Evaluating the Effects of Surotomycin Treatment on Clostridium difficile Toxin A and B Production, Immune Response, and Morphological Changes.

Surotomycin is a cyclic lipopeptide in development for Clostridium difficile-associated diarrhea. This study aimed to assess the impact of surotomycin exposure on C. difficile toxin A and B concentrations and the associated changes in immune response in comparison to vancomycin and metronidazole. Time-kill curve assays were performed using strain R20291 (BI/NAP1/027) at supra-MICs (4× and 40×) and sub-MICs (0.5×) of surotomycin and comparators. Following treatment, CFU counts, toxin A and B concentrations, and cellular morphological changes using scanning electron microscopy were examined. Inflammatory response was determined by measuring interleukin-8 (IL-8) concentrations from polarized Caco-2 cells exposed to antibiotic-treated C. difficile growth media. Supra-MICs (4× and 40×) of surotomycin resulted in a reduction of vegetative cells over 72 h (4-log difference, P < 0.01) compared to controls. These results correlated with decreases of 77% and 68% in toxin A and B production at 48 h, respectively (P < 0.005, each), which resulted in a significant reduction in IL-8 concentration compared to controls. Similar results were observed with comparator antibiotics. Bacterial cell morphology showed that the cell wall was broken apart by surotomycin treatment at supra-MICs while sub-MIC studies showed a "deflated" phenotype plus a rippling effect. These results suggest that surotomycin has potent killing effects on C. difficile that results in reduced toxin production and attenuates the immune response similar to comparator antibiotics. The morphological data also confirm observations that surotomycin is a membrane-active antibiotic.

Impact on toxin production and cell morphology in Clostridium difficile by ridinilazole (SMT19969), a novel treatment for C. difficile infection.

OBJECTIVES: Ridinilazole (SMT19969) is a narrow-spectrum, non-absorbable antimicrobial with activity against Clostridium difficile undergoing clinical trials. The purpose of this study was to assess the pharmacological activity of ridinilazole and assess the effects on cell morphology. METHODS: Antibiotic killing curves were performed using the epidemic C. difficile ribotype 027 strain, R20291, using supra-MIC (4× and 40×) and sub-MIC (0.125×, 0.25× and 0.5×) concentrations of ridinilazole. Following exposure, C. difficile cells were collected for cfu counts, toxin A and B production, and morphological changes using scanning electron and fluorescence microscopy. Human intestinal cells (Caco-2) were co-incubated with ridinilazole-treated C. difficile growth medium to determine the effects on host inflammatory response (IL-8). RESULTS: Treatment at supra-MIC concentrations (4× and 40× MIC) of ridinilazole resulted in a significant reduction in vegetative cells over 72 h (4 log difference, P < 0.01) compared with controls without inducing spore formation. These results correlated with a 75% decrease in toxin A production (P < 0.05) and a 96% decrease in toxin B production (P < 0.05). At sub-MIC levels (0.5× MIC), toxin A production was reduced by 91% (P < 0.01) and toxin B production was reduced by 100% (P < 0.001), which resulted in a 74% reduction in IL-8 release compared with controls (P < 0.05). Sub-MIC (0.5×)-treated cells formed filamentous structures ∼10-fold longer than control cells. Following fluorescence labelling, the cell septum was not forming in sub-MIC-treated cells, yet the DNA was dividing. CONCLUSIONS: Ridinilazole had robust killing effects on C. difficile that significantly reduced toxin production and attenuated the inflammatory response. Ridinilazole also elicited significant cell division effects suggesting a potential mechanism of action.

A pilot study to assess bacterial and toxin reduction in patients with Clostridium difficile infection given fidaxomicin or vancomycin.

BACKGROUND: To assess the effect of fidaxomicin and vancomycin on Clostridium difficile toxins and correlation with clinical and microbiologic outcomes. METHODS: Hospitalized patients with C. difficile infection were randomly assigned a 10-day course of fidaxomicin or vancomycin. Stool samples collected at baseline (day 0), mid-therapy (days 3-5), end of therapy (days 10-13) and follow-up (days 19-38) were assessed for quantity of toxins A and B as well as spore and vegetative cells counts. Correlation of toxins concentrations with microbiologic and clinical findings were evaluated. RESULTS: Among 34 patients 12 had detectable toxin concentrations at baseline seven were randomized to fidaxomicin and five to vancomycin. Overall both fidaxomicin and vancomycin resulted in drop of both toxins concentrations by midpoint of therapy. The drop in toxin A concentrations was maintained up to the follow-up period with fidaxomicin but not with vancomycin even in patients who developed recurrence. Patients who developed recurrence in the fidaxomicin group had lower concentrations of toxin B versus the recurrence patient of vancomycin group. Presence of vegetative cells and spores was significantly linked with high toxin A (P = 0.003 and <0.001 respectively) and toxin B (P = 0.007 and <0.001 respectively) concentrations across time points. Toxin B concentrations but not A significantly correlated with stool consistency (P < 0.001) and frequency (P = 0.05). CONCLUSIONS: Fidaxomicin was associated with sustained reduction of both toxins up to 30 days post therapy versus vancomycin. Multiple clinical or microbiologic observations were correlated with toxin A or B concentrations.

Evaluation of portability and cost of a fluorescent PCR ribotyping protocol for Clostridium difficile epidemiology.

Clostridium difficile is the most commonly identified pathogen among health care-associated infections in the United States. There is a need for accurate and low-cost typing tools that produce comparable data across studies (i.e., portable data) to help characterize isolates during epidemiologic investigations of C. difficile outbreaks and sporadic cases of disease. The most popular C. difficile-typing technique is PCR ribotyping, and we previously developed methods using fluorescent PCR primers and amplicon sizing on a Sanger-style sequencer to generate fluorescent PCR ribotyping data. This technique has been used to characterize tens of thousands of C. difficile isolates from cases of disease. Here, we present validation of a protocol for the cost-effective generation of fluorescent PCR ribotyping data. A key component of this protocol is the ability to accurately identify PCR ribotypes against an online database (http://walklab.rcg.montana.edu) at no cost. We present results from a blinded multicenter study to address data portability across four different laboratories and three different sequencing centers. Our standardized protocol and centralized database for typing of C. difficile pathogens will increase comparability between studies so that important epidemiologic linkages between cases of disease and patterns of emergence can be rapidly identified.

Molecular mechanism of species-dependent sweet taste toward artificial sweeteners.

The heterodimer of Tas1R2 and Tas1R3 is a broadly acting sweet taste receptor, which mediates mammalian sweet taste toward natural and artificial sweeteners and sweet-tasting proteins. Perception of sweet taste is a species-selective physiological process. For instance, artificial sweeteners aspartame and neotame taste sweet to humans, apes, and Old World monkeys but not to New World monkeys and rodents. Although specific regions determining the activation of the receptors by these sweeteners have been identified, the molecular mechanism of species-dependent sweet taste remains elusive. Using human/squirrel monkey chimeras, mutagenesis, and molecular modeling, we reveal that the different responses of mammalian species toward the artificial sweeteners aspartame and neotame are determined by the steric effect of a combination of a few residues in the ligand binding pocket. Residues S40 and D142 in the human Tas1R2, which correspond to residues T40 and E142 in the squirrel monkey Tas1R2, were found to be the critical residues for the species-dependent difference in sweet taste. In addition, human Tas1R2 residue I67, which corresponds to S67 in squirrel monkey receptor, modulates the higher affinity of neotame than of aspartame. Our studies not only shed light on the molecular mechanism of species-dependent sweet taste toward artificial sweeteners, but also provide guidance for designing novel effective artificial sweet compounds.

Functional characterization of the heterodimeric sweet taste receptor T1R2 and T1R3 from a New World monkey species (squirrel monkey) and its response to sweet-tasting proteins.

The family C G protein-coupled receptor (GPCR) T1R2 and T1R3 heterodimer functions as a broadly acting sweet taste receptor. Perception of sweet taste is a species-dependent physiological process. It has been widely reported that New World monkeys and rodents are not able to perceive some of the artificial sweeteners and sweet-tasting proteins that can be perceived by humans, apes, and Old World monkeys. Until now, only the sweet receptors of humans, mice and rats have been functionally characterized. Here we report characterization of the sweet taste receptor (T1R2/T1R3) from a species of New World primate, squirrel monkey. Our results show that the heterodimeric receptor of squirrel monkey does not respond to artificial sweeteners aspartame, neotame, cyclamate, saccharin and sweet-tasting protein monellin, but surprisingly, it does respond to thaumatin at high concentrations (>18 µM). This is the first report demonstrating that species of New World monkey can perceive some specific sweet-tasting proteins. Furthermore, the sweet receptor of squirrel monkey responses to the such sweeteners cannot be inhibited by the sweet inhibitor lactisole. We compared the response differences of the squirrel monkey and human receptors and found that the residues in T1R2 determine species-dependent sweet taste toward saccharin, while the residues in either T1R2 or T1R3 are responsible for the sweet taste difference between humans and squirrel monkeys toward monellin. Molecular models indicated that electrostatic properties of the receptors probably mediate the species-dependent response to sweet-tasting proteins.

Toll-like receptor 7 is not necessary for retroviral neuropathogenesis but does contribute to virus-induced neuroinflammation.

Toll-like receptor 7 (TLR7) recognizes guanidine-rich single-stranded (ss) viral RNA and is an important mediator of peripheral immune responses to several ssRNA viruses. However, the role that TLR7 plays in regulating the innate immune response to ssRNA virus infections in specific organs is not as clear. This is particularly true in the central nervous system (CNS) where microglia and astrocytes are often the first cells responding to virus infection instead of dendritic cells. In the current study, we examined the mechanism by which TLR7 contributes to ssRNA virus-induced neuroinflammation using a mouse model of polytropic retrovirus infection. The authors found that TLR7 was necessary for the early production of certain cytokines and chemokines, including CCL2 and tumor necrosis factor (TNF) and was also involved in the early activation of astrocytes. However, TLR7 was not necessary for cytokine production and astrocyte activation at later stages of infection and did not alter viral pathogenesis or viral replication in the brain. This suggests that other pathogen recognition receptors may be able to compensate for the lack of TLR7 during retrovirus infection in the CNS.

Community Environmental Contamination of Toxigenic Clostridium difficile.

BACKGROUND: Clostridium difficile infection is often considered to result from recent acquisition of a C difficile isolate in a healthcare setting. However, C difficile spores can persist for long periods of time, suggesting a potentially large community environmental reservoir. The objectives of this study were to assess community environmental contamination of toxigenic C difficile and to assess strain distribution in environmental versus clinical isolates. METHODS: From 2013 to 2015, we collected community environmental swabs from homes and public areas in Houston, Texas to assess C difficile contamination. All positive isolates were tested for C difficile toxins A and B, ribotyped, and compared with clinical C difficile isolates obtained from hospitalized patients in Houston healthcare settings. RESULTS: A total of 2538 environmental samples were collected over the study period. These included samples obtained from homes (n = 1079), parks (n = 491), chain stores (n = 225), fast food restaurants (n = 123), other commercial stores (n = 172), and hospitals (n = 448). Overall, 418 environmental isolates grew toxigenic C difficile (16.5%; P < .001) most commonly from parks (24.6%), followed by homes (17.1%), hospitals (16.5%), commercial stores (8.1%), chain stores (7.6%), and fast food restaurants (6.5%). A similar distribution of ribotypes was observed between clinical and environmental isolates with the exception that ribotype 027 was more common in clinical isolates compared with environmental isolates (P < .001). CONCLUSIONS: We identified a high prevalence of toxigenic C difficile from community environs that were similar ribotypes to clinical isolates. These findings suggest that interventions beyond isolation of symptomatic patients should be targeted for prevention of C difficile infection.

In the Endemic Setting, Clostridium difficile Ribotype 027 Is Virulent But Not Hypervirulent.

BACKGROUND: Conflicting reports have been published on the association between Clostridium difficile ribotypes and severe disease outcomes in patients with C. difficile infection (CDI); several so-called hypervirulent ribotypes have been described. We performed a multicenter study to assess severe disease presentation and severe outcomes among CDI patients infected with different ribotypes. METHODS: Stool samples that tested positive for C. difficile toxin were collected and cultured from patients who presented to any of 7 different hospitals in Houston, Texas (2011-2013). C. difficile was characterized using a fluorescent PCR ribotyping method. Medical records were reviewed to determine clinical characteristics and ribotype association with severe CDI presentation (ie, leukocytosis and/or hypoalbuminemia) and severe CDI outcomes (ie, ICU admission, ileus, toxic megacolon, colectomy, and/or in-hospital death). RESULTS: Our study included 715 patients aged 61±18 years (female: 63%; median Charlson comorbidity index: 2.5±2.4; hospital-onset CDI: 45%; severe CDI: 36.7%; severe CDI outcomes: 12.3%). The most common ribotypes were 027, 014-020, FP311, 002, 078-126, and 001. Ribotype 027 was a significant independent predictor of severe disease (adjusted odds ratio [aOR], 2.24; 95% confidence interval [CI], 1.53-3.29; P<.001) and severe CDI outcomes (aOR, 1.71; 95% CI, 1.02-2.85; P=.041) compared with all other ribotypes in aggregate. However, in an analysis using all common ribotypes as individual variables, ribotype 027 was not associated with severe CDI outcomes more often than other ribotypes. CONCLUSION: Ribotype 027 showed virulence equal to that of other ribotypes identified in this endemic setting. Clinical severity markers of CDI may be more predictive of severe CDI outcomes than a particular ribotype.

Nuclear factor 45 (NF45) is a regulatory subunit of complexes with NF90/110 involved in mitotic control.

Nuclear factor 90 (NF90) and its C-terminally extended isoform, NF110, have been isolated as DNA- and RNA-binding proteins together with the less-studied protein NF45. These complexes have been implicated in gene regulation, but little is known about their cellular roles and whether they are redundant or functionally distinct. We show that heterodimeric core complexes, NF90-NF45 and NF110-NF45, exist within larger complexes that are more labile and contain multiple NF90/110 isoforms and additional proteins. Depletion of the NF45 subunit by RNA interference is accompanied by a dramatic decrease in the levels of NF90 and NF110. Reciprocally, depletion of NF90 but not of NF110 greatly reduces the level of NF45. Coregulation of NF90 and NF45 is a posttranscriptional phenomenon, resulting from protein destabilization in the absence of partners. Depletion of NF90-NF45 complexes retards cell growth by inhibition of DNA synthesis. Giant multinucleated cells containing nuclei attached by constrictions accumulate when either NF45 or NF90, but not NF110, is depleted. This study identified NF45 as an unstable regulatory subunit of NF90-NF45 complexes and uncovered their critical role in normal cell division. Furthermore, the study revealed that NF90 is functionally distinct from NF110 and is more important for cell growth.

Infection of cardiomyocytes and induction of left ventricle dysfunction by neurovirulent polytropic murine retrovirus.

Viral infections of the heart are a causative factor of myocarditis as well as of sudden, unexpected deaths of children, yet the mechanisms of pathogenesis remain unclear, in part due to the relatively few animal models of virus-induced myocarditis. In the current study, we examined the ability of polytropic murine retroviruses to infect the heart and induce cardiac dysfunction. In situ hybridization and immunohistochemistry analysis detected virus-infected cardiomyocytes and macrophages in the heart. A significant decrease in left ventricle function, as measured by fractional shortening, was detected in mice infected with the neurovirulent retrovirus Fr98 but not in mice infected with the nonneurovirulent retrovirus Fr54. Virus infection was not associated with consistent findings of fibrosis or substantial cellular infiltrate. Fr98-induced left ventricle dysfunction was associated with a higher virus load, increased mRNA expression of the macrophage marker F4/80, increased chemokine production, and a small number of apoptotic cells in the heart.