In vitro activity of amixicile against T. vaginalis from clinical isolates.

Trichomoniasis is a sexually transmitted infection in humans caused by the protozoan Trichomonas vaginalis, the leading causative agent of vaginitis in women and urethritis in men worldwide. Metronidazole is the standard treatment for trichomoniasis, with tinidazole as the second line. There are currently no FDA-approved non-nitroimidazole alternative treatments for resistant strains. This study compares the efficacy of a newly synthesized non-nitroimidazole oral drug, amixicile, to that of both metronidazole and the synthetic precursor of amixicile, nitazoxanide with in vitro sensitivity testing. One standard strain from ATCC and three patient-isolated strains of T. vaginalis were used to compare treatments under anaerobic conditions. The minimum inhibitory concentration for metronidazole, nitazoxanide, and amixicile were 12.5 µM, 100 µM, and 6.25 µM, respectively. These results suggest that amixicile may be highly active against T. vaginalis and warrants further investigation as a potential alternative to metronidazole in the treatment of trichomoniasis.

The small molecule nitazoxanide selectively disrupts BAM-mediated folding of the outer membrane usher protein.

Bacterial pathogens assemble adhesive surface structures termed pili or fimbriae to initiate and sustain infection of host tissues. Uropathogenic Escherichia coli, the primary causative agent of urinary tract infections, expresses type 1 and P pili required for colonization of the bladder and kidney, respectively. These pili are assembled by the conserved chaperone-usher (CU) pathway, in which a periplasmic chaperone works together with an outer membrane (OM) usher protein to build and secrete the pilus fiber. Previously, we found that the small molecule and antiparasitic drug nitazoxanide (NTZ) inhibits CU pathway-mediated pilus biogenesis in E. coli by specifically interfering with proper maturation of the usher protein in the OM. The usher is folded and inserted into the OM by the ß-barrel assembly machine (BAM) complex, which in E. coli comprises five proteins, BamA-E. Here, we show that sensitivity of the usher to NTZ is modulated by BAM expression levels and requires the BamB and BamE lipoproteins. Furthermore, a genetic screen for NTZ-resistant bacterial mutants isolated a mutation in the essential BamD lipoprotein. These findings suggest that NTZ selectively interferes with an usher-specific arm of the BAM complex, revealing new details of the usher folding pathway and BAM complex function. Evaluation of a set of NTZ derivatives identified compounds with increased potency and disclosed that NTZ's nitrothiazole ring is critical for usher inhibition. In summary, our findings indicate highly specific effects of NTZ on the usher folding pathway and have uncovered NTZ analogs that specifically decrease usher levels in the OM.

Small molecule promotes ß-catenin citrullination and inhibits Wnt signaling in cancer.

Wnt (wingless)/ß-catenin signaling is critical for tumor progression and is frequently activated in colorectal cancer as a result of the mutation of adenomatous polyposis coli (APC); however, therapeutic agents targeting this pathway for clinical use are lacking. Here we report that nitazoxanide (NTZ), a clinically approved antiparasitic drug, efficiently inhibits Wnt signaling independent of APC. Using chemoproteomic approaches, we have identified peptidyl arginine deiminase 2 (PAD2) as the functional target of NTZ in Wnt inhibition. By targeting PAD2, NTZ increased the deamination (citrullination) and turnover of ß-catenin in colon cancer cells. Replacement of arginine residues disrupted the transcriptional activity, and NTZ induced degradation of ß-catenin. In Wnt-activated colon cancer cells, knockout of either PAD2 or ß-catenin substantially increased resistance to NTZ treatment. Our data highlight the potential of NTZ as a modulator of ß-catenin citrullination for the treatment of cancer patients with Wnt pathway mutations.

Amixicile Reduces Severity of Cryptosporidiosis but Does Not Have In Vitro Activity against Cryptosporidium.

Cryptosporidium species cause significant morbidity in malnourished children. Nitazoxanide (NTZ) is the only approved treatment for cryptosporidiosis, but NTZ has diminished effectiveness during malnutrition. Here, we show that amixicile, a highly selective water-soluble derivative of NTZ diminishes Cryptosporidium infection severity in a malnourished mouse model despite a lack of direct anticryptosporidial activity. We suggest that amixicile, by tamping down anaerobes associated with intestinal inflammation, reverses weight loss and indirectly mitigates infection-associated pathology.

Enhanced Klebsiella pneumoniae Carbapenemase Expression from a Novel Tn4401 Deletion.

The Klebsiella pneumoniae carbapenemase gene (blaKPC) is typically located within mobile transposon Tn4401 Enhanced KPC expression has been associated with deletions in the putative promoter region upstream of blaKPC Illumina sequences from blaKPC-positive clinical isolates from a single institution were mapped to a Tn4401b reference sequence, which carries no deletions. The novel isoform Tn4401h (188-bp deletion [between istB and blaKPC]) was present in 14% (39/281) of clinical isolates. MICs showed that Escherichia coli strains containing plasmids with Tn4401a and Tn4401h were more resistant to meropenem (≥16 and ≥16, respectively), ertapenem (≥8 and 4, respectively), and cefepime (≥64 and 4, respectively) than E. coli strains with Tn4401b (0.5, ≤0.5, and ≤1, respectively). Quantitative real-time PCR (qRT-PCR) demonstrated that Tn4401a had a 16-fold increase and Tn4401h a 4-fold increase in blaKPC mRNA levels compared to the reference Tn4401b. A lacZ reporter plasmid was used to test the activity of the promoter regions from the different variants, and the results showed that the Tn4401a and Tn4401h promoter sequences generated higher ß-galactosidase activity than the corresponding Tn4401b sequence. Further dissection of the promoter region demonstrated that putative promoter P1 was not functional. The activity of the isolated P2 promoter was greatly enhanced by inclusion of the P1-P2 intervening sequence. These studies indicated that gene expression could be an important consideration in understanding resistance phenotypes predicted by genetic signatures in the context of sequencing-based rapid diagnostics.

Legionella pneumophila utilizes a single-player disulfide-bond oxidoreductase system to manage disulfide bond formation and isomerization.

Legionella pneumophila uses a single homodimeric disulfide bond (DSB) oxidoreductase DsbA2 to catalyze extracytoplasmic protein folding and to correct DSB errors through protein-disulfide isomerase (PDI) activity. In Escherichia coli, these functions are separated to avoid futile cycling. In L. pneumophila, DsbA2 is maintained as a mixture of disulfides (S-S) and free thiols (SH), but when expressed in E. coli, only the SH form is observed. We provide evidence to suggest that structural differences in DsbB oxidases (LpDsbB1 and LpDsbB2) and DsbD reductases (LpDsbD1 and LpDsbD2) (compared with E. coli) permit bifunctional activities without creating a futile cycle. LpdsbB1 and LpdsbB2 partially complemented an EcdsbB mutant while neither LpdsbD1 nor LpdsbD2 complemented an EcdsbD mutant unless DsbA2 was also expressed. When the dsb genes of E. coli were replaced with those of L. pneumophila, motility was restored and DsbA2 was present as a mixture of redox forms. A dominant-negative approach to interfere with DsbA2 function in L. pneumophila determined that DSB oxidase activity was necessary for intracellular multiplication and assembly/function of the Dot/Icm Type IVb secretion system. Our studies show that a single-player system may escape the futile cycle trap by limiting transfer of reducing equivalents from LpDsbDs to DsbA2.

Nitazoxanide Inhibits Pilus Biogenesis by Interfering with Folding of the Usher Protein in the Outer Membrane.

Many bacterial pathogens assemble surface fibers termed pili or fimbriae that facilitate attachment to host cells and colonization of host tissues. The chaperone/usher (CU) pathway is a conserved secretion system that is responsible for the assembly of virulence-associated pili by many different Gram-negative bacteria. Pilus biogenesis by the CU pathway requires a dedicated periplasmic chaperone and an integral outer membrane (OM) assembly and secretion platform termed the usher. Nitazoxanide (NTZ), an antiparasitic drug, was previously shown to inhibit the function of aggregative adherence fimbriae and type 1 pili assembled by the CU pathway in enteroaggregativeEscherichia coli, an important causative agent of diarrhea. We show here that NTZ also inhibits the function of type 1 and P pili from uropathogenicE. coli(UPEC). UPEC is the primary causative agent of urinary tract infections, and type 1 and P pili mediate colonization of the bladder and kidneys, respectively. By analysis of the different stages of the CU pilus biogenesis pathway, we show that treatment of bacteria with NTZ causes a reduction in the number of usher molecules in the OM, resulting in a loss of pilus assembly on the bacterial surface. In addition, we determine that NTZ specifically prevents proper folding of the usher ß-barrel domain in the OM. Our findings demonstrate that NTZ is a pilicide with a novel mechanism of action and activity against diverse CU pathways. This suggests that further development of the NTZ scaffold may lead to new antivirulence agents that target the usher to prevent pilus assembly.

Synthesis and Antimicrobial Evaluation of Amixicile-Based Inhibitors of the Pyruvate-Ferredoxin Oxidoreductases of Anaerobic Bacteria and Epsilonproteobacteria.

Amixicile is a promising derivative of nitazoxanide (an antiparasitic therapeutic) developed to treat systemic infections caused by anaerobic bacteria, anaerobic parasites, and members of the Epsilonproteobacteria (Campylobacter and Helicobacter). Amixicile selectively inhibits pyruvate-ferredoxin oxidoreductase (PFOR) and related enzymes by inhibiting the function of the vitamin B1 cofactor (thiamine pyrophosphate) by a novel mechanism. Here, we interrogate the amixicile scaffold, guided by docking simulations, direct PFOR inhibition assays, and MIC tests against Clostridium difficile, Campylobacter jejuni, and Helicobacter pylori Docking simulations revealed that the nitro group present in nitazoxanide interacts with the protonated N4'-aminopyrimidine of thiamine pyrophosphate (TPP). The ortho-propylamine on the benzene ring formed an electrostatic interaction with an aspartic acid moiety (B456) of PFOR that correlated with improved PFOR-inhibitory activity and potency by MIC tests. Aryl substitution with electron-withdrawing groups and substitutions of the propylamine with other alkyl amines or nitrogen-containing heterocycles both improved PFOR inhibition and, in many cases, biological activity against C. difficile Docking simulation results correlate well with mechanistic enzymology and nuclear magnetic resonance (NMR) studies that show members of this class of antimicrobials to be specific inhibitors of vitamin B1 function by proton abstraction, which is both novel and likely to limit mutation-based drug resistance.

Response to metronidazole and oxidative stress is mediated through homeostatic regulator HsrA (HP1043) in Helicobacter pylori.

Metronidazole (MTZ) is often used in combination therapies to treat infections caused by the gastric pathogen Helicobacter pylori. Resistance to MTZ results from loss-of-function mutations in genes encoding RdxA and FrxA nitroreductases. MTZ-resistant strains, when cultured at sub-MICs of MTZ (5 to 20 µg/ml), show dose-dependent defects in bacterial growth; depressed activities of many Krebs cycle enzymes, including pyruvate:ferredoxin oxidoreductase (PFOR); and low transcript levels of porGDAB (primer extension), phenotypes consistent with an involvement of a transcriptional regulator. Using a combination of protein purification steps, electrophoretic mobility shift assays (EMSAs), and mass spectrometry analyses of proteins bound to porG promoter sequences, we identified HP1043, an essential homeostatic global regulator (HsrA [for homeostatic stress regulator]). Competition EMSAs and supershift analyses with HsrA-enriched protein fractions confirmed specific binding to porGDAB and hsrA promoter sequences. Exposure to MTZ resulted in >10-fold decreases in levels of HsrA and in levels of the HsrA-regulated gene products PFOR and TlpB. Exposure to paraquat (PQ), hydrogen peroxide, or organic peroxides showed near equivalence with MTZ, revealing a common oxidative stress response pathway. Finally, direct superoxide dismutase (SOD) assays showed an inverse relationship between HsrA levels and SOD activity, suggesting that HsrA may serve as a repressor of sodB. As a homeostatic sentinel, HsrA appears to be ideally positioned to enable rapid shutdown of genes associated with metabolism and growth while activating (directly or indirectly) oxidative defense genes in response to low levels of toxic metabolites (MTZ or oxygen) before they reach DNA-damaging levels.

Preclinical studies of amixicile, a systemic therapeutic developed for treatment of Clostridium difficile infections that also shows efficacy against Helicobacter pylori.

Amixicile shows efficacy in the treatment of Clostridium difficile infections (CDI) in a mouse model, with no recurrence of CDI. Since amixicile selectively inhibits the action of a B vitamin (thiamine pyrophosphate) cofactor of pyruvate:ferredoxin oxidoreductase (PFOR), it may both escape mutation-based drug resistance and spare beneficial probiotic gut bacteria that do not express this enzyme. Amixicile is a water-soluble derivative of nitazoxanide (NTZ), an antiparasitic therapeutic that also shows efficacy against CDI in humans. In comparative studies, amixicile showed no toxicity to hepatocytes at 200 µM (NTZ was toxic above 10 µM); was not metabolized by human, dog, or rat liver microsomes; showed equivalence or superiority to NTZ in cytochrome P450 assays; and did not activate efflux pumps (breast cancer resistance protein, P glycoprotein). A maximum dose (300 mg/kg) of amixicile given by the oral or intraperitoneal route was well tolerated by mice and rats. Plasma exposure (rats) based on the area under the plasma concentration-time curve was 79.3 h · µg/ml (30 mg/kg dose) to 328 h · µg/ml (100 mg/kg dose), the maximum concentration of the drug in serum was 20 µg/ml, the time to the maximum concentration of the drug in serum was 0.5 to 1 h, and the half-life was 5.6 h. Amixicile did not concentrate in mouse feces or adversely affect gut populations of Bacteroides species, Firmicutes, segmented filamentous bacteria, or Lactobacillus species. Systemic bioavailability was demonstrated through eradication of Helicobacter pylori in a mouse infection model. In summary, the efficacy of amixicile in treating CDI and other infections, together with low toxicity, an absence of mutation-based drug resistance, and excellent drug metabolism and pharmacokinetic metrics, suggests a potential for broad application in the treatment of infections caused by PFOR-expressing microbial pathogens in addition to CDI.

New functions of pirin proteins and a 2-ketoglutarate: Ferredoxin oxidoreductase ortholog in Bacteroides fragilis metabolism and their impact on antimicrobial susceptibility to metronidazole and amixicile.

The understanding of how central metabolism and fermentation pathways regulate antimicrobial susceptibility in the anaerobic pathogen Bacteroides fragilis is still incomplete. Our study reveals that B. fragilis encodes two iron-dependent, redox-sensitive regulatory pirin protein genes, pir1 and pir2. The mRNA expression of these genes increases when exposed to oxygen and during growth in iron-limiting conditions. These proteins, Pir1 and Pir2, influence the production of short-chain fatty acids and modify the susceptibility to metronidazole and amixicile, a new inhibitor of pyruvate: ferredoxin oxidoreductase in anaerobes. We have demonstrated that Pir1 and Pir2 interact directly with this oxidoreductase, as confirmed by two-hybrid system assays. Furthermore, structural analysis using AlphaFold2 predicts that Pir1 and Pir2 interact stably with several central metabolism enzymes, including the 2-ketoglutarate:ferredoxin oxidoreductases Kor1AB and Kor2CDAEBG. We used a series of metabolic mutants and electron transport chain inhibitors to demonstrate the extensive impact of bacterial metabolism on metronidazole and amixicile susceptibility. We also show that amixicile is an effective antimicrobial against B. fragilis in an experimental model of intra-abdominal infection. Our investigation led to the discovery that the kor2AEBG genes are essential for growth and have dual functions, including the formation of 2-ketoglutarate via the reverse TCA cycle. However, the metabolic activity that bypasses the function of Kor2AEBG following the addition of phospholipids or fatty acids remains undefined. Overall, our study provides new insights into the central metabolism of B. fragilis and its regulation by pirin proteins, which could be exploited for the development of new narrow-spectrum antimicrobials in the future.

Disulfide bond oxidoreductase DsbA2 of Legionella pneumophila exhibits protein disulfide isomerase activity.

The extracytoplasmic assembly of the Dot/Icm type IVb secretion system (T4SS) of Legionella pneumophila is dependent on correct disulfide bond (DSB) formation catalyzed by a novel and essential disulfide bond oxidoreductase DsbA2 and not by DsbA1, a second nonessential DSB oxidoreductase. DsbA2, which is widely distributed in the microbial world, is phylogenetically distinct from the canonical DsbA oxidase and the DsbC protein disulfide isomerase (PDI)/reductase of Escherichia coli. Here we show that the extended N-terminal amino acid sequence of DsbA2 (relative to DsbA proteins) contains a highly conserved 27-amino-acid dimerization domain enabling the protein to form a homodimer. Complementation tests with E. coli mutants established that L. pneumophila dsbA1, but not the dsbA2 strain, restored motility to a dsbA mutant. In a protein-folding PDI detector assay, the dsbA2 strain, but not the dsbA1 strain, complemented a dsbC mutant of E. coli. Deletion of the dimerization domain sequences from DsbA2 produced the monomer (DsbA2N), which no longer exhibited PDI activity but complemented the E. coli dsbA mutant. PDI activity was demonstrated in vitro for DsbA2 but not DsbA1 in a nitrocefin-based mutant TEM ß-lactamase folding assay. In an insulin reduction assay, DsbA2N activity was intermediate between those of DsbA2 and DsbA1. In L. pneumophila, DsbA2 was maintained as a mixture of thiol and disulfide forms, while in E. coli, DsbA2 was present as the reduced thiol. Our studies suggest that DsbA2 is a naturally occurring bifunctional disulfide bond oxidoreductase that may be uniquely suited to the majority of intracellular bacterial pathogens expressing T4SSs as well as in many slow-growing soil and aquatic bacteria.

Mutations to essential orphan response regulator HP1043 of Helicobacter pylori result in growth-stage regulatory defects.

Helicobacter pylori establishes lifelong infections of the gastric mucosa, a niche considered hostile to most microbes. While responses to gastric acidity and local inflammation are understood, little is known as to how they are integrated into homeostatic control of cell division and growth-stage gene expression. Here we investigate the essential orphan response regulator HP1043, a member of the OmpR/PhoB subfamily of transcriptional regulators that is unique to the Epsilonproteobacteria and that lacks phosphorylation domains. To test the hypothesis that conformational changes in the homodimer might lead to defects in gene expression, we sought mutations that might alter DNA-binding efficiency. Two introduced mutations (C215S, C221S) C terminal to the DNA-binding domain of HP1043 (HP1043CC11) resulted in a 2-fold higher affinity for its own promoter by footprinting. Modeling studies with the crystal structure of HP1043 suggested that C215S might affect the helix-turn-helix domain. Genomic replacement of the hp1043 allele with the hp1043CC11 mutant allele resulted in a 2-fold decrease in protein levels, despite a dramatic increase in mRNA. The mutations did not affect in vitro growth rates or colonization efficiency in a mouse model. Proteomic profiling (CC11 mutant strain versus wild type) identified many expression differences, and quantitative PCR further revealed that 11 out of 12 examined genes had lost growth-stage regulation and that 6 of the genes contained HP1043 binding consensus sequences within the promoter regions (fur, cagA, cag23, flhA, flip, and napA). Our studies show that mutations that affect DNA-binding affinity can be used to identify new members of the HP1043 regulon.

Vancomycin treatment's association with delayed intestinal tissue injury, clostridial overgrowth, and recurrence of Clostridium difficile infection in mice.

Antibiotic treatment, including vancomycin, for Clostridium difficile infection (CDI) has been associated with recurrence of disease in up to 25% of infected persons. This study investigated the effects of vancomycin on the clinical outcomes, intestinal histopathology, and anaerobic community during and after treatment in a murine model of CDI. C57BL/6 mice were challenged with C. difficile strain VPI 10463 after pretreatment with an antibiotic cocktail. Twenty-four hours after infection, mice were treated daily with vancomycin, nitazoxanide, fidaxomicin, or metronidazaole for 5 days. Mice were monitored for either 6 or 12 days postinfection. Clinical, diarrhea, and histopathology scores were measured. Cecal contents or stool samples were assayed for clostridial or Bacteroides DNA and C. difficile toxins A and B. Vancomycin treatment of infected mice was associated with improved clinical, diarrhea, and histopathology scores and survival during treatment. However, after discontinuation of the drug, clinical scores and histopathology were worse in treated mice than in untreated infected controls. At the end of the study, 62% of the vancomycin-treated mice succumbed to recurrence, with an overall mortality rate equivalent to that of the untreated infected control group. Fidaxomicin-treated mice had outcomes similar to those of vancomycin-treated mice. C. difficile predominated over Bacteroides in cecal contents of vancomycin-treated mice, similar to findings for untreated infected mice. Decreasing the duration of vancomycin treatment from 5 days to 1 day decreased recurrence and deaths. In conclusion, vancomycin improved clinical scores and histopathology acutely but was associated with poor outcome posttreatment in C. difficile-infected mice. Decreasing vancomycin exposure may decrease relapse and improve survival in CDI.

DsbA2 (27 kDa Com1-like protein) of Legionella pneumophila catalyses extracytoplasmic disulphide-bond formation in proteins including the Dot/Icm type IV secretion system.

In Gram-negative bacteria, thiol oxidoreductases catalyse the formation of disulphide bonds (DSB) in extracytoplasmic proteins. In this study, we sought to identify DSB-forming proteins required for assembly of macromolecular structures in Legionella pneumophila. Here we describe two DSB-forming proteins, one annotated as dsbA1 and the other annotated as a 27 kDa outer membrane protein similar to Com1 of Coxiella burnetii, which we designate as dsbA2. Both proteins are predicted to be periplasmic, and while dsbA1 mutants were readily isolated and without phenotype, dsbA2 mutants were not obtained. To advance studies of DsbA2, a cis-proline residue at position 198 was replaced with threonine that enables formation of stable disulphide-bond complexes with substrate proteins. Expression of DsbA2 P198T mutant protein from an inducible promoter produced dominant-negative effects on DsbA2 function that resulted in loss of infectivity for amoeba and HeLa cells and loss of Dot/Icm T4SS-mediated contact haemolysis of erythrocytes. Analysis of captured DsbA2 P198T-substrate complexes from L. pneumophila by mass spectrometry identified periplasmic and outer membrane proteins that included components of the Dot/Icm T4SS. More broadly, our studies establish a DSB oxidoreductase function for the Com1 lineage of DsbA2-like proteins which appear to be conserved among those bacteria also expressing T4SS.

Amixicile, a novel inhibitor of pyruvate: ferredoxin oxidoreductase, shows efficacy against Clostridium difficile in a mouse infection model.

Clostridium difficile infection (CDI) is a serious diarrheal disease that often develops following prior antibiotic usage. One of the major problems with current therapies (oral vancomycin and metronidazole) is the high rate of recurrence. Nitazoxanide (NTZ), an inhibitor of pyruvate:ferredoxin oxidoreductase (PFOR) in anaerobic bacteria, parasites, Helicobacter pylori, and Campylobacter jejuni, also shows clinical efficacy against CDI. From a library of ∼250 analogues of NTZ, we identified leads with increased potency for PFOR. MIC screens indicated in vitro activity in the 0.05- to 2-µg/ml range against C. difficile. To improve solubility, we replaced the 2-acetoxy group with propylamine, producing amixicile, a soluble (10 mg/ml), nontoxic (cell-based assay) lead that produced no adverse effects in mice by oral or intraperitoneal (i.p.) routes at 200 mg/kg of body weight/day. In initial efficacy testing in mice treated (20 mg/kg/day, 5 days each) 1 day after receiving a lethal inoculum of C. difficile, amixicile showed slightly less protection than did vancomycin by day 5. However, in an optimized CDI model, amixicile showed equivalence to vancomycin and fidaxomicin at day 5 and there was significantly greater survival produced by amixicile than by the other drugs on day 12. All three drugs were comparable by measures of weight loss/gain and severity of disease. Recurrence of CDI was common for mice treated with vancomycin or fidaxomicin but not for mice receiving amixicile or NTZ. These results suggest that gut repopulation with beneficial (non-PFOR) bacteria, considered essential for protection against CDI, rebounds much sooner with amixicile therapy than with vancomycin or fidaxomicin. If the mouse model is indeed predictive of human CDI disease, then amixicile, a novel PFOR inhibitor, appears to be a very promising new candidate for treatment of CDI.

Germination and amplification of anthrax spores by soil-dwelling amoebas.

While anthrax is typically associated with bioterrorism, in many parts of the world the anthrax bacillus (Bacillus anthracis) is endemic in soils, where it causes sporadic disease in livestock. These soils are typically rich in organic matter and calcium that promote survival of resilient B. anthracis spores. Outbreaks of anthrax tend to occur in warm weather following rains that are believed to concentrate spores in low-lying areas where runoff collects. It has been concluded that elevated spore concentrations are not the result of vegetative growth as B. anthracis competes poorly against indigenous bacteria. Here, we test an alternative hypothesis in which amoebas, common in moist soils and pools of standing water, serve as amplifiers of B. anthracis spores by enabling germination and intracellular multiplication. Under simulated environmental conditions, we show that B. anthracis germinates and multiplies within Acanthamoeba castellanii. The growth kinetics of a fully virulent B. anthracis Ames strain (containing both the pX01 and pX02 virulence plasmids) and vaccine strain Sterne (containing only pX01) inoculated as spores in coculture with A. castellanii showed a nearly 50-fold increase in spore numbers after 72 h. In contrast, the plasmidless strain 9131 showed little growth, demonstrating that plasmid pX01 is essential for growth within A. castellanii. Electron and time-lapse fluorescence microscopy revealed that spores germinate within amoebal phagosomes, vegetative bacilli undergo multiplication, and, following demise of the amoebas, bacilli sporulate in the extracellular milieu. This analysis supports our hypothesis that amoebas contribute to the persistence and amplification of B. anthracis in natural environments.

Caenorhabditis is a metazoan host for Legionella.

We investigated whether nematodes contribute to the persistence, differentiation and amplification of Legionella species in soil, an emerging source for Legionnaires' disease. Here we show that Legionella spp. colonize the intestinal tracts of Caenorhabditis nematodes leading to worm death. Susceptibility to Legionella is influenced by innate immune responses governed by the p38 mitogen-activated protein kinase and insulin/insulin growth factor-1 receptor signalling pathways. We also show that L. pneumophila colonizes the intestinal tract of nematodes cultivated in soil. To distinguish between transient infection and persistence, plate-fed and soil-extracted nematodes-fed fluorescent strains of L. pneumophila were analysed. Bacteria replicated within the nematode intestinal tract, did not invade surrounding tissue, and were excreted as differentiated forms that were transmitted to offspring. Interestingly, the ultrastructural features of the differentiated bacterial forms were similar to cyst-like forms observed within protozoa, amoeba and mammalian cell lines. While intestinal colonization of L. pneumophila dotA and icmT mutant strains did not alter the survival rate of nematodes in comparison to wild-type strains, nematodes colonized with the dot/icm mutant strains exhibited significantly increased levels of germline apoptosis. Taken together, these studies show that nematodes may serve as natural hosts for these organisms and thereby contribute to their dissemination in the environment and suggest that the remarkable ability of L. pneumophila to subvert host cell signalling and evade mammalian immune responses evolved through the natural selection associated with cycling between protozoan and metazoan hosts.

Non-human Primate Macaca mulatta as an Animal Model for Testing Efficacy of Amixicile as a Targeted Anti-periodontitis Therapy.

Periodontitis is an inflammatory condition triggered by selected oral microbiota; thus treatment strategies should be aimed at reducing the abundance of the pathogenic bacteria. An obstacle to preclinical testing of such strategies is the availability of reliable animal models. Here, a non-human primate (NHP), Macaca mulatta, was used to examine the effectiveness of a novel antimicrobial, amixicile, which inhibits pyruvate-ferredoxin oxidoreductase (PFOR) present in anaerobic bacteria. Animals were assessed for their periodontal health, including radiography, clinical attachment loss (CAL), presence of plaque (PI), bleeding on probing (BOP) and pocket depth (PD), and sampled for saliva, gingival crevicular fluid (GCF), and subgingival plaque to determine their baseline clinical status. Amixicile was then administered for 2 weeks (40 mg/kg/day) and the animals were monitored for periodontal health immediately after the antibiotic treatment, then at 1 month-, 3 months-, and 6-months posttreatment. Microbial species present in plaque and saliva were determined through 16S rDNA sequencing. Baseline assessment of the microbiome has shown a significant proportion of bacteria belonging to the Streptococcus, Haemophilus, Porphyromonas, Gemella, and Fusobacterium genera. The abundance of Porphyromonas and Fusobacterium was reduced following treatment with amixicile, whereas that of Escherichia, Haemophilus, and Gemella were elevated. CAL, PD, and BOP were also significantly reduced following the treatment. In conclusion, the NHP model proves useful for preclinical studies of strategies targeting selected members of the oral microbiome. We show that amixicile reduces the levels of anaerobic bacteria under in vivo conditions, correlating with a reduction in CAL, PD, and BOP, thus validating its usefulness as an antimicrobial strategy.

Nitazoxanide inhibits biofilm production and hemagglutination by enteroaggregative Escherichia coli strains by blocking assembly of AafA fimbriae.

Enteroaggregative Escherichia coli (EAEC) strains have emerged as common causes of persistent diarrhea and malnutrition among children and HIV-infected persons. During infection, EAEC typically adheres to the intestinal mucosa via fimbrial adhesins, which results in a characteristic aggregative pattern. In the study described here we investigated whether the broad-spectrum antiparasitic and antidiarrheal drug nitazoxanide (NTZ) might be active against EAEC in vitro. While E. coli strains were resistant to NTZ in rich Luria-Bertani medium (MIC > 64 microg/ml), the drug was slightly inhibitory in a minimal medium supplemented with glucose (MinA-G medium; MIC, approximately 32 microg/ml). NTZ also inhibited biofilm production by strain EAEC 042 in both Dulbecco's modified Eagle's medium and MinA-G medium with a 50% inhibitory concentration of approximately 12 microg/ml. Immunofluorescence and immunoblot analyses with antibody against the major fimbrial subunit AafA of aggregative adherence fimbriae vaariant II (AAF/II) established that the numbers of AAF/II filaments on bacteria grown in the presence of NTZ were dramatically reduced. Comparative quantitative reverse transcription-PCR and reporter gene fusions (aafA::phoA) indicated that aafA expression was unaffected by NTZ, while aggR transcript levels and aggR::lacZ expression were increased approximately 10- and 2.5-fold, respectively, compared with that for the untreated controls. More generally, NTZ inhibited hemagglutination (HA) of red blood cells by the non-biofilm-producing strain JM221 expressing either AAF/I or type I fimbriae. Our findings suggest that the inhibitory action of NTZ on biofilm formation and HA is likely due to inhibition of fimbrial assembly. Antimicrobial agents that inhibit the assembly or function of fimbrial filaments should be good candidates for the prevention of infection.