Cellular adaptation of Clostridioides difficile to high salinity encompasses a compatible solute-responsive change in cell morphology

Infections by the pathogenic gut bacterium Clostridioides difficile cause severe diarrheas up to a toxic megacolon and are currently among the major causes of lethal bacterial infections. Successful bacterial propagation in the gut is strongly associated with the adaptation to changing nutrition-caused environmental conditions; e.g. environmental salt stresses. Concentrations of 350 mM NaCl, the prevailing salinity in the colon, led to significantly reduced growth of C. difficile. Metabolomics of salt- stressed bacteria revealed a major reduction of the central energy generation pathways, including the Stickland-fermentation reactions. No obvious synthesis of compatible solutes was observed up to 24 h of growth. The ensuing limited tolerance to high salinity and absence of compatible solute synthesis might result from an evolutionary adaptation to the exclusive life of C. difficile in the mammalian gut. Addition of the compatible solutes carnitine, glycine-betaine, γ-butyrobetaine, crotonobetaine, homobetaine, proline-betaine and dimethylsulfoniopropionate (DMSP) restored growth (choline and proline failed) under conditions of high salinity. A bioinformatically-identified OpuF-type ABC-transporter imported most of the used compatible solutes. A long-term adaptation after 48 h included a shift of the Stickland fermentation-based energy metabolism from the utilization to the accumulation of L-proline and resulted in restored growth. Surprisingly, salt stress resulted in the formation of coccoid C. difficile cells instead of the typical rod-shaped cells, a process reverted by the addition of several compatible solutes. Hence, compatible solute import via OpuF is the major immediate adaptation strategy of C. difficile to high salinity-incurred cellular stress. This article is protected by copyright. All rights reserved.

Influence of L-lactate and low glucose concentrations on the metabolism and the toxin formation of Clostridioides difficile

The virulence of Clostridioides difficile (formerly Clostridium difficile) is mainly caused by its two toxins A and B. Their formation is significantly regulated by metabolic processes. Here we investigated the influence of various sugars (glucose, fructose, mannose, trehalose), sugar derivatives (mannitol and xylitol) and L-lactate on toxin synthesis. Fructose, mannose, trehalose, mannitol and xylitol in the growth medium resulted in an up to 2.2-fold increase of secreted toxin. Low glucose concentration of 2 g/L increased the toxin concentration 1.4-fold compared to growth without glucose, while high glucose concentrations in the growth medium (5 and 10 g/L) led to up to 6.6-fold decrease in toxin formation. Transcriptomic and metabolic investigation of the low glucose effect pointed towards an inactive CcpA and Rex regulatory system. L-lactate (500 mg/L) significantly reduced extracellular toxin formation. Transcriptome analyses of the later process revealed the induction of the lactose utilization operon encoding lactate racemase (larA), electron confurcating lactate dehydrogenase (CDIF630erm_01321) and the corresponding electron transfer flavoprotein (etfAB). Metabolome analyses revealed L-lactate consumption and the formation of pyruvate. The involved electron confurcation process might be responsible for the also observed reduction of the NAD⁺/NADH ratio which in turn is apparently linked to reduced toxin release from the cell.

Iron Regulation in Clostridioides difficile

The response to iron limitation of several bacteria is regulated by the ferric uptake regulator (Fur). The Fur-regulated transcriptional, translational and metabolic networks of the Gram-positive, pathogen Clostridioides difficile were investigated by a combined RNA sequencing, proteomic, metabolomic and electron microscopy approach. At high iron conditions (15 μM) the C. difficile fur mutant displayed a growth deficiency compared to wild type C. difficile cells. Several iron and siderophore transporter genes were induced by Fur during low iron (0.2 μM) conditions. The major adaptation to low iron conditions was observed for the central energy metabolism. Most ferredoxin-dependent amino acid fermentations were significantly down regulated (had, etf, acd, grd, trx, bdc, hbd). The substrates of these pathways phenylalanine, leucine, glycine and some intermediates (phenylpyruvate, 2-oxo-isocaproate, 3-hydroxy-butyryl-CoA, crotonyl-CoA) accumulated, while end products like isocaproate and butyrate were found reduced. Flavodoxin (fldX) formation and riboflavin biosynthesis (rib) were enhanced, most likely to replace the missing ferredoxins. Proline reductase (prd), the corresponding ion pumping RNF complex (rnf) and the reaction product 5-aminovalerate were significantly enhanced. An ATP forming ATPase (atpCDGAHFEB) of the F₀F₁-type was induced while the formation of a ATP-consuming, proton-pumping V-type ATPase (atpDBAFCEKI) was decreased. The [Fe-S] enzyme-dependent pyruvate formate lyase (pfl), formate dehydrogenase (fdh) and hydrogenase (hyd) branch of glucose utilization and glycogen biosynthesis (glg) were significantly reduced, leading to an accumulation of glucose and pyruvate. The formation of [Fe-S] enzyme carbon monoxide dehydrogenase (coo) was inhibited. The fur mutant showed an increased sensitivity to vancomycin and polymyxin B. An intensive remodeling of the cell wall was observed, Polyamine biosynthesis (spe) was induced leading to an accumulation of spermine, spermidine, and putrescine. The fur mutant lost most of its flagella and motility. Finally, the CRISPR/Cas and a prophage encoding operon were downregulated. Fur binding sites were found upstream of around 20 of the regulated genes. Overall, adaptation to low iron conditions in C. difficile focused on an increase of iron import, a significant replacement of iron requiring metabolic pathways and the restructuring of the cell surface for protection during the complex adaptation phase and was only partly directly regulated by Fur.

Clostridioides difficile Activates Human Mucosal-Associated Invariant T Cells

Clostridioides difficile infection (CDI) causes severe inflammatory responses at the intestinal mucosa but the immunological mechanisms underlying CDI-related immunopathology are still incompletely characterized. Here we identified for the first time that both, non-toxigenic strains as well as the hypervirulent ribotypes RT027 and RT023 of Clostridioides difficile (formerly Clostridium difficile), induced an effector phenotype in mucosal-associated invariant T (MAIT) cells. MAIT cells can directly respond to bacterial infections by recognizing MR1-presented metabolites derived from the riboflavin synthesis pathway constituting a novel class of antigens. We confirmed functional riboflavin synthesis of C. difficile and found fixed bacteria capable of activating primary human MAIT cells in a dose-dependent manner. C. difficile-activated MAIT cells showed an increased and MR1-dependent expression of CD69, proinflammatory IFNγ, and the lytic granule components granzyme B and perforin. Effector protein expression was accompanied by the release of lytic granules, which, in contrast to other effector functions, was mainly induced by IL-12 and IL-18. Notably, this study revealed hypervirulent C. difficile strains to be most competent in provoking MAIT cell responses suggesting MAIT cell activation to be instrumental for the immunopathology observed in C. difficile-associated colitis. In conclusion, we provide first evidence for a link between C. difficile metabolism and innate T cell-mediated immunity in humans.

Metabolic Reprogramming of Clostridioides difficile During the Stationary Phase With the Induction of Toxin Production

The obligate anaerobe, spore forming bacterium Clostridioides difficile (formerly Clostridium difficile) causes nosocomial and community acquired diarrhea often associated with antibiotic therapy. Major virulence factors of the bacterium are the two large clostridial toxins TcdA and TcdB. The production of both toxins was found strongly connected to the metabolism and the nutritional status of the growth environment. Here, we systematically investigated the changes of the gene regulatory, proteomic and metabolic networks of C. difficile 630Δerm underlying the adaptation to the non-growing state in the stationary phase. Integrated data from time-resolved transcriptome, proteome and metabolome investigations performed under defined growth conditions uncovered multiple adaptation strategies. Overall changes in the cellular processes included the downregulation of ribosome production, lipid metabolism, cold shock proteins, spermine biosynthesis, and glycolysis and in the later stages of riboflavin and coenzyme A (CoA) biosynthesis. In contrast, different chaperones, several fermentation pathways, and cysteine, serine, and pantothenate biosynthesis were found upregulated. Focusing on the Stickland amino acid fermentation and the central carbon metabolism, we discovered the ability of C. difficile to replenish its favored amino acid cysteine by a pathway starting from the glycolytic 3-phosphoglycerate via L-serine as intermediate. Following the growth course, the reductive equivalent pathways used were sequentially shifted from proline via leucine/phenylalanine to the central carbon metabolism first to butanoate fermentation and then further to lactate fermentation. The toxin production was found correlated mainly to fluxes of the central carbon metabolism. Toxin formation in the supernatant was detected when the flux changed from butanoate to lactate synthesis in the late stationary phase. The holistic view derived from the combination of transcriptome, proteome and metabolome data allowed us to uncover the major metabolic strategies that are used by the clostridial cells to maintain its cellular homeostasis and ensure survival under starvation conditions.

Quality Control by Isoleucyl-tRNA Synthetase of Bacillus subtilis Is Required for Efficient Sporulation

Isoleucyl-tRNA synthetase (IleRS) is an aminoacyl-tRNA synthetase whose essential function is to aminoacylate tRNA^Ile with isoleucine. Like some other aminoacyl-tRNA synthetases, IleRS can mischarge tRNA^Ile and correct this misacylation through a separate post-transfer editing function. To explore the biological significance of this editing function, we created a ileS(T233P) mutant of Bacillus subtilis that allows tRNA^Ile mischarging while retaining wild-type Ile-tRNA^Ile synthesis activity. As seen in other species defective for aminoacylation quality control, the growth rate of the ileS(T233P) strain was not significantly different from wild-type. When the ileS(T233P) strain was assessed for its ability to promote distinct phenotypes in response to starvation, the ileS(T233P) strain was observed to exhibit a significant defect in formation of environmentally resistant spores. The sporulation defect ranged from 3-fold to 30-fold and was due to a delay in activation of early sporulation genes. The loss of aminoacylation quality control in the ileS(T233P) strain resulted in the inability to compete with a wild-type strain under selective conditions that required sporulation. These data show that the quality control function of IleRS is required in B. subtilis for efficient sporulation and suggests that editing by aminoacyl-tRNA synthetases may be important for survival under starvation/nutrient limitation conditions.

Nitric oxide synthase inhibitor blocks light-induced phase shifts of the circadian activity rhythm, but not c-fos expression in the suprachiasmatic nucleus of the Syrian hamster

Circadian rhythms in mammals are entrained to the environmental light cycle by daily adjustments in the phase of the circadian pacemaker located in the suprachiasmatic nuclei (SCN) of the hypothalamus. Brief exposure of hamsters maintained under constant darkness to ambient light during subjective nighttime produces both phase shifts of the circadian activity rhythm and characteristic patterns of c-fos protein (Fos) immunoreactivity in the SCN. In this study, we demonstrate that light-induced phase shifts of the circadian activity rhythm are blocked by intracerebroventricular (i.c.v.) injection of the competitive nitric oxide synthase (NOS) inhibitor, N-nitro-L-arginine methyl ester (L-NAME), but not by the inactive isomer, D-NAME. The effects of L-NAME are reversible and dose-related, and are countered by co-injection of arginine, the natural substrate for NOS. While effects on behavioral rhythms are pronounced, similar treatment does not alter the pattern of light-induced Fos immunoreactivity in the SCN. These results suggest that nitric oxide is a component of the signal transduction pathway that communicates photic information to the SCN circadian pacemaker, and that nitric oxide production is either independent of, or downstream from, pathways involved in induction of c-fos expression.

[2 cases of anaphylaxis from droperidol]

Following two cases of anaphylactoid reactions during anaesthesia, immunoallergological investigations showed up the responsibility of droperidol, which probably acted by way of an anaphylactic mechanism. In both cases, there were no cardiovascular signs, the main clinical symptom being bronchospasm. The exceptional nature of allergic accidents due to neuroleptic drugs, as opposed to extrapyramidal phenomena, must be underlined. However, these reactions should cast doubts on the safety and usefulness of neuroleptanalgesia.

Separation of adaptive mucosal growth and transport after small bowel resection

In rats 70% of the small bowel was resected with preservation of duodenum and terminal ileum. Two and four weeks later transport of sodium, chloride, water, and galactose was studied in duodenum and ileum. Controls were sham-operated and unoperated rats. There was significant mucosal growth 2 and 4 wk after resection. By 2 wk postresection transport specific activities (transport per gram mucosa) were generally decreased. Mucosal growth compensated only sufficiently so that transport capacities (transport per centimeter segment length) remained unaltered from controls. By 4 wk postresection transport specific activities had either increased or were unchanged from controls. Therefore, in association with mucosal growth, transport capacities increased. The major adaptive increases for electrolytes and water occurred in duodenum; ileum was the site of increased galactose transport. The data indicate that 1) mucosal growth and functional transport changes occur as separate adaptive phenomena and 2) adaptive transport mechanisms are selectively localized to particular regions of the intestine.

Morphologic and functional adaptations of large bowel after small-bowel resection in the rat

Seventy percent small bowel was resected in rats. Two and four weeks later transport of sodium, chloride, and water was examined in cecum and more distal large bowel (colon) using a well-established in vivo luminal perfusion technique. Sham-operated and unoperated rats served as controls. In cecum mucosa grew 29% by two weeks after resection but transport remained unchanged. There were no further adaptive changes by four weeks after resection. Unexpectedly, cecum of all rats secreted water and electrolytes. The mechanism remains unclear. In colon there were no adaptive changes by two weeks after resection but by four weeks colon mucosa increased 14% and luminal absorption increased proportionately. Separate studies showed hexose transport could not be induced in cecum or colon, although we have previously demonstrated its induction in contiguous remnant ileum.

Permeability of polyethylene glycol in remnant small bowel after massive intestinal resection

Studies were designed to determine if permeability of adapted (remnant) small bowel mucosa to polyethylene glycol (PEG) was altered after major intestinal resection. Rats underwent 50% small bowel resection with preservation of duodenum and terminal ileum. Sham-operated animals served as controls. Two and four weeks later we cannulated the portal vein and measured mucosal permeability to luminal [3H]PEG and [14C]PEG in isotonic Ringer solution in remnant proximal or distal in situ closed intestinal loops. A lumen-to-portal blood gradient of at least 1000/1 persisted throughout the one-hour experimental period in both resected and sham-operated animals. Thus the adapted remnant intestinal mucosa was highly impermeable to luminal radiotracer PEG. In separate experiments 2 and 4 weeks after 70% small bowel resection or sham operation, in vivo segments of proximal and distal small intestinal were perfused through the lumen for one hour with hypertonic (800 mOsm) mannitol or NaCl solution containing [3H]PEG. There was equal and almost total recovery of [3H]PEG at the end of the experimental period in resected and control animals. The combined data of all experiments indicate that radiotracer PEG may be confidently used as a luminal water phase marker in transport studies of remnant bowel following intestinal resection.

[Severe anaphylactoid accidents occurring during general anesthesia]

Four patients were studied following an anaphylactoid accident occurring during general anaesthesia. Histamine release was assessed on clinical signs, basophil degranulation and, in one case, an early serum histamine peak. Past medical history revealed previous allergies in all cases. An immunological study showed that IgE, CH50, C3 and C4 serum levels were within the normal range. Skin reactivity to histamine was normal in all but one case. In every case, one of the drugs used during the anaesthetic gave a positive skin test and was considered as the causative agent. There were discrepancies between the in vitro and in vivo tests of basophil degranulation, a second drug being positive in one case, and several drugs inducing abnormal degranulation reactions in the other cases. The drugs considered as involved in these accidents are noteworthy: suxamethonium (two cases), fluid gelatin (Plasmion) and droperidol. The results are discussed by the authors.

[Immediate hypersensitivity in brucellosis. New data (author's transl)]

The presence of clinical manifestations of the "immediate hypersensitivity" process has been frequently described in veterinarians, bacteriological laboratory technicians and some patients with chronic brucellosis. We have looked for the presence of specific IgE in these conditions. Twenty-four patients, three months at least after the acute phase of their brucellosis, were given exploration of their humoral, cellular and specific immunity against brucellosis. For this purpose, beside usual classical tests: serodiagnosis, total and specific IgE assays, intradermoreaction and lymphoblastic transformation test with specific antigen (PI fraction) and an adaptation of human basophil degranulation test (HBDT) with PI fraction were performed on all 24 patients. Exploration of immediate hypersensitivity allows us to show neither an abnormal increase of hyper-IgE frequency nor an increase of anti-brucella specific IgE. HBDT is positive in 41 p. cent of the patients. It confirms that immediate hypersensitivity exists. HBDT gives justification for trying desensitization which has been proposed in the past. HBDT will possibly allow us to evaluate desensitization effectiveness.

[Two-dimensional immuno-electrophoresis of cephalospinal fluid proteins wih a study of the IgG/albumin ratio in psychiatry (author's transl)]

The purpose of this study (about 187 adult psychiatric patients) is to investigate correlations between "organic brain syndrome" (vascular or abiotrophic) and values of CSF proteins (technique of two-dimensional immunoelectrophoresis). The authors show positive correlations between 'vascular' brain syndrome and increase of one alpha 2 globulin, between 'abiotrophic' brain syndrome and decrease in all globulins, the importance of brain damage and increase of IgG/albumin ratio.

[Bidimensional electrophoresis in the study of cerebrospinal fluid protein (author's transl)]

The authors report 650 bidimensional electrophoreses of the cerebrospinal fluid (CSF). All examinations were carried out after prior concentration of CSF protein. The technic used is that described by Rebeyrotte in 1970. Four types of tracing were noted: -- Two tracings were unusual by the presence of a large peak in the alpha-2 region. -- One tracing was of the hypergamma type. -- One tracing was comparable to serum by the richness of the precipitations. A change in the first migration permitted us to obtain electrophoretic separations from 100 microlitres of pure CSF. The bidimensional immunoelectrophoresis tracings are comparable to those described previously.

[2-dimensional immunoelectrophoresis of CSF proteins]

Two-dimensional electrophoresis isolates the various proteins in the CSF in peaks ; this a method which gives very reliable results ; the height of the peaks has a certain quantitative value, similar to that obtained with electro-immunodiffusion. The peaks visible in the CSF can be increased separately -- mainly the "alpha 2", "alpha 2 beta", the IgA and IgG peaks -- in another type of recording, the height and number of the peaks may be increased, indicating the presence in the CSF of normally absent protein originating in the serum. An increase in the "alpha 2" or "alpha 2 beta" peaks is not specific, but it is always indicative that the development of a neurological process is under way ; the increase of IgG and IgA retains its character of great specificity in evolutive inflammatory conditions. Multiple peaks indicate the passage of serum proteins into the CSF in oedematous and destructive processes, in expansive or compressive processes and in polyradiculoneuritis. This method with its well-codified technique, which may be carried out on an unconcentrated CSF without risk of denaturing the proteins, may be carried out routinely in clinical practice with human anti-serum immune serum or with more specific serum, anti CSF for example, which seems to give quite reliable results.

Colestipol hydrochloride, a new hypolipidemic drug: a two-year study

Colestipol hydrochloride is an insoluble, nonabsorbable copolymer with bile-acid-binding capacity. It prevents reabsorption of cholates from the intestinal tract into the enterohepatic circulation causing a net loss of bile acids, and therefore of cholesterol. Sixty subjects with cholesterol levels over 250 mg/100 ml were studied for 104 weeks. Patients with normal phenotypes, types 2,3, and 4, were given 5 gm three times daily and experienced an average drop of 40 mg/100 ml (14%). While patients with types 2,3, and 4 hyperlipidemia responded effectively, cholesterol levels in type 2 patients dropped earliest and most consistently with an average decrease of 58 mg/100 ml (19%). A comparable group of patients with hyperlipidemia taking placebo showed on average no change in serum cholesterol. Serum triglyceride values were not altered significantly. The resin is not absorbed from the gastrointestinal tract and produces a slight increase in fecal volume. Results of chemistries, enzyme assays, prothrombin times, hematology, and urinalysis and body weights wer unaltered. There was no evidence of lithogenic bile production. Colestipol is a tasteless and ordorless copolymer with high acceptability. Side effects were limited to occasional bloating, gas, and constipation. The drug is a safe, effective, palatable hypolipedmic agent.