Browsing by Subject "Escherichia coli O157"
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Item A Meta-analysis of the association of Lactobacillus acidophilus NP51 administration with Escherichia coli O157 in feces and on hides of feedlot cattle.(2013-05) Ison, Josh; Loneragan, Guy H.; Johnson, Bradley J.; Brashears, Mindy M.; Nightingale, Kendra K.Inclusion of the direct-fed microbial (DFM) Lactobacillus acidophilus NP51 (L. acidophilus NP51), in feedlot rations has been associated with decreased burden of Escherichia coli O157:H7 (E. coli O157) in feces and on hides of cattle. The objectives of this meta-analysis were to a) assemble available data from studies that have evaluated an association of L. acidophilus NP51 with E. coli O157; b) reanalyze the data using harmonized statistical models; and c) perform a meta-analysis to produce a summary effect measure and evaluate between study variance. Pen-level fecal and hide prevalence data were gathered from 15 trials that administered L. acidophilus NP51 at 109 CFU/animal/day, 107 CFU/ animal/day, or both. Fecal and hide data were available for 15 and 8 studies, respectively. Data were analyzed to produce study-level relative risk estimates (and their 95% confidence intervals) using generalized linear mixed models. The inverse of study-level variance was used to weight each observation and study-to-study variance was assessed. Outcomes of interest include post-exposure measure of effect, terminal measure of effect, and a dose response. Summary measures of effect from the meta-analysis revealed that E. coli O157 was 42 and 33% less likely to be recovered from feces and hides, respectively, of harvest-ready cattle receiving L. acidophilus NP51 at 109 CFU/animal/day compared to control animals. Fecal E. coli O157 prevalence averaged over time was reduced by 42 and 45% among cohorts receiving high and low doses, respectively. Furthermore, supplementation of L. acidophilus NP51 was associated with a 1.1 log10 CFU/g and 0.26 log10 CFU/g reduction of E. coli O157 concentration in positive fecal samples from cattle receiving high and low doses, respectively.Item Characterization of QSEA and QSED in the Quorum Sensing Cascade of Enterohemorrhagic Escherichia Coli(2005-08-11) Sharp, Faith Christine; Sperandio, VanessaEnterohemorrhagic E. coli O157:H7 (EHEC) is an enteric pathogen that has been implicated in many outbreaks of bloody diarrhea worldwide. EHEC senses its environment through quorum sensing, a mechanism by which bacteria use chemical signals, termed autoinducers, to regulate key genes. In the gastrointestinal tract, EHEC responds to AI-3 produced by the endogenous gastrointestinal microbial flora and epinephrine/norepinephrine produced by the host to regulate expression of virulence genes. In particular, EHEC utilizes quorum sensing to regulate virulence processes, including motility and chemotaxis and the production of attaching and effacing lesions. Motility and chemotaxis processes are controlled under the complex flagella regulon in EHEC. The expression of genes within the locus of enterocyte effacement (LEE) results in the production of the characteristic attaching and effacing lesions created as a result of production of a type III secretion apparatus. The LEE1 operon encodes for a transcriptional activator, Ler, which is responsible for the activation of other genes within the pathogenicity island. The virulence mechanisms that enable EHEC to circumvent the host defenses and compete for essential nutrients for survival are controlled by several transcriptional regulators, many of which are controlled in response to quorum sensing in EHEC. Quorum sensing E. coli regulator A, QseA, recently was described as a transcription factor that is activated via quorum sensing in EHEC. QseA, which belongs to the family of LysR transcription factors, activates the transcription of LEE1/ler directly; therefore, QseA indirectly activates the expression of other genes within the LEE pathogenicity island. The work in the first specific aim of this thesis examines the specific regulation of the LEE1/ler promoter by QseA through the use of genetic and biochemical methods. Quorum sensing E. coli regulator D, QseD, is a previously uncharacterized transcription factor that is repressed through quorum sensing in EHEC. QseD appears to play a significant role in the overall quorum sensing cascade, as it is involved in the modulation of both motility and type III secretion in EHEC. The second aim of this thesis is to study the role of QseD modulation in quorum sensing signaling in EHEC.Item The characterization of quorum sensing E. coli regulators E,F, and G (Qse EFG) and their role in pathogenesis(2008-09-18) Reading, Nicola Catherine; Sperandio, VanessaEscherichia coli O157:H7 (EHEC) causes hemorrhagic colitis and life-threatening hemolytic uremic syndrome (HUS) worldwide. EHEC colonizes the large intestine and adheres to intestinal epithelial cells by forming attaching and effacing lesions (AE). These lesions result in the rearrangement of the actin cytoskeleton to pedestal-like structures, which cup each bacterium. The genes necessary for formation of pedestals are encoded in the Locus of Enterocyte Effacement (LEE), including a type III secretion system, an effector protein, Tir, and the outer membrane protein, Intimin. Also, a prophage encoded effector protein, EspFu, is required. EHEC regulates many of its virulence genes including the AE lesion genes in response to environmental signals. Utilizing these signals allows EHEC to colonize the intestine efficiently and effectively. Environmental signals are often recognized by bacterial sensor kinases. In response to cognate signals, sensor kinases autophosphorylate and transfer the phosphate to a response regulator. The regulator then binds downstream genes to regulate transcription. This pathway for flagellation and motility, which allows EHEC to be motile, has been well-characterized and involves the two-component sytem QseBC. Less is known about the signaling towards EHEC's AE lesion formation capability. Here, we describe a unique signaling system important for EHEC pedestal formation. In contrast to conventional two-component signaling systems, this one consists of three-components. Quorum sensing E.coli regulators E (qseE), qseG, and qseF, encode a sensor kinase, membrane protein, and response regulator respectively. qseF and qseG mutant strains cannot form pedestals on epithelial cells. We have shown that QseF transcriptionally regulates espFu. When espFu is expressed on a plasmid, pedestal formation is restored to the qseF mutant. Microarray analysis comparing qseE, qseF, and qseG mutants to wild-type revealed that these genes may also play a role in metabolism and stress. The similar profiles of these mutants in the microarray indicate that these proteins may work together. QseE is able to autophosphorylate and this activity is stimulated by epinephrine, phosphate, and sulfate sources. These data indicate that QseEFG is a three-component system involved in regulation of virulence and metabolism in EHEC. The following study undertakes a genetic and functional analysis of these proteins.Item Improvements, challenges, and validation of enumeration of Escherichia coli O157 and sampling methods for Escherichia coli O157 and Salmonella in feedlot cattle(Texas Tech University, 2006-12) Stephens, Tyler; Brashears, Mindy M.; Alvarado, Christine Z.; Loneragan, Guy H.; Carroll, Jeffery A.; Pond, Kevin R.; Warner, Ronald D.Escherichia coli O157 and Salmonella have been targeted as food-borne pathogens of concern to the beef industry. Enumeration of and proper detection protocols for E. coli O157 and Salmonella has become an important part of pre-harvest surveillance and testing of intervention strategies. The objectives of this research were: (1) to improve and validate a Most Probable Number (MPN) / Immunomagnetic Separation (IMS) method to enumerate E. coli O157 in fecal samples from feedlot cattle; and (2) to determine the distribution of E. coli O157 and Salmonella on cattle hides (back, flank, hock, neck, perineum, and ventrum), the oral cavity, rectal-anal junction, and feces of feedlot cattle. Known quantities of E. coli O157:H7 were inoculated into feces and populations were determined by direct plating and compared to a MPN/IMS method. The MPN/IMS methodology compared to direct plating was tested in five experiments with varying E. coli O157 concentrations and it was found that there were differences (P < 0.01) between the two methodologies with negligible biological importance due to a low difference between least squares means (LS-means) (0.29 ± 0.01). The overall correlation coefficient was high (r = 0.93) which indicated that the MPN/IMS method was precise when compared to the direct plating method. Nine samples were obtained from feedlot cattle from the above mentioned locations (objective 2) and subjected to E. coli O157 and Salmonella detection protocols. Several measurements were taken: (1) prevalence of both pathogens at each location; (2) odds ratios comparing the fecal grab samples to all other locations; and (3) odds ratios comparing the perineum hide swab samples to all other hide swab samples. These data suggest that using multiple sample locations are useful when isolating these pathogens from feedlot cattle.