Interaction of uropathogenic Escherichia coli with host uroepithelium

Investigation into the pathogenesis of Escherichia coli urinary tract infection has provided numerous insights into the mechanisms by which bacteria adhere, grow and persist in association with host tissue. Many molecular details concerning the interaction of these bacteria with their host have been elucidated, and the murine model of cystitis has generated a new paradigm by which acute and recurrent urinary tract infections may proceed. These advances could potentially result in the development of novel vaccines and therapies for this very costly disease.     

Variation in endogenous oxidative stress in Escherichia coli natural isolates during growth in urine

ABSTRACT: BACKGROUND: Uropathogenic strains of Escherichia coli cause symptomatic infections whereas asymptomatic bacteriuria (ABU) strains are well adapted for growth in the human urinary tract, where they establish long-term bacteriuria. Human urine is a very complex growth medium that could be perceived by certain bacteria as a stressful environment. To investigate a possible imbalance between endogenous oxidative response and antioxidant mechanisms, lipid oxidative damage estimated as thiobarbituric acid reactive substances (TBARS) content was evaluated in twenty-one E. coli belonging to various pathovars and phylogenetic groups. Antioxidant defense mechanisms were also analysed. RESULTS: During exponential growth in urine, TBARS level differs between strains, without correlation with the ability to grow in urine which was similarly limited for commensal, ABU and uropathogenic strains. In addition, no correlation between TBARS level and the phylogroup or pathogenic group is apparent. The growth of ABU strain 83972 was associated with a high level of TBARS and more active antioxidant defenses that reduce the imbalance. CONCLUSIONS: Our results indicate that growth capacity in urine is not a property of ABU strains. However, E. coli isolates respond very differently to this stressful environment. In strain ABU 83972, on one hand, the increased level of endogenous reactive oxygen species may be responsible for adaptive mutations. On the other hand, a more active antioxidant defense system could increase the capacity to colonize the bladder.     

Fecal microbiota transplantation prevents Candida albicans from colonizing the gastrointestinal tract

Gut microbes symbiotically colonize the gastrointestinal (GI) tract, interacting with each other and their host to maintain GI tract homeostasis. Recent reports have shown that gut microbes help protect the gut from colonization by pathogenic microbes. Here, we report that commensal microbes prevent colonization of the GI tract by the pathogenic fungus, Candida albicans. Wild‐type specific pathogen‐free (SPF) mice are resistant to C. albicans colonization of the GI tract. However, administering certain antibiotics to SPF mice enables C. albicans colonization. Quantitative kinetics of commensal bacteria are inversely correlated with the number of C. albicans in the gut. Here, we provide further evidence that transplantation of fecal microbiota is effective in preventing Candida colonization of the GI tract. These data demonstrate the importance of commensal bacteria as a barrier for the GI tract surface and highlight the potential clinical applications of commensal bacteria in preventing pathogenic fungal infections.     

基因芯片在细菌基因组学和细胞微生物学研究中的应用

利用基因芯片可以鉴定病原菌在不同宿主微环境中受到差异调节的基因、直接或间接由转录因子控制的基因,以及编码多步骤代谢和生物合成途径中各种组分的基因;通过比较基因组学研究,评价相关菌种和菌株的自然群体内遗传多样性的范围和特性,并在ORF水平描述病原体和共生体之间的差异;同时也可进行感染组织细胞基因表达分析,研究病原体和宿主之间复杂的相互作用关系。     

Measurements of fitness and competition in commensal Escherichia coli and E. coli O157:H7 strains

Although the main reservoirs for pathogenic Escherichia coli O157:H7 are cattle and the cattle environment, factors that affect its tenure in the bovine host and its survival outside humans and cattle have not been well studied. It is also not understood what physiological properties, if any, distinguish these pathogens from commensal counterparts that live as normal members of the human and bovine gastrointestinal tracts. To address these questions, individual and competitive fitness experiments, indirect antagonism assays, and antibiotic resistance and carbon utilization analyses were conducted using a strain set consisting of 122 commensal and pathogenic strains. The individual fitness experiments, under four different environments (rich medium, aerobic and anaerobic; rumen medium, anaerobic; and a minimal medium, aerobic) revealed no differences in growth rates between commensal E. coli and E. coli O157:H7 strains. Indirect antagonism assays revealed that E. coli O157:H7 strains more frequently produced inhibitory substances than commensal strains did, under the conditions tested, although both groups displayed moderate sensitivity. Only minor differences were noted in the antibiotic resistance patterns of the two groups. In contrast, several differences between commensal and O157:H7 groups were observed based on their carbon utilization profiles. Of 95 carbon sources tested, 27 were oxidized by commensal E. coli strains but not by the E. coli O157:H7 strains. Despite the observed physiological and biochemical differences between these two groups of E. coli strains, however, the O157:H7 strains did not appear to possess traits that would confer advantages in the bovine or extraintestinal environment.     

Intergenic sequence comparison of Escherichia coli isolates reveals lifestyle adaptations but not host specificity

Establishing the risk of human infection is one of the goals of public health. For bacterial pathogens, the virulence and zoonotic potential can often be related to their host source. Escherichia coli bacteria are common contaminants of water associated with human recreation and consumption, and many strains are pathogenic. In this study, we analyzed three promoter-containing intergenic regions from 284 diverse E. coli isolates in an attempt to identify molecular signatures associated with specific host types. Promoter sequences controlling production of curli fimbriae, flagella, and nutrient import yielded a phylogenetic tree with isolates clustered by established phylogenetic grouping (A, B1, B2, and D) but not by host source. Virulence genes were more prevalent in groups B2 and D isolates and in human isolates. Group B1 isolates, primarily from nonhuman sources, were the most genetically similar, indicating that they lacked molecular adaptations to specific host environments and were likely host generalists. Conversely, B2 isolates, primarily from human sources, displayed greater genetic distances and were more likely to be host adapted. In agreement with these hypotheses, prevalence of σ(S) activity and the rdar morphotype, phenotypes associated with environmental survival, were significantly higher in B1 isolates than in B2 isolates. Based on our findings, we speculate that E. coli host specificity is not defined by genome-wide sequence changes but, rather, by the presence or absence of specific genes and associated promoter elements. Furthermore, the requirements for colonization of the human gastrointestinal tract may lead to E. coli lifestyle changes along with selection for increased virulence.     

The role of E. coli adhesiveness in the pathogenesis and clinical course of urinary tract infections]

An infection with E. coli is the most frequent cause of the urinary infections in childhood. Virulence depends on several factors out of which a principal role is played by the adhesion of bacteria to the urinary tract epithelium. Such a property have E. coli strains with adherence mannose-positive fimbriae of type P with antigens recognizing and binding glycolipid receptors on epithelial cells in the urinary tract. Children with such infections owe their "sensitivity+" (10% of the population) to genetically determined large number o receptors binding E. coli strains. Incidence and clinical course of the urinary tract infections have been analysed in the group of 184 children. Moreover, sequelae of the urinary tract infections with E. coli have been analysed in dependence on E. coli strain characteristics, i.e. presence or absence of adherent fimbriae from cases of cystitis and significant asymptomatic bacteriuria. Considering pathogenesis of the urinary tract infections as the result of interactions between bacteria and host, antigenic properties of adherent fimbriae might be used for preparation of a vaccine preventing such infections.     

Escherichia coli from animal reservoirs as a potential source of human extraintestinal pathogenic E. coli

Extraintestinal pathogenic Escherichia coli (ExPEC) are an important cause of urinary tract infections, neonatal meningitis and septicaemia in humans. Animals are recognized as a reservoir for human intestinal pathogenic E. coli, but whether animals are a source for human ExPEC is still a matter of debate. Pathologies caused by ExPEC are reported for many farm animals, especially for poultry, in which colibacillosis is responsible for huge losses within broiler chickens. Cases are also reported for companion animals. Commensal E. coli strains potentially carrying virulence factors involved in the development of human pathologies also colonize the intestinal tract of animals. This review focuses on the recent evidence of the zoonotic potential of ExPEC from animal origin and their potential direct or indirect transmission from animals to humans. As antimicrobials are commonly used for livestock production, infections due to antimicrobial-resistant ExPEC transferred from animals to humans could be even more difficult to treat. These findings, combined with the economic impact of ExPEC in the animal production industry, demonstrate the need for adapted measures to limit the prevalence of ExPEC in animal reservoirs while reducing the use of antimicrobials as much as possible.     

Rho GTPase-activating bacterial toxins: from bacterial virulence regulation to eukaryotic cell biology

Studies on the interactions of bacterial pathogens with their host have provided an invaluable source of information on the major functions of eukaryotic and prokaryotic cell biology. In addition, this expanding field of research, known as cellular microbiology, has revealed fascinating examples of trans-kingdom functional interplay. Bacterial factors actually exploit eukaryotic cell machineries using refined molecular strategies to promote invasion and proliferation within their host. Here, we review a family of bacterial toxins that modulate their activity in eukaryotic cells by activating Rho GTPases and exploiting the ubiquitin/proteasome machineries. This family, found in human and animal pathogenic Gram-negative bacteria, encompasses the cytotoxic necrotizing factors (CNFs) from Escherichia coli and Yersinia species as well as dermonecrotic toxins from Bordetella species. We survey the genetics, biochemistry, molecular and cellular biology of these bacterial factors from the standpoint of the CNF1 toxin, the paradigm of Rho GTPase-activating toxins produced by urinary tract infections causing pathogenic Escherichia coli. Because it reveals important connections between bacterial invasion and the host inflammatory response, the mode of action of CNF1 and its related Rho GTPase-targetting toxins addresses major issues of basic and medical research and constitutes a privileged experimental model for host-pathogen interaction.     

Importance of the Candida albicans cell wall during commensalism and infection

An imbalance of the normal microbial flora, breakage of epithelial barriers or dysfunction of the immune system favour the transition of the human pathogenic yeast Candida albicans from a commensal to a pathogen. C. albicans has evolved to be adapted as a commensal on mucosal surfaces. As a commensal it has also acquired attributes, which are necessary to avoid or overcome the host defence mechanisms. The human host has also co-evolved to recognize and eliminate potential fungal invaders. Many of the fungal genes that have been the focus of this co-evolutionary process encode cell wall components. In this review, we will discuss the transition from commensalism to pathogenesis, the key players of the fungal cell surface that are important for this transition, the role of the morphology and the mechanisms of host recognition and response.     

Lack of the RNA chaperone Hfq attenuates pathogenicity of several Escherichia coli pathotypes towards Caenorhabditis elegans

Escherichia coli is an important agent of Gram-negative bacterial infections worldwide, being one of the leading causes of diarrhoea and urinary tract infections. Strategies to understand pathogenesis and develop therapeutic compounds include the use of the nematode Caenorhabditis elegans as a model for virulence characterization and screening for novel antimicrobial entities. Several E. coli human pathotypes are also pathogenic towards C. elegans, and we show here that lack of the RNA chaperone Hfq significantly reduces pathogenicity of VTEC, EAEC, and UPEC in the nematode model. Thus, Hfq is intrinsically essential to pathogenic E. coli for survival and virulence exerted in the C. elegans host.     

人体泌尿系微生物感染与耐药及宿主状态分析

目的了解泌尿系感染常见病原细菌和真菌分布、耐药性及宿主相关状态,为理解相关微生物感染影响因素及临床合理用药提供资料和依据。方法对门诊及住院患者中段尿培养分离的179株病原细菌和真菌进行微生物学鉴定和K-B法药敏试验,同时记录门诊和住院的菌株相关的泌尿系感染患者情况。结果泌尿系感染微生物以大肠埃希菌居首位,占62.4%,其次为真菌和肠球菌,各占12.4%、14.0%。药敏结果显示,大肠埃希菌产ESBLs占62.2%;肠杆菌科细菌对亚胺培南、美罗培南的敏感率为100%,其次敏感性较好的为氨基糖苷类阿米卡星、头孢头霉类头孢西丁及第三代头孢类头孢哌酮/舒巴坦、头孢他啶,敏感率均大于80%。革兰阳性球菌万古霉素敏感率为100%,对呋喃妥因敏感率为70.8%。大肠埃希菌感染率与患者的身体状态和行为具有显著的相关性(P<0.01)。结论革兰阴性杆菌是泌尿系感染的主要病原菌,机体免疫状态低下、不洁等生活行为与尿路微生物感染密切相关,但与耐药性不相关。维护机体正常免疫力、注意合适的生活行为,对预防泌尿道病原细菌与真菌的感染十分重要。     

Neisseria genes required for persistence identified via in vivo screening of a transposon mutant library

The mechanisms used by human adapted commensal Neisseria to shape and maintain a niche in their host are poorly defined. These organisms are common members of the mucosal microbiota and share many putative host interaction factors with Neisseria meningitidis and Neisseria gonorrhoeae. Evaluating the role of these shared factors during host carriage may provide insight into bacterial mechanisms driving both commensalism and asymptomatic infection across the genus. We identified host interaction factors required for niche development and maintenance through in vivo screening of a transposon mutant library of Neisseria musculi, a commensal of wild-caught mice which persistently and asymptomatically colonizes the oral cavity and gut of CAST/EiJ and A/J mice. Approximately 500 candidate genes involved in long-term host interaction were identified. These included homologs of putative N. meningitidis and N. gonorrhoeae virulence factors which have been shown to modulate host interactions in vitro. Importantly, many candidate genes have no assigned function, illustrating how much remains to be learned about Neisseria persistence. Many genes of unknown function are conserved in human adapted Neisseria species; they are likely to provide a gateway for understanding the mechanisms allowing pathogenic and commensal Neisseria to establish and maintain a niche in their natural hosts. Validation of a subset of candidate genes confirmed a role for a polysaccharide capsule in N. musculi persistence but not colonization. Our findings highlight the potential utility of the Neisseria musculi-mouse model as a tool for studying the pathogenic Neisseria; our work represents a first step towards the identification of novel host interaction factors conserved across the genus.     

The intestinal flora: the scales without the sword

The intestine is colonised by a vast population of resident bacteria which have established mutualistic relationships with their host throughout evolution, progressing from commensalism to symbiotic interactions. Intestinal bacteria benefit from resources available in their host, but reciprocally provide advantages to their host, by supplying enzymatic activities not encoded in the host genome, by promoting maturation of the intestine and of the gut associated immune system as well as by modifying the host metabolism. The commensal bacteria, although deprived of pathogenic attributes, might however become a danger for the host in case of translocation, acquisition of pathogenic features or via the inappropriate activation of intestinal inflammation. Remarkably, the commensal flora promotes the onset of innate and adaptive immune defences which, in turn, allow to set up a subtle balance between the host and the flora that promotes the symbiosis.     

A role for IL-22 in the relationship between intestinal helminths,gut microbiota and mucosal immunity

The intestinal tract is home to nematodes as well as commensal bacteria (microbiota), which have coevolved with the mammalian host. The mucosal immune system must balance between an appropriate response to dangerous pathogens and an inappropriate response to commensal microbiota that may breach the epithelial barrier, in order to maintain intestinal homeostasis. IL-22 has been shown to play a critical role in maintaining barrier homeostasis against intestinal pathogens and commensal bacteria. Here we review the advances in our understanding of the role of IL-22 in helminth infections, as well as in response to commensal and pathogenic bacteria of the intestinal tract. We then consider the relationship between intestinal helminths and gut microbiota and hypothesize that this relationship may explain how helminths may improve symptoms of inflammatory bowel diseases. We propose that by inducing an immune response that includes IL-22, intestinal helminths may enhance the mucosal barrier function of the intestinal epithelium. This may restore the mucosal microbiota populations from dysbiosis associated with colitis and improve intestinal homeostasis.     

Ecological implications of the reproductive biology of symbiotic nemerteans

A major problem for parasites is to ensure that offspring will reach a correct host. Responses to this problem include several reproductive adaptations. This review paper shows that Carcinonemertes has several such adaptations, including increased number of gonads and offspring, synchrony of hatching with host larval hatching, facultative parthenogenesis, and mating. Other nemerteans show different, but comparably adaptive, reproductive modifications for parasitism. In contrast, reproductive biology of the commensal Malacobdella resembles that of free-living nemerteans, being timed to coincide with plankton blooms that are food for settling young.It has been thought that nemerteans found in association with other animals usually have only causal relationships with those animals, and that actual parasitism is rare among nemerteans. However, it is being found that parasitism is both well developed and more common among nemerteans than was previously thought. Nemerteas show in their reproductive biology that they are adapted to the selective factors that are important in their ways of life, and we should be able to predict the life styles of these worms by knowing their reproductive ecology.     

Escherichia coli-induced epithelial hyporesponsiveness to secretagogues is associated with altered CFTR localization

Both pathogenic and commensal strains of Escherichia coli colonize the human intestinal tract. Pathogenic strains differ only in the expression of virulence factors, many of which comprise a type III secretion system (TTSS). Little is known regarding the effect of E. coli on the intestinal epithelial response to the secretagogues that drive ion secretion, despite its importance in causing clinically significant diarrhoea. Using Ussing chambers to measure electrogenic ion transport of T84 intestinal epithelial cell monolayers, we found that all strains of E. coli tested (pathogenic, commensal, probiotic and lab strain) significantly reduced cAMP-dependent ion secretion after 4-8 h exposure. Enteropathogenic E. coli mutants lacking a functional TTSS caused similar hyposecretion while not causing significant apoptosis (as shown by caspase-3 cleavage) or necrosis (lactate dehydrogenase release), as did the commensal strain F18, indicating that epithelial cell death was not the cause of hyposecretion. Enteropathogenic E. coli and the TTSS mutant significantly reduced cell surface expression of the apical anion channel, cystic fibrosis transmembrane conductance regulator, which is likely the mechanism behind the pathogen-induced hyposecretion. However, F18 did not cause cystic fibrosis transmembrane conductance regulator mislocalization and the commensal-induced mechanism remains unclear.     

Proteomic analysis of Escherichia coli associated with urinary tract infections

Escherichia coli is a major cause of urinary tract infections (UTIs) where the initial infection arises from bacteria originating in the bowel. However, significant differences are observed between the genomes of intestinal and urinary E. coli strains with the latter possessing many adaptations that promote growth in the urinary tract. To define further the adaptation of urinary E. coli isolates, the cellular proteomes of 41 E. coli strains, collected from cases of UTIs or random faecal samples, were compared by 2-D gel electrophoresis and principal component analysis. The data indicated that individual patients carried relatively homogenous E. coli populations, as defined by their cellular proteomes, but the populations were distinct between patients. For one patient, E. coli, isolated during two recurrent infections 3 months apart, were indistinguishable, indicating that for this patient the infections were possibly caused by the same bacterial population. To understand the basis of the discrimination of the bacteria, selected protein spots were identified by peptide fragment fingerprinting. The identified proteins were involved in a variety of metabolic and structural roles. The data obtained for these E. coli strains provide a basis from which to target key bacterial proteins for further investigation into E. coli pathogenesis.     

泌尿系感染病原菌分布及耐药性分析

目的了解深圳市人民医院泌尿系感染病原菌的分布及耐药性,为临床医师合理使用抗菌药物提供科学依据。方法对655株泌尿系统感染病原菌进行常规鉴定,用k-B法或ATB-FUNGUS 3对其进行药敏试验。结果病原菌构成比前5位分别为大肠埃希菌（37.9%）、假丝酵母（18.0%）、肠球菌（13.1%）、肺炎克雷伯菌（6.6%）、铜绿假单胞菌（6.3%）。病原菌对各种抗菌药物产生了不同程度的耐药,肺炎克雷伯菌、铜绿假单胞菌对亚胺培南和美罗培南的耐药率为14.3%～26.8%。结论深圳市人民医院泌尿系感染病原菌主要以大肠埃希菌、假丝酵母和肠球菌等为主,病原菌对抗菌药物已产生了一定的耐药性,应加强监测与控制。     

Autotransporter-encoding sequences are phylogenetically distributed among Escherichia coli clinical isolates and reference strains

Autotransporters are secreted bacterial proteins exhibiting diverse virulence functions. Various autotransporters have been identified among Escherichia coli associated with intestinal or extraintestinal infections; however, the specific distribution of autotransporter sequences among a diversity of E. coli strains has not been investigated. We have validated the use of a multiplex PCR assay to screen for the presence of autotransporter sequences. Herein, we determined the presence of 13 autotransporter sequences and five allelic variants of antigen 43 (Ag43) among 491 E. coli isolates from human urinary tract infections, diarrheagenic E. coli, and avian pathogenic E. coli (APEC) and E. coli reference strains belonging to the ECOR collection. Clinical isolates were also classified into established phylogenetic groups. The results indicated that Ag43 alleles were significantly associated with clinical isolates (93%) compared to commensal isolates (56%) and that agn43K12 was the most common and widely distributed allele. agn43 allelic variants were also phylogenetically distributed. Sequences encoding espC, espP, and sepA and agn43 alleles EDL933 and RS218 were significantly associated with diarrheagenic E. coli strains compared to other groups. tsh was highly associated with APEC strains, whereas sat was absent from APEC. vat, sat, and pic were associated with urinary tract isolates and were identified predominantly in isolates belonging to either group B2 or D of the phylogenetic groups based on the ECOR strain collection. Overall, the results indicate that specific autotransporter sequences are associated with the source and/or phylogenetic background of strains and suggest that, in some cases, autotransporter gene profiles may be useful for comparative analysis of E. coli strains from clinical, food, and environmental sources.