between V. cholerae isolates of fish and shellfish origins. A number of novel proteins with unknown function and strain-specific proteins were also discovered in the V. cholerae isolates. SIGNIFICANCE: V. cholerae can cause pandemic cholera in humans. The bacterium is distributed in aquatic environments worldwide. Identification of risk factors of V. cholerae in aquatic products is imperative for assuming food safety. Non-O1/O139 V. cholerae has been reported to cause sporadic cholera-like diarrhea and bacteremia diseases, which indicates virulence factors rather than the major cholera toxin (CT) exist. This study for the first time investigated proteomes and secretomes of non-O1/O139 V. cholerae originating from aquatic animals. This resulted in the identification of a number of virulence and coresistance-related factors, as well as novel proteins and strain-specific proteins in V. cholerae isolates recovered from 16 species of consumable aquatic animals. These results fill gaps for better understanding of pathogenesis and resistance of V. cholerae, and also support the increasing need for novel diagnosis and vaccine targets against the leading waterborne pathogen worldwide.

Biostimulation of Bacteria in Liquid Culture for Identification of New Antimicrobial Compounds

We hypothesized that environmental microbiomes contain a wide range of bacteria that produce yet uncharacterized antimicrobial compounds (AMCs) that can potentially be used to control pathogens. Over 600 bacterial strains were isolated from soil and food compost samples, and 68 biocontrol bacteria with antimicrobial activity were chosen for further studies based on inhibition assays against a wide range of food and plant pathogens. For further characterization of the bioactive compounds, a new method was established that used living pathogens in a liquid culture to stimulate bacteria to produce high amounts of AMCs in bacterial supernatants. A peptide gel electrophoresis microbial inhibition assay was used to concurrently achieve size separation of the antimicrobial peptides. Fifteen potential bioactive peptides were then further characterized by tandem MS, revealing cold-shock proteins and 50S ribosomal proteins. To identify non-peptidic AMCs, bacterial supernatants were analyzed by HPLC followed by GC/MS. Among the 14 identified bioactive compounds, 3-isobutylhexahydropyrrolo[1,2-a]pyrazine-1,4-dione and 2-acetyl-3-methyl-octahydropyrrolo[1,2-a]piperazine-1,4-dione were identified as new AMCs. Our work suggests that antimicrobial compound production in microbes is enhanced when faced with a threat from other microorganisms, and that this approach can rapidly lead to the development of new antimicrobials with the potential for upscaling.

Unusual Initial Abdominal Presentations of Invasive Meningococcal Disease

Background

Invasive meningococcal disease (IMD) is recognized as septicemia and/or meningitis. However, early symptoms may vary and are frequently nonspecific. Early abdominal presentations have been increasingly described. We aimed to explore a large cohort of patients with initial abdominal presentations for association with particular meningococcal strains.

Methods

Confirmed IMD cases in France between 1991 and 2016 were screened for the presence within the 24 hours before diagnosis of at least 1 of the following criteria (1) abdominal pain, (2) gastroenteritis with diarrhea and vomiting, or (3) diarrhea only. Whole-genome sequencing was performed on all cultured isolates.

Results

We identified 105 cases (median age, 19 years) of early abdominal presentations with a sharp increase since 2014. Early abdominal pain alone was the most frequent symptom (n = 67 [64%]), followed by gastroenteritis (n = 26 [25%]) and diarrhea alone (n = 12 [11%]). Twenty patients (20%) had abdominal surgery. A higher case fatality rate (24%) was observed in these cases compared to 10.4% in all IMD in France (P = .007) with high levels of inflammation markers in the blood. Isolates of group W were significantly more predominant in these cases compared to all IMD. Most of these isolates belonged to clonal complex 11 of the sublineages of the South American-UK strain.

Conclusions

Abdominal presentations are frequently provoked by hyperinvasive isolates of meningococci. Delay in the management of these cases and the virulence of the isolates may explain the high fatality rate. Rapid recognition is a key element to improve their management.

Analysis of the effect of temperature on protein abundance in Demodex-associated Bacillus oleronius

A potential role for bacteria in the induction of rosacea has been suggested. The aim of this work was to characterise the effect of temperature on the production of immunostimulatory proteins by Bacillus oleronius-a bacterium to which rosacea patients show sera reactivity and which was originally isolated from a Demodex mite from a rosacea patient. The affected skin of rosacea patients is at a higher temperature than unaffected skin, and it was postulated that this might alter the protein expression pattern of B. oleronius. B. oleronius growth was reduced at 37°C compared to 30°C but resulted in increased expression of the immune-reactive 62kDa protein (1.65 fold [P < 0.05]). Proteomic analysis revealed increased abundance of a wide range of proteins involved in the stress response (e.g. stress proteins [21.7-fold increase], phosphocarrier protein HPr [438.5-fold increase], 60 kDa chaperonin [12.6-fold increase]). Proteins decreased in abundance after growth at 37°C included ferredoxin (325-fold decrease) and peptidase (244-fold decrease). This work indicates that the increased skin temperature of rosacea patients may alter the growth and protein production pattern of B. oleronius and lead to the greater production of immuo-stimulatory proteins.

Ixodes scapularis Tick Cells Control Anaplasma phagocytophilum Infection by Increasing the Synthesis of Phosphoenolpyruvate from Tyrosine

The obligate intracellular pathogen, Anaplasma phagocytophilum, is the causative agent of life-threatening diseases in humans and animals. A. phagocytophilum is an emerging tick-borne pathogen in the United States, Europe, Africa and Asia, with increasing numbers of infected people and animals every year. It is increasingly recognized that intracellular pathogens modify host cell metabolic pathways to increase infection and transmission in both vertebrate and invertebrate hosts. Recent reports have shown that amino acids are central to the host–pathogen metabolic interaction. In this study, a genome-wide search for components of amino acid metabolic pathways was performed in Ixodes scapularis, the main tick vector of A. phagocytophilum in the United States, for which the genome was recently published. The enzymes involved in the synthesis and degradation pathways of the twenty amino acids were identified. Then, the available transcriptomics and proteomics data was used to characterize the mRNA and protein levels of I. scapularis amino acid metabolic pathway components in response to A. phagocytophilum infection of tick tissues and ISE6 tick cells. Our analysis was focused on the interplay between carbohydrate and amino acid metabolism during A. phagocytophilum infection in ISE6 cells. The results showed that tick cells increase the synthesis of phosphoenolpyruvate (PEP) from tyrosine to control A. phagocytophilum infection. Metabolic pathway analysis suggested that this is achieved by (i) increasing the transcript and protein levels of mitochondrial phosphoenolpyruvate carboxykinase (PEPCK-M), (ii) shunting tyrosine into the tricarboxylic acid (TCA) cycle to increase fumarate and oxaloacetate which will be converted into PEP by PEPCK-M, and (iii) blocking all the pathways that use PEP downstream gluconeogenesis (i.e., de novo serine synthesis pathway (SSP), glyceroneogenesis and gluconeogenesis). While sequestering host PEP may be critical for this bacterium because it cannot actively carry out glycolysis to produce PEP, excess of this metabolite may be toxic for A. phagocytophilum. The present work provides a more comprehensive view of the major amino acid metabolic pathways involved in the response to pathogen infection in ticks, and provides the basis for further studies to develop novel strategies for the control of granulocytic anaplasmosis.

Sophisticated Regulation of Transcriptional Factors by the Bacterial Phosphoenolpyruvate: Sugar Phosphotransferase System

The phosphoenolpyruvate:sugar phosphotransferase system (PTS) is a carbohydrate transport and phosphorylation system present in bacteria of all different phyla and in archaea. It is usually composed of three proteins or protein complexes, enzyme I, HPr, and enzyme II, which are phosphorylated at histidine or cysteine residues. However, in many bacteria, HPr can also be phosphorylated at a serine residue. The PTS not only functions as a carbohydrate transporter but also regulates numerous cellular processes either by phosphorylating its target proteins or by interacting with them in a phosphorylation-dependent manner. The target proteins can be catabolic enzymes, transporters, and signal transduction proteins but are most frequently transcriptional regulators. In this review, we will describe how PTS components interact with or phosphorylate proteins to regulate directly or indirectly the activity of transcriptional repressors, activators, or antiterminators. We will briefly summarize the well-studied mechanism of carbon catabolite repression in firmicutes, where the transcriptional regulator catabolite control protein A needs to interact with seryl-phosphorylated HPr in order to be functional. We will present new results related to transcriptional activators and antiterminators containing specific PTS regulation domains, which are the phosphorylation targets for three different types of PTS components. Moreover, we will discuss how the phosphorylation level of the PTS components precisely regulates the activity of target transcriptional regulators or antiterminators, with or without PTS regulation domain, and how the availability of PTS substrates and thus the metabolic status of the cell are connected with various cellular processes, such as biofilm formation or virulence of certain pathogens.