Browsing by Subject "Clostridium difficile"
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Item Bacteriophage therapy of Clostridium difficile induced intestinal disease in a hamster model(Texas Tech University, 1998-12) Ramesh, VijayashreeNot avaiableItem Characterization of immunoglobulin and non-immunoglobulin components of human milk which block binding of C. difficile toxin A to intestinal receptors(Texas Tech University, 1998-08) Dallas, Steven DwayneNot Available.Item Comparison of the Prevalence and Genotypic Characteristics of Clostridium difficile in a Closed and Integrated Human and Swine Population in Texas(2011-10-21) Norman, Keri NoelleClostridium difficile has been recognized as one of the leading causes of nosocomial diarrhea and pseudomembranous colitis in human hospitals and nursing homes since the 1970s; however, recent occurrences of community-acquired cases have led researchers to search for additional sources of these infections. Some of the possible sources being investigated include food animals and retail meat. The objective of this study was to compare the prevalence and genotypic characteristics of C. difficile isolated from a closed population in Texas consisting of both humans and swine. Implicit in this objective, we seek to investigate the possible food safety and occupational risks associated with swine and C. difficile. Isolation of C. difficile was performed utilizing an enrichment technique and restrictive media. Polymerase chain reaction (PCR) was used to test for the presence of the toxin A and B genes, the tcdC gene deletion, and the binary toxin gene. Genotypic characteristics were compared using PCR toxinotyping and pulsed-field gel electrophoresis (PFGE). Antimicrobial susceptibility was tested using commercially available tests (ETest?) for 11 different antibiotics. Statistical comparisons (both parametric and non-parametric, and appropriate to the data) were performed both between and among host species. We tested 2,292 aggregated human wastewater samples and 2,936 swine fecal samples from 2004 to 2006 and found 271 (11.8 percent) and 252 (8.6 percent) to be positive for C. difficile, respectively. The prevalence of C. difficile among swine production groups differed significantly (p<0.05); however, prevalence in the human occupational group cohorts (swine workers and non-workers) did not differ (p=0.81). The majority of the human and swine isolates were a PFGE NAP7 (a variant pattern with 90.5 percent similarity) toxinotype V strain. Antimicrobial resistance levels and multi-resistance patterns were generally similar between host species; however, there was decreased susceptibility (p<0.05) to ampicillin, clindamycin, and imipenem observed in swine isolates, whereas there was decreased susceptibility (p<0.05) to ciprofloxacin in the human isolates. The similarity in C. difficile prevalence between swine workers and non-workers suggests a low occupational hazard of working with swine as it relates to C. difficile source. We also found that there is a decreased prevalence of C. difficile in late production groups in swine suggesting a lowered risk of food-borne exposure. However, the majority of the isolates derived from the human wastewater and swine appeared to be of very similar strain types, suggesting that a common environmental point source predominates for both hosts.Item Defining the catalytic domain of toxin A through structural and functional studies of Clostridium difficile toxins A and B(Texas Tech University, 1998-05) Ye, BeixingClostridium difficile is one of the most frequently encountered pathogens in human enteric diseases. The major virulence factors produced by C. difficile are toxins A and B. These two toxins, as well as the lethal toxin and the hemorrhage toxin of C. sordellii, and the atoxin of C. novyi constitute a family of large clostridial cytotoxins. All these toxins are glucosyltransferases, which use a co-substrate UDPsugar to glucosylate and inactive small GTPases of the Rho or Ras subfamily proteins. The enzymatic activity of these toxins is apparently responsible for their cytotoxicity. However, mechanistic details including the catalytic region(s) of these toxin molecules and the enzymatically essential amino acid residues are unknown. Toxin A was the principal focus of this study, because of its prime clinical relevance in mediating the major tissue damage in C. difficileassociated diseases by enterotoxic and cytotoxic activities. Some additional information from the preliminary study of toxin B is also presented, as it relates to toxin A. A catalytic and receptor binding, two-domain structure model was proposed for both C. difficile toxins. This study tests the hypothesis that the N-terminal portion of toxin A is responsible for the enzymatic activity by examining a series of toxin A deletion mutant proteins. By correlation of the glucosylation activity with the deleted regions of the toxin mutant proteins, the catalytic domain of toxin A was localized within its first N-terminal 659 amino acids — less than 25% of the length of native toxin A. Previous studies showed that the cytotoxicity of toxins A and B was inactivated by chemical modification using the arginine-specific 1,2-cyclohexanedione. Therefore, this study hypothesized that the loss of cytotoxicity resulted from the loss of enzymatic activity. Indeed, both toxins and active toxin A mutant derivatives lost enzymatic activity upon 1,2-cyclohexanedione treatment. Importantly, toxin A inactivation by 1,2-cyclohexanedione was prevented in the presence of excess amount of the co-substrate, UDP-glucose, suggesting functional arginine(s) are in or very near the UDP-glucose binding site. Four of 21 candidate arginines within the toxin A enzymatic domain are conserved, based on comparisons with the large clostridial cytotoxins. Therefore, site-directed mutagenesis studies were used to further identify essential arginines. Since, substitution of alanine for arginine 272 or 405 abolished enzymatic activity, the need for the positive charges was then confirmed by lysine replacement, which resulted in lower enzymatic activity for both mutants. However, the double mutant, R272K+R405K, had no detectable enzymatic activity, suggesting disposition of the positive charges is important for enzymatic activity. These results are consistent with an atomic crystal structure of T4 DNA-glucosyltransferase with its co-substrate, UDPglucose, in which positive charges of three arginines interact with negative phosphates of the co-substrate, thus stabilizing it in the catalytic site of the enzyme.Item Epidemiology and recurrence risk prediction of Clostridium difficile Infections: A retrospective cohort study of the United States Veterans Health Care System(2014-08) Reveles, Kelly Renee; Frei, Christopher R.Clostridium difficile infection (CDI) is the leading cause of bacterial infectious diarrhea in nosocomial settings and approximately 25% of patients with CDI experience disease recurrence. Prior CDI epidemiological investigations are limited though. They do not reflect the burden of CDI in federal facilities, nor do they capture recent estimates on patient health outcomes. Furthermore, few studies have integrated CDI recurrence risk factors into a tool that clinicians can use to identify patients at risk for CDI recurrence. This study 1) described the epidemiology of CDI in the national Veterans Health Administration (VHA), 2) derived and validated a clinical prediction rule for 60-day CDI first recurrence, and 3) derived and validated a clinical prediction rule for 60-day CDI second recurrence. This was a retrospective cohort study of VHA beneficiaries with CDI between October 1, 2001 and September 30, 2012. VHA clinical and pharmacy data were integrated to develop several independent variables, including patient baseline demographics, CDI characteristics, comorbidities, concomitant medications, prior medications, prior hospitalization, hospital length of stay (LOS), and CDI severity. The dependent variables included 30/60/90-day mortality, and 30/60/90-day CDI recurrence. CDI incidence and outcomes were presented descriptively and compared using generalized linear regression models. CDI recurrence prediction rules were derived using multivariable logistic regression models and validated using the area under the receiver-operating-characteristic curve (AUROC), sensitivity, specificity, positive predictive value, and negative predictive value. Our study demonstrated that CDI first episodes, recurrences, and severity increased over the study period, while mortality decreased. Our CDI first recurrence prediction rule included the following predictor variables: dyslipidemia, CDI type, renal disease, hospital LOS <7 days, principal CDI diagnosis, concomitant gastric acid suppressors, and concomitant antibiotics. This model demonstrated moderate 60-day first recurrence discrimination (AUROC=0.62). Our CDI second recurrence prediction rule was similar in predictor variables and validity. In conclusion, CDI is an important, rapidly-emerging public health problem in the VHA. A clinical prediction rule might aid clinicians in directing preventative therapies to patients at high risk for CDI recurrence.Item Evidence supporting an operon model for the expression of toxins A and B by Clostridium difficile(Texas Tech University, 1995-08) Song, Keang-PengClostridium difficile is a human pathogen which produces two protein toxins, A and B, that cause a potentially lethal gastrointestinal syndrome termed pseudomembranous colitis. Production of both toxins correlates with the onset of sporulation of this organism. In addition, although C. difficile strains vary significantly in how much of both toxins they produce, a 1:1 ratio is maintained by all strains, suggesting that the production of both toxins is coordinately regulated. Moreover, both toxin genes are adjacent on the bacterial chromosome with the toxin B gene being upstream of the toxin A gene. Nevertheless, nothing is known about the regulation of toxin production, and cis-regulatory region(s) of neither toxin gene have yet been identified. Therefore, the hypothesis being examined here is whether these toxin genes are under operon control, thereby implying a single promoter for both toxin genes. To test this hypothesis, a putative promoter region upstream of toxin B was localized to a 245-bp DNA fragment and characterized in an Escherichia coli system by nested deletion, gel retardation and binding competition analyses. Further studies of this promoter region revealed two sets of overlapping promoters that showed homology to both the consensus sequences oiE. coli and Gram (+) bacteria. This promoter region upstream of the toxin B gene was also footprinted with the purified E. coli RNA polymerase for additional characterization.Item Inhibition of C. difficile toxin a receptor binding by cow's milk, cow's formula, and soy formula(Texas Tech University, 1996-12) Cheng, Stephen H.Not Available.Item Outcomes and expenditures of clostridium difficile infection in pediatric solid organ transplant recipients(2014-05) Ling, You-Li; Rascati, Karen L.The main purpose of this study was to assess outcomes (i.e., inpatient mortality, transplant failure or rejection, colectomy, and hospital length of stay) of clostridium difficile infection (CDI) and the association of expenditures (i.e., charges and costs) and CDI in pediatric solid organ transplant (SOT) recipients. Data from the 2000, 2003, 2006, and 2009 Kids’ Inpatient Database (KID) files were used to identify events with SOT- related ICD-9-CM diagnosis codes. Logistic regression was used to assess the association of CDI and dichotomous outcome variables, while log-linked gamma regression models were used to assess the association of CDI and continuous outcome variables. Methods accounting for the complex survey sample design of the KID were used when performing all statistical analyses. The total number of pediatric SOT hospital events was 48,286. The overall prevalence of CDI for pediatric SOT hospitalizations was 1.76%. For SOT hospitalizations with CDI, inpatient mortality was 1.63%; the prevalence of transplant failure or rejection events was 27.71%; the prevalence of a colectomy was 4.86%. The median hospital length of stay was seven days; the median charge and cost for each hospitalization was $48,409 and $17,412, respectively. The results showed that CDI was not significantly associated with inpatient mortality or transplant failure/ rejection in pediatric SOT hospitalizations. SOT patients with CDI were 2.6 times more likely to have a colectomy than SOT patient without CDI. The mean hospital length of stay (LOS) for a SOT admission with CDI was approximately 2 times the mean LOS for a SOT admission without CDI. The mean charges and the mean costs for a SOT admission with CDI was approximately 2 times that for a SOT admission without CDI. In conclusion, CDI diagnoses were not significantly associated with higher inpatient mortality or transplant failure/ rejection for pediatric SOT hospitalizations. But CDI was significantly associated with a higher prevalence of a colectomy, longer hospital LOS, higher charges, and higher costs (all p<0.05). To avoid substantially higher expenditures and health care utilization, CDI in pediatric SOT recipients should be prevented when possible and promptly diagnosed and treated when it occurs.Item Role of antibody in Clostridium difficile-associated intestinal disease in infant and adult hamsters(Texas Tech University, 1988-05) Kim, Pyeung-hyeunNot available