Genetics of digalactoside-binding adhesin from a uropathogenic Escherichia coli strain

Local induction of bladder Th1 responses to combat urinary tract infections

Given the high frequency of urinary tract infections (UTIs) and their recurrence, there is keen interest in developing effective UTI vaccines. Currently, most vaccine studies, including those in humans, involve parenteral vaccination aimed at evoking and sustaining elevated levels of systemic antibody directed at the uropathogens. In view of recent reports of aberrant Th2-biased bladder immune responses to infection, we hypothesized that immunizing mice intravesically with antigens from uropathogenic Escherichia coli (UPEC) combined with a Th1-skewing adjuvant could correct this defect and promote protection against UTIs. Here we report that compared with mice immunized subcutaneously with this vaccine combination, intravesically immunized mice were markedly more protected from UTIs because of their distinctive ability to recruit Th1 cells into the bladder. This mode of vaccination was effective even in mice that experienced multiple UTIs and displayed pronounced aberrant bladder immune responses. Thus, intravesical vaccination with one or more UPEC antigens to induce bladder Th1 responses represents a superior strategy to combat UTIs, especially in UTI-prone subjects.

A highly polarized TH2 bladder response to infection promotes epithelial repair at the expense of preventing new infections

Urinary tract infections (UTIs) typically evoke prompt and vigorous innate bladder immune responses, including extensive exfoliation of the epithelium. To explain the basis for the extraordinarily high recurrence rates of UTIs, we examined adaptive immune responses in mouse bladders. We found that, following each bladder infection, a highly T helper type 2 (TH2)-skewed immune response directed at bladder re-epithelialization is observed, with limited capacity to clear infection. This response is initiated by a distinct subset of CD301b+OX40L+ dendritic cells, which migrate into the bladder epithelium after infection before trafficking to lymph nodes to preferentially activate TH2 cells. The bladder epithelial repair response is cumulative and aberrant as, after multiple infections, the epithelium was markedly thickened and bladder capacity was reduced relative to controls. Thus, recurrence of UTIs and associated bladder dysfunction are the outcome of the preferential focus of the adaptive immune response on epithelial repair at the expense of bacterial clearance.

Rapid Waterborne Pathogen Detection with Mobile Electronics

Pathogen detection in water samples, without complex and time consuming procedures such as fluorescent-labeling or culture-based incubation, is essential to public safety. We propose an immunoagglutination-based protocol together with the microfluidic device to quantify pathogen levels directly from water samples. Utilizing ubiquitous complementary metal–oxide–semiconductor (CMOS) imagers from mobile electronics, a low-cost and one-step reaction detection protocol is developed to enable field detection for waterborne pathogens. 10 mL of pathogen-containing water samples was processed using the developed protocol including filtration enrichment, immune-reaction detection and imaging processing. The limit of detection of 10 E. coli O157:H7 cells/10 mL has been demonstrated within 10 min of turnaround time. The protocol can readily be integrated into a mobile electronics such as smartphones for rapid and reproducible field detection of waterborne pathogens.

Animal Enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) is the most common cause of E. coli diarrhea in farm animals. ETEC are characterized by the ability to produce two types of virulence factors: adhesins that promote binding to specific enterocyte receptors for intestinal colonization and enterotoxins responsible for fluid secretion. The best-characterized adhesins are expressed in the context of fimbriae, such as the F4 (also designated K88), F5 (K99), F6 (987P), F17, and F18 fimbriae. Once established in the animal small intestine, ETEC produce enterotoxin(s) that lead to diarrhea. The enterotoxins belong to two major classes: heat-labile toxins that consist of one active and five binding subunits (LT), and heat-stable toxins that are small polypeptides (STa, STb, and EAST1). This review describes the disease and pathogenesis of animal ETEC, the corresponding virulence genes and protein products of these bacteria, their regulation and targets in animal hosts, as well as mechanisms of action. Furthermore, vaccines, inhibitors, probiotics, and the identification of potential new targets by genomics are presented in the context of animal ETEC.

The arsenal of pathogens and antivirulence therapeutic strategies for disarming them

Pathogens deploy an arsenal of virulence factors (VFs) to establish themselves within their infectious niche. The discovery of antimicrobial compounds and their development into therapeutics has made a monumental impact on human and microbial populations. Although humans have used antimicrobials for medicinal and agricultural purposes, microorganism populations have developed and shared resistance mechanisms to persevere in the face of classical antimicrobials. However, a positive substitute is antivirulence therapy; antivirulence therapeutics prevent or interrupt an infection by counteracting a pathogen's VFs. Their application can reduce the use of broad-spectrum antimicrobials and dampen the frequency with which resistant strains emerge. Here, we summarize the contribution of VFs to various acute and chronic infections. In correspondence with this, we provide an overview of the research and development of antivirulence strategies.

Adhesins of Enterotoxigenic Escherichia coli Strains That Infect Animals

The first described adhesive antigen of Escherichia coli strains isolated from animals was the K88 antigen, expressed by strains from diarrheic pigs. The K88 antigen was visible by electron microscopy as a surface-exposed filament that was thin and flexible and had hemagglutinating properties. Many different fimbriae have been identified in animal enterotoxigenic E. coli (ETEC) and have been discussed in this article. The role of these fimbriae in the pathogenesis of ETEC has been best studied with K88, K99, 987P, and F41. Each fimbrial type carries at least one adhesive moiety that is specific for a certain host receptor, determining host species, age, and tissue specificities. ETEC are the most frequently diagnosed pathogens among neonatal and post-weaning piglets that die of diarrhea. Immune electron microscopy of animal ETEC fimbriae usually shows that the minor subunits are located at the fimbrial tips and at discrete sites along the fimbrial threads. Since fimbriae most frequently act like lectins by binding to the carbohydrate moieties of glycoproteins or glycolipids, fimbrial receptors have frequently been studied with red blood cells of various animal species. Identification and characterization of the binding moieties of ETEC fimbrial adhesins should be useful for the design of new prophylactic or therapeutic strategies. Some studies describing potential receptor or adhesin analogues that interfere with fimbria-mediated colonization have been described in the article.

Fimbriae: Classification and Biochemistry

Proteinaceous, nonflagellar surface appendages constitute a variety of structures, including those known variably as fimbriae or pili. Constructed by distinct assembly pathways resulting in diverse morphologies, fimbriae have been described to mediate functions including adhesion, motility, and DNA transfer. As these structures can represent major diversifying elements among Escherichia and Salmonella isolates, multiple fimbrial classification schemes have been proposed and a number of mechanistic insights into fimbrial assembly and function have been made. Herein we describe the classifications and biochemistry of fimbriae assembled by the chaperone/usher, curli, and type IV pathways.

Mast cell interleukin-10 drives localized tolerance in chronic bladder infection

The lower urinary tract's virtually inevitable exposure to external microbial pathogens warrants efficient tissue-specialized defenses to maintain sterility. The observation that the bladder can become chronically infected in combination with clinical observations that antibody responses after bladder infections are not detectable suggest defects in the formation of adaptive immunity and immunological memory. We have identified a broadly immunosuppressive transcriptional program specific to the bladder, but not the kidney, during infection of the urinary tract that is dependent on tissue-resident mast cells (MCs). This involves localized production of interleukin-10 and results in suppressed humoral and cell-mediated responses and bacterial persistence. Therefore, in addition to the previously described role of MCs orchestrating the early innate immunity during bladder infection, they subsequently play a tissue-specific immunosuppressive role. These findings may explain the prevalent recurrence of bladder infections and suggest the bladder as a site exhibiting an intrinsic degree of MC-maintained immune privilege.

Adhesive threads of extraintestinal pathogenic Escherichia coli

The ability to adhere to host surfaces is by far the most vital step in the successful colonization by microbial pathogens. Colonization begins with the attachment of the bacterium to receptors expressed by cells forming the lining of the mucosa. Long hair like extracellular appendages called fimbriae, produced by most Gram-negative pathogens, mediate specific attachment to the epithelial cell surface. Associated with the fimbriae is a protein called an adhesin, which directs high-affinity binding to specific cell surface components. In the last couple of years, an enormous amount of research has been undertaken that deals with understanding how bacterial pathogens adhere to host cells. E. coli in all probability is one of the best studied free-living organisms. A group of E. coli called Extraintestinal pathogenic E. coli (ExPEC) including both human and animal pathogens like Uropathogenic E. coli (UPEC), Newborn meningitic E. coli (NMEC) and Avian pathogenic E. coli (APEC), have been found to harbour many fimbriae including Type 1 fimbriae, P fimbriae, curli fibres, S fimbriae, F1C fimbriae, Dr fimbriae, afimbrial adhesins, temperature-sensitive haemagglutinin and many novel adhesin gene clusters that have not yet been characterized. Each of these adhesins is unique due to the recognition of an adhesin-specific receptor, though as a group these adhesins share common genomic organization. A newly identified putative adhesin temporarily termed ExPEC Adhesin I, encoded by gene yqi, has been recently found to play a significant role in the pathogenesis of APEC infection, thus making it an interesting candidate for future research. The aim of this review is to describe the role of ExPEC adhesins during extraintestinal infections known till date, and to suggest the idea of investigating their potential role in the colonization of the host gut which is said to be a reservoir for ExPEC.

Uropathogenic Escherichia coli

The urinary tract is among the most common sites of bacterial infection, and Escherichia coli is by far the most common species infecting this site. Individuals at high risk for symptomatic urinary tract infection (UTI) include neonates, preschool girls, sexually active women, and elderly women and men. E. coli that cause the majority of UTIs are thought to represent only a subset of the strains that colonize the colon. E. coli strains that cause UTIs are termed uropathogenic E. coli (UPEC). In general, UPEC strains differ from commensal E. coli strains in that the former possess extragenetic material, often on pathogenicity-associated islands (PAIs), which code for gene products that may contribute to bacterial pathogenesis. Some of these genes allow UPEC to express determinants that are proposed to play roles in disease. These factors include hemolysins, secreted proteins, specific lipopolysaccharide and capsule types, iron acquisition systems, and fimbrial adhesions. The current dogma of bacterial pathogenesis identifies adherence, colonization, avoidance of host defenses, and damage to host tissues as events vital for achieving bacterial virulence. These considerations, along with analysis of the E. coli CFT073, UTI89, and 536 genomes and efforts to identify novel virulence genes should advance the field significantly and allow for the development of a comprehensive model of pathogenesis for uropathogenic E. coli.Further study of the adaptive immune response to UTI will be especially critical to refine our understanding and treatment of recurrent infections and to develop vaccines.

Extraintestinal pathogenic Escherichia coli strains of avian and human origin: link between phylogenetic relationships and common virulence patterns

Extraintestinal pathogenic Escherichia coli (ExPEC) strains of human and avian origin show similarities that suggest that the avian strains potentially have zoonotic properties. However, the phylogenetic relationships between avian and human ExPEC strains are poorly documented, so this possibility is difficult to assess. We used PCR-based phylotyping and multilocus sequence typing (MLST) to determine the phylogenetic relationships between 39 avian pathogenic E. coli (APEC) strains of serogroups O1, O2, O18, and O78 and 51 human ExPEC strains. We also compared the virulence genotype and pathogenicity for chickens of APEC strains and human ExPEC strains. Twenty-eight of the 30 APEC strains of serogroups O1, O2, and O18 were classified by MLST into the same subcluster (B2-1) of phylogenetic group B2, whereas the 9 APEC strains of serogroup O78 were in phylogenetic groups D (3 strains) and B1 (6 strains). Human ExPEC strains were closely related to APEC strains in each of these three subclusters. The 28 avian and 25 human strains belonging to phylogenetic subcluster B2-1 all expressed the K1 antigen and presented no significant differences concerning the presence of other virulence factors. Moreover, human strains of this phylogenetic subcluster were highly virulent for chicks, so no host specificity was identified. Thus, APEC strains of serotypes O1:K1, O2:K1, and O18:K1 belong to the same highly pathogenic clonal group as human E. coli strains of the same serotypes isolated from cases of neonatal meningitis, urinary tract infections, and septicemia. These APEC strains constitute a potential zoonotic risk.

Human body temperature (37degrees C) increases the expression of iron, carbohydrate, and amino acid utilization genes in Escherichia coli K-12

Using DNA microarrays, we identified 126 genes in Escherichia coli K-12 whose expression is increased at human body temperature (37 degrees C) compared to growth at 23 degrees C. Genes involved in the uptake and utilization of amino acids, carbohydrates, and iron dominated the list, supporting a model in which temperature serves as a host cue to increase expression of bacterial genes needed for growth. Using quantitative real-time PCR, we investigated the thermoregulatory response for representative genes in each of these three categories (hisJ, cysP, srlE, garP, fes, and cirA), along with the fimbrial gene papB. Increased expression at 37 degrees C compared to 23 degrees C was retained in both exponential and stationary phases for all of the genes and in most of the various media tested, supporting the relative importance of this cue in adapting to changing environments. Because iron acquisition is important for both growth and virulence, we analyzed the regulation of the iron utilization genes cirA and fes and found that growth in iron-depleted medium abrogated the thermoregulatory effect, with high-level expression at both temperatures, contrasting with papB thermoregulation, which was not greatly altered by limiting iron levels. A positive role for the environmental regulator H-NS was found for fes, cirA, hisJ, and srlE transcription, whereas it had a primarily negative effect on cysP and garP expression. Together, these studies indicate that temperature is a broadly used cue for regulating gene expression in E. coli and that H-NS regulates iron, carbohydrate, and amino acid utilization gene expression.

Regulation of Fimbrial Expression

Fimbria-mediated interaction with the host elicits both innate and adaptive immune responses, and thus their expression may not always be beneficial in vivo. Furthermore, the metabolic drain of producing fimbriae is significant. It is not surprising, therefore, to find that fimbrial production in Escherichia coli and Salmonella enterica is under extensive environmental regulation. In many instances, fimbrial expression is regulated by phase variation, in which individual cells are capable of switching between fimbriate and afimbriate states to produce a mixed population. Mechanisms of phase variation vary considerably between different fimbriae and involve both genetic and epigenetic processes. Notwithstanding this, fimbrial expression is also sometimes controlled at the posttranscriptional level. In this chapter, we review key features of the regulation of fimbrial gene expression in E. coli and Salmonella. The occurrence and distribution of fimbrial operons vary significantly among E. coli pathovars and even among the many Salmonella serovars. Therefore, general principles are presented on the basis of detailed discussion of paradigms that have been extensively studied, including Pap, type 1 fimbriae, and curli. The roles of operon specific regulators like FimB or CsgD and of global regulatory proteins like Lrp, CpxR, and the histone-like proteins H-NS and IHF are reviewed as are the roles of sRNAs and of signalling nucleotide cyclic-di-GMP. Individual examples are discussed in detail to illustrate how the regulatory factors cooperate to allow tight control of expression of single operons. Molecular networks that allow coordinated expression between multiple fimbrial operons and with flagella in a single isolate are also presented. This chapter illustrates how adhesin expression is controlled, and the model systems also illustrate general regulatory principles germane to our overall understanding of bacterial gene regulation.

Common virulence factors and genetic relationships between O18:K1:H7 Escherichia coli isolates of human and avian origin

Extraintestinal pathogenic (ExPEC) Escherichia coli strains of serotype O18:K1:H7 are mainly responsible for neonatal meningitis and sepsis in humans and belong to a limited number of closely related clones. The same serotype is also frequently isolated from the extraintestinal lesions of colibacillosis in poultry, but it is not well known to what extent human and avian strains of this particular serotype are related. Twenty-two ExPEC isolates of human origin and 33 isolates of avian origin were compared on the basis of their virulence determinants, lethality for chicks, pulsed-field gel electrophoresis (PFGE) patterns, and classification in the main phylogenetic groups. Both avian and human isolates were lethal for chicks and harbored similar virulence genotypes. A major virulence pattern, identified in 75% of the isolates, was characterized by the presence of F1 variant fimbriae; S fimbriae; IbeA; the aerobactin system; and genomic fragments A9, A12, D1, D7, D10, and D11 and by the absence of P fimbriae, F1C fimbriae, Afa adhesin, and CNF1. All but one of the avian and human isolates also belonged to major phylogenetic group B2. However, various subclonal populations could be distinguished by PFGE in relation to animal species and geographical origin. These results demonstrate that very closely related clones can be recovered from extraintestinal infections in humans and chickens and suggest that avian pathogenic E. coli isolates of serotype O18:K1:H7 are potential human pathogens.

Structure and assembly of P-pili: a protruding hinge region used for assembly of a bacterial adhesion filament

High-resolution structures of macromolecular complexes offer unparalleled insight into the workings of biological systems and hence the interplay of these systems in health and disease. We have adopted a multifaceted approach to understanding the pathogenically important structure of P-pili, the class I adhesion pili from pyelonephritic Escherichia coli. Our approach combines electron cryomicroscopy, site-directed mutagenesis, homology modeling, and energy calculations, resulting in a high-resolution model of PapA, the major structural element of these pili. Fitting of the modeled PapA subunit into the electron cryomicroscopy data provides a detailed view of these pilins within the supramolecular architecture of the pilus filament. A structural hinge in the N-terminal region of the subunit is located at the site of a newly resolved electron density that protrudes from the P-pilus surface. The structural flexibility provided by this hinge is necessary for assembly of P-pili, illustrating one solution to construction of large macromolecular complexes from small repeating units. These data support our hypothesis that domain-swapped pilin subunits transit the outer cell membrane vertically and rotate about the hinge for final positioning into the pilus filament. Our data confirm and supply a structural basis for much previous genetic, biochemical, and structural data. This model of the P-pilus filament provides an insight into the mechanism of assembly of a macromolecular complex essential for initiation of kidney infection by these bacteria.

Genomic subtraction for the identification of putative new virulence factors of an avian pathogenic Escherichia coli strain of O2 serogroup

To identify putative new virulence factors of avian pathogenicEscherichia coli(APEC) strains, a genomic subtraction was performed between the APEC strain MT512 and the non-pathogenicE. colistrain of avian origin EC79. Seventeen DNA fragments were cloned that were specific for the APEC strain. Among them, nine were identified that were more frequent among pathogenic than non-pathogenic isolates in a collection of 67 avianE. coli. Chromosome or plasmid location, and the nucleotide sequence of these nine fragments were characterized. Four fragments were plasmid-located. The nucleotide sequence of two of them exhibited identity with the sequence of the RepF1B replicon ofE. coliplasmids, and the amino-acid deduced sequences from the two other fragments exhibited similarity to the products of genessitAofSalmonellaTyphimurium andiroDofE. coli, which are involved in iron metabolism. Of the five chromosome-located fragments, three were predicted to encode parts of proteins that were significantly homologous to previously described proteins: TktA (transketolase) ofHaemophilus influenzae, a FruA (fructokinase) homologue ofListeria innocuaand Gp2 (large terminal subunit) of phage 21. The putative products of the two other chromosome-located fragments were homologous to proteins with unknown functions: Z0255 ofE. colistrain EDL933 (EHEC) and RatA ofSalmonellaTyphimurium strain LT2. Both these chromosomal fragments, whose presence is correlated with serogroups O1 and O2 and to the virulence of APEC strains belonging to these serogroups, are good candidates for being part of novel virulence determinants of APEC. Moreover, several fragments were shown to be located close to tRNAselC,asnTorthrW, which suggests they could be part of pathogenicity islands. Six fragments that were shown to be part of whole ORFs present in the APEC strain MT 512 were also present in extra-intestinal pathogenicE. coli(ExPEC) strains of human and animal origin. Thus, the putative novel virulence factors identified in this study could be shared by ExPEC strains of different origins.

The N-acetyltransferase RimJ responds to environmental stimuli to repress pap fimbrial transcription in Escherichia coli

In uropathogenic Escherichia coli, P pili (Pap) facilitate binding to host epithelial cells and subsequent colonization. Whereas P pili can be produced at 37 degrees C, the expression of these fimbriae is suppressed at 23 degrees C. Previously, insertion mutations in rimJ, a gene encoding the N-terminal acetyltransferase of ribosomal protein S5, were shown to disrupt this thermoregulatory response, allowing papBA transcription at low temperature. In this study, we created an in-frame deletion of rimJ. This deletion relieved the repressive effects not only of low temperature but also of rich (Luria-Bertani [LB]) medium and glucose on papBA transcription, indicating that RimJ modulates papBA transcription in response to multiple environmental stimuli. papI transcription was also shown to be regulated by RimJ. papBA transcription is also controlled by a phase variation mechanism. We demonstrated that the regulators necessary to establish a phase ON state--PapI, PapB, Dam, Lrp, and cyclic AMP-CAP-are still required for papBA transcription in a rimJ mutant strain. rimJ mutations increase the rate at which bacteria transition into the phase ON state, indicating that RimJ inhibits the phase OFF-->ON transition. A DeltarimJ hns651 mutant is viable on LB medium but not on minimal medium. This synthetic lethality, along with transcriptional analyses, indicates that RimJ and H-NS work through separate pathways to control papBA transcription. Mutations in rimJ do not greatly influence the transcription of the fan, daa, or fim operon, suggesting that RimJ may be a pap-specific regulator. Overexpression of rimJ under conditions repressive for papBA transcription complements the DeltarimJ mutation but has little effect on transcription under activating conditions, indicating that the ability of RimJ to regulate transcription is environmentally controlled.

The N-acetyltransferase RimJ responds to environmental stimuli to repress pap fimbrial transcription in Escherichia coli

In uropathogenic Escherichia coli, P pili (Pap) facilitate binding to host epithelial cells and subsequent colonization. Whereas P pili can be produced at 37 degrees C, the expression of these fimbriae is suppressed at 23 degrees C. Previously, insertion mutations in rimJ, a gene encoding the N-terminal acetyltransferase of ribosomal protein S5, were shown to disrupt this thermoregulatory response, allowing papBA transcription at low temperature. In this study, we created an in-frame deletion of rimJ. This deletion relieved the repressive effects not only of low temperature but also of rich (Luria-Bertani [LB]) medium and glucose on papBA transcription, indicating that RimJ modulates papBA transcription in response to multiple environmental stimuli. papI transcription was also shown to be regulated by RimJ. papBA transcription is also controlled by a phase variation mechanism. We demonstrated that the regulators necessary to establish a phase ON state--PapI, PapB, Dam, Lrp, and cyclic AMP-CAP-are still required for papBA transcription in a rimJ mutant strain. rimJ mutations increase the rate at which bacteria transition into the phase ON state, indicating that RimJ inhibits the phase OFF-->ON transition. A DeltarimJ hns651 mutant is viable on LB medium but not on minimal medium. This synthetic lethality, along with transcriptional analyses, indicates that RimJ and H-NS work through separate pathways to control papBA transcription. Mutations in rimJ do not greatly influence the transcription of the fan, daa, or fim operon, suggesting that RimJ may be a pap-specific regulator. Overexpression of rimJ under conditions repressive for papBA transcription complements the DeltarimJ mutation but has little effect on transcription under activating conditions, indicating that the ability of RimJ to regulate transcription is environmentally controlled.

Virulence Factors of Avian Pathogenic Escherichia coli Isolated from Broilers from the South of Brazil

Sixty-three Escherichia coli strains isolated from broilers with respiratory problems were examined for virulence factors, hemolysin synthesis ability, motility, hemagglutination capacity, operon pap presence, colicin production, and serum resistance. The capacity to hemagglutinate guinea pig erythrocytes was found in 53 (84.1%) of the samples, but only 30 (47.6%) agglutinated chicken erythrocytes. D-mannose-sensitive hemagglutination against guinea pig erythrocytes was found in 19 (30.2%) samples and against chicken erythrocytes, in 15 (23.8%) samples, whereas the D-mannose-resistant hemagglutination with guinea pig erythrocytes was found in 34 (54%) samples, and 13 of these (20.6%) showed this characteristic against chicken erythrocytes. Operon pap, P fimbria codifier, was detected in 26 samples in a total of 34 D-mannose-resistant samples. Colicin production was observed in 55 (87.3%) of the strains, and 41.8% presented V colicin production. Of the samples analyzed, 56 (88.9%) presented serum resistance, six (9.5%) were intermediate, and only one (1.6%) was sensitive to the action of the complement. The diversity of virulence profiles detected in the samples in this study explains in part the multifactorial characteristics of avian colibacillosis.

Cpx signaling pathway monitors biogenesis and affects assembly and expression of P pili

P pili are important virulence factors in uropathogenic Escherichia coli. The Cpx two-component signal transduction system controls a stress response and is activated by misfolded proteins in the periplasm. We have discovered new functions for the Cpx pathway, indicating that it may play a critical role in pathogenesis. P pili are assembled via the chaperone/usher pathway. Subunits that go 'OFF-pathway' during pilus biogenesis generate a signal. This signal is derived from the misfolding and aggregation of subunits that failed to come into contact with the chaperone in the periplasm. In response, Cpx not only controls the stress response, but also controls genes necessary for pilus biogenesis, and is involved in regulating the phase variation of pap expression and, potentially, the expression of a panoply of other virulence factors. This study demonstrates how the prototypic chaperone/usher pathway is intricately linked and dependent upon a signal transduction system.

H-NS controls pap and daa fimbrial transcription in Escherichia coli in response to multiple environmental cues

A comparative study was completed to determine the influence of various environmental stimuli on the transcription of three different fimbrial operons in Escherichia coli and to determine the role of the histone-like protein H-NS in this environmental regulation. The fimbrial operons studied included the pap operon, which encodes pyelonephritis-associated pili (P pili), the daa operon, which encodes F1845 fimbriae, and the fan operon, which encodes K99 fimbriae. Using lacZYA transcriptional fusions within each of the fimbrial operons, we tested temperature, osmolarity, carbon source, rich medium, oxygen levels, pH, amino acids, solid medium, and iron concentration for their effects on fimbrial gene expression. Low temperature, high osmolarity, glucose as a carbon source, and rich medium repressed transcription of all three operons. High iron did not alter transcription of any of the operons tested, whereas the remaining stimuli had effects on individual operons. For the pap and daa operons, introduction of the hns651 mutation relieved the repression, either fully or partially, due to low temperature, glucose as a carbon source, rich medium, and high osmolarity. Taken together, these data indicate that there are common environmental cues that regulate fimbrial transcription in E. coli and that H-NS is an important environmental regulator for fimbrial transcription in response to several stimuli.

Identification of sat, an autotransporter toxin produced by uropathogenic Escherichia coli

Urinary tract infection (UTI) is a very common extraintestinal infection, and Escherichia coli is by far the most common causative organism. Uropathogenic E. coli possess traits that distinguish them from commensal strains of E. coli, such as secretion systems that allow virulence factors to be targeted to extracytoplasmic compartments. One of at least five characterized secretion mechanisms is the autotransporter system, which involves translocation of a protein across the inner membrane, presumably via the sec system, and across the outer membrane through a beta-barrel porin structure formed by the carboxy-terminus autotransporter domain. We identified a 107 kDa protein that was expressed significantly more often by E. coli strains associated with the clinical syndrome of acute pyelonephritis than by faecal strains (P = 0.029). We isolated the protein from E. coli CFT073, a strain cultured from the blood and urine of a patient with acute pyelonephritis. The N-terminal amino acid sequence showed highest similarity to two known SPATE (serine protease autotransporters of Enterobacteriaceae) proteins, Pet and EspC. Using a 509 bp probe from the 5' region of pet, 10 cosmid clones of an E. coli CFT073 gene library were positive for hybridization. From one cosmid clone, a 7.5 kb EcoRI restriction fragment, which reacted strongly with the probe, was shown to include the entire 3885 bp gene. The predicted 142 kDa protein product possesses the three domains that are typical of SPATE autotransporters: an unusually long signal sequence of 49 amino acids; a 107 kDa passenger domain containing a consensus serine protease active site (GDSGSG); and a C-terminal autotransporter domain of 30 kDa. The protein exhibited serine protease activity and displayed cytopathic activity on VERO primary kidney, HK-2 bladder and HEp-2 cell lines; the name Sat (secreted autotransporter toxin) was derived from these properties. In addition, Sat antibodies were present in the serum of mice infected with E. coli CFT073. Based upon its association with pathogenic isolates, its cytopathic phenotype and its ability to elicit a strong antibody response after infection, we postulate that Sat represents a novel virulence determinant of uropathogenic E. coli.

Expression of virulence factors among Escherichia coli isolated from the periurethra and urine of children with neurogenic bladder on intermittent catheterization

BACKGROUND

Patients with neurogenic bladder caused by spinal cord injury or myelomeningocele empty their bladder several times a day by intermittent catheterization. Bacteriuria without symptoms of infection is frequently present in these patients. Occasionally a clone of Escherichia coli that has been carried for weeks without symptoms causes a symptomatic urinary tract infection. Virulence factors are commonly expressed among E. coli causing infection in patients with normal urinary tracts. However, it is unknown whether expression of virulence factors by an E. coli clone colonizing the neurogenic bladder increases the risk of subsequent infection. In this study we examined the prevalence of virulence factor expression among E. coli isolated from the periurethra and urine of patients with neurogenic bladder.

METHODS

The prevalence of virulence factors was examined among E. coli isolated from the periurethra and urine in patients with neurogenic bladder who received intermittent catheterization and were followed for 6 months. Representative isolates from the 37 clonal types of E. coli detected in the periurethra and urine of children with neurogenic bladder were assessed for O antigen, hemolysin, aerobactin, serum resistance and type I and P-adhesin.

RESULTS

All clones were serum-resistant and expressed type I adhesin, none expressed aerobactin and two expressed hemolysin. The presence of P-adhesin was not unique to clones associated with symptomatic infection. The presence of P-adhesin carried for weeks in a clone did not predict subsequent infection in the neurogenic bladder.

CONCLUSION

Bacterial virulence factors did not predict infection of the neurogenic bladder.

Virulence-associated factors of uropathogenic Escherichia coli strains isolated from pigs

Thirty one Escherichia coli strains isolated from pigs with urinary tract infections were investigated for presence of virulence factors and plasmid DNA profile. The most frequent virulence factors presented by these strains were mannose-resistant fimbriae, including P. fimbriae (54.8%) and aerobactin production (45.2%). The pap) operon, detected by PCR, was found in 54.8% of the strains, which is similar to its frequency in human strains. Other characteristics such as the presence of mannose-sensitive hemagglutinin (16.1%), indicative of type 1 pili, and production of hemolysin (25.8%), colicin (38.7%) and toxins (22.6% for LT and for VT) were less frequent. No strains were positive for STa production. Plasmid profiles were variable among isolates from either the same or different farms.

Genomic analysis of a pathogenicity island in uropathogenic Escherichia coli CFT073: distribution of homologous sequences among isolates from patients with pyelonephritis, cystitis, and Catheter-associated bacteriuria and from fecal samples

Urinary tract infection is the most frequently diagnosed kidney and urologic disease and Escherichia coli is by far the most common etiologic agent. Uropathogenic strains have been shown to contain blocks of DNA termed pathogenicity islands (PAIs) which contribute to their virulence. We have defined one of these regions of DNA within the chromosome of a highly virulent E. coli strain, CFT073, isolated from the blood and urine of a woman with acute pyelonephritis. The 57,988-bp stretch of DNA has characteristics which define PAIs, including a size greater than 30 kb, the presence of insertion sequences, distinct segmentation of K-12 and J96 origin, GC content (42.9%) different from that of total genomic DNA (50.8%), and the presence of virulence genes (hly and pap). Within this region, we have identified 44 open reading frames; of these 44, 10 are homologous to entries in the complete K-12 genome sequence, 4 are nearly identical to the sequences of E. coli J96 encoding the HlyA hemolysin, 11 encode P fimbriae, and 19 show no homology to J96 or K-12 entries. To determine whether sequences found within the junctions of the PAI of CFT073 were common to other uropathogenic strains of E. coli, 11 probes were isolated along the length of the PAI and were hybridized to dot blots of genomic DNA isolated from clinical isolates (67 from patients with acute pyelonephritis, 38 from patients with cystitis, 49 from patients with catheter-associated bacteriuria, and 27 from fecal samples). These sequences were found significantly more often in strains associated with the clinical syndromes of acute pyelonephritis (79%) and cystitis (82%) than in those associated with catheter-associated bacteriuria (58%) and in fecal strains (22%) (P < 0.001). From these regions, we have identified a putative iron transport system and genes other than hly and pap that may contribute to the virulent phenotype of uropathogenic E. coli strains.

The globoseries glycosphingolipid sialosyl galactosyl globoside is found in urinary tract tissues and is a preferred binding receptor In vitro for uropathogenic Escherichia coli expressing pap-encoded adhesins

Women with a history of recurrent Escherichia coli urinary tract infections (UTIs) are significantly more likely to be nonsecretors of blood group antigens than are women without such a history, and vaginal epithelial cells (VEC) from women who are nonsecretors show enhanced adherence of uropathogenic E. coli isolates compared with cells from secretors. We previously extracted glycosphingolipids (GSLs) from native VEC and determined that nonsecretors (but not secretors) selectively express two extended globoseries GSLs, sialosyl galactosyl globoside (SGG) and disialosyl galactosyl globoside (DSGG), which specifically bound uropathogenic E. coli R45 expressing a P adhesin. In this study, we demonstrated, by purifying the compounds from this source, that SGG and DSGG are expressed in human kidney tissue. We also demonstrated that SGG and DSGG isolated from human kidneys bind uropathogenic E. coli isolates expressing each of the three classes of pap-encoded adhesins, including cloned isolates expressing PapG from J96, PrsG from J96, and PapG from IA2, and the wild-type isolates IA2 and R45. We metabolically 35S labeled these five E. coli isolates and measured their relative binding affinities to serial dilutions of SGG and DSGG as well as to globotriaosylceramide (Gb3) and globotetraosylceramide (Gb4), two other globoseries GSLs present in urogenital tissues. Each of the five E. coli isolates bound to SGG with the highest apparent avidity compared with their binding to DSGG, Gb3, and Gb4, and each isolate had a unique pattern of GSL binding affinity. These studies further suggest that SGG likely plays an important role in the pathogenesis of UTI and that its presence may account for the increased binding of E. coli to uroepithelial cells from nonsecretors and for the increased susceptibility of nonsecretors to recurrent UTI.

Bacterial adhesion pili are heterologous assemblies of similar subunits

P-pili on uropathogenic bacteria are 68-A-diameter rods typically 1 microm in length. These structures project from the outer membrane of Escherichia coli, and contain on their distal tip a thin fibrillum, 25 A in diameter and 150 A long, displaying an adhesin protein responsible for the binding of the bacterium to the surface of epithelial cells lining the urinary tract. Operationally, it is possible to identify three morphologically distinct states of the 68-A-diameter P-pili rods, based on the degree of curvature each can adopt. These states are designated "straight," "curved," and "highly curved." The rods can also be unwound to form thin "threads" that are very similar to the tip fibrillae. Electron microscope data are used to distinguish among these four morphological states and to define limits on the shapes of the pilus proteins. The mechanical properties of the PapA polymers are assessed, and implications of rod polymorphism for pilus function are discussed. A wide variety of data are considered in light of the possibility that all pilins are similar in molecular architecture, with specific differences designed to optimize their specialized functions in the pilus assembly.

Adherence pili of pathogenic strains of avian Escherichia coli

Fifty strains of Escherichia coli isolated from colisepticemic chickens in Londrina, Brazil, were examined for presence of gene sequences for pil and pap, hemagglutination, and adherence to chicken tracheal cells. Forty-one strains were pil+ and 22 of these showed mannose sensitive (MS) hemagglutination (MSHA) of guinea-pig erythrocytes, indicating that they possessed only type 1 pili. Seven strains were pap+ and 6 of these caused mannose resistant (MR) hemagglutination (MRHA) of human erythrocytes. Twenty-four strains (17 of which caused MSHA) showed MS-adherence to chicken tracheal cells and the remaining 26 showed MR-adherence. The former typically adhered to the mucus layer whereas the latter usually adhered to the mucosal epithelium. It is concluded that MS adherence to chicken tracheal cells is correlated with expression of type 1 fimbriae and that MR-adherence to chicken tracheal cells cannot always be attributed to P pili.

Role of type 1 fimbriae in EPEC infections

Several fimbriae have been implicated as potentially important in EPEC adhesion and pathogenesis. EPEC strain E2348/69 produced only bundle forming pili and type 1 fimbriae, and did not produce other accesory adhesins identified in EPEC strain B171. Cloning and mutagenesis of these EPEC fim genes indicated that type 1 pili had no affect on levels or patterns of adhesion to cultured human cells.

Genotypic and phenotypic determination of five virulence markers in clinical isolates of Escherichia coli

The presence of the virulence markers K1 capsule, serum resistance, aerobactin, S and P/PR fimbriae were examined in a total of 395 E. coli strains from different extraintestinal infections and in 81 faecal isolates of healthy volunteers using specific DNA probes and classical phenotypic methods. All markers were more frequently detected when genotypic assays were applied. The simultaneous occurrence of 3-4 virulence determinants was typical for isolates derived from patients with septicaemia or meningitis. Isolates from blood cultures and cerebrospinal fluid were expressing the virulence phenotypes to a greater extent than isolates from urine or faeces. The use of colony hybridization with specific oligonucleotide and polynucleotide probes for the detection of virulence determinants has been proven to be more specific and reliable than phenotypic approaches.

Characterization of Escherichia coli strains isolated from environmental water habitats and from stool samples of healthy volunteers

This study was undertaken to determine the frequency of pathogenic Escherichia coli strains among wild-type E. coli strain isolates from the microbial flora of healthy volunteers and from natural residential water habitats of a defined geographic area. In total, 131 stool and 95 water isolates as well as 14 E.coli K12 strains were examined for DNA sequences specific for 20 different genes encoding E. coli pathogenicity factors, including adherence factors, toxins, invasins, capsules and iron uptake systems. The expression of the corresponding pathogenicity factors was also investigated. No pathogenicity factors were found to be present in the tested E. coli K12 strains. In contrast, 41.0% of the water samples and 63.4% of the stool samples contained pathogenicity factors specific for extraintestinal E. coli pathogens. While no virulence determinants specific for intestinal E. coli pathogens were found among the investigated environmental water isolates, 4.5% of the stool samples contained either only intestinal or both intestinal and extraintestinal virulence genes. Both the prevalence of the virulence genes and the expression of the corresponding pathogenicity factors were, in general, higher in stool than in water samples. These findings might indicate the prevalence of different clonal types and/or differential regulation of pathogenicity factor expression in diverse ecological niches.

Molecular and structural aspects of fimbriae biosynthesis and assembly in Escherichia coli

Fimbriae are long filamentous polymeric protein structures located at the surface of bacterial cells. They enable the bacteria to bind to specific receptor structures and thereby to colonise specific surfaces. Fimbriae consist of so-called major and minor subunits, which form, in a specific order, the fimbrial structure. In this review emphasis is put on the genetic organisation, regulation and especially on the biosynthesis of fimbriae of enterotoxigenic Escherichia coli strains, and more in particular on K88 and related fimbriae, with ample reference to well-studied P and type 1 fimbriae. The biosynthesis of these fimbriae requires two specific and unique proteins, a periplasmic chaperone and an outer membrane located molecular usher ('doorkeeper'). Molecular and structural aspects of the secretion of fimbrial subunits across the cytoplasmic membrane, the interaction of these subunits with periplasmic molecular chaperone, their translocation to the inner site of the outer membrane and their interaction with the usher protein, as well as the (ordered) translocation of the subunits across the outer membrane and their assembly into a growing fimbrial structure will be described. A model for K88 fimbriae is presented.

P-fimbriation and haemolysin production are the most important virulence factors in diabetic patients with Escherichia coli bacteraemia: a multivariate statistical analysis of seven bacterial virulence factors

Diabetic patients, as compared to non-diabetic subjects, run an increased risk of acquiring Gram-negative bacteraemia. We therefore studied the prevalence and coexpression of seven bacterial virulence markers of 69 Escherichia coli strains isolated from 64 bacteraemic patients with diabetes mellitus and 67 E. coli strains from faeces of healthy controls. The strains were analyzed for haemolysin (HLY) production, aerobactin-mediated iron uptake (AMI), cytotoxic necrotizing factor (CNF) production, expression of cell surface hydrophobicity, P-fimbriae, mannose-resistant haemagglutination (MRHA) and mannose-sensitive haemagglutination (MSHA). All bacterial properties were significantly more common among the bacteraemic strains (P < 0.02 vs. controls). Correlations between HLY and CNF (P < 0.0004) and between P-fimbriae and MRHA (P < 0.0001), MSHA (P < 0.0002) or AMI (P < 0.05), as well as between MRHA and MSHA (P < 0.0005) were observed. In patients with proteinuria, as sign of diabetic complications in the urinary tract, HLY-negative strains, P-fimbriae-negative strains, and strains which were both HLY-/CNF-negative, were more common (P = 0.04, P < 0.01 and P = 0.048, respectively). Using a multivariate statistical analysis, production of HLY and the expression of P-fimbriae were the two virulence factors with the highest discrimination between bacteraemic and control strains. In conclusion, all virulence factors studied were more prevalent in bacteraemic than in control strains, although HLY and P-fimbriae were shown to be of greatest and independent importance. Low virulent strains (P-fimbriae-, HLY- and CNF-negative) were more prevalent in diabetic patients with signs of renal complications.

Cable (cbl) type II pili of cystic fibrosis-associated Burkholderia (Pseudomonas) cepacia: nucleotide sequence of the cblA major subunit pilin gene and novel morphology of the assembled appendage fibers

Previous studies have shown that appendage pili of Burkholderia cepacia strains isolated from patients with cystic fibrosis (CF) at The Hospital for Sick Children, Toronto, Canada, mediate adherence to mucus glycoproteins and also enhance adherence to epithelial cells. The specific pilin-associated adhesin molecule is a 22-kDa protein. In the present study we purified the major subunit pilin (17 kDa) and immunolocalized it to peritrichously arranged pili. On the basis of their novel morphological appearance as giant intertwined fibers, we refer to them as cable (Cbl) pili. Using an oligonucleotide probe corresponding to regions of the N-terminal amino acid sequence of the pilin subunit, we detected the encoding cblA gene in a chromosomal DNA library. Sequencing revealed this structural gene to be 555 bp in length, encoding a leader sequence of 19 amino acids, a cleavage site between the alanine at position 19 and the valine at position 20, and a mature pilin sequence of 165 amino acids. The calculated molecular mass is 17.3 kDa. Hydrophobic plus apolar amino acids account for 60% of the total residues. The pilin exhibits some similarities in its amino acid sequence to colonization factor antigen I and CS1 fimbriae of Escherichia coli. With the cblA gene used as a probe, hybridization assays of 59 independent isolates, including those from several geographically separated CF centers, plus environmental and clinical (non-CF) strains, gave positive results with all of the 15 CF-associated B. cepacia isolates from Toronto, plus a single strain from one other CF center (Jackson, Mississippi). The cblA gene is the first pilin subunit gene of B. cepacia to be identified.

Structurally variant classes of pilus appendage fibers coexpressed from Burkholderia (Pseudomonas) cepacia

One or more of five morphologically distinct classes of appendage pili were determined to be peritrichously expressed by Burkholderia (formerly Pseudomonas) cepacia isolated from disparate sources. B. cepacia-encoded cblA pilin gene hybridization-based analysis revealed that one associated class, cable (Cbl) adhesin type IIB. cepacia pili, correlates with epidemically transmitted strains from a single cystic fibrosis (CF) center. When only phenotypic assays were available, correlations between the source and the pilus type were nonetheless observed: filamentous (Fil) type IIIB. cepacia pili correlated with CF-associated nonepidemic isolates, spine (Spn) type IVB. cepacia pili correlated with clinical (non-CF) isolates, and spike (Spk) type VB. cepacia pili correlated with environmental isolates. Further, Cbl, Fil, or Spk pili typically appear as an internal framework for constitutively coexpressed, peritrichously arranged dense mats of fine, curly mesh (Msh) type IB. cepacia pili. Constitutive coexpression of dense mats of Msh type IB. cepacia pili in association with a labyrinth of either Cbl, Fil, or Spk pili suggests possible cooperative pilus interactions mediating adhesion-based colonization in the differing environments from which the strains were isolated. Despite such correlations, phylogenetic analyses indicate that with the exception of the epidemically transmitted clusters of isolates, the remaining B. cepacia strains from the other three sources exhibited an equal degree of genetic relatedness independent of origin. As previously found for Escherichia coli, this discrepancy could be accounted for by selection-driven, in vivo horizontal transfer events between distantly related members of the species B. cepacia, leading to the genetic acquisition of environmentally appropriate adhesion-based colonization pilus operons.

Effect of Lewis blood group antigen expression on bacterial adherence to COS-1 cells

Epithelial cells from secretor individuals demonstrate decreased bacterial adherence compared with cells from nonsecretors. Lewis blood group antigen expression is one component of the secretor/nonsecretor phenotype and several epidemiologic studies have suggested a link between Lewis blood group antigen phenotype and susceptibility to urinary tract infections. In this study, we examined the possibility that the expression of the difucosylated Lewis blood group determinants, Leb and Ley (associated with the secretor phenotype), made cells less susceptible to Escherichia coli adherence by masking receptors for pili. COS-1 cells, which do not produce Lewis (Lea, Leb, Le(x), and Ley) blood group antigens, were used as target cells for bacterial adherence. The surface blood group antigen expression pattern of the cells was then modified by cotransfection with plasmids containing DNA inserts encoding alpha (1,2)-fucosyltransferase and alpha (1,3)- and alpha (1,4)-fucosyltransferases, resulting in the expression of Leb and Ley. E. coli HB101 expressing various adhesins (type 1, PapJ96, PapIA2, PapAD110, Prs, and S) from recombinant plasmids bound equally well to untransfected cells and transfected cells expressing Lea and Le(x) (nonsecretor phenotype) and Leb and Ley (secretor phenotype) antigens. We conclude that the presence of Leb and Ley antigens on cells from secretors does not alone mask receptors for E. coli pili or hinder bacterial adherence.

Effect of salicylate, bismuth, osmolytes, and tetracycline resistance on expression of fimbriae by Escherichia coli

Adherence of Escherichia coli is facilitated by fimbriae and several outer membrane proteins (OMPs). Hypertonic conditions, salicylate, and Mar mutations are known to reduce OmpF expression. We speculated that OMPs involved in export or assembly of fimbrial subunits might be similarly affected. To explore this hypothesis, E. coli expressing P, type 1, S, colonization factor antigen I (CFA/I), or CFA/II fimbriae was grown in the presence of salicylate, bismuth salts, NaCl, and nonfermented sugars. Tetracycline-resistant clones were derived from several P-fimbriated strains. The bacteria were tested for the ability to agglutinate erythrocytes, yeast cells, and alpha-D-Gal(-4)-beta-D-Gal-bonded latex (Gal-Gal) beads and were examined for fimbriae by electron microscopy. Hyperosmolar conditions decreased fimbrial expression for all strains. Expression of P fimbriae by pyelonephritic strains, all of which were OmpF+, was reversibly repressed by salicylate and bismuth salts. CFA strains were similarly affected. Tetracycline-resistant P-fimbriated strains were OmpF deficient, were unable to agglutinate erythrocytes and Gal-Gal beads, and lacked fimbriae as observed by electron microscopy. Strains with plasmid-encoded P-fimbrial genes did not demonstrate OmpF on polyacrylamide gel electrophoresis profiles and were not affected by salicylate. The type 1-fimbriated phenotype was not affected by salicylate or bismuth unless the strains also expressed P fimbriae. S-fimbriated strains were not affected. The mechanism by which salicylates, bismuth salts, and tetracycline resistance inhibit or modulate the expression of P fimbriae may be mediated through OmpF and other OMPs.

Production and characterisation of monoclonal antibodies against pyelonephritis-associated P-pili of Escherichia coli

Pyelonephritis-associated P-pili (PAP) of Escherichia coli O6,H(-),K1(-),F12,haemolysin(-) were purified by salt precipitation and affinity chromatography using Synsorb P1. Purified PAP showed a single band with a molecular weight of 18 kDa by electrophoretic analysis. A monoclonal antibody (mAb) was produced by fusion of the PAI myeloma cell line with splenic lymphocytes from BALB/c mice immunised with the purified PAP. The mAb was of IgM class with kappa light chains and reacted with a 18-kDa moeity of the salt precipitate; the epitope was present near the apical part of the pilus filaments. The mAb reacted with PAP in both immunofluorescence and haemagglutination tests when 108 strains isolated from urine samples were tested; the two tests were in agreement for 202 of 204 strains isolated from faecal samples.

Occurrence of genes for P and S fimbriae and hemolysin in urinary Escherichia coli

Escherichia coli is the common causative agent of urinary tract infections. Sixty-one strains of E. coli isolated from children with urinary tract infections were tested by colony hybridization for the presence of genes determining P and S fimbriae and hemolysin. Of these strains, 46 possess a gene for hemolysin, 44 for P fimbriae and 28 for S fimbriae. Only 30 strains formed lytic zones around the colonies on plates with sheep erythrocytes. The results indicated that simultaneous occurrence of genes in urinary E. coli was highest for P fimbriae and hemolysin and lower for other combinations of the tested genes.

Alanine-scanning mutagenesis reveals residues involved in binding of pap-3-encoded pili

In order to identify functionally important residues in the pap-3-encoded adhesin, oligonucleotide-directed mutagenesis was used to substitute alanine(s) at sixteen positions in the adhesion. These alanine substitutions span nearly every domain and hydrophilic peak of the protein. The effects of these substitutions were measured by evaluating the patterns of hemagglutination exhibited by the mutant strains. It was found that strains harboring alanine substitutions at positions 88 and 89, 128 to 130, and 316 had lost the capacity to hemagglutinate. The presence of the mutated adhesin in the assembled pilus structure was verified by the reactions of purified pili with an adhesin-specific monoclonal antibody in an enzyme-linked immunosorbent assay and with a polyclonal antibody in Western blotting (immunoblotting). Alanine substitutions at positions 68, 110 and 111, and 143 to 146 had no effect upon hemagglutination, whereas substitutions at positions 203 and 204 and position 291 resulted in diminished binding. Thus, the residues necessary for hemagglutination are scattered throughout the adhesin in both the amino and carboxy regions. Delineation of these residues may prove useful in designing a preventive treatment that would cross-react with the essential binding residues from the adhesins of several different pyelonephritis-causing strains.

Isogenic P-fimbrial deletion mutants of pyelonephritogenic Escherichia coli: the role of alpha Gal(1-4) beta Gal binding in virulence of a wild-type strain

Escherichia coli strains causing acute pyelonephritis often express multiple fimbrial types and haemolysin, which may contribute to their ability to adhere to, and interact with, kidney epithelial cells. Strain CFT073, a pap+, sfa+, pil+, hly+ pyelonephritis strain, previously established as virulent in the CBA mouse model of ascending urinary tract infection and cytotoxic for cultured human renal epithelial cells, was selected for construction of isogenic strains. From a gene bank of this strain, two distinct copies of the pap operon were isolated. The two P-fimbrial determinants were subcloned into pCVD442, a positive selection suicide vector containing the sacB gene of Bacillus subtilis. Deletion mutations were introduced into each of the two constructs, within papEFG of one operon and papDEFG of the other. Suicide vectors carrying pap deletions were mobilized from E. coli SM10 lambda pir into CFT073 (NalR) and cointegrates were passaged on non-selective medium. The first pap mutation was identified by screening a Southern blot of DNA from sucrose-resistant colonies using a papEFG probe. This mutant retained the MRHA+ phenotype since a second functional copy of pap was still present. A double pap-deletion mutant, UPEC76, confirmed by Southern blotting, was unable to agglutinate human type O erythrocytes or alpha Gal(1-4)beta Gal-coated latex beads. CBA mice (N = 100) were challenged transurethrally with 10(5), 10(6), 10(7), or 10(9) cfu of strains CFT073 or UPEC76. After one week, quantitative cultures of urine, bladder, and kidney were done and histologic changes were examined. No substantive differences in organism concentration or histological findings between parent and mutant were detected in urine, bladder, or kidney at any challenge concentration. We conclude that adherence by P fimbriae of uropathogenic E. coli strain CFT073 plays only a subtle role in the development of acute pyelonephritis in the CBA mouse model.

Application of biotinylated and 32P probes for detection of P-fimbriae in urinary E. coli

Escherichia coli is the common causative agent of urinary tract infections. Twenty-six strains of Escherichia coli were isolated from children with pyelonephritis, symptomatic urinary tract infections and asymptomatic bacteriuria. Biotinylated and 32P-DNA probes were prepared for detection of P-fimbriae in the isolates. Of the 13 strains isolated from patients with pyelonephritis 11 were positive for the presence of the P gene by both probes. Strains isolated from cases of symptomatic urinary tract infections revealed the presence of P gene only in three samples of the total of nine isolated. None of the isolated E. coli strains from asymptomatic bacteriuria was found positive for the presence of the P gene. The biotinylated probe was simple and easily applicable in standard laboratory conditions and therefore the authors recommend it for use in diagnostic laboratories.

Clonal differentiation of uropathogenic Escherichia coli isolates of serotype O6:K5 by fimbrial antigen typing and DNA long-range mapping techniques

Escherichia coli isolates of serotype O6:K5 are the most common causative agents of cystitis and pyelonephritis in adults. To answer the question, as to whether strains of this particular serotype represent one special clonal group, out of a collection of 34 serotype O6:K5 isolates [Zingler et al. (1990) Zentralbl. Bakteriol Mikrobiol Hyg [A] 274:372-381] 15 strains were selected and analyzed in detail. The flagellar (H) antigen and the outer membrane protein (OMP) pattern were determined. Further serum resistance properties and the genetic presence and expression of other virulence factors, including hemolysin, aerobactin, P fimbriae, S/F1C fimbriae and type 1 fimbriae was evaluated. In addition the XbaI-macrorestriction pattern of ten representative isolates was elaborated and the fimbrial (F) antigen type of the P fimbriae was determined, to obtain the complete O:K:H:F pattern. These analyses could clearly show that the O6:K5 isolates do not represent one clonal group. The XbaI-macrorestriction profiles were heterogeneous and marked differences in the hybridization patterns, using virulence-associated gene probes in Southern hybridization of long-range-separated genomic DNA, were observed among the strains. However, some of strains showed similarities in the genomic profiles, arguing for clonal groupings among the O6:K5 isolates. Interestingly the strains grouped together exhibited the same fimbrial F type that many indicate a coincidence of this phenotypic trait with clonality.

Pathogenicity of an Escherichia coli O115:K"V165" mutant negative for F165(1) fimbriae in septicemia of gnotobiotic pigs

To evaluate the role of the F165(1) fimbrial system in the pathogenesis of septicemia, 2-day-old germfree pigs were inoculated intragastrically with Escherichia coli O115:K"V165":F165 wild-type strain 5131, its F165(1)-negative TnphoA mutant M48, or E. coli O115:K(-):F165(-) wild-type strain 862B. Pigs were sacrificed at different times (3, 6, 12, 24, 48, and 96 h) postinfection (p.i.). Pigs inoculated with strain 5131 developed clinical signs (anorexia, lameness, reluctance to move, or lack of motor coordination) and were moribund within 48 h p.i., and, at necropsy, infecting bacteria were isolated in various extraintestinal organs. Strain 5131 was isolated as early as 6 h p.i. from the blood of inoculated pigs. Pigs inoculated with mutant M48 developed only mild clinical signs at 96 h p.i. Mutant M48 colonized extraintestinal organs of pigs but to a lesser extent than the parent strain did. In contrast to the parent strain, this mutant was not isolated in the blood of inoculated pigs. Pigs inoculated with strain 862B remained normal during the experiment. All of the strains colonized the mucus layer of the intestine, but no histological changes of intestinal mucosa were observed by either light or electron microscopy. The parent strain, but not the mutant M48, expressed F165(1) in vivo. In a competitive study in which the parent strain and its afimbrial mutant were inoculated simultaneously, clinical signs of septicemia developed 24 h after inoculation, and only the parent strain 5131 was isolated from the blood of inoculated pigs. Our results suggest that the F165(1) fimbrial system of E. coli O115:K"V165" strains may play an important role in the ability of the bacteria to survive in the blood and spread systemically through the porcine host.

The RpoS sigma factor relieves H-NS-mediated transcriptional repression of csgA, the subunit gene of fibronectin-binding curli in Escherichia coli

Curli encoded by the curlin subunit gene, csgA, are fibronectin- and laminin-binding fibres expressed by many natural Escherichia coli and E. coli K-12 strains in response to low temperature, low osmolarity and stationary-phase growth conditions. Curli expression is dependent on RpoS, a sigma factor that controls many stationary phase-inducible genes. Many commonly used K-12 strains carry an amber mutation in rpoS. Strains able to form curli carry an amber suppressor whereas curli-negative E. coli K-12 strains, in general, are sup0. Introduction of SupD, SupE, or supF suppressors into sup0 strains resulted in expression of temperature-regulated curli. In curli-deficient, RpoS- E. coli K-12 strains, csgA is transcriptionally activated by mutations in hns, which encodes the histone-like protein H-NS. Curli expression, fibronectin binding, and csgA transcription remain temperature- and osmoregulated in such double mutants. Our data suggest that RpoS+ strains, and hence curli-proficient strains of E. coli K-12, are relieved for the transcriptional repression mediated by the H-NS protein upon accumulating RpoS as cells reach stationary phase.