Identification and Characterization of a Phase-Variable Element That Regulates the Autotransporter UpaE in Uropathogenic Escherichia coli

Uropathogenic Escherichia coli (UPEC) is the most common etiologic agent of uncomplicated urinary tract infection (UTI). An important mechanism of gene regulation in UPEC is phase variation that involves inversion of a promoter-containing DNA element via enzymatic activity of tyrosine recombinases, resulting in biphasic, ON or OFF expression of target genes. The UPEC reference strain CFT073 has five tyrosine site-specific recombinases that function at two previously characterized promoter inversion systems, fimS and hyxS Three of the five recombinases are located proximally to their cognate target elements, which is typical of promoter inversion systems. The genes for the other two recombinases, IpuA and IpuB, are located distal from these sites. Here, we identified and characterized a third phase-variable invertible element in CFT073, ipuS, located proximal to ipuA and ipuB The inversion of ipuS is catalyzed by four of the five CFT073 recombinases. Orientation of the element drives transcription of a two-gene operon containing ipuR, a predicted LuxR-type regulator, and upaE, a predicted autotransporter. We show that the predicted autotransporter UpaE is surface located and facilitates biofilm formation as well as adhesion to extracellular matrix proteins in a K-12 recombinant background. Consistent with this phenotype, the ipuS ON condition in CFT073 results in defective swimming motility, increased adherence to human kidney epithelial cells, and a positive competitive kidney colonization advantage in experimental mouse UTIs. Overall, the identification of a third phase switch in UPEC that is regulated by a shared set of recombinases describes a complex phase-variable virulence network in UPEC.IMPORTANCE Uropathogenic Escherichia coli (UPEC) is the most common cause of urinary tract infection (UTI). ON versus OFF phase switching by inversion of small DNA elements at two chromosome sites in UPEC regulates the expression of important virulence factors, including the type 1 fimbria adhesion organelle. In this report, we describe a third invertible element, ipuS, in the UPEC reference strain CFT073. The inversion of ipuS controls the phase-variable expression of upaE, an autotransporter gene that encodes a surface protein involved in adherence to extracellular matrix proteins and colonization of the kidneys in a murine model of UTI.

Comparative genomic and protein signatures and intratumoral treatment responses in patients with metastatic breast cancer (MBC) treated with paclitaxel (PTX) and 2-methoxyestradiol (2ME2)

e22049

Background: Tumors respond to both chemotherapy and radiation through a number of poorly understood survival mechanisms. These potential mechanisms include upregulation of anti-apoptotic and pro-angiogenic pathways, including those regulated by HIF-1α. Sequential MBC biopsies were used to examine 1) the effects of PTX on intratumoral HIF-1α mediated pathways; and 2) the ability of a HIF-1α inhibitor (2ME2) to modulate the tumor's HIF- 1α response to PTX. Methods: Key eligibility included pts with MBC, ECOG 0–2, unlimited prior therapies, and biopsiable tumors. Pts were treated on a 28-day schedule with weekly PTX (90 mg/m2 D1, D8, D15) and daily oral 2ME2 (1000, 1250,1500 or 2000 mg qid starting D8) and had 3 tumor biopsies: baseline (A); D8 post-PTX/pre-2ME2 (B); D22 post-PTX/post- 2ME2 (C). Serial biopsies were compared for genomic and single protein changes. Results: 20 pts (median age 52 yrs [31- 75]) were treated. 60% had ≥2 prior regimens for MBC, 35% had ≥3. No unexpected grade 3/4 toxicities were seen: neutropenia (n=6), anemia (2), hypophosphatemia (2), PE (1). The clinical benefit rate was 25% (4 PR, 1 SD). There were 13 pairs of tumor biopsies to compare points A/B and 10 to compare B/C. There were no consistent gene expression changes between A and B. Significant differences at C vs. B included changes in hypoxia-responsive genes (including CA9, HIF-2α) and upregulation of pro- angiogenic factors and hemoglobin transcripts. For the B/C comparison, 2 distinct groups emerged: the first (biopsy site liver) showed downregulation of gene expression programs driven by ER and the second (lymph node, breast) showed upregulation of endothelial cell- related genes. Conclusions: Combination therapy with PTX and 2ME2 is a well-tolerated and viable option for delaying disease progression for patients with heavily pretreated MBC. Significant gene expression changes before and after exposure to 2ME2 may reflect changes in tumor microcirculation consistent with the idea of vascular normalization. The potential significance of the differences in gene expression observed in the 2 distinct groups remains to be investigated. Supported by Komen Grant BCTR0504044 (MWD).

[Table: see text]

A phase II study to optimize dasatinib dosing in metastatic breast cancer patients using real-time pharmacodynamic tissue and urinary biomarkers

Abstract #3123

Background: In order to optimize drug efficacy and patient selection for targeted agents such as dasatinib, a tyrosine kinase inhibitor, there is a need for adaptive trial methodologies and validated marker endpoints. Predictive and pharmacodynamic (PD) biomarkers of dasatinib activity will be crucial for individualized drug dosing and enrichment of patient populations treated with the drug. Multiple potential predictive and PD markers exist for dasatinib including active/total Src, active/total EphA2, and downstream targets of Src such as focal adhesion kinase (FAK) and paxillin (pax). Given Src's role in bone modeling, markers of bone resorption may also serve as important biomarkers. We designed a phase II trial in metastatic breast cancer (MBC) wherein real-time assessment of these potential biomarkers is used to optimize the dose and anti-tumor effects of dasatinib.
 Material and methods: Key eligibility includes patient with MBC, ECOG 0-1, unlimited prior therapies, and biopsiable tumor. Patients with bone-only MBC were excluded due to tissue quality required for PD analysis. Metastatic biopsies at baseline and week 4 of dasatinib therapy were analyzed using quantitative immunohistochemistry (IHC) (measured in optical densitometry (OD) units) for the following markers: phospho-Src (p-Src), phospho-FAK (p-FAK) and phospho-pax (p-pax). For patients who tolerated the starting dose of dasatinib (50 mg bid), and displayed suboptimal Src inhibition (<80% inhibition of phosphorylation of either biomarker), dasatinib dosing was escalated at week 4 to 70 mg bid. Urinary N-telopeptide (NTX), a marker of bone resorption, was measured monthly.
 Results: Since 12/2007, 12 patients have enrolled and 8 have evaluable, paired metastatic biopsies. Of the other 4 patients, 2 withdrew due to toxicity, 1 voluntarily withdrew, and 1 patient has not yet reached week 4. There has been one case of dyspnea related to possible drug toxicity. Other grade 3/4 toxicities are as follows: anorexia (3), pleural effusion (1), DVT (1). All eligible patients underwent dasatinib dose escalation at week 4 based on their individual tumor biomarker results. All tumors displayed some level of Src inhibition but none of the tumors reached the pre-defined "optimal" level of Src inhibition at week 4; the median changes in tissue biomarker levels are as follows: p-FAK -20%, p-pax -13%, p-Src -9%, and urinary NTX level -11%.
 Conclusions: Our initial analysis of sequential tumor biopsies collected in a phase II trial of single-agent dasatinib in MBC illustrates that real-time biomarkers will both optimize the dosing of targeted agents and define potential on- and off-target drug effects. Accrual is ongoing and updated results of all biomarker endpoints as well as efficacy and toxicity data will be presented.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 3123.

Extensive mosaic structure revealed by the complete genome sequence of uropathogenic Escherichia coli

We present the complete genome sequence of uropathogenic Escherichia coli, strain CFT073. A three-way genome comparison of the CFT073, enterohemorrhagic E. coli EDL933, and laboratory strain MG1655 reveals that, amazingly, only 39.2% of their combined (nonredundant) set of proteins actually are common to all three strains. The pathogen genomes are as different from each other as each pathogen is from the benign strain. The difference in disease potential between O157:H7 and CFT073 is reflected in the absence of genes for type III secretion system or phage- and plasmid-encoded toxins found in some classes of diarrheagenic E. coli. The CFT073 genome is particularly rich in genes that encode potential fimbrial adhesins, autotransporters, iron-sequestration systems, and phase-switch recombinases. Striking differences exist between the large pathogenicity islands of CFT073 and two other well-studied uropathogenic E. coli strains, J96 and 536. Comparisons indicate that extraintestinal pathogenic E. coli arose independently from multiple clonal lineages. The different E. coli pathotypes have maintained a remarkable synteny of common, vertically evolved genes, whereas many islands interrupting this common backbone have been acquired by different horizontal transfer events in each strain.

TonB-dependent systems of uropathogenic Escherichia coli: aerobactin and heme transport and TonB are required for virulence in the mouse

The uropathogenic Escherichia coli strain CFT073 has multiple iron acquisition systems, including heme and siderophore transporters. A tonB mutant derivative of CFT073 failed to use heme as an iron source or to utilize the siderophores enterobactin and aerobactin, indicating that transport of these compounds in CFT073 is TonB dependent. The TonB(-) derivative showed reduced virulence in a mouse model of urinary tract infection. Virulence was restored when the tonB gene was introduced on a plasmid. To determine the importance of the individual TonB-dependent iron transport systems during urinary tract infections, mutants defective in each of the CFT073 high-affinity iron transport systems were constructed and tested in the mouse model. Mouse virulence assays indicated that mutants defective in a single iron transport system were able to infect the kidney when inoculated as a pure culture but were unable to efficiently compete with the wild-type strain in mixed infections. These results indicate a role for TonB-dependent systems in the virulence of uropathogenic E. coli strains.

RTX toxin structure and function: a story of numerous anomalies and few analogies in toxin biology

It can be agreed that RTX toxins contribute to the pathogenesis of different diseases by causing dysfunction of the general cellular reactions of the immune response. The suggestion that RTX toxins induce cytokine production in nonimmune cells that would ultimately cause tissue damage is an expansion of their role in disease pathogenesis (Uhlen et al. 2000). Investigators in the RTX toxin field may not agree with me, but precise and satisfactory answers to the following questions are not yet available. How do RTX toxins mechanistically damage a cell? Do RTX toxins have receptors in the classic sense, in which there is a reversible ligand and receptor complex? What is responsible for the common Ca2+ ion influx in affected cells? The recent observation that an RTX toxin stimulates host-cell-mediated Ca2+ ion oscillation in part challenges the long held concept that these toxins damage cells by the direct formation of pores. Are the Ca2+ ion fluxes truly the noxious cellular insult? What is the final molecular structure of RTX toxins at the time they cause cellular death? How does the common requirement for acyl modification among RTX toxins fit into the toxin structure and mechanism of cellular killing, particularly when mixtures of unusual fatty acids are used by some toxins? There are a number of outstanding laboratories throughout the world that are seeking answers to these questions. We can reasonably expect that during the next decade research on the structure and function of RTX toxins will lead to new chemotherapeutic targets and reagents for basic cell biology and biotechnology.

Obstetrician-gynecologists performing genetic amniocentesis may be misleading themselves and their patients

OBJECTIVE

Our purpose was to compare midtrimester amniocentesis-related fetal loss rates between obstetrician-gynecologists and perinatologists.

STUDY DESIGN

This cohort study analyzes 1384 midtrimester amniocenteses from January 1, 1996, to December 31, 1999. Obstetrician-gynecologists who split their practices between two or more hospitals and explained fetal losses (eg, fetal anomalies, aneuploidy) were excluded from analysis. Eight obstetrician-gynecologists performed 138 procedures; 3 perinatologists performed 1246 procedures. Three experienced obstetrician-gynecologists accounted for 113 procedures. Analysis was by chi2.

RESULTS

Within 30 days of midtrimester amniocentesis, there were 3 fetal losses for obstetrician-gynecologists and 4 for perinatologists (P =.02, chi2 = 5.19, degrees of freedom = 1). Obstetrician-gynecologist loss rates were 1 in 46 procedures versus 1 in 312 procedures for perinatologists. Losses were clustered among the 3 experienced obstetrician-gynecologists (P <.01, chi2 = 6.93, degrees of freedom = 1). The experienced obstetrician-gynecologist fetal loss rate was 1 in 38 amniocenteses, and the perinatologist fetal loss rate was 1 in 312.

CONCLUSION

The risk of fetal loss from midtrimester amniocentesis appears to be higher when performed by an obstetrician-gynecologist compared with a perinatologist.

Genome sequence of enterohaemorrhagic Escherichia coli O157:H7

The bacterium Escherichia coli O157:H7 is a worldwide threat to public health and has been implicated in many outbreaks of haemorrhagic colitis, some of which included fatalities caused by haemolytic uraemic syndrome. Close to 75,000 cases of O157:H7 infection are now estimated to occur annually in the United States. The severity of disease, the lack of effective treatment and the potential for large-scale outbreaks from contaminated food supplies have propelled intensive research on the pathogenesis and detection of E. coli O157:H7 (ref. 4). Here we have sequenced the genome of E. coli O157:H7 to identify candidate genes responsible for pathogenesis, to develop better methods of strain detection and to advance our understanding of the evolution of E. coli, through comparison with the genome of the non-pathogenic laboratory strain E. coli K-12 (ref. 5). We find that lateral gene transfer is far more extensive than previously anticipated. In fact, 1,387 new genes encoded in strain-specific clusters of diverse sizes were found in O157:H7. These include candidate virulence factors, alternative metabolic capacities, several prophages and other new functions--all of which could be targets for surveillance.

Escherichia coli alpha-hemolysin (HlyA) is heterogeneously acylated in vivo with 14-, 15-, and 17-carbon fatty acids

alpha-Hemolysin (HlyA) is a secreted protein virulence factor observed in certain uropathogenic strains of Escherichia coli. The active, mature form of HlyA is produced by posttranslational modification of the protoxin that is mediated by acyl carrier protein and an acyltransferase, HlyC. We have now shown using mass spectrometry that these modifications, when observed in protein isolated in vivo, consist of acylation at the epsilon-amino groups of two internal lysine residues, at positions 564 and 690, with saturated 14- (68%), 15- (26%), and 17- (6%) carbon amide-linked side chains. Thus, HlyA activated in vivo consists of a heterogeneous family of up to nine different covalent structures, and the substrate specificity of the HlyC acyltransferase appears to differ from that of the closely related CyaC acyltransferase expressed by Bordetella pertussis.

Pathogenicity of an enterotoxigenic Escherichia coli hemolysin (hlyA) mutant in gnotobiotic piglets

Pigs infected with hemolytic F4(+) strains of enterotoxigenic Escherichia coli often develop septicemia secondary to intestinal infection. We tested the hypothesis that inactivation of hemolysin would reduce the ability of F4(+) enterotoxigenic E. coli to cause septicemia in swine following oral inoculation. Inactivation of the hemolysin structural gene (hlyA) did not decrease the incidence of septicemia in the gnotobiotic piglet model.

Identification and characterization of staphylococcal enterotoxin types G and I from Staphylococcus aureus

Staphylococcal enterotoxins are exotoxins produced by Staphylococcus aureus that possess emetic and superantigenic properties. Prior to this research there were six characterized enterotoxins, staphylococcal enterotoxin types A to E and H (referred to as SEA to SEE and SEH). Two new staphylococcal enterotoxin genes have been identified and designated seg and sei (staphylococcal enterotoxin types G and I, respectively). seg and sei consist of 777 and 729 nucleotides, respectively, encoding precursor proteins of 258 (SEG) and 242 (SEI) deduced amino acids. SEG and SEI have typical bacterial signal sequences that are cleaved to form toxins with 233 (SEG) and 218 (SEI, predicted) amino acids, corresponding to mature proteins of 27,043 Da (SEG) and 24,928 Da (SEI). Biological activities for SEG and SEI were determined with recombinant S. aureus strains. SEG and SEI elicited emetic responses in rhesus monkeys upon nasogastric administration and stimulated murine T-cell proliferation with the concomitant production of interleukin 2 (IL-2) and gamma interferon (IFN-gamma), as measured by cytokine enzyme-linked immunoassays. SEG and SEI are related to other enterotoxins of S. aureus and to streptococcal pyrogenic exotoxin A (SpeA) and streptococcal superantigen (SSA) of Streptococcus pyogenes. Phylogenetic analysis and comparisons of amino acid and nucleotide sequence identities were performed on related staphylococcal and streptococcal protein toxins to group SEG and SEI among the characterized toxins. SEG is most similar to SpeA, SEB, SEC, and SSA (38 to 42% amino acid identity), while SEI is most similar to SEA, SEE, and SED (26 to 28% amino acid identity). Polyclonal antiserum was generated against purified histidine-tagged SEG and SEI (HisSEG and HisSEI). Immunoblot analysis of the enterotoxins, toxic-shock syndrome toxin 1, and SpeA with antiserum prepared against HisSEG and HisSEI revealed that SEG shares some epitopes with SEC1 while SEI does not.

Prelytic and lytic conformations of erythrocyte-associated Escherichia coli hemolysin

Flow cytometry was developed as a method to assess the conformation of erythrocyte-bound Escherichia coli hemolysin polypeptide (HlyA). Topology of membrane-associated hemolysin (HlyA(E)) was investigated by testing surface accessibility of HlyA regions in lytic and nonlytic bound states, using a panel of 12 anti-HlyA monoclonal antibodies (MAbs). Hemolysin associates nonlytically with erythrocytes at 0 to 2 degrees C. To test the hypothesis that the nonlytic HlyA(E) conformation at 0 to 2 degrees C differs from the lytic conformation at 23 degrees C, MAb epitope reactivity profiles at the two temperatures were compared by flow cytometry. Four MAbs have distinctly increased reactivity at 0 to 2 degrees C compared to 23 degrees C. HlyA requires HlyC-dependent acylation at lysine residues 563 and 689 for lytic function. Toxin with cysteine substitution mutations at each lysine (HlyA(K563C) and HlyA(K689C)) as well as the nonacylated form of hemolysin made in a HlyC-deficient strain were examined by flow cytometry at 0 to 2 and 23 degrees C. The three mutants bind erythrocytes at wild-type toxin levels, but there are conformational changes reflected by altered MAb epitope accessibility for six of the MAbs. To test further the surface accessibility of regions in the vicinity of MAb-reactive epitopes, HlyA(E) was proteolytically treated prior to testing for MAb reactivity. Differences in protease susceptibility at 0 to 2 degrees and 23 degrees C for the reactivities of three of the MAbs further support the model of two distinct conformations of cell-associated toxin.

Enhancing transcription through the Escherichia coli hemolysin operon, hlyCABD: RfaH and upstream JUMPStart DNA sequences function together via a postinitiation mechanism

Escherichia coli hlyCABD operons encode the polypeptide component (HlyA) of an extracellular cytolytic toxin as well as proteins required for its acylation (HlyC) and sec-independent secretion (HlyBD). The E. coli protein RfaH is required for wild-type hemolysin expression at the level of hlyCABD transcript elongation (J. A. Leeds and R. A. Welch, J. Bacteriol. 178:1850-1857, 1996). RfaH is also required for the transcription of wild-type levels of mRNA from promoter-distal genes in the rfaQ-K, traY-Z, and rplK-rpoC gene clusters, supporting the role for RfaH in transcriptional elongation. All or portions of a common 39-bp sequence termed JUMPStart are present in the untranslated regions of RfaH-enhanced operons. In this study, we tested the model that the JUMPStart sequence and RfaH are part of the same functional pathway. We examined the effect of JUMPStart deletion mutations within the untranslated leader of a chromosomally derived hlyCABD operon on hly RNA and HlyA protein levels in either wild-type or rfaH null mutant E. coli. We also provide in vivo physical evidence that is consistent with RNA polymerase pausing at the wild-type JUMPStart sequences.

Pleiotropic effects of a mutation in rfaC on Escherichia coli hemolysin

Several genes involved in the lipopolysaccharide (LPS) biosynthetic pathway have been shown to affect the expression or activity of Escherichia coli hemolysin (Hly), a secreted cytotoxin that is the prototype of the RTX family of toxins. To further study this relationship, E. coli K-12 strains harboring mutations in the LPS biosynthetic genes rfaS, rfaQ, rfaJ, rfaP, and rfaC were transformed with a recombinant plasmid harboring the hlyCABD operon and examined for their effects on extracellular expression and hemolytic activity. A mutation in rfaC that affected both extracellular expression and activity of Hly was studied in greater detail. This mutation led to a growth-phase-dependent decrease up to 16-fold in the steady-state level of extracellular HlyA, although transcription and secretion of HlyA were decreased no more than 2-fold. Specific hemolytic activity in toxin produced from the rfaC mutant strain was significantly reduced, in a growth-phase-dependent manner. With the rfaC gene supplied in trans, both the decreased expression and activity of Hly were restored to wild-type levels. Hly from the rfaC mutant strain exhibited much slower kinetics of hemolysis, a more rapid rate of decay of activity, and greater formation of apparently inactive HlyA-containing aggregates in culture supernatants than was exhibited in the wild-type strain. A model is proposed for a physical interaction between LPS and Hly in which LPS with intact inner core participates in forming or maintaining an active conformation of Hly and helps to protect it from aggregation or degradation.

Association of RTX toxins with erythrocytes

A critical step in the target cell attack by RTX cytotoxins is their association with target cells. A binding assay was used to study the association of the Escherichia coli hemolysin protein (HlyA) with erythrocytes. Several parameters required for lysis by HlyA were tested for their effects on its initial association with erythrocytes. The results demonstrate that HlyA binding to target cells is independent of several structural components of the active toxin, including the N-terminal hydrophobic region, the glycine-rich repeat region, and the HlyC-dependent acylation of HlyA. Further, the association with erythrocytes was independent of Ca2+ concentration or temperature, while the lytic event is both Ca2+ dependent and temperature dependent. The association of two other RTX toxin proteins, the Pasteurella haemolytica leukotoxin (LktA) and the enterohemorrhagic E. coli toxin (EhxA), were also examined; these toxins bound to erythrocytes much less efficiently than did HlyA. The association of HlyA with erythrocytes occurred rapidly, within 12 s of incubation, and demonstrated no measurable dissociation. HlyA bound to erythrocytes with a maximum of approximately 2,000 molecules per cell. Competition between active HlyA and unacylated HlyA demonstrated no inhibition of binding by unacylated HlyA; rather, active HlyA appeared to displace unacylated HlyA on the cell surface. These data demonstrate that binding and lysis by HlyA are separable events and challenge the concept of nonspecific binding to the cell surface by RTX toxins.

Two pathogenicity islands in uropathogenic Escherichia coli J96: cosmid cloning and sample sequencing

Many of the virulence genes of pathogenic strains of Escherichia coli are carried in large multigene chromosomal segments called pathogenicity islands (PAIs) that are absent from normal fecal and laboratory K-12 strains of this bacterium. We are studying PAIs in order to better understand factors that govern virulence and to assess how such DNA segments are gained or lost during evolution. The isolation and sample sequencing of a set of 11 cosmid clones that cover all of one and much of a second large PAI in the uropathogenic E. coli J96 are described. These PAIs were mapped to the 64- and 94-min regions of the E. coli K-12 chromosome, which differ from the locations of three PAIs identified in other pathogenic E. coli strains. Analysis of the junction sequences with E. coli K-12-like DNAs showed that the insert at 94 min is within the 3' end of a phenylalanine tRNA gene, pheR, and is flanked by a 135-bp imperfect direct repeat. Analysis of the one junction recovered from the insert at 64 min indicated that it lies near another tRNA gene, pheV. To identify possible genes unique to these PAIs, 100 independent subclones of the cosmids were made by PstI digestion and ligation into a pBS+ plasmid and used in one-pass sample DNA sequencing from primer binding sites at the cloning site in the vector DNA. Database searches of the J96 PAI-specific sequences identified numerous instances in which the cloned DNAs shared significant sequence similarities to adhesins, toxins, and other virulence determinants of diverse pathogens. Several likely insertion sequence elements (IS100, IS630, and IS911) and conjugative R1 plasmid and P4 phage genes were also found. We propose that such mobile genetic elements may have facilitated the spread of virulence determinants within PAIs among bacteria.

Escherichia coli hemolysin mutants with altered target cell specificity

In order to understand the functional significance of HlyC-dependent acylation of the Escherichia coli hemolysin structural protein (HlyA), random as well as site-directed substitutions at the known regions of modification, i.e., those at lysine residues at amino acid positions 563 and 689 (HlyAK563 and HlyAK689, respectively), were isolated. Sixteen random hlyA mutations were identified on the basis of a screen for loss of immunoreactivity to the hemolysin-neutralizing D12 monoclonal antibody that reacts to only HlyC-activated HlyA. These substitutions occurred at the region from HlyAE684 to HlyAY696. A recombinant glutathione S-transferase-hemolysin gene fusion encoding glutathione S-transferase-HlyAS608-T725 residues reacts with monoclonal antibody when HlyC is coexpressed with the fusion protein. Therefore, at most only 12% of the total HlyA primary sequence is needed for HlyC-facilitated acylation at the HlyAK689 position, and this modification can occur in the absence of the proximal HlyAK563 acylation site. The cytolytic activities of these HlyA mutants against sheep erythrocytes and bovine and human lymphocyte cell lines (BL-3 and Raji cells, respectively) were analyzed. HlyAK563 and HlyAK689 substitutions displayed various degrees of loss of cytotoxicity that depended on the particular amino acid replacement. An HlyAK563C variant retained greater than 59 and 21% of its BL-3-lytic and erythrolytic activities, respectively, but was nearly inactive against Raji cells. An HlyA mutant with a K-to-E substitution at amino acid 689 (HlyAK689E) was essentially inactive against all three cell types, whereas an HlyAK689R substitution had a pattern of activity similar to that of the HlyAK563C mutant. Preceding the two in vitro acylated HlyA lysines are glycines that appear to be the only amino acids conserved in alignments of these regions among the RTX toxins. Remarkably, considering the retention of cytotoxic activity by some HlYAK689 mutants, each of three different substitutions at the HlyAG688 position was relatively inactive against all three cell types tested. This suggests that HlyAG688 plays a significant structural role in cytotoxic activity apart from its possible participation in an HlyC activation process which presumably requires recognition of pro-HlyA structures. The related RTX toxin, the Pasteurella haemolytica leukotoxin structural protein (LktA), can be activated in an E. coli recombinant background by HlyC. In amino acid sequence alignments, LktAK554 is equivalent to the HlyAK563 position but it has an asparagine (LktAN684) at the homologous HlyAK689 site. An LktAN684K substitution possesses wild-type leukotoxin activity against BL-3 cells and does not acquire hemolytic or Raji cell cytotoxic activity. Surprisingly, both LktAK554C and LktAK554T substitutions retain considerable BL-3 cytotoxicity (45 and 49%, respectively), indicating that there may be additional lysines within LktA that the HlyC activation mechanism is capable of acylating. Based on these results and a comparison of amino acid sequence alignments of 12 RTX toxins, a putative consensus structure of the RTX residues necessary for HlyC activation is hypothesized.

RfaH enhances elongation of Escherichia coli hlyCABD mRNA

Escherichia coli hlyCABD operons encode the polypeptide component (Hly A) of an extracellular cytolytic toxin, as well as proteins required for its acylation (HlyC) and sec-independent secretion (HlyBD). Previous reports suggested that the E. coli protein RfaH is required for wild-type hemolysin expression, either by positively activating hly transcript initiation (M. J. A. Bailey, V. Koronakis, T. Schmoll, and C. Hughes, Mol. Microbiol. 6:1003-1012, 1992) or by promoting proper insertion of hemolysin export machinery in the E. coli outer membrane (C. Wandersman and S. Letoffe, Mol. Microbiol. 7:141-150, 1993). RfaH is also required for wild-type levels of mRNA transcribed from promoter-distal genes in the rfaQ-K, traY-Z, and rplK-rpoC gene clusters, suggesting that RfaH is a transcriptional antiterminator. We tested these models by analyzing the effects of rfaH mutations on hlyCABD mRNA synthesis and decay, HlyA protein levels, and hemolytic activity. The model system included a uropathogenic strain of E. coli harboring hlyCABD on the chromosome and E. coli K-12 transformed with the hlyCABD operon on a recombinant plasmid. Our results suggest that RfaH enhances hlyCABD transcript elongation, consistent with the model of RfaH involvement in transcriptional antitermination in E. coli. We also demonstrated that RfaH increases toxin efficacy. Modulation of hemolysin activity may be an indirect effect of RfaH-dependent E. coli outer membrane chemotype, which is consistent with the model of lipopolysaccharide involvement in hemolytic activity.

Characterization of an RTX toxin from enterohemorrhagic Escherichia coli O157:H7

A hemolytic determinant of enterohemorrhagic Escherichia coli O157:H7 is encoded on a 90-kbp plasmid (pO157). This enterohemorrhagic E. coli toxin (Ehx) is a newly described RTX cytotoxin. The prototype RTX toxin is the E. coli hemolysin (Hly) associated with extraintestinal E. coli infections. We expressed Ehx from E. coli K-12 strains harboring either pSK3, a pO157 derivative marked with Tn801 unlinked to Ehx, or a recombinant plasmid containing an 11.9-kbp subclone (pEO40) of pSK3. The Ehx activities and antibody reactivities were compared with those of Hly. Little Ehx was secreted extracellularly from the strain harboring pSK3; however, when the Hly transport genes hlyBD were supplied in trans, both intracellular and extracellular levels of Ehx were enhanced more than 15-fold. The strain harboring pEO40 secreted at least 140-fold more Ehx than did the strain harboring pSK3, and neither intracellular nor extracellular levels were significantly enhanced by the addition of hlyBD in trans. Polyclonal anti-HlyA antiserum and several anti-HlyA monoclonal antibodies, including the monoclonal antibody A10, which is panreactive for nearly all RTX toxins, reacted with EhxA antigen by immunoblot analysis. In hemolysis and 51Cr release assays, Ehx demonstrated similar efficiencies in lysis of BL-3 cells (cells from a bovine lymphoma cell line) and sheep and human erythrocytes. Surprisingly, it demonstrated very little activity against two human lymphoma cell lines. In contrast, Hly lysed all five cell types tested, each to a greater extent than that demonstrated by comparable amounts of Ehx. As with other RTX toxins, Ehx activity was calcium dependent and heat labile.

Battling against host phagocytes: the wherefore of the RTX family of toxins?

The RTX family of bacterial exotoxins is a group of related cytolytic proteins produced by a wide variety of gram-negative human and animal pathogens. While diverse in their associated diseases and in their target cell specificities, there remain several themes common to RTX toxins, including genetic organization, structural and functional features, and effects on target cells. In this review, we summarize and discuss the genetics, regulation, epidemiology, structure/function relationships, and in vivo and in vitro activities of the best characterized RTX toxins, and speculate on their roles in pathogenesis and their use in immunotherapy.

Biological effects of RTX toxins: the possible role of lipopolysaccharide

RTX toxins are a family of related exotoxins with hemolytic, leukotoxi c and leukocyte-stimulating activities that are produced by a diverse array of Gram-negative bacteria. Lipopolysaccharide might be required for the maximal production of some RTX toxins and might be a cofactor in some of the biological effects of RTX toxins.

Binding of antibodies to functional epitopes on the pore formed by Escherichia coli hemolysin in cells and model membranes

Escherichia coli hemolysin (HlyA) inserts into target membranes producing a cation-selective pore. We approached the problem of determining which portions of this protein remain exposed on the side of attack by applying specific antibodies. Results obtained with resealed erythrocyte ghosts and planar phospholipid membranes were compared. The effects of one polyclonal and four monoclonal anti-hemolysin antibodies (mAbs) were studied. Using ghosts we found one mAb which strongly reduced the ion-permeability through the preinserted HlyA channels and one which clearly increased it. Experiments with planar bilayers corroborated these results by showing that the former mAb effectively promoted the closed state of the channel whereas the latter forced the HlyA channel into an open configuration. Anti-hemolysin polyclonal antibodies initially stimulated but then prevented channel opening, indicating they contained clones able to act on both these channel determinants. They were effective only when applied on the same side as the hemolysin indicating that the epitopes were exposed to that side. Finally, the antigenic epitopes of three of the mAbs were localised on the HlyA molecule by using different mutants (amber and frame shift mutants and hemolysin gene hybrids).

Construction of Actinobacillus pleuropneumoniae-Escherichia coli shuttle vectors: expression of antibiotic-resistance genes

We constructed several cloning vectors, designated pGZRS-18/19 and pGZRS-38/39, which were based on an endogenous Actinobacillus pleuropneumoniae (Apl) 4.3-kb plasmid. They carry the lacZ alpha-complementation fragment and MCS from pUC18/19, and either the bla gene under the control of a putative Apl promoter or the KmR gene from Tn903. These vectors replicate in representative strains of Apl serotypes 1 and 7, Escherichia coli, Pasteurella haemolytica (Ph) and Haemophilus (Actinobacillus) actinomycetemcomitans. We also found that Apl and Ph did not express genes under the control of the lacZ or bla promoters, suggesting that their RNA polymerases may not utilize these promoters.

Use of two Greenfield caval filters to prevent recurrent pulmonary embolism in a heparin-allergic gravida

BACKGROUND

Maternal mortality may be reduced by prompt diagnosis and treatment of pulmonary embolism.

CASE

A 25-year-old pregnant woman required a second Greenfield filter after developing a heparin allergy and recurrent pulmonary embolism.

CONCLUSION

Heparin allergy has not been reported previously in pregnancy. A Greenfield filter may be used in this circumstance. Extension of the thrombus cephalad to the filter can cause recurrent emboli, so deployment of a second caval filter may be an effective remedy.

Effects of temperature, time, and toxin concentration on lesion formation by the Escherichia coli hemolysin

We performed osmotic protection experiments to test the hypothesis that the Escherichia coli hemolysin forms a discrete-size pore in erythrocyte membranes. The effects of toxin concentration, assay time, temperature, and protectant concentrations were examined. The results we present here raise doubts about the existing model of pore formation by hemolysin. We demonstrate that osmotic protection by various sugars of different sizes is a function of hemolysin concentration and assay time. The data indicate that under various conditions, lesion sizes with a diameter ranging from < 0.6 to > 1.2 nm can be inferred. Quantification of hemolysin permitted the estimation of the number of HlyA structural protein molecules required per erythrocyte for lysis in the presence of each protectant. It appears that hemolysin induces heterogeneous erythrocyte lesions which increase in size over time. Influx experiments utilizing radioactive sugar markers indicated that time-dependent osmotic protection patterns are independent of the diffusion rates of individual protectants. We demonstrate that the rate of the putative growth in the size of hemolysin-mediated lesions is temperature dependent. The erythrocyte membrane lesions formed at 37 degrees C can be stabilized in size when shifted to 4 degrees C. On the basis of these data, new models for the nature of the hemolysin-mediated erythrocyte membrane lesions are presented.

Laparoscopically assisted vaginal hysterectomy appears to be an alternative to total abdominal hysterectomy

Seventy percent of hysterectomies in the United States are performed as total abdominal hysterectomies (TAH). Laparoscopic assisted vaginal hysterectomy (LAVH) has been promoted by some to be a low morbidity substitute for TAH. In this study, we compared the outcomes of 61 recent LAVH cases to 65 TAH cases performed during an earlier time interval. Data were abstracted from the charts of 65 TAH cases performed between August 1988 and December 1990 and 61 LAVH cases performed between June 1991 and September 1992 by the same gynecologist (E.D.R.). Patient characteristics and perioperative morbidities were compared. Patient characteristics were similar between the two groups except that LAVH procedures were performed on thinner women (148 +/- 3.4 vs 162 +/- 4.3 lbs, p < or = 0.01, LAVH vs TAH) and operating time was longer (137 +/- 4.1 vs 66 +/- 1.7 min, p < or = 0.0001). Uterine weights were comparable (152 +/- 12 vs 194 +/- 31 g, p = 0.2). There was less intraoperative blood loss (337 +/- 21 vs 417 +/- 16 ml, p < or = 0.003), febrile morbidity (9.8 vs 66%, p < or = 0.0001), respiratory complications (6.6 vs 22%, p < or = 0.05), and urinary morbidity (6.6 vs 24.4%, p < or = 0.02) and shorter postoperative hospitalization (22 +/- 1.2 vs 99 +/- 2.3 h, p < or = 0.0001) in the LAVH group. Thinner patients were selected for the LAVH procedure, and operating room time was twice that of those undergoing TAH. Conversely, perioperative morbidity and postoperative hospitalization time were significantly less with LAVH. LAVH appears to be an alternative to TAH.

Analysis of toxinogenic functions associated with the RTX repeat region and monoclonal antibody D12 epitope of Escherichia coli hemolysin

Amino acids (aa) 550 through 850 of the Escherichia coli hemolysin (HlyA) contain sequences important for several steps in cytolysis. These include the Ca(2+)-binding glycine-rich tandem repeats recognized by the monoclonal antibody A10, the putative HlyC-dependent acylation site that corresponds to the monoclonal antibody D12 epitope, and the erythrocyte specificity domain which confers erythrolytic activity to the Pasteurella haemolytica leukotoxin. To further investigate the toxinogenic functions associated with this region of HlyA, we constructed mutants in the hlyA sequences coding for the repeat region and the D12 epitope. Mutants were analyzed for anti-HlyA antibody reactivity, cytolytic activities, target cell binding, Ca2+ requirements, and virulence. The D12 epitope was mapped to aa 673 through 726, with portions of the epitope both amino terminal and carboxy terminal to aa 700. This region was necessary, but not sufficient, for toxin binding to erythrocytes. A substitution at aa 684 resulted in loss of the D12 epitope, while cytolytic activity was retained. The nature of the D12 epitope and its associated functions are discussed. The A10 epitope mapped to residues 745 through 829, corresponding to repeats 4 through 11. Insertions within the glycine-rich repeats resulted in mutant forms of HlyA which retained A10 reactivity but required increased Ca2+ for lytic activity. These in vitro effects on cytolysis corresponded to a significant decrease in HlyA-mediated virulence in mice. HlyA from one insertion mutant was able to associate with leukocyte membranes under conditions that were Ca2+ deficient for cytolysis. The role of the glycine-rich repeats and Ca2+ in HlyA activity are discussed.

Assays of hemolytic toxins

The ability to produce a cytolytic toxin contributes to the success of many organisms in a particular niche by such diverse means as lysis of a phagolysosomal membrane of the macrophage by hemolysin from the intracellular parasite Trypanosoma cruzi, disruption of leukocyte activity by the Escherichia coli hemolysin, and destruction of invading bacteria by hemolysin from the annelid Glycera dibranchiata. The relative contribution of erythrocyte lysis to survival of the cytolysin producer is still under investigation. Nevertheless, the hemolytic phenotype is both a powerful tool for identifying novel cytolysins and a convenient marker for studying cytolytic activity in established toxins.

Low periconceptional maternal serum thymosin alpha 1 levels are associated with blighted pregnancies

OBJECTIVE

The thymus-derived peptides, thymosin alpha 1 and thymosin beta 4, are believed to contribute to the maintenance of immune homeostasis. They are also associated with the hypothalamic-pituitary-adrenal-gonadal axis and may play a role in reproduction.

STUDY DESIGN

Patients were recruited from a university hospital setting. Eligible candidates were 24 to 38 years old who were being seen in an ovulation induction and in vitro fertilization program. Serial maternal serum thymosin alpha 1 and beta 4 levels were assayed preconceptual and then twice in the first trimester by ELISA in 28 women with known ovulation dates who successfully conceived as demonstrated by positive serum beta human chorionic gonadotropin (hCG). Thymosin alpha 1 and beta 4 serum levels for viable pregnancies (group I; N = 19) were compared to pregnancies that aborted (group II; N = 9) using repeated measures of multivariate analysis of variance (MANOVA). Periconceptional (preovulatory and early pregnancy) thymosin alpha 1 and beta 4 values between groups I and II were compared using repeated measure one-way ANOVA.

RESULTS

Thymosin alpha 1 levels from pregnancies that remained viable were significantly higher than those from pregnancies that spontaneously aborted. Preovulation thymosin alpha 1 levels also tended to be lower in pregnancies that subsequently aborted. Thymosin beta 4 levels were similar between the two groups.

CONCLUSION

Decreased maternal serum thymosin alpha 1 levels may be associated with periconceptional endocrine and/or immune disturbances preceding miscarriage.

A heterologous membrane protein domain fused to the C-terminal ATP-binding domain of HlyB can export Escherichia coli hemolysin

The hydrophobic-rich NH2-terminal 34 amino acids of a tetracycline resistance determinant (TetC) were fused to the COOH-terminal 240 amino acids of the hemolysin transporter, HlyB, which contains a putative ATP-binding domain. This hybrid protein replaced the NH2-terminal 467-amino-acid portion of HlyB and could still export the Escherichia coli hemolysin (HlyA). Export by the hybrid protein was approximately 10% as efficient as transport by HlyB. Extracellular secretion of HlyA by the TetC-HlyB hybrid required HlyD and TolC. The extracellular and periplasmic levels of beta-galactosidase and beta-lactamase in strains that produced the hybrid were similar to the levels in controls. Thus, HlyA transport was specific and did not appear to be due to leakage of cytoplasmic contents alone. Antibodies raised against the COOH terminus of HlyB reacted with the hybrid protein, as well as HlyB. HlyB was associated with membrane fractions, while the hybrid protein was found mainly in soluble extracts. Cellular fractionation studies were performed to determine whether transport by the hybrid occurred simultaneously across both membranes like wild-type HlyA secretion. However, we found that HlyA was present in the periplasm of strains that expressed the TetC-HlyB hybrid. HlyA remained in the periplasm unless the hlyD and tolC gene products were present in addition to the hybrid.

Markers for endothelial injury, clotting and platelet activation in preeclampsia

The etiology of disseminated intravascular coagulation (DIC) in preeclampsia is not well understood. We measured plasma levels of fibronectin (FN), which may reflect endothelial cell injury, fibrinopeptide A (FPA), a specific marker of clotting, platelet counts (PLC) and mean platelet volumes (MPV), as well as beta-thromboglobulin (beta TG) and platelet factor 4 (Pf4), products of irreversible platelet activation in 24 preeclamptic patients and 24 controls matched for age, gestational age, labor status, and parity. In preeclampsia, FN and FPA were significantly elevated while PLC were significantly decreased (P less than 0.0001, less than 0.05 and less than 0.01, respectively). beta TG, Pf4, and MPV values did not show significant differences. These findings support the hypothesis that endothelial injury, clotting activation and platelet consumption are increased in preeclampsia. However, the much closer association of preeclampsia with FN levels as compared to FPA, beta TG, Pf4, suggests that endothelial injury is a more basic mechanism of preeclampsia than clotting or platelet activation.

The synthesis and function of the Escherichia coli hemolysin and related RTX exotoxins

The RTX group of exotoxins represents a branch of a family of exoproteins produced by Gram-negative bacteria which share the properties of being secreted by a leader-independent pathway and a tandemly-repeated nine-amino-acid sequence that is responsible for calcium binding. The Escherichia coli hemolysin (HlyA) is the prototype for the RTX exotoxin family which includes the leukotoxins of Pasteurella haemolytica and Actinobacillus actinomycetemcomitans and hemolysins from four Gram-negative genera. A review of the genetics, synthesis, export and target cell reactivity of the E. coli hemolysin is given. An evolutionary tree of the RTX toxin family based on amino acid sequence similarity is presented.

Identification of RTX toxin target cell specificity domains by use of hybrid genes

The Escherichia coli hemolysin (HlyA) and Pasteurella haemolytica leukotoxin (LktA) are cytolytic toxins encoded by genes belonging to the recently described RTX gene family. These cytotoxins are, respectively, 1,023 and 953 amino acids in length and are encoded by genes within identically organized operons. They share 45% amino acid sequence identities but differ in their target cell specificities. In vitro-derived recombinant hybrid genes between hlyA and lktA were constructed by using restriction endonuclease sites created by oligonucleotide site-directed mutagenesis. The cytolytic activity of hybrid proteins was investigated using as targets sheep erythrocytes and two cultured cell lines from different species (BL3, bovine leukemia-derived B lymphocytes; and Raji, human B-cell lymphoma cells). HlyA is cytolytic to all three cell types. LktA lyses only BL3 cells. Among the hybrid proteins displaying cytolytic activity, the striking finding is that the hemolytic activity of several LktA-HlyA hybrids was independent of any cytolytic activity against either cultured cell species. The hemolytic activity was associated with the HlyA region between amino acids 564 and 739. Structures that are critical for HlyA cytolytic activity against BL3 or Raji cells were destroyed when LktA-HlyA and HlyA-LktA hybrids were made, respectively, at amino acid positions 564 and 739 of HlyA. In contrast to HlyA, which lysed the two different cultured cell lines with equal efficiency, Lkt-HlyA hybrids possessing the amino-terminal 169 residues of LktA lysed BL3 cells more efficiently than Raji cells. This suggests that a significant but not exclusive element of the LktA ruminant cell specificity resides in the amino-terminal one-fifth of the protein. A molecular model of the functional domains of HlyA and LktA is presented.

Detection of prenatal drug exposure in the pregnant women and her newborn infant

Although urine testing remains the standard method for identifying and monitoring drug addicts, recent data suggest that it seriously underdiagnoses the prevalence of fetal exposure to various drugs. Results obtained with other body fluids and tissues (meconium and hair) are reviewed and the laboratory methodologies used to detect drugs are discussed in details.

Cytotoxicity of the HpmA hemolysin and urease of Proteus mirabilis and Proteus vulgaris against cultured human renal proximal tubular epithelial cells

Proteus mirabilis, a common agent of nosocomially acquired and catheter-associated bacteriuria, can cause acute pyelonephritis. In ascending infections, bacteria colonize the bladder and ascend the ureters to the proximal tubules of the kidney. We postulate that Proteus species uses the HpmA hemolysin and urease to elicit tissue damage that allows entry of these bacteria into the kidney. To study this interaction, strains of Proteus mirabilis and P. vulgaris and their isogenic hemolysin-negative (hpmA) or isogenic urease-negative (ureC) constructs were overlaid onto cultures of human renal proximal tubular epithelial cells (HRPTEC) isolated from kidneys obtained by immediate autopsy. Cytotoxicity was measured by release of soluble lactate dehydrogenase (LDH). Two strains of P. mirabilis inoculated at 10(6) CFU caused a release of 80% of total LDH after 6 h, whereas pyelonephritogenic hemolytic Escherichia coli CFT073 released only 25% at 6 h (P less than 0.012). Ten P. mirabilis isolates and five P. vulgaris isolates were all hemolytic and cytotoxic and produced urease which was induced by urea. The HpmA hemolysin is apparently responsible for the majority of cytotoxicity in vitro since the hemolysin-negative (hpmA) mutants of P. mirabilis and P. vulgaris were significantly less cytotoxic than wild-type strains. P. mirabilis WPM111 (hemolysin negative) was used to test the effect of urease-catalyzed urea hydrolysis on HRPTEC viability. In the presence of 50 mM urea, WPM111 caused the release of 42% of LDH versus 1% at 6 h in the absence of substrate (P = 0.003). We conclude that the HpmA hemolysin of Proteus species acts as a potent cytotoxin against HRPTEC. In addition, urease apparently contributes to this process when substrate urea is available.

Pore-forming cytolysins of gram-negative bacteria

A great deal is known about the structure, function and metabolic effects of enzymatic bacterial toxins such as the diphtheria, pertussis and cholera toxins. By comparison, our understanding of the pore-forming, cytolytic toxins, particularly those produced by Gram-negative bacterial pathogens, is far less complete. The genetics and biochemistry of a large, newly discovered family of calcium-dependent, pore-forming cytotoxins (RTX toxins) produced by different genera of the Enterobacteriaceae and Pasteurellaceae are discussed in this review. This toxin family is especially noteworthy because the individual toxins often exhibit different cell- and host-specificity. A brief review is also included of two ancestrally unrelated groups of calcium-independent, pore-forming toxins, the haemolysins produced by Proteus mirabilis and Serratia marcescens and the aerolysins secreted by species of Aeromonas. Their structure and function are contrasted with those of the RTX family members. Emerging questions about the role of cytolysins in pathogenesis are presented. Perhaps the most important issue raised is whether or not less attention should be paid to the lytic capacity of these cytotoxins, with more energy being devoted to the understanding of their non-lytic inhibitory activities against host cells.

Cocaine abuse is associated with abruptio placentae and decreased birth weight, but not shorter labor

Many of our patients report having ingested cocaine hoping to decrease the duration of labor. We reviewed the computerized records of 592 women who abused cocaine. Compared with 4687 controls, women who ingested cocaine were older and had higher parity. Birth weight, birth weight percentile, and gestational age at delivery were significantly decreased among their neonates, and the incidence of abruptio placentae was nearly doubled among these women. Although these factors tend to shorten labor, the total duration of labor was not significantly different between the two groups. These data add to the accumulating evidence that cocaine abuse is associated with increased obstetric morbidity, but do not support the belief that cocaine shortens labor.

Home uterine activity monitoring is associated with a reduction in preterm birth

The value of home uterine activity monitoring plus perinatal nursing support in the prevention of preterm birth among high-risk patients has been demonstrated by several studies. Other reports with less stringent guidelines and less intensive nursing contact have questioned the contribution of home uterine activity monitoring and perinatal nursing support to a preterm birth prevention program. In this large, prospective, randomized multicenter study, patients were assigned to receive either daily monitoring and nursing contact or a preterm birth prevention program including intensive education and more frequent prenatal visits. Among the monitored patients, there was a significant increase in early detection of preterm labor (2 cm or less), successful tocolysis, and prolongation of pregnancy to term. Thirty-one percent of these diagnoses of preterm labor resulted from evaluation of increased uterine activity without associated patient-perceived symptoms. We conclude that a program of daily uterine activity monitoring and perinatal nursing support results in earlier diagnosis of preterm labor and subsequently more effective tocolysis.

The contribution of symptomatology and/or uterine activity to the incidence of unscheduled visits

Home uterine activity monitoring and perinatal nursing support have been shown to be associated with a decrease in preterm births with no increase in the number of unscheduled patient visits. This prospective, randomized multicenter study compared the frequency of unscheduled visits in patients receiving home uterine activity monitoring and perinatal nursing support with that of patients receiving education regarding the detection and reporting of preterm labor symptomatology. The contribution of patient-reported signs and symptoms versus objective uterine activity data to unscheduled visits is assessed. The overall frequency of unscheduled visits was similar in both groups. In the home uterine activity monitoring and perinatal nursing support group, the contributions of uterine activity versus signs and symptoms to the diagnosis of preterm labor were equal, with 36% of patients diagnosed with preterm labor sent to the physician for increased uterine activity and 36% for signs and symptoms. The sensitivity for the group receiving monitoring and nursing support in detecting preterm labor was 93%. The majority of false-positive visits were associated with patient symptoms. These data show that this combination service does not lead to a clinically significant increase in unscheduled visits. Further, the visits resulting from the combination service provide a sensitive predictive method to aid physicians in detecting early labor.

Relationship of uterine contractility to preterm labor

An increased uterine contraction rate is associated with preterm labor. The contraction rate in individual patients, however, has not been evaluated critically as to its predictive value in forecasting early labor. In this randomized multicenter study, 105 patients at high risk for preterm delivery monitored their contraction rate at home on a daily basis. An analysis was conducted to determine the association of at least four contractions per hour on a routine strip followed by at least four contractions per hour on a repeat tracing with subsequent preterm labor. Using this threshold, 70% of the patients were correctly classified. This contraction rate resulted in a sensitivity of 57%, a specificity of 80%, a positive predictive value of 72%, and a negative predictive value of 68%. A threshold rate of at least four contractions per hour on a remonitor strip identifies a patient at increased risk for preterm labor (P = .003).

Uterine activity compared with symptomatology in the detection of preterm labor

The relative contribution of uterine activity obtained by home monitoring with a guard ring tocodynamometer compared with seven specific signs and symptoms reported during patient/nurse contact as an aid in detecting preterm labor has not been studied. In this prospective, multicenter study, patients at risk for developing early labor who were randomized to receive home uterine activity monitoring and perinatal nursing support were assessed. The initiator of provider contact (uterine activity detected on routine transmission, patient-perceived signs and symptoms of preterm labor during perinatal nurse contact, or both) resulting in a diagnosis of preterm labor was recorded. Contraction data were then analyzed for an association with preterm labor. There was a strong association of increased uterine activity (four or more contractions per hour) on a repeat monitoring strip with preterm labor (P less than .001). Among patients diagnosed with preterm labor, 31% had increased uterine activity detected on a routine transmission without patient-reported signs and symptoms, compared with 24% who were diagnosed as the result of patient-reported symptoms without increased uterine activity. Daily objective uterine activity data alone have greater incremental value over and above other signs and symptoms as an aid to the physician in diagnosing preterm labor.

Management of preterm labor patients at home: does daily uterine activity monitoring and nursing support make a difference?

Daily home uterine activity monitoring and perinatal nursing support were compared with standard care in managing patients with recurrent preterm labor during the current pregnancy in an effort to reduce preterm birth. Sixty-seven successfully treated preterm labor patients were randomly assigned in this multicenter study to daily home uterine activity monitoring and perinatal nursing support or to a standard-care group. Recurrent preterm labor occurred in 15 (45%) of monitored patients and 19 (56%) of standard-care patients. The risk of preterm birth (before 37 weeks) for patients with recurrent preterm labor was significantly reduced (P = .025) in the monitored group (seven, or 47%) compared with the standard-care group (16, or 84%). The relative risk of delivering because of failed tocolysis was 2.8 for the standard-care group versus the monitored group. There were no patients in the monitored group who delivered at the first recurrence of preterm labor for failed tocolysis. The data suggest that home uterine activity monitoring and perinatal nursing support are helpful in achieving term birth through earlier detection and treatment of recurrent preterm labor.

Preventing preterm birth in twin gestation: home uterine activity monitoring and perinatal nursing support

In this investigation, 45 women with twin gestations in four centers were randomly assigned to either daily home uterine activity monitoring and perinatal nursing support (19) or an education group (26). Patients in the home uterine activity monitoring and perinatal nursing support group monitored uterine activity twice daily, transmitted the data each day, and had 24 hour-a-day access to nursing support. Education patients were counseled regarding the common signs and symptoms of preterm labor. Both groups had scheduled prenatal visits at least every 2 weeks. Sixteen (62%) of the education group and 14 (74%) of the home uterine activity monitoring and perinatal nursing support group developed preterm labor, values that were not significantly different. Of the monitored group who experienced preterm labor, all 14 were dilated 3 cm or less at diagnosis of the first preterm labor, compared with ten of 16 in the education group (P = .01; one-tailed Fisher test). The mean cervical dilatation at the first preterm labor episode in the group receiving daily monitoring and contact (1.6 cm) was significantly less (P = .01) than that in the education group (2.9 cm). Thus, fewer preterm births were recorded in the home uterine activity monitoring and perinatal nursing support group and significantly fewer patients delivered because of failed tocolysis (P = .03).

Calcium is required for binding of Escherichia coli hemolysin (HlyA) to erythrocyte membranes

The calcium requirement for hemolytic activity of Escherichia coli hemolysin was investigated by using hemolytic assays and immunoblotting of toxin-treated erythrocytes. The hemolytic activity of cell culture supernatants obtained during growth of E. coli in Luria-Bertani (LB) broth or calcium-free LB broth was calcium dependent. The hemolytic activity of culture supernatants obtained during growth in LB broth supplemented with calcium was calcium independent. Osmotic protection experiments using Dextran 4 to prevent cell lysis indicated that calcium was required for the binding of hemolysin to erythrocytes at both 4 and 37 degrees C. The binding efficiency at 4 degrees C was 50% of that occurring at 37 degrees C. The calcium-dependent binding was confirmed by immunoblotting saline-washed, toxin-treated erythrocytes with a monoclonal antibody after sodium dodecyl sulfate-polyacrylamide gel electrophoresis separation of membrane proteins. Bound hemolysin increased the calcium permeability of the cell membranes as evidenced by calcium-induced membrane protein alterations. The alterations in membrane proteins did not directly cause lysis of the cells. The results were consistent with a mechanism of lysis involving the formation of cation-selective pores in the membranes of target cells.