Attachment of different Escherichia coli strains to cultured rumen epithelial cells

Does feeding starch contribute to the risk of systemic inflammation in dairy cattle?

In the high-producing dairy cow, providing an adequate supply of digestible energy is essential. One strategy to meet this need is to provide fermentable starch from cereal grains or silages like corn, barley, or wheat. Unfortunately, excess dietary starch increases the risk of rumen acidosis. Rumen acidosis challenge models using high-grain diets, particularly with wheat and barley, have demonstrated that a sudden change in starch concentration or digestibility leads to the breakdown of the rumen epithelial barrier. As a result, increases in circulating lipopolysaccharide (a marker of bacterial translocation) and acute phase proteins (APP) have been observed. Feeding increasing amounts of starch in chronic feeding studies does not appear to consistently modulate inflammation in early-lactation cows that already experience inflammation. In mid- and late-lactation cows, increasing starch above 30% may increase APP, but the response is inconsistent and has not been investigated using different grains or differently processed starch sources. Abomasal starch infusion experiments indicate that increasing the intestinal starch supply consistently reduces fecal pH but does not lead to an APP response or changes in gut integrity. Increasing intestinal starch supply increases fecal butyrate concentrations, and butyrate has had positive effects on gut health and integrity in other species and experimental models. More chronic feeding experiments are needed to investigate how starch concentrations, sources, processing methods, and interactions affect inflammation and gut integrity. There is a paucity of data investigating the role that carbohydrate concentrations and sources play on ruminant hindgut health, integrity, function, structure, or microbiome. Currently, data indicate that feeding diets with less than 30% starch to lactating dairy cows does not contribute to systemic inflammation.

PchE Regulation of Escherichia coli O157:H7 Flagella, Controlling the Transition to Host Cell Attachment

Shiga toxins and intimate adhesion controlled by the locus of enterocyte effacement are major enterohemorrhagic Escherichia coli (EHEC) virulence factors. Curli fimbriae also contribute to cell adhesion and are essential biofilm components. The transcriptional regulator PchE represses the expression of curli and their adhesion to HEp-2 cells. Past studies indicate that pchE also represses additional adhesins that contribute to HEp-2 cell attachment. In this study, we tested for pchE regulation of several tissue adhesins and their regulators. Three adhesin-encoding genes (eae, lpfA1, fliC) and four master regulators (csgD, stpA, ler, flhDC) were controlled by pchE. pchE over-expression strongly up-regulated fliC but the marked flagella induction reduced the attachment of O157:H7 clinical isolate PA20 to HEp-2 cells, indicating that flagella were blocking cell attachments rather than functioning as an adhesin. Chemotaxis, motor, structural, and regulatory genes in the flagellar operons were all increased by pchE expression, as was PA20 motility. This study identifies new members in the pchE regulon and shows that pchE stimulates flagellar motility while repressing cell adhesion, likely to support EHEC movement to the intestinal surface early in infection. However, induced or inappropriate pchE-dependent flagellar expression could block cell attachments later during disease progression.

EHEC Adhesins

Adhesins are a group of proteins in enterohemorrhagic Escherichia coli (EHEC) that are involved in the attachment or colonization of this pathogen to abiotic (plastic or steel) and biological surfaces, such as those found in bovine and human intestines. This review provides the most up-to-date information on these essential adhesion factors, summarizing important historical discoveries and analyzing the current and future state of this research. In doing so, the proteins intimin and Tir are discussed in depth, especially regarding their role in the development of attaching and effacing lesions and in EHEC virulence. Further, a series of fimbrial proteins (Lpf1, Lpf2, curli, ECP, F9, ELF, Sfp, HCP, and type 1 fimbriae) are also described, emphasizing their various contributions to adherence and colonization of different surfaces and their potential use as genetic markers in detection and classification of different EHEC serotypes. This review also discusses the role of several autotransporter proteins (EhaA-D, EspP, Saa and Sab, and Cah), as well as other proteins associated with adherence, such as flagella, EibG, Iha, and OmpA. While these proteins have all been studied to varying degrees, all of the adhesins summarized in this chapter have been linked to different stages of the EHEC life cycle, making them good targets for the development of more effective diagnostics and therapeutics.

Screening of an E. coli O157:H7 Bacterial Artificial Chromosome Library by Comparative Genomic Hybridization to Identify Genomic Regions Contributing to Growth in Bovine Gastrointestinal Mucus and Epithelial Cell Colonization

Enterohemorrhagic E. coli (EHEC) O157:H7 can cause serious gastrointestinal and systemic disease in humans following direct or indirect exposure to ruminant feces containing the bacterium. The main colonization site of EHEC O157:H7 in cattle is the terminal rectum where the bacteria intimately attach to the epithelium and multiply in the intestinal mucus. This study aimed to identify genomic regions of EHEC O157:H7 that contribute to colonization and multiplication at this site. A bacterial artificial chromosome (BAC) library was generated from a derivative of the sequenced E. coli O157:H7 Sakai strain. The library contains 1152 clones averaging 150 kbp. To verify the library, clones containing a complete locus of enterocyte effacement (LEE) were identified by DNA hybridization. In line with a previous report, these did not confer a type III secretion (T3S) capacity to the K-12 host strain. However, conjugation of one of the BAC clones into a strain containing a partial LEE deletion restored T3S. Three hundred eighty-four clones from the library were subjected to two different selective screens; one involved three rounds of adherence assays to bovine primary rectal epithelial cells while the other competed the clones over three rounds of growth in bovine rectal mucus. The input strain DNA was then compared with the selected strains using comparative genomic hybridization (CGH) on an E. coli microarray. The adherence assay enriched for pO157 DNA indicating the importance of this plasmid for colonization of rectal epithelial cells. The mucus assay enriched for multiple regions involved in carbohydrate utilization, including hexuronate uptake, indicating that these regions provide a competitive growth advantage in bovine mucus. This BAC-CGH approach provides a positive selection screen that complements negative selection transposon-based screens. As demonstrated, this may be of particular use for identifying genes with redundant functions such as adhesion and carbon metabolism.

Population structure of rumen Escherichia coli associated with subacute ruminal acidosis (SARA) in dairy cattle

Previous studies indicated that only subacute ruminal acidosis (SARA), induced by feeding a high-grain diet, is associated with an inflammatory response and increased abundance of Escherichia coli in the rumen. We hypothesized that ruminal E. coli in grain pellet-induced SARA carried virulence factors that potentially contribute to the immune activation during SARA. One hundred twenty-nine E. coli isolates were cultured from the rumens of 8 cows (4 animals per treatment) in which SARA had been nutritionally induced by feeding a high-grain diet (GPI-SARA) or a diet containing alfalfa pellets (API-SARA). The population structure of the E. coli was evaluated with the ABD genotyping system and repetitive sequence-based (rep)-PCR fingerprinting. Twenty-five virulence factors were evaluated with PCR. Escherichia coli numbers were higher in the GPI-SARA treatment than in the API-SARA treatment. The genetic structure of the E. coli was significantly different between SARA challenge models. Isolates from GPI-control (46%), API-control (70%), and API-SARA (53%) were closely related and fell into one cluster, whereas isolates from GPI-SARA (54%) grouped separately. The ABD typing indicated a shift from an A-type E. coli population to a B1-type population only due to GPI-SARA. Of the 25 virulence factors tested, curli fiber genes were highly associated with GPI. Curli fibers were first identified in E. coli mastitis isolates and are potent virulence factors that induce a range of immune responses. Results suggest that under low rumen pH conditions induced by a grain diet, there is a burst in the number of E. coli with virulence genes that can take advantage of these rumen conditions to trigger an inflammatory response.

Escherichia coli serogroup O26--a new look at an old adversary

Escherichia coli serogroup O26 played an important part in the early work on Verocytotoxin and is an established diarrhoeal pathogen. Recently, Verocytotoxigenic E. coli (VTEC) O26 has been increasingly associated with diarrhoeal disease and frequently linked to outbreaks and cases of haemolytic uraemic syndrome (HUS). This review investigates the pathogenicity, geographical distribution, changing epidemiology, routes of transmission and improved detection of VTEC O26. Laboratory data on VTEC O26 isolates and clinical data on HUS suggest a true difference in the incidence of VTEC O26 in different geographic locations. However, few diagnostic laboratories use molecular methods to detect VTEC and so it is difficult to assess the role of VTEC O26 in causing diarrhoeal disease. VTEC O26 is frequently found in the cattle population but rarely in food. However, the small number of outbreaks analysed to date are thought to be food-borne rather than associated with direct or indirect contact with livestock or their faeces. The increase in awareness of VTEC O26 in the clinical and veterinary setting has coincided with the development of novel techniques that have improved our ability to detect and characterize this pathogen.

Enterohemorrhagic Escherichia coli (EHEC)

Enterohaemorrhagic Escherichia coli has since the last 2 decades been known to cause severe and bloody diarrhoea as well as haemorrhagic colitis (HC) and haemorrhagic uraemic syndrome (HUS) especially among children. The importance of screening for EHEC among children and older patients with severe symptoms is apparent. Production of the verocytotoxins VT1 and VT2 are the main features of EHEC, and the VT types and mode of action during human infection is described. There are, however, other features adding to the pathogenicity. In this review we deal with the importance of properties such as fimbriae and adhesins as well as systems to meet the bacterial need for iron during infection. These factors are probably important for the establishment of EHEC in the gut and add to the bacterial virulence. It has now become evident that VT producing E. coli, irrespective of serogroup, might be human pathogens. We conclude that knowledge of the different possible virulence factors adds to the possibility of separating more virulent from less virulent isolates.

Opportunities to improve fiber degradation in the rumen: microbiology, ecology, and genomics

The degradation of plant cell walls by ruminants is of major economic importance in the developed as well as developing world. Rumen fermentation is unique in that efficient plant cell wall degradation relies on the cooperation between microorganisms that produce fibrolytic enzymes and the host animal that provides an anaerobic fermentation chamber. Increasing the efficiency with which the rumen microbiota degrades fiber has been the subject of extensive research for at least the last 100 years. Fiber digestion in the rumen is not optimal, as is supported by the fact that fiber recovered from feces is fermentable. This view is confirmed by the knowledge that mechanical and chemical pretreatments improve fiber degradation, as well as more recent research, which has demonstrated increased fiber digestion by rumen microorganisms when plant lignin composition is modified by genetic manipulation. Rumen microbiologists have sought to improve fiber digestion by genetic and ecological manipulation of rumen fermentation. This has been difficult and a number of constraints have limited progress, including: (a) a lack of reliable transformation systems for major fibrolytic rumen bacteria, (b) a poor understanding of ecological factors that govern persistence of fibrolytic bacteria and fungi in the rumen, (c) a poor understanding of which glycolyl hydrolases need to be manipulated, and (d) a lack of knowledge of the functional genomic framework within which fiber degradation operates. In this review the major fibrolytic organisms are briefly discussed. A more extensive discussion of the enzymes involved in fiber degradation is included. We also discuss the use of plant genetic manipulation, application of free-living lignolytic fungi and the use of exogenous enzymes. Lastly, we will discuss how newer technologies such as genomic and metagenomic approaches can be used to improve our knowledge of the functional genomic framework of plant cell wall degradation in the rumen.

Escherichia coli in the rumen and colon of slaughter cattle, with particular reference to E. coli O157

The distribution of Escherichia coli O157 and of total E. coli was surveyed in the digestive tract of cattle under 30 months of age, slaughtered between August 1999 and May 2000 in three abattoirs in southern England. Samples were taken from the dorsal and ventral rumen wall, the rumen contents, the colon wall and colon contents, and from faeces or caudal rectal contents. Gut wall samples were processed by vortex-mixer to release loosely adherent bacteria, and by Stomacher to release firmly attached bacteria. E. coli O157 was detected by immunomagnetic separation followed by growth on selective culture media. The numbers of E. coli were higher in the colon than the rumen, and most were located in the digesta phase, rather than associated with the gut wall. The number of E. coli found in the gut and in faeces decreased during the winter months. E. coli O157 was detected more frequently in the colon than in the rumen, but the majority of detections(7/8) were in samples of rumen wall.

Dietary effects on the microbiological safety of food

The high mortality rate associated with human infections caused by Escherichia coli strains of the serotype O157:H7 has brought to public attention the importance of ruminants as reservoirs of food-borne pathogens. In addition to established examples such as salmonella, campylobacter and listeria, recent evidence is emerging of the role of food in the transmission of Helicobacter pylori and Mycobacterium paratuberculosis. Food-borne pathogens harboured by ruminants are spread through shedding in the faeces and subsequent faecal contamination of raw food. Ruminant shedding appears to be affected by diet and, of particular concern, may be increased during fasting regimens imposed during transport to the slaughterhouse. The survival of food-borne pathogens in the ruminant gut is affected by many factors including microbe-microbe interactions, interactions involving plant metabolites and the presence of inhibitory end-product metabolites such as short-chain fatty acids. The potential importance of digesta flow and bacterial detachment in shedding of food-borne pathogens is discussed. Experimental procedures with dangerous pathogens have constraints, particularly in animal experimentation. This situation may be overcome by the use of rumen-simulating fermentors. One such system which, like the natural rumen, has a different turnover rate for solid and liquid digesta, was found to maintain rumen-like variables over an 11 d period. This system may prove useful for the study of dietary effects on food-borne pathogens.

Analysis of type 1 fimbriae expression in verotoxigenic Escherichia coli: a comparison between serotypes O157 and O26

Previous research has shown that verotoxin-producing Escherichia coli (VTEC) O157 strains appear unable to express type 1 fimbriae although other serotypes such as O26 and O118 can. This study has investigated the molecular basis of this difference. The study confirmed the presence of a 16 bp deletion within the regulatory region of fimA (fim switch) in 63 VTEC O157 strains but not in other VTEC serotypes tested. The fim switch was shown to be detectable only in the phase off orientation in VTEC O157, but detection of the switch in the phase on orientation correlated with the degree of mannose-sensitive yeast agglutination in VTEC O26. Repair of the 16 bp deletion in the VTEC O157 fim switch region restored phase-variable expression of fimA in a permissive background. Non-O157 VTEC, especially O26 and O118, can be pathogenic in cattle; the role of type 1 fimbriae in this and colonization is discussed.

Characteristics of sheep-rumen isolates of Pseudomonas aeruginosa inhibitory to the growth of Escherichia coli O157

Screening facultative sheep-rumen bacteria which inhibit growth of Escherichia coli produced 11 strains of Pseudomonas aeruginosa. The isolates showed three different pulsed-field gel electrophoresis patterns and strains from different sheep produced pyocins that varied in strain specificity. Representative strains were resistant to ampicillin, methicillin, erythromycin, fusidic acid and augmentin, but not to tetracycline or nalidixic acid. Tested strains attached in large numbers to cultured rumen epithelial cells, potentially providing a means of survival in this ecosystem.