Expression of CFA/I fimbriae is positively regulated

Evaluation of targeting αVβ3 in breast cancers using RGD peptide-based agents

Patients with HER2-positive and triple negative breast cancer (TNBC) are associated with increased risk to develop metastatic disease including reoccurring disease that is resistant to standard and targeted therapies. The αVβ3 has been implicated in BC including metastatic disease. The aims of this study were to investigate the potential of αVβ3-targeted peptides to deliver radioactive payloads to BC tumors expressing αVβ3 on the tumor cells or limited to the tumors' neovascular. Additionally, we aimed to assess the pharmacokinetic profile of the targeted α-particle therapy (TAT) agent [225Ac]Ac-DOTA-cRGDfK dimer peptide and the in vivo generated decay daughters. The expression of αVβ3 in a HER2-positive and a TNBC cell line were evaluated using western blot analysis. The pharmacokinetics of [111In]In-DOTA-cRGDfK dimer, a surrogate for the TAT-agent, was evaluated in subcutaneous mouse tumor models. The pharmacokinetic of the TAT-agent [225Ac]Ac-DOTA-cRGDfK dimer and its decay daughters were evaluated in healthy mice. Selective uptake of [111In]In-DOTA-cRGDfK dimer was shown in subcutaneous tumor models using αVβ3-positive tumor cells as well as αVβ3-negative tumor cells where the expression is limited to the neovasculature. Pharmacokinetic studies demonstrated rapid accumulation in the tumors with clearance from non-target organs. Dosimetric analysis of [225Ac]Ac-DOTA-cRGDfK dimer showed the highest radiation absorbed dose to the kidneys, which included the contributions from the free in vivo generated decay daughters. This study shows the potential of delivering radioactive payloads to BC tumors that have αVβ3 expression on the tumor cells as well as limited expression to the neovascular of the tumor. Furthermore, this work determines the radiation absorbed doses to normal organs/tissues and identified key organs that act as suppliers and receivers of the actinium-225 free in vivo generated α-particle-emitting decay daughters.

Designing and determining immunogenicity of a recombinant protein due to producing a new vaccine against Enterotoxigenic Escherichia coli containing CfaE and CotD subunits

Enterotoxigenic Escherichia coli (ETEC) is one of the most common bacterial causes of mortalities in developing countries due to diarrhea. Since mucosal immune responses to CFs can prevent the disease, a chimeric protein containing ETEC's CFA/I (CfaE) tip subunits and CS2 (CotD) sub-structural units is developed to produce effective vaccine. Using bioinformatics tools, the chimeric construct was analyzed and then the optimized gene was synthesized and expressed in E. coli. The recombinant protein was expressed and purified by the Ni-NTA chromatography column and confirmed by anti-his tag antibody by western blotting. Mice were immunized with recombinant protein, and the IgG and IgA antibodies' titrations of the sera were analyzed by ELISA. In addition, the immunogenicity and protective efficacy against the live ETEC bacteria in the challenge test were determined. Western blot analysis verified the chimeric protein expression of CotD-CfaE. The outcome of ELISA was a substantial improvement in the IgG antibody titer in immunized mice. In a live ETEC challenge, the survival percentage of 30% was shown for immunized mice. The developed recombinant chimeric protein could be suggested as an effective component in producing an efficient vaccine against Enterotoxigenic E. coli with other crucial subunits, different immunization route, and other factors.

Molecular determinants of surface colonisation in diarrhoeagenic Escherichia coli (DEC): from bacterial adhesion to biofilm formation

Escherichia coli is primarily known as a commensal colonising the gastrointestinal tract of infants very early in life but some strains being responsible for diarrhoea, which can be especially severe in young children. Intestinal pathogenic E. coli include six pathotypes of diarrhoeagenic E. coli (DEC), namely, the (i) enterotoxigenic E. coli, (ii) enteroaggregative E. coli, (iii) enteropathogenic E. coli, (iv) enterohemorragic E. coli, (v) enteroinvasive E. coli and (vi) diffusely adherent E. coli. Prior to human infection, DEC can be found in natural environments, animal reservoirs, food processing environments and contaminated food matrices. From an ecophysiological point of view, DEC thus deal with very different biotopes and biocoenoses all along the food chain. In this context, this review focuses on the wide range of surface molecular determinants acting as surface colonisation factors (SCFs) in DEC. In the first instance, SCFs can be broadly discriminated into (i) extracellular polysaccharides, (ii) extracellular DNA and (iii) surface proteins. Surface proteins constitute the most diverse group of SCFs broadly discriminated into (i) monomeric SCFs, such as autotransporter (AT) adhesins, inverted ATs, heat-resistant agglutinins or some moonlighting proteins, (ii) oligomeric SCFs, namely, the trimeric ATs and (iii) supramolecular SCFs, including flagella and numerous pili, e.g. the injectisome, type 4 pili, curli chaperone-usher pili or conjugative pili. This review also details the gene regulatory network of these numerous SCFs at the various stages as it occurs from pre-transcriptional to post-translocational levels, which remains to be fully elucidated in many cases.

Pili Assembled by the Chaperone/Usher Pathway in Escherichia coli and Salmonella

Gram-negative bacteria assemble a variety of surface structures, including the hair-like organelles known as pili or fimbriae. Pili typically function in adhesion and mediate interactions with various surfaces, with other bacteria, and with other types of cells such as host cells. The chaperone/usher (CU) pathway assembles a widespread class of adhesive and virulence-associated pili. Pilus biogenesis by the CU pathway requires a dedicated periplasmic chaperone and integral outer membrane protein termed the usher, which forms a multifunctional assembly and secretion platform. This review addresses the molecular and biochemical aspects of the CU pathway in detail, focusing on the type 1 and P pili expressed by uropathogenic Escherichia coli as model systems. We provide an overview of representative CU pili expressed by E. coli and Salmonella, and conclude with a discussion of potential approaches to develop antivirulence therapeutics that interfere with pilus assembly or function.

Virulence Gene Regulation in Escherichia coli

Escherichia colicauses three types of illnesses in humans: diarrhea, urinary tract infections, and meningitis in newborns. The acquisition of virulence-associated genes and the ability to properly regulate these, often horizontally transferred, loci distinguishes pathogens from the normally harmless commensal E. coli found within the human intestine. This review addresses our current understanding of virulence gene regulation in several important diarrhea-causing pathotypes, including enteropathogenic, enterohemorrhagic,enterotoxigenic, and enteroaggregativeE. coli-EPEC, EHEC, ETEC and EAEC, respectively. The intensely studied regulatory circuitry controlling virulence of uropathogenicE. coli, or UPEC, is also reviewed, as is that of MNEC, a common cause of meningitis in neonates. Specific topics covered include the regulation of initial attachment events necessary for infection, environmental cues affecting virulence gene expression, control of attaching and effacing lesionformation, and control of effector molecule expression and secretion via the type III secretion systems by EPEC and EHEC. How phage control virulence and the expression of the Stx toxins of EHEC, phase variation, quorum sensing, and posttranscriptional regulation of virulence determinants are also addressed. A number of important virulence regulators are described, including the AraC-like molecules PerA of EPEC, CfaR and Rns of ETEC, and AggR of EAEC;the Ler protein of EPEC and EHEC;RfaH of UPEC;and the H-NS molecule that acts to silence gene expression. The regulatory circuitry controlling virulence of these greatly varied E. colipathotypes is complex, but common themes offerinsight into the signals and regulators necessary forE. coli disease progression.

Virulence Gene Regulation in Shigella

Shigella species are the causative agents of bacillary dysentery in humans, an invasive disease in which the bacteria enter the cells of the epithelial layer of the large intestine, causing extensive tissue damage and inflammation. They rely on a plasmid-encoded type III secretion system (TTSS) to cause disease; this system and its regulation have been investigated intensively at the molecular level for decades. The lessons learned have not only deepened our knowledge of Shigella biology but also informed in important ways our understanding of the mechanisms used by other pathogenic bacteria to cause disease and to control virulence gene expression. In addition, the Shigella story has played a central role in the development of our appreciation of the contribution of horizontal DNA transfer to pathogen evolution.A 30-kilobase-pair "Entry Region" of the 230-kb virulence plasmid lies at the heart of the Shigella pathogenesis system. Here are located the virB and mxiE regulatory genes and most of the structural genes involved in the expression of the TTSS and its effector proteins. Expression of the virulence genes occurs in response to an array of environmental signals, including temperature, osmolarity, and pH.At the top of the regulatory hierarchy and lying on the plasmid outside the Entry Region isvirF, encoding an AraC-like transcription factor.Virulence gene expression is also controlled by chromosomal genes,such as those encoding the nucleoid-associated proteins H-NS, IHF, and Fis, the two-component regulators OmpR/EnvZ and CpxR/CpxA, the anaerobic regulator Fnr, the iron-responsive regulator Fur, and the topoisomerases of the cell that modulate DNA supercoiling. Small regulatory RNAs,the RNA chaperone Hfq,and translational modulation also affect the expression of the virulence phenotypetranscriptionally and/orposttranscriptionally.

Colonization factors of enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) is a major cause of life-threatening diarrheal disease around the world. The major aspects of ETEC virulence are colonization of the small intestine and the secretion of enterotoxins which elicit diarrhea. Intestinal colonization is mediated, in part, by adhesins displayed on the bacterial cell surface. As colonization of the intestine is the critical first step in the establishment of an infection, it represents a potential point of intervention for the prevention of infections. Therefore, colonization factors (CFs) have been important subjects of research in the field of ETEC virulence. Research in this field has revealed that ETEC possesses a large array of serologically distinct CFs that differ in composition, structure, and function. Most ETEC CFs are pili (fimbriae) or related fibrous structures, while other adhesins are simple outer membrane proteins lacking any macromolecular structure. This chapter reviews the genetics, structure, function, and regulation of ETEC CFs and how such studies have contributed to our understanding of ETEC virulence and opened up potential opportunities for the development of preventive and therapeutic interventions.

Distribution of IS91 family insertion sequences in bacterial genomes: evolutionary implications

IS91 is the prototype element of a family of bacterial insertion sequences that transpose by a rolling-circle mechanism. Although previously considered a rarity among IS elements, many new examples have been identified by sequence analysis of bacterial genomes. In this work we provide a summary of occurrences of IS91-like sequences in the GenBank database, characterise the genetic organisation of adjacent sequences, and analyse IS91 ecological significance under the light of current transposition mechanisms. Interestingly, IS91 family elements were usually found adjacent to pathogenicity- and virulence-related genes. Thus, this might constitute the niche for IS91 and IS91 family elements to play an important role in the dissemination and evolution of virulence and pathogenicity types of genes.

Role of overexpressed CFA/I fimbriae in bacterial swimming

Enterotoxigenic Escherichia coli CFA/I is a protective antigen and has been overexpressed in bacterial vectors, such as Salmonella Typhimurium H683, to generate vaccines. Effects that overexpressed CFA/I may engender on the bacterial host remain largely unexplored. To investigate, we constructed a high CFA/I expression strain, H683-pC2, and compared it to a low CFA/I expression strain, H683-pC, and to a non-CFA/I expression strain, H683-pY. The results showed that H683-pC2 was less able to migrate into semisolid agar (0.35%) than either H683-pC or H683-pY. Bacteria that migrated showed motility halo sizes of H683-pC2 < H683-pC < H683-pY. In the liquid culture media, H683-pC2 cells precipitated to the bottom of the tube, while those of H683-pY did not. In situ imaging revealed that H683-pC2 bacilli tended to auto-agglutinate within the semisolid agar, while H683-pY bacilli did not. When the cfaBE fimbrial fiber encoding genes were deleted from pC2, the new plasmid, pC2(-), significantly recovered bacterial swimming capability. Our study highlights the negative impact of overexpressed CFA/I fimbriae on bacterial swimming motility.

The complete nucleotide sequence of region 1 of the CFA/I fimbria! operon of human enterotoxigenicEscherichia coli

The production of the plasmid-encoded fimbrial antigen CFA/I of enterotoxigenic Escherichia coli requires two DNA regions: CFA/I region 1 and CFA/I region 2. These two regions are separated by about 40 kb on the wildtype plasmid. CFA/I region 1 contains the structural genes, whereas CFA/I region 2 contains a positive regulator. The first two genes (cfaA and cfaB) and the cfaD' sequence of region 1 have already been described. Here the total nucleotide sequence of region 1 is presented. Two new genes in region 1 are described, named cfaC and cfaE. The GC content of the genes in region 1 is 33.6% which is substantially lower than normally found in E. coli genes (50%). The codon usage also differs from the standard codons used in E. coli.

CfaD-dependent expression of a novel extracytoplasmic protein from enterotoxigenic Escherichia coli

H10407 is a strain of enterotoxigenic Escherichia coli (ETEC) that utilizes CFA/I pili to adhere to surfaces of the small intestine, where it elaborates toxins that cause profuse watery diarrhea in humans. Expression of the CFA/I pilus is positively regulated at the level of transcription by CfaD, a member of the AraC/XylS family. DNase I footprinting revealed that the activator has two binding sites upstream of the pilus promoter cfaAp. One site extends from positions -23 to -56, and the other extends from positions -73 to -103 (numbering relative to the transcription start site of cfaAp). Additional CfaD binding sites were predicted within the genome of H10407 by computational analysis. Two of these sites lie upstream of a previously uncharacterized gene, cexE. In vitro DNase I footprinting confirmed that both sites are genuine binding sites, and cexEp::lacZ reporters demonstrated that CfaD is required for the expression of cexE in vivo. The amino terminus of CexE contains a secretory signal peptide that is removed during translocation across the cytoplasmic membrane through the general secretory pathway. These studies suggest that CexE may be a novel ETEC virulence factor because its expression is controlled by the virulence regulator CfaD, and its distribution is restricted to ETEC.

Repression of the inner membrane lipoprotein NlpA by Rns in enterotoxigenic Escherichia coli

The expression of the inner membrane protein NlpA is repressed by the enterotoxigenic Escherichia coli (ETEC) virulence regulator Rns, a member of the AraC/XylS family. The Rns homologs CfaD from ETEC and AggR from enteroaggregative E. coli also repress expression of nlpA. In vitro DNase I and potassium permanganate footprinting revealed that Rns binds to a site overlapping the start codon of nlpA, preventing RNA polymerase from forming an open complex at nlpAp. A second Rns binding site between positions -152 and -195 relative to the nlpA transcription start site is not required for repression. NlpA is not essential for growth of E. coli under laboratory conditions, but it does contribute to the biogenesis of outer membrane vesicles. As outer membrane vesicles have been shown to contain ETEC heat-labile toxin, the repression of nlpA may be an indirect mechanism through which the virulence regulators Rns and CfaD limit the release of toxin.

Linker regions of the RhaS and RhaR proteins

Substitutions within the interdomain linkers of the AraC/XylS family proteins RhaS and RhaR were tested to determine whether side chain identity or linker structure was required for function. Neither was found crucial, suggesting that the linkers do not play a direct role in activation, but rather simply connect the two domains.

CooB is required for assembly but not transport of CS1 pilin

CS1 pili are filamentous proteinaceous appendages found on many enterotoxigenic Escherichia coli (ETEC) strains isolated from human diarrhoeal disease. They are thought to effect colonization of the upper intestine by facilitating binding to human ileal epithelial cells. We have identified a gene, cooB, which lies directly upstream of cooA, the gene that encodes the major structural CS1 protein. When translated in vitro, the protein product of cooB migrates in sodium dodecyl sulphate/polyacrylamide gel with an apparent molecular mass of 26 kDa, which is consistent with that predicted from its DNA sequence. We constructed a mutant allele (cooB-1) by insertion of the omega fragment, which inhibits transcription and translation, into the cooB gene in vitro. In a derivative of an ETEC strain with the cooB-1 mutation (JEF100) and a plasmid that encodes Rns (pEU2030), the positive regulator required for CS1 expression, no cooB and a greatly reduced level of cooA product was detectable in total cell extracts. The reduction of cooA in this strain appears to result from polarity of the cooB mutation because introduction of the wild-type cooA gene in trans causes production of CooA protein, which is found in cell pellet extracts, in extracts containing only surface proteins and in the culture supernatant. Therefore, in the absence of CooB, CooA is stable and it is transported through both inner and outer membranes. However, the cooB-1 strain with cooA in trans does not cause haemagglutination of bovine erythrocytes (the model system used to assay adherence mediated by coli surface antigen 1 (CS1) pili).(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of enterotoxigenic Escherichia coli colonization factors in Vibrio cholerae

As a first step towards a vaccine against diarrhoeal disease caused by enterotoxigenic Escherichia coli (ETEC), we have studied the expression of several ETEC antigens in the live attenuated Vibrio cholerae vaccine strain CVD 103-HgR. Colonization factors (CF) CFA/I, CS3, and CS6 were expressed at the surface of V. cholerae CVD 103-HgR. Both CFA/I and CS3 required the co-expression of a positive regulator for expression, while CS6 was expressed without regulation. Up-regulation of CF expression in V. cholerae was very efficient, so that high amounts of CFA/I and CS3 similar to those in wild-type ETEC were synthesized from chromosomally integrated CF and positive regulator loci. Increasing either the operon and/or the positive regulator gene dosage resulted in only a small increase in CFA/I and CS3 expression. In contrast, the level of expression of the non-regulated CS6 fimbriae appeared to be more dependent on gene dosage. While CF expression in wild-type ETEC is known to be tightly thermoregulated and medium dependent, it seems to be less stringent in V. cholerae. Finally, co-expression of two or three CFs in the same strain was efficient even under the control of one single regulator gene.

Construction and characterization of bivalent Shigella flexneri 2a vaccine strains SC608(pCFAI) and SC608(pCFAI/LTB) that express antigens from enterotoxigenic Escherichia coli

An invasive strain of Shigella flexneri 2a (SC608) has been developed as a vector for the expression and delivery of heterologous antigens. SC608 is an aspartate semialdehyde dehydrogenase (asd) derivative of SC602 (icsA iuc), a well-characterized live attenuated vaccine strain which has undergone several clinical trials in human volunteers. When administered orally at a single 10(4) (CFU) dose, SC602 is both immunogenic and efficacious against shigellosis. Using asd-based plasmid vectors, we designed SC608 to express the enterotoxigenic Escherichia coli (ETEC) fimbrial subunit CfaB (CFA/I structural subunit) alone or in combination with the E. coli B subunit of heat-labile enterotoxin (LTB). The expression of each heterologous protein in SC608 was verified by immunoblot analysis. Each strain was comparable to the parent strain, SC602, in a HeLa cell invasion assay. After intranasal immunizations of guinea pigs, serum and mucosal immune responses were detected against both Shigella lipopolysaccharide and heterologous ETEC antigens by enzyme-linked immunosorbent assay and ELISPOT analysis. All immunized animals were subsequently protected against a challenge with wild-type S. flexneri 2a in a keratoconjunctivitis Sereny test. Serum antibodies generated against LTB and CfaB demonstrated antitoxin and agglutination activities, respectively. These results suggest that CfaB and LTB expressed in SC608 retain important conformational epitopes that are required for the generation of antibodies that have functional activities. These initial experiments demonstrate that a fully invasive Shigella vaccine strain can be engineered to deliver antigens from other diarrheal pathogens.

Genomic interrogation of the dassie bacillus reveals it as a unique RD1 mutant within the Mycobacterium tuberculosis complex

Despite their remarkable genetic homology, members of the Mycobacterium tuberculosis complex express very different phenotypes, most notably in their spectra of clinical presentation. For example, M. tuberculosis is regarded as pathogenic to humans, whereas members having deleted RD1, such as Mycobacterium microti and Mycobacterium bovis BCG, are not. The dassie bacillus, an infrequent variant of the M. tuberculosis complex characterized as being most similar to M. microti, is the causative agent of tuberculosis (TB) in the dassie (Procavia capensis). Intriguingly, the dassie bacillus is not pathogenic to rabbits or guinea pigs and has never been documented to infect humans. Although it was identified more than a half-century ago, the reasons behind its attenuation are unknown. Because large sequence polymorphisms have presented themselves as the most obvious genomic distinction among members of the M. tuberculosis complex, the DNA content of the dassie bacillus was interrogated by Affymetrix GeneChip to identify regions that are absent from it but present in M. tuberculosis H37Rv. Comparison has led to the identification of nine regions of difference (RD), five of which are shared with M. microti (RDs 3, 7, 8, 9, and 10). Although the dassie bacillus does not share the other documented deletions in M. microti (RD1(mic), RD5(mic), MID1, MID2, and MID3), it has endured unique deletions in the regions of RD1, RD5, N-RD25, and Rv3081-Rv3082c (virS). RD1(das), affecting only Rv3874-Rv3877, is the smallest natural deletion of the RD1 region uncovered and points to genes within this region that are likely implicated in virulence. Newfound deletions from the dassie bacillus are discussed in relation to their evolutionary and biological significance.

Phase variation of the 987P-like CS18 fimbriae of human enterotoxigenic Escherichia coli is regulated by site-specific recombinases

The gene cluster of the CS18 (PCFO20) fimbriae of human enterotoxigenic Escherichia coli (ETEC) was found to include seven genes (fotA to fotG) that are similar to each of the seven structural and export proteins of the 987P fimbriae. However, no analogous gene to the fasH regulatory gene, which is located at the 3' end of the 987P gene cluster and encodes an AraC-like activator of transcription, could be detected. Surprisingly, two novel genes (fotS and fotT) encoding proteins similar to the site-specific recombinases of the type 1 fimbriae (FimB and FimE) were identified at the 5' end of the fot gene cluster. These genes were shown to be required for the catalysis of a 312 bp-inversion just upstream of fotA. The inversion determines CS18 fimbrial phase variation. FotS participates in inverting the 312 bp-segment in both the ON and OFF orientation, whereas FotT has a bias for the OFF oriented recombination. Similar regulators of fimbriation by phase variation were described in uropathogenic and commensal Enterobacteriaceae. In contrast, only AraC-like transcriptional activators were previously described as regulators of the intestinal colonization factors of human ETEC isolates. Thus, the CS18 and 987P gene clusters encode similar components for fimbrial biogenesis but different types of regulators for fimbriation. The combination of blocks of genes encoding similar structural products but different regulatory proteins underlines how modular DNA rearrangements can evolve by serving pathogen diversification. Acquisition of a phase variation module to regulate fimbrial genes is proposed to be beneficial for the adaptation and transmission of pathogens.

Genetic characterization and immunogenicity of coli surface antigen 4 from enterotoxigenic Escherichia coli when it is expressed in a Shigella live-vector strain

The genes that encode the enterotoxigenic Escherichia coli (ETEC) CS4 fimbriae, csaA, -B, -C, -E, and -D', were isolated from strain E11881A. The csa operon encodes a 17-kDa major fimbrial subunit (CsaB), a 40-kDa tip-associated protein (CsaE), a 27-kDa chaperone-like protein (CsaA), a 97-kDa usher-like protein (CsaC), and a deleted regulatory protein (CsaD'). The predicted amino acid sequences of the CS4 proteins are highly homologous to structural and assembly proteins of other ETEC fimbriae, including CS1 and CS2, and to CFA/I in particular. The csaA, -B, -C, -E operon was cloned on a stabilized plasmid downstream from an osomotically regulated ompC promoter. pGA2-CS4 directs production of CS4 fimbriae in both E. coli DH5alpha and Shigella flexneri 2a vaccine strain CVD 1204, as detected by Western blot analysis and bacterial agglutination with anti-CS4 immune sera. Electron-microscopic examination of Shigella expressing CS4 confirmed the presence of fimbriae on the bacterial surface. Guinea pigs immunized with CVD 1204(pGA2-CS4) showed serum and mucosal antibody responses to both the Shigella vector and the ETEC fimbria CS4. Among the seven most prevalent fimbrial antigens of human ETEC, CS4 is the last to be cloned and sequenced. These findings pave the way for CS4 to be included in multivalent ETEC vaccines, including an attenuated Shigella live-vector-based ETEC vaccine.

Clonal clustering and colonization factors among thermolabile and porcine thermostable enterotoxin-producing Escherichia coli

A considerable proportion of enterotoxigenic Escherichia coli (ETEC) do not possess identifiable colonization factors (CFs). Genetic fingerprint analyses based on repetitive sequence-based polymerase chain reaction (rep-PCR) showed that 9 of 10 such CF-negative isolates which produced the thermolabile and the porcine thermostabile enterotoxin could be divided into three clusters. Following transformation with a plasmid harbouring the gene encoding CfaR, a positive regulator for several ETEC adhesins, three of the six strains in the first cluster expressed coli surface antigen 20 (CS20). No CFs were identified on the two transformed strains in the second cluster while the transformants of the two strains in the last cluster expressed CS12, the N-terminal amino acid sequence of which was deciphered. The study illustrates the potential of using genetic fingerprinting to group ETEC into clusters of strains with genes encoding different CFs and confirms the ability of CfaR to induce the expression of several different CFs.

In vivo DNA-binding and oligomerization properties of the Shigella flexneri AraC-like transcriptional regulator VirF as identified by random and site-specific mutagenesis

In Shigella flexneri expression of the plasmid-encoded virulence genes is regulated via a complex mechanism involving both environmental signals and specific transactivators. The primary regulator protein, VirF, is a member of the AraC family of transcription factors and shares with other AraC-like proteins a conserved carboxy-terminal domain thought to be important for DNA binding. Random and site-directed mutagenesis of the virF gene encoding VirF yielded a number of mutations along the length of the protein which severely affected the ability of VirF to activate gene expression. The mutant proteins were shown to be affected in their ability to activate the virulence genes virB and icsA, both known to be regulated directly by VirF, as well as the virB-dependent virulence gene mxiC. Mutating key residues predicted to be important for DNA recognition had a significant negative effect, thereby suggesting that VirF interacts with its target sequence via two helix-turn-helix motifs. Two mutants that were dominant negative when coexpressed with the wild-type VirF protein were also isolated, indicating a role for protein-protein oligomerization in normal VirF function.

Genetic evidence that transcription activation by RhaS involves specific amino acid contacts with sigma 70

RhaS activates transcription of the Escherichia coli rhaBAD and rhaT operons in response to L-rhamnose and is a member of the AraC/XylS family of transcription activators. We wished to determine whether sigma(70) might be an activation target for RhaS. We found that sigma(70) K593 and R599 appear to be important for RhaS activation at both rhaBAD and rhaT, but only at truncated promoters lacking the binding site for the second activator, CRP. To determine whether these positively charged sigma(70) residues might contact RhaS, we constructed alanine substitutions at negatively charged residues in the C-terminal domain of RhaS. Substitutions at four RhaS residues, E181A, D182A, D186A, and D241A, were defective at both truncated promoters. Finally, we assayed combinations of the RhaS and sigma(70) substitutions and found that RhaS D241 and sigma(70) R599 met the criteria for interacting residues at both promoters. Molecular modeling suggests that sigma(70) R599 is located in very close proximity to RhaS D241; hence, this work provides the first evidence for a specific residue within an AraC/XylS family protein that may contact sigma(70). More than 50% of AraC/XylS family members have Asp or Glu at the position of RhaS D241, suggesting that this interaction with sigma(70) may be conserved.

Genetic rearrangements of the regions adjacent to genes encoding heat-labile enterotoxins (eltAB) of enterotoxigenic Escherichia coli strains

One of the most common bacterially mediated diarrheal infections is caused by enterotoxigenic Escherichia coli (ETEC) strains. ETEC-derived plasmids are responsible for the distribution of the genes encoding the main toxins, namely, the heat-labile and heat-stable enterotoxins. The origins and transfer modes (intra- or interplasmid) of the toxin-encoding genes have not been characterized in detail. In this study, we investigated the DNA regions located near the heat-labile enterotoxin-encoding genes (eltAB) of several clinical isolates. It was found that the eltAB region is flanked by conserved 236- and 280-bp regions, followed by highly variable DNA sequences which consist mainly of partial insertion sequence (IS) elements. Furthermore, we demonstrated that rearrangements of the eltAB region of one particular isolate, which harbors an IS91R sequence next to eltAB, could be produced by a recA-independent but IS91 sequence-dependent mechanism. Possible mechanisms of dissemination of IS element-associated enterotoxin-encoding genes are discussed.

CS5 pilus biosynthesis genes from enterotoxigenic Escherichia coli O115:H40

We have sequenced the entire region of DNA required for the biosynthesis of CS5 pili from enterotoxigenic Escherichia coli O115:H40 downstream of the major subunit gene, designated csfA (for coli surface factor five A). Five more open reading frames (ORFs) (csfB, csfC, csfE, csfF, and csfD) which are transcribed in the same direction as the major subunit and are flanked by a number of insertion sequence regions have been identified. T7 polymerase-mediated overexpression of the cloned csf ORFs confirmed protein sizes based on the DNA sequences that encode them. The expression of only the csf region in E. coli K-12 resulted in the hemagglutination of human erythrocytes and the cell surface expression of CS5 pili, suggesting that the cluster contains all necessary information for CS5 pilus biogenesis and function.

Amino acid-DNA contacts by RhaS: an AraC family transcription activator

RhaS, an AraC family protein, activates rhaBAD transcription by binding to rhaI, a site consisting of two 17-bp inverted repeat half-sites. In this work, amino acids in RhaS that make base-specific contacts with rhaI were identified. Sequence similarity with AraC suggested that the first contacting motif of RhaS was a helix-turn-helix. Assays of rhaB-lacZ activation by alanine mutants within this potential motif indicated that residues 201, 202, 205, and 206 might contact rhaI. The second motif was identified based on the hypothesis that a region of especially high amino acid similarity between RhaS and RhaR (another AraC family member) might contact the nearly identical DNA sequences in one major groove of their half-sites. We first made targeted, random mutations and then made alanine substitutions within this region of RhaS. Our analysis identified residues 247, 248, 250, 252, 253, and 254 as potentially important for DNA binding. A genetic loss-of-contact approach was used to identify whether any of the RhaS amino acids in the first or second contacting motif make base-specific DNA contacts. In motif 1, we found that Arg202 and Arg206 both make specific contacts with bp -65 and -67 in rhaI1, and that Arg202 contacts -46 and Arg206 contacts -48 in rhaI2. In motif 2, we found that Asp250 and Asn252 both contact the bp -79 in rhaI1. Alignment with the recently crystallized MarA protein suggest that both RhaS motifs are likely helix-turn-helix DNA-binding motifs.

Analysis, expression and prevalence of the Mycobacterium tuberculosis homolog of bacterial virulence regulating proteins

We have previously reported the identification of a gene from Mycobacterium tuberculosis, H37Rv, which on the basis of its nucleotide sequence encoded a protein product of 38 kDa. This 38-Kda mycobacterial protein designated as VirS exhibits homology with the VirF protein of Shigella, the VirFy protein of Yersinia and the Cfad, Rns and FapR proteins from various enterotoxigenic Escherichia coli strains. In this communication, we show the close sequence and structural similarities of the VirS protein with VirF, VirFy, Cfad, Rns and FapR and describe the results of our studies on the characterization of the virS gene promoter and its expression in E. coli and mycobacteria. virS was present exclusively in the species belonging to the M. tuberculosis complex as revealed by Southern blot and PCR analysis. Our findings suggest the involvement of virS in the regulation of pathogenesis of M. tuberculosis.

Two highly related regulatory proteins, Shigella flexneri VirF and enterotoxigenic Escherichia coli Rns, have common and distinct regulatory properties

The Rns protein of enterotoxigenic Escherichia coli (ETEC) and the VirF protein of Shigella flexneri are members of the AraC family of transcription regulators. Rns is required for positive activation of the CS1 fimbrial genes, while VirF is a positive regulator of an invasion gene regulon. The amino acid sequences of the proteins are 36% identical, and both proteins activate transcription in response to increases in temperature. Here, we show that Rns is capable of complementing fully a null mutation in the S. flexneri virF gene. However, the VirF protein cannot replace Rns as an activator of CS1 gene expression in ETEC. This failure is not due to the absence from ETEC of a co-factor required by VirF since it also occurs when the CS1 system is moved into an S. flexneri genetic background. Nor is it a function of growth medium composition or a failure in virF gene expression. Instead, these findings point to important differences in the mechanisms by which these related transcription factors regulate gene expression in Gram-negative pathogens.

Immunization against the colonization factor antigen I of enterotoxigenic Escherichia coli by administration of a bivalent Salmonella typhimurium aroA strain

An expression plasmid (pCFA-1) carrying the cfaB gene that codes for the enterotoxigenic Escherichia coli (ETEC) fimbrial adhesin colonization factor antigen I (CFA/I) subunit was constructed and used to transform a derivative of the attenuated Salmonella typhimurium aroA vaccine strain SL3261 carrying an F'lacIq. Treatment of the transformed strain with isopropyl-beta-D-thiogalactopyranoside (IPTG) resulted in elevated in vitro expression of the CFA/I subunit. Although flagellar function and lipopolysaccharide (LPS) synthesis were similar in both the parental and the recombinant strains, spleen colonization was reduced in the recombinant strain. All BALB/c mice parenterally inoculated with the recombinant strain developed significant anti-CFA/I and anti-LPS serum antibody titers (P < 0.05). Moreover, 2 of 5 mice orally inoculated with the engineered Salmonella strain developed anti-CFA/I intestinal IgA (P > 0.05) while 4/5 of the same mice developed anti-LPS IgA (P < 0.05). The results indicate that the vaccine strain elicited an antibody response against the bacterial host both after oral and intravenous immunization while the response against the CFA/I antigen was significant only after inoculation by the intravenous route.

Arac/XylS family of transcriptional regulators

The ArC/XylS family of prokaryotic positive transcriptional regulators includes more than 100 proteins and polypeptides derived from open reading frames translated from DNA sequences. Members of this family are widely distributed and have been found in the gamma subgroup of the proteobacteria, low- and high-G + C-content gram-positive bacteria, and cyanobacteria. These proteins are defined by a profile that can be accessed from PROSITE PS01124. Members of the family are about 300 amino acids long and have three main regulatory functions in common: carbon metabolism, stress response, and pathogenesis. Multiple alignments of the proteins of the family define a conserved stretch of 99 amino acids usually located at the C-terminal region of the regulator and connected to a nonconserved region via a linker. The conserved stretch contains all the elements required to bind DNA target sequences and to activate transcription from cognate promoters. Secondary analysis of the conserved region suggests that it contains two potential alpha-helix-turn-alpha-helix DNA binding motifs. The first, and better-fitting motif is supported by biochemical data, whereas existing biochemical data neither support nor refute the proposal that the second region possesses this structure. The phylogenetic relationship suggests that members of the family have recruited the nonconserved domain(s) into a series of existing domains involved in DNA recognition and transcription stimulation and that this recruited domain governs the role that the regulator carries out. For some regulators, it has been demonstrated that the nonconserved region contains the dimerization domain. For the regulators involved in carbon metabolism, the effector binding determinants are also in this region. Most regulators belonging to the AraC/XylS family recognize multiple binding sites in the regulated promoters. One of the motifs usually overlaps or is adjacent to the -35 region of the cognate promoters. Footprinting assays have suggested that these regulators protect a stretch of up to 20 bp in the target promoters, and multiple alignments of binding sites for a number of regulators have shown that the proteins recognize short motifs within the protected region.

The CS6 colonization factor of human enterotoxigenic Escherichia coli contains two heterologous major subunits

The genes encoding the CS6 colonization factor were cloned from two human enterotoxigenic Escherichia coli strains of different serotypes. The DNA sequences from both clones were nearly identical and contained four open reading frames. Two of them have homology to genes encoding molecular chaperones and ushers found in many other operons encoding colonization factors. The two remaining open reading frames encode two heterologous major subunit proteins which makes CS6 unique because other colonization factors have only one major subunit. Upstream and downstream of the CS6 operon the DNA sequences of the clones diverged abruptly.

Expression of colonization factor antigen I fimbriae by enterotoxigenic Escherichia coli; influence of growth conditions and a recombinant positive regulatory gene

Enterotoxigenic Escherichia coli (ETEC) may spontaneously lose the positive regulatory cfaR gene and thereby the capacity to express colonization factor antigen I (CFA/I). A recombinant plasmid harbouring the cfaR gene was transformed into cfaR-negative mutant ETEC strains. CFA/I expression of wild-type and cfaR-transformed ETEC cultivated in different liquid media was quantified. At 37 degrees C, a high level of CFA/I expression from wild-type and cfaR-transformed strains was observed after growth in CFA broth. Transformation enhanced CFA/I expression only marginally. The transformant cultures showed a considerable variation in CFA/I expression which was paralleled by the proportion of individual bacteria producing CFA/I. This heterogeneity could be explained by a variable tendency to structural CFA/I gene loss among individual cfaR-transformed bacteria.

A new putative fimbrial colonization factor, CS19, of human enterotoxigenic Escherichia coli

A gene probe derived from the colonization factor antigen I (CFA/I) operon cross-hybridized at very low stringency to plasmid DNA from coli surface antigen 17 (CS17)-producing enterotoxigenic Escherichia coli (ETEC) and from the ETEC strain F595C, which was negative for previously described CFAs, CSs, and putative colonization factors (PCFs). A 16-kDa protein was identified in sodium dodecyl sulfate-polyacrylamide gel electrophoresis of heat extracts prepared after growth of strain F595C at 37 degrees C on CFA agar containing bile salts. Transmission electron microscopy revealed bile salt- and temperature-dependent expression of fimbriae with a diameter of 7 nm. After transformation with a recombinant plasmid harboring the cfaR gene, which encodes a positive regulator of several CFAs, PCFs, and CSs, the 16-kDa protein was hyperexpressed. Polyclonal antibodies raised against this protein bound to the fimbriae and inhibited the adhesion of F595C bacteria to tissue-cultured Caco-2 cells. Nucleotide sequence determination of the gene encoding the 16-kDa fimbrial subunit revealed a high degree of amino acid sequence homology to the CFA/I, CS1, CS2, CS4, CS14, and CS17 polypeptides. The term CS19 is proposed for the new fimbria.

Identification and characterization of CS20, a new putative colonization factor of enterotoxigenic Escherichia coli

An enterotoxigenic Escherichia coli (ETEC) strain producing a previously undescribed putative colonization factor was isolated from a child with diarrhea in India. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of bacterial heat extracts revealed a polypeptide band of 20.8 kDa when the bacteria were grown at 37 degrees C which was absent after growth at 22 degrees C. A specific rabbit antiserum raised against the purified 20.8-kDa protein bound specifically to the fimbriae, as shown by immunoelectron microscopy, and inhibited bacterial adhesion to tissue-cultured Caco-2 cells. Transformation with a recombinant plasmid harboring the cfaD gene, which encodes a positive regulator for several ETEC fimbriae, induced hyperexpression of the 20.8-kDa fimbrial subunit and a substantial increase in the proportion of bacterial cells that were fimbriated. The N-terminal amino acid sequence of the polypeptide showed 65 and 60% identity to the PCFO20 and 987P fimbriae of human and porcine ETEC, respectively. We propose the term CS20 for this new putative colonization factor of human ETEC.

Molecular characterization of adiY, a regulatory gene which affects expression of the biodegradative acid-induced arginine decarboxylase gene (adiA) of Escherichia coli

A transcriptional regulator gene, designated adiY, was found downstream of the biodegradative arginine decarboxylase (adiA) gene (previously known as adi) of Escherichia coli. The arginine decarboxylase system is maximally induced under conditions of acidic pH, anaerobiosis and rich medium, and AdiY was found to increase the expression of adiA. The DNA sequence of adiY encodes a protein of 253 amino acids. Primer extension analysis defined the promoter. The amino acid sequence of AdiY showed homology to the XylS/AraC family of transcriptional regulators, which includes EnvY and AppY. Studies suggested that sequences required for acid induction were also necessary to observe the stimulation by AdiY. An examination of the substitution of AdiY, AppY and EnvY showed that these three proteins can, to some extent, stimulate the other systems.

Effect of growth conditions on expression of the acid phosphatase (cyx-appA) operon and the appY gene, which encodes a transcriptional activator of Escherichia coli

The expression and transcriptional regulation of the Escherichia coli cyx-appA operon and the appY gene have been investigated under different environmental conditions with single-copy transcriptional lacZ fusions. The cyx-appA operon encodes acid phosphatase and a putative cytochrome oxidase. ArcA and AppY activated transcription of the cyx-appA operon during entry into stationary phase and under anaerobic growth conditions. The expression of the cyx-appA operon was affected by the anaerobic energy metabolism. The presence of the electron acceptors nitrate and fumarate repressed the expression of the cyx-appA operon. The nitrate repression was partially dependent on NarL. A high level of expression of the operon was obtained in glucose medium supplemented with formate, in which E. coli obtains energy by fermentation. The formate induction was independent of the fhlA gene product. The results presented in this paper indicate a clear difference in the regulation of the cyx-appA operon and that of the cyd operon, encoding the cytochrome d oxidase complex. The results suggest that cytochrome x oxidase has a function under even more-oxygen-limiting conditions than cytochrome d oxidase. The expression of the appY gene is induced immediately by anaerobiosis, and this anaerobic induction is independent of Fnr, and AppY, but dependent on ArcA. The expression of the appY gene is not affected significantly by the anaerobic energy metabolism, i.e., fermentation versus anaerobic respiration. A model incorporating the anaerobic regulation of the appY gene and the two operons which are controlled by AppY, the hydrogenase 1 (hya) operon and the acid phosphatase (cyx-appA) operon, is presented. The expression of the appY gene is inversely correlated with the growth rate and is induced by phosphate starvation as well as during entry into stationary phase. During oxygen-limiting conditions the stationary-phase induction is partially dependent on ArcA. The alternative sigma factor sigma S has limited influence on the transcription of the appY gene during entry into stationary phase and no effect on the induction by phosphate starvation.

Immune responses to novel Escherichia coli and Salmonella typhimurium vectors that express colonization factor antigen I (CFA/I) of enterotoxigenic E. coli in the absence of the CFA/I positive regulator cfaR

An asd-stabilized plasmid carrying enterotoxigenic Escherichia coli cfaABCE genes was constructed and called pJGX15C-asd+. Expression of colonization factor antigen I (CFA/I) by this plasmid occurs independently of the cfaABCE positive regulator cfaR in attenuated Salmonella delta aro delta asd strain H683 and nonpathogenic laboratory E. coli asd strain chi 6212. Oral immunization of mice with nonpathogenic E. coli chi 6212 (pJGX15C-asd+) does not elicit significant serum or mucosal responses against CFA/I. In contrast, oral immunization with a single dose of attenuated S. typhimurium H683(pJGX15C-asd+) elicits a 10(5)-fold increase in CFA/I-specific serum immunoglobulin G and significant elevation of CFA/I-specific immunoglobulin A-secreting B cells in the lamina propria, mesenteric lymph nodes, and spleen. Thus, only the Salmonella-CFA/I construct effectively delivered CFA/I to the inductive sites of the gut-associated and systemic lymphoid tissues.

Genes for CS2 pili of enterotoxigenic Escherichia coli and their interchangeability with those for CS1 pili

We have cloned and sequenced the DNA needed for production of CS2 pili in Escherichia coli K-12. The four open reading frames, cotB, cotA, cotC, and cotD, show homology with the genes needed for production of CS1 and CFA/I pili, which are also found on enterotoxigenic E. coli associated with human diarrheal disease. We also report that CotA plus CotB interact with the CS1 gene products CooC and CooD to form pili that can be visualized by electron microscopy and, conversely, that the CS1 gene products CooA and CooB interact with CotC and CotD to form pili.

Proteus mirabilis urease: operon fusion and linker insertion analysis of ure gene organization, regulation, and function

Urease is an inducible virulence factor of uropathogenic Proteus mirabilis. Although eight contiguous genes necessary for urease activity have been cloned and sequenced, the transcriptional organization and regulation of specific genes within the Proteus gene cluster has not been investigated in detail. The first gene, ureR, is located 400 bp upstream and is oriented in the direction opposite the other seven genes, ureDABCEFG. The structural subunits of urease are encoded by ureABC. Previously, UreR was shown to contain a putative helix-turn-helix DNA-binding motif 30 residues upstream of a consensus sequence which is a signature for the AraC family of positive regulators; this polypeptide is homologous to other DNA-binding regulatory proteins. Nested deletions of ureR linked to either ureD-lacZ or ureA-lacZ operon fusions demonstrated that an intact ureR is required for urea-induced synthesis of LacZ from either ureA or ureD and identified a urea-regulated promoter in the ureR-ureD intergenic region. However, lacZ operon fusions to fragments encompassing putative promoter regions upstream of ureA and ureF demonstrated that no urea-regulated promoters occur upstream of these open reading frames; regions upstream of ureR, ureE, and ureG were not tested. These data suggest that UreR acts as a positive regulator in the presence of urea, activating transcription of urease structural and accessory genes via sequences upstream of ureD. To address the role of the nonstructural regulatory and accessory genes, we constructed deletion, cassette, and linker insertion mutations throughout the ure gene cluster and determined the effect of these mutations on production and regulation of urease activity in Escherichia coli. Mutations were obtained, with locations determine by DNA sequencing, in all genes except ureA and ureE. In each case, the mutation resulted in a urease-negative phenotype.

Colonization factors of diarrheagenic E. coli and their intestinal receptors

While Escherichia coli is common as a commensal organism in the distal ileum and colon, the presence of colonization factors (CF) on pathogenic strains of E. coli facilitates attachment of the organism to intestinal receptor molecules in a species- and tissue-specific fashion. After the initial adherence, colonization occurs, and the involvement of additional virulence determinants leads to illness. Enterotoxigenic E. coli (ETEC) is the most extensively studied of the five categories of E. coli that cause diarrheal disease, and has the greatest impact on health worldwide. ETEC can be isolated from domestic animals and humans. The biochemistry, genetics, epidemiology, antigenic characteristics, and cell and receptor binding properties of ETEC have been extensively described. Another major category, enteropathogenic E. coli (EPEC), has virulence mechanisms, primarily effacement and cytoskeletal rearrangement of intestinal brush borders, that are distinct from ETEC. An EPEC CF receptor has been purified and characterized as a sialidated transmembrane glycoprotein complex directly attached to actin, thereby associating CF-binding with host-cell response. Three additional categories of E. coli diarrheal disease, their colonization factors and their host cell receptors, are discussed. It appears that biofilms exist in the intestine in a manner similar to oral bacterial biofilms, and that E. coli is part of these biofilms as both commensals and pathogens.

Simultaneous expression of CFA/I and CS3 colonization factor antigens of enterotoxigenic Escherichia coli by delta aroC, delta aroD Salmonella typhi vaccine strain CVD 908

Among the known colonization factors of enterotoxigenic Escherichia coli (ETEC), CFA/I and CS3 (the common antigen in the CFA/II family of fimbrial antigens) are two of the most prevalent fimbrial antigens found in clinical isolates but are never expressed by the same wild-type strain. We manipulated the genetic determinants encoding CS3 and CFA/I fimbriae so that these two important colonization factors are expressed simultaneously in attenuated Salmonella typhi live oral vaccine strain CVD 908, including after growth in liquid medium (CFA/I is poorly expressed by wild-type ETEC in broth culture). The recombinant fimbrial structures produced by CVD 908 are morphologically indistinguishable from the CS3 fibrillae and CFA/I rod-like fimbriae produced by ETEC, and are recognized by monospecific CS3 and CFA/I antibodies. This prototype construct may prove useful in investigating the live vector approach to immunoprophylaxis of ETEC diarrheal disease.

A plasmid-encoded regulatory region activates chromosomal eaeA expression in enteropathogenic Escherichia coli

Enteropathogenic Escherichia coli (EPEC) organisms produce a characteristic histopathology in intestinal epithelial cells called attaching and effacing lesions. The eaeA gene is associated with attaching and effacing lesions and encodes intimin, a 94-kDa outer membrane protein. A 60-MDa plasmid, pMAR2, is essential for full virulence of EPEC strain E2348/69 (O127:H6). We have cloned sequences from pMAR2 that increase expression of the chromosomal eaeA gene as shown by increased alkaline phosphatase activity of an eaeA::TnphoA gene fusion, increased expression of the intimin protein, and increased production of eaeA mRNA. These sequences are called per for plasmid-encoded regulator. pMAR2-cured JPN15 containing cloned per sequences adheres to HEp-2 cells in greater numbers than JPN15 carrying the plasmid vector only. The cloned per sequences contain four open reading frames (ORFs) which have been designated perA through perD. Only perC can by itself activate expression of eaeA::TnphoA, although the levels of alkaline phosphatase activity seen with this ORF alone are considerably lower than those seen when all four ORFs are present. The molecular sizes of polypeptides predicted from perA, perB, perC, and perD ORFs are 24, 14.8, 10.5, and 9.4 kDa, respectively. The PerA predicted protein shares homology with members of the AraC family of bacterial regulators, but PerB, PerC, and PerD have no striking homology with previously described prokaryotic proteins. Our studies indicate that plasmid-encoded factors regulate the expression of eaeA and possibly genes encoding other outer membrane proteins and may be important for virulence of EPEC.

MyfF, an element of the network regulating the synthesis of fibrillae in Yersinia enterocolitica

The Yersinia enterocolitica surface antigen Myf is a fibrillar structure that resembles CS3 fimbriae. Gene myfA encodes the 21-kDa major subunit of the antigen, while genes myfB and myfC are required for the transport and assembly of pilin subunits at the bacterial cell surface. Here we show that the expression of Myf is regulated at the transcriptional level by temperature and pH. Gene myfA is transcribed at 37 degrees C and in acidic medium. The transcription start is preceded by a putative -10 box for the vegetative RNA polymerase as well as by sequences resembling the consensus sequence recognized by sigma 28. Thus, myfA could be transcribed either from a classical sigma 70 promoter or from a sigma 28 promoter. Transcription of myfA requires at least two genes, myfF and myfE, situated immediately upstream from myfA. The myfF product does not show similarity to any known regulatory protein. It is an 18.5-kDa protein with no typical helix-turn-helix motif and a unique hydrophobic domain in the NH2-terminal part. T7 expression, osmotic shock, fractionation experiments, and TnphoA fusion analyses carried out in Escherichia coli suggest that MyfF is associated with the inner membrane by means of its hydrophobic domain whereas the hydrophilic part protrudes in the periplasm. These features strikingly evoke ToxS, a protein involved in regulation of Tcp pilus production in Vibrio cholerae. MyfE resembles PsaE, a protein involved in regulation of pH6 antigen in Yersinia pestis. Genes myfF and myfE are presumably part of a whole regulatory network. MyfF could be an element of the signal transducing system.

Regulation of rns, a positive regulatory factor for pili of enterotoxigenic Escherichia coli

Attachment of enterotoxigenic Escherichia coli to the human gut is considered an important early step in infection that leads to diarrhea. This attachment is mediated by pili, which belong to a limited number of serologically distinguishable types. Many of these pili require the product of rns, or a closely related gene, for their expression. We have located the major promoter for rns and found that although its sequence diverges significantly from a sigma-70 promoter consensus sequence, it is very strong. Transcription of rns is negatively regulated both at a region upstream of this promoter and at a region internal to the rns open reading frame. In addition, rns positively regulates its own transcription, probably by counteracting these two negative effects.

AggR, a transcriptional activator of aggregative adherence fimbria I expression in enteroaggregative Escherichia coli

Enteroaggregative Escherichia coli (EAggEC) has been associated with persistent pediatric diarrhea in the developing world, yet the pathogenetic mechanisms of EAggEC infection are unknown. Our previous data have suggested that aggregative adherence of some EAggEC strains to HEp-2 cells is mediated by flexible, bundle-forming fimbriae, which we have termed aggregative adherence fimbriae I (AAF/I). Genes sufficient to confer expression of AAF/I are located on the 60-MDa plasmid of EAggEC 17-2; AAF/I genes are present as two unlinked plasmid regions (regions 1 and 2), separated by 9 kb of DNA. Here we report the complete DNA sequencing of region 2 and the identification of an open reading frame which is involved in the expression of AAF/I. One open reading frame of 794 bp encodes a protein (designated AggR) with a predicted molecular size of 29.4 kDa, which shows a high degree of amino acid sequence identity to CfaR and other members of the AraC class of gene regulators. The cloned aggR gene (or, alternatively, a cloned cfaR gene) was sufficient to complement a region 1 clone to confer AAF/I expression. To further substantiate the role of aggR in the regulation of AAF/I, we constructed a 289-bp in-frame aggR deletion and replaced the native gene in 17-2 by allelic exchange, using the temperature-sensitive vector pIB307. The resulting aggR deletions were negative for AAF/I expression, but expression was restored when the aggR gene (cloned into pBluescript II SK) was reintroduced into the aggR mutant. RNA slot blot experiments using a probe for the putative AAF/I pilin subunit (aggA) revealed that aggR operates as a transcriptional activator of aggA expression. aggA::phoA fusions were constructed in 17-2 and in 17-2 delta aggR. AggR was found to promote expression of the aggA gene under a variety of conditions of temperature, osmolarity, oxygen tension, and medium. At acid pH, aggA expression was maximal and was regulated by both AggR-dependent and AggR-independent mechanisms.

CooC and CooD are required for assembly of CS1 pili

Many strains of enterotoxigenic Escherichia coli (ETEC) isolated from patients with diarrhoeal disease exhibit CS1 pili on their surfaces. These appendages, which are thought to be important for colonization of the upper intestine, are composed largely of multiple identical protein subunits encoded by cooA. We have sequenced the DNA directly downstream of cooA and identified two open reading frames, cooC and cooD, transcribed in the same direction as cooB and cooA. Following cooD is DNA homologous to an insertion sequence, so cooB, A, C and D appear to encode all the information needed for E. coli K-12 to synthesize CS1 pili. Complementation analysis of mutants cloned in E. coli K-12 and constructed in an ETEC-derived strain indicates that cooC and cooD are not required for stability of the major CS1 pilin protein or for its transport to the periplasm, but, like cooB, both are needed for assembly of cooA into pili.

Genotypic and phenotypic identification of coli surface antigen 6-positive enterotoxigenic Escherichia coli

A polynucleotide probe comprising the gene encoding a major structural subunit protein of coli surface antigen 6 (CS6) of enterotoxigenic Escherichia coli (ETEC) was developed. Eighty-nine ETEC isolates were examined in parallel with the probe in a colony hybridization assay and in a recently developed polyclonal-antibody-based inhibition enzyme-linked immunosorbent assay (ELISA). The two assays showed a high level of concordance in the detection of CS6-positive ETEC (kappa = 0.84, P < 0.00001). Thus, 36 of the 89 ETEC isolates were identified as CS6-positive by both assays. Six strains that were negative for other colonization factor antigens were positive with the CS6 probe but negative in the ELISA, suggesting lack of surface CS6 expression in these strains. One strain was probe negative but positive in the ELISA, while the remaining 46 strains were negative in both assays. The phenotypic and genotypic assays will prove useful in vaccine-oriented studies of ETEC disease.

Adhesin regulatory genes within large, unstable DNA regions of pathogenic Escherichia coli: cross-talk between different adhesin gene clusters

The uropathogenic Escherichia coli strain 536 possesses two large, unstable DNA regions on its chromosome, which were termed pathogenicity islands (pais). Deletions of pais, which occur with relatively high frequency in vitro and in vivo, lead to avirulent mutants. The genetic determinants for production of haemolysin (Hly) and P-related fimbriae (Prf) are located in one of these islands. Deletion of this pathogenicity island (paill) not only removes the hly- and prf-specific genes, but also represses S fimbriae (Sfa), although the sfa genes of this virulence factor are not located on paill. We have identified two regulatory genes, prfB and prfl, of the prf gene cluster that are homologous to the sfa regulatory genes sfaB and sfaC, respectively. Mutations in sfaB and sfaC that inhibit transcription of the major fimbrial subunit gene sfaA were complemented by the homologous prf genes, suggesting communication between the two fimbrial gene clusters in the wild-type strain. Chromosomal mutagenesis of the two prf regulators in strain 536 repressed transcription of sfaA, detected by Northern hybridization and a chromosomal sfaA-lacZ fusion. In addition, haemagglutination assays measured a lower level of S fimbriae in these mutants. Expression of the cloned prf regulators in trans reversed the effect of the mutations; furthermore, constitutive expression of prfB or prfl could also over-come the repression of S fimbriae in a strain that had lost the pathogenicity islands. Virulence assays in mice established that the prf mutants were less virulent than the wild-type strain. The results demonstrate that cross-regulation of two unlinked virulence gene clusters together with the co-ordinate loss of large DNA regions significantly influences the virulence of an extraintestinal E. coli wild-type isolate.

Regions of the CFA/I promoter involved in the activation by the transcriptional activator CfaD and repression by the histone-like protein H-NS

Expression of CFA/I fimbriae of Escherichia coli requires the transcriptional activator CfaD. The mechanism by which CfaD activates the CFA/I promoter is to overcome the repression by H-NS, one of the histone-like proteins in E coli. This study addresses the question of which sequences in the promoter region of CFA/I interact with CfaD and H-NS. In order to determine this, deletion mutants of the CFA/I promoter were constructed and cloned upstream of the promoterless lacZ gene. The effect of CfaD and H-NS on the expression of these constructs was determined.