Establishment of the first international repository for transfusion-relevant bacteria reference strains: ISBT working party transfusion-transmitted infectious diseases (WP-TTID), subgroup on bacteria

BACKGROUND

Bacterial contamination of platelet concentrates (PCs) still remains a significant problem in transfusion with potential important clinical consequences, including death. The International Society of Blood Transfusion Working Party on Transfusion-Transmitted Infectious Diseases, Subgroup on Bacteria, organised an international study on Transfusion-Relevant Bacteria References to be used as a tool for development, validation and comparison of both bacterial screening and pathogen reduction methods.

MATERIAL AND METHODS

Four Bacteria References (Staphylococcus epidermidis PEI-B-06, Streptococcus pyogenes PEI-B-20, Klebsiella pneumoniae PEI-B-08 and Escherichia coli PEI-B-19) were selected regarding their ability to proliferate to high counts in PCs and distributed anonymised to 14 laboratories in 10 countries for identification, enumeration and bacterial proliferation in PCs after low spiking (0·3 and 0·03 CFU/ml), to simulate contamination occurring during blood donation.

RESULTS

Bacteria References were correctly identified in 98% of all 52 identifications. S. pyogenes and E. coli grew in PCs in 11 out of 12 laboratories, and K. pneumoniae and S. epidermidis replicated in all participating laboratories. The results of bacterial counts were very consistent between laboratories: the 95% confidence intervals were for S. epidermidis: 1·19-1·32 × 10(7) CFU/ml, S. pyogenes: 0·58-0·69 × 10(7) CFU/ml, K. pneumoniae: 18·71-20·26 × 10(7) CFU/ml and E. coli: 1·78-2·10 × 10(7) CFU/ml.

CONCLUSION

The study was undertaken as a proof of principle with the aim to demonstrate (i) the quality, stability and suitability of the bacterial strains for low-titre spiking of blood components, (ii) the property of donor-independent proliferation in PCs, and (iii) their suitability for worldwide shipping of deep frozen, blinded pathogenic bacteria. These aims were successfully fulfilled. The WHO Expert Committee Biological Standardisation has approved the adoption of these four bacteria strains as the first Repository for Transfusion-Relevant Bacteria Reference Strains and, additionally, endorsed as a project the addition of six further bacteria strain preparations suitable for control of platelet contamination as the next step of enlargement of the repository.

Evaluation of a new generation of culture bottle using an automated bacterial culture system for detecting nine common contaminating organisms found in platelet components

BACKGROUND

An automated bacterial culture system (BacT/ALERT 3D, bioMérieux) has been previously validated with a variety of bacteria in platelets. The recovery of bacteria in platelets using a new generation of culture bottles that do not require venting and that use a liquid emulsion sensor was studied.

STUDY DESIGN AND METHODS

Bacillus cereus, Enterobacter cloacae, Escherichia coli, Klebsiella oxytoca, Staphylococcus aureus, Staphylococcus epidermidis, Serratia marcescens, Streptococcus viridans, and Propionibacterium acnes isolates were inoculated into Day 2 platelets to concentrations of 10 and 100 CFU per mL. Samples were then studied with current and new aerobic, anaerobic, and pediatric bottles.

RESULTS

All organisms, except P. acnes, were detected in a mean time of 9.2 to 20.4 (10 CFU/mL) or 8.7 to 18.6 (100 CFU/mL) hours. P. acnes was detected in a mean time of 69.2 (10 CFU/mL) or 66.0 (100 CFU/mL) hours. The 10-fold increase in inoculum was associated with a mean 9.2 percent difference in detection time. The aerobic, anaerobic, and pediatric bottles had a mean difference in detection time (hours) between the current and new bottles of 0.10 (p=0.61), 0.4 (p=0.38), and 1.0 (p < 0.001), respectively.

CONCLUSION

No difference in detection time between the current and new aerobic and anaerobic bottles was demonstrated. The new pediatric bottles had a small but significant delay in detection.

Lung transplantation for cystic fibrosis patients with Burkholderia cepacia complex. Survival linked to genomovar type

The number of cystic fibrosis (CF) patients undergoing lung transplant has risen over the past decade, because of a clear-cut survival benefit. However, patients with Burkholderia cepacia complex are often excluded from transplantation because of increased mortality. To determine the influence of B. cepacia complex genomovar type on transplant outcome, we undertook a retrospective study in 121 CF patients transplanted at UNC. Twenty-one and three patients, respectively, were infected pre- or postoperatively with B. cepacia complex. All posttransplant acquisitions were successfully treated. However, excess mortality occurred over the first 6 postoperative months in those infected preoperatively with B. cepacia complex compared with those not infected (33% versus 12%, p = 0.01). The 1-, 3-, and 5-yr survival were significantly lower in the B. cepacia complex cohort. Of the patients infected preoperatively, genomovar III patients were at the highest risk of B. cepacia complex-related mortality (5 of 12 versus 0 of 8, one isolate not typed; p = 0.035). Each of the B. cepacia complex-related deaths was caused by a unique genotype as determined by pulsed-field gel electrophoresis. All isolates were negative for the cable pilin gene. These results warrant a multicenter analysis of B. cepacia complex-infected patients with genomovar-typing to confirm that genomovar III patients are at highest risk for post-transplant complications.

CT angiography with volume rendering for quantifying vascular stenoses: in vitro validation of accuracy

OBJECTIVE

The purpose of this study was to evaluate the accuracy of CT angiography with volume rendering for quantifying vascular stenoses in vitro.

MATERIALS AND METHODS

Vascular models with three degrees of stenosis (33%, 67%, and 83%) were imaged at three orientations to the axial plane (parallel, perpendicular, or 45 degrees ) using helical CT with 2-mm collimation and two pitches (1 or 2), two reconstruction intervals (1 or 2 mm), and two scan times (.75 or 1 sec). Diameter and percentage of stenosis were measured from volume renderings using full width at half maximum. Images were measured in two planes whenever resolution varied with direction. Statistical analysis was performed using analysis of variance.

RESULTS

Mean absolute error of the measured percentage of stenosis was 7% (range, 0-27%). The actual percentage of stenosis and vessel orientation had the most significant effects on accuracy (p < .001). The measured percentage of stenosis was significantly less accurate with phantoms parallel to the axial plane than with other orientations (p < .001). Mean absolute error in the measured percentage of stenosis was 4% when the parallel-to-the-axial-plane orientation was excluded. Overlapping (1-mm) reconstructions were significantly more accurate than 2-mm reconstructions (p < .05) and direction of measurement significantly affected accuracy (p < .05), but these effects were secondary.

CONCLUSION

CT angiography with volume rendering can accurately quantify vascular stenoses, but it is less accurate for vessels in the axial plane. With 2-mm collimation, vessel characteristics have greater effects on accuracy than do acquisition parameters.

Renal artery stenosis: CT angiography--comparison of real-time volume-rendering and maximum intensity projection algorithms

PURPOSE

To compare results of helical computed tomographic (CT) angiography with real-time interactive volume rendering (VR) to CT angiography with maximum intensity projection (MIP) for the detection of renal artery stenosis.

MATERIALS AND METHODS

Twenty-five patients underwent both conventional and CT angiography of the renal arteries. Images were blindly reviewed after rendering with MIP and VR algorithms. MIP images were viewed in conjunction with axial CT images; VR models were evaluated in real time at the workstation without CT images. Findings in 50 main and 11 accessory renal arteries were categorized as normal or by degree of stenosis.

RESULTS

All arteries depicted on conventional angiograms were visualized on MIP and VR images. Receiver operating characteristic (ROC) analysis for MIP and VIR images demonstrated excellent discrimination for the diagnosis of stenosis of at least 50% (area under the ROC curve, 0.96-0.99). Although sensitivity was not significantly different for VR and MIP (89% vs 94%, P > .1), specificity was greater with VR (99% vs 87%, P = .008 to .08). Stenosis of at least 50% was overestimated with CT angiography in four accessory renal arteries, but three accessory renal arteries not depicted at conventional angiography were depicted at CT angiography.

CONCLUSION

In the evaluation of renal artery stenosis, CT angiography with VR is faster and more accurate than CT angiography with MIP. Accessory arteries not depicted with conventional angiography were depicted with both CT angiographic algorithms.

Three-dimensional volume rendering of spiral CT data: theory and method

Three-dimensional (3D) medical images of computed tomographic (CT) data sets can be generated with a variety of computer algorithms. The three most commonly used techniques are shaded surface display, maximum intensity projection, and, more recently, 3D volume rendering. Implementation of 3D volume rendering involves volume data management, which relates to operations including acquisition, resampling, and editing of the data set; rendering parameters including window width and level, opacity, brightness, and percentage classification; and image display, which comprises techniques such as "fly-through" and "fly-around," multiple-view display, obscured structure and shading depth cues, and kinetic and stereo depth cues. An understanding of both the theory and method of 3D volume rendering is essential for accurate evaluation of the resulting images. Three-dimensional volume rendering is useful in a wide variety of applications but is just now being incorporated into commercially available software packages for medical imaging. Although further research is needed to determine the efficacy of 3D volume rendering in clinical applications, with wider availability and improved cost-to-performance ratios in computing, 3D volume rendering is likely to enjoy widespread acceptance in the medical community.

Immune response to Yersinia outer proteins and other Yersinia pestis antigens after experimental plague infection in mice

There is limited information concerning the nature and extent of the immune response to the virulence determinants of Yersinia pestis during the course of plague infection. In this study, we evaluated the humoral immune response of mice that survived lethal Y. pestis aerosol challenge after antibiotic treatment. Such a model may replicate the clinical situation in humans and indicate which virulence determinants are expressed in vivo. Immunoglobulin G enzyme-linked immunosorbent assay and immunoblotting were performed by using purified, recombinant antigens including F1, V antigen, YpkA, YopH, YopM, YopB, YopD, YopN, YopE, YopK, plasminogen activator protease (Pla), and pH 6 antigen as well as purified lipopolysaccharide. The major antigens recognized by murine convalescent sera were F1, V antigen, YopH, YopM, YopD, and Pla. Early treatment with antibiotics tended to reduce the immune response and differences between antibiotic treatment regimens were noted. These results may indicate that only some virulence factors are expressed and/or immunogenic during infection. This information may prove useful for selecting potential vaccine candidates and for developing improved serologic diagnostic assays.

Dual-phase spiral CT angiography with volumetric 3D rendering for preoperative liver transplant evaluation: preliminary observations

PURPOSE

The goal of our study was to determine whether dual-phase spiral CT angiography with 3D volume rendering could be used for preoperative evaluation and patient selection for orthotopic liver transplantation candidates.

METHOD

Fifty consecutive potential candidates for liver transplantation were evaluated with dual-phase spiral CT with 3D volume rendering. Intravenous contrast medium was administered as bolus peripheral injection at 3 ml/s. The protocol consisted of a contrast-enhanced dual-phase spiral CT (arterial phase acquisition at 30 s after initiation of contrast medium injection followed by portal venous phase beginning at 60 s) with scan parameters of 0.75 s gantry rotation speed, 3 mm collimation, 5 to 6 mm/s table speed, and reconstruction at 1 mm intervals for arterial-phase images and 3 mm collimation for portal venous-phase studies (Siemens Plus 4 scanner; Siemens Medical Systems, Iselin, NJ, U.S.A.). All scan information was sent to a free-standing workstation (Silicon Graphics Onyx or Infinite Reality, Mountain View, CA, U.S.A.) for interactive real-time 3D volume rendering using a customized version of the Volren volume renderer (Silicon Graphics; Advanced Imaging Laboratory, Johns Hopkins Medical Institutions, Baltimore, MD, U.S.A.). The arterial phase was used to create vascular maps of the celiac axis including the origin(s) of the hepatic artery and origin of the superior mesenteric artery. The portal phase was used to define portal venous patency as well as the hepatic venous anatomy. All images were analyzed for vascular patency, shunting, or collateralization as well as the status of the underlying liver (i.e., liver size, cirrhosis, tumor, etc.).

RESULTS

All 50 studies were successfully completed without complication. The 3D CT angiograms defined key arterial and venous structures including origin(s) of the hepatic artery, portal vein and/or superior mesenteric vein thrombosis, cavernous transformation of the portal vein, and/or other collateral vasculature. Ten patients (20%) demonstrated anomalous anatomy at the origin(s) of the hepatic artery. Portal vein thrombosis with cavernous transformation of the portal vein was shown in six patients, and there were three cases of partial venous thrombosis. Underlying liver tumors as well as parenchymal liver disease were well defined. Hepatic masses were found in five patients. Masses were pathologically proven as hepatocellular carcinoma (n = 1), giant cavernous hemangioma (n = 1), hepatic adenoma (n = 1), and focal nodular hyperplasia (n = 2).

CONCLUSION

Preliminary results suggest that dual-phase spiral CT with CT angiography can provide a comprehensive preoperative liver transplant evaluation, supplying the necessary information for patient selection and surgical planning. As a single, minimally invasive examination, this should significantly impact patient care by minimizing procedures and avoiding potential complications.

Evaluating the potential and problems of three-dimensional computed tomography measurements of arterial stenosis

Volume visualization is gaining widespread acceptance in medical applications. As its use increases, the issue of accuracy becomes critical. There have been very few studies examining the accuracy of volume rendering techniques. We studied the accuracy of hardware-assisted volume rendering for measurement of arterial stenosis in computed tomography (CT) data. The results of our study reveal that accurate measurements can be made from volume rendered CT data. However, error is present (absolute average error from 5.1% to 13.6%) and there is some variability, even for experts (standard deviation ranged from 4.8% to 15%). The evidence suggests that the choice of volume rendering (transfer function) parameters greatly affects the accuracy of the results. Accurate transfer function parameter selection is a difficult problem. Parameters that produce realistic images often provide inaccurate measurements. As the use of volume visualization grows and more inexperienced users begin using these tools for medical diagnosis and staging, new guidelines, aids, and techniques must be developed to ensure reliable, accurate visualization results.

Protection against experimental bubonic and pneumonic plague by a recombinant capsular F1-V antigen fusion protein vaccine

The current human whole-cell vaccine is ineffective against pneumonic plague caused by typical F1 capsule positive (F1+) strains of Yersinia pestis. The authors found this vaccine to also be ineffective against F1-negative (F1-) Y. pestis strains, which have been isolated from a human case and from rodents. For these reasons, the authors developed a recombinant vaccine composed of a fusion protein of F1 with a second protective immunogen, V antigen. This vaccine protected experimental mice against pneumonic as well as bubonic plague produced by either an F1+ or F1- strain of Y. pestis, gave better protection than F1 or V alone against the F1+ strain, and may provide the basis for an improved human plague vaccine.

Short- and long-term efficacy of single-dose subunit vaccines against Yersinia pestis in mice

A single, subcutaneous, 30-microg dose of either a combination of the Yersinia pestis proteins F1+V or a F1-V fusion protein adsorbed to the adjuvant aluminum hydroxide, protected Hsd:ND4 mice for one year against pneumonic plague. The recombinant F1+V vaccine provided significant protection as early as day 14 postimmunization. The current Plague Vaccine USP in a single 0.2-ml dose did not provide significant protection in this mouse model. Antibody titers to F1 and V peaked at approximately 5-12 weeks postimmunization and were still detectable one year later. These F1 and V subunit vaccines may offer effective long-term immunity with a reduced dosage schedule when compared with the presently licensed, formalin-killed, whole-cell vaccine.

Abdominal image segmentation using three-dimensional deformable models

RATIONALE AND OBJECTIVES

The authors develop a three-dimensional (3-D) deformable surface model-based segmentation scheme for abdominal computed tomography (CT) image segmentation.

METHODS

A parameterized 3-D surface model was developed to represent the human abdominal organs. An energy function defined on the direction of the image gradient and the surface normal of the deformable model was introduced to measure the match between the model and image data. A conjugate gradient algorithm was adapted to the minimization of the energy function.

RESULTS

Test results for synthetic images showed that the incorporation of surface directional information improved the results over those using only the magnitude of the image gradient. The algorithm was tested on 21 CT datasets. Of the 21 cases tested, 11 were evaluated visually by a radiologist and the results were judged to be without noticeable error. The other 10 were evaluated over a distance function. The average distance was less than 1 voxel.

CONCLUSIONS

The deformable model-based segmentation scheme produces robust and acceptable outputs on abdominal CT images.

Virtual angioscopy using spiral CT and real-time interactive volume-rendering techniques

Our purpose was to describe a technique for visualizing the inner contours of the vasculature using contrast enhanced spiral CT and volume rendering techniques. Because the technique is similar to using a camera to look inside vessels, we call this technique "virtual angioscopy." Preliminary results suggest virtual angioscopy using volumetric 3D rendering techniques as a potentially useful technique for the noninvasive evaluation of vascular pathology.

Interactive three-dimensional volume rendering of spiral CT data: current applications in the thorax

Spiral computed tomographic (CT) data sets coupled with a real-time volume-rendering technique allow creation of accurate three-dimensional (3D) images that can be used for a wide range of clinical applications. The image contrast of and relative pixel attenuations in the final image can be interactively modified by the user in real time by manipulating trapezoidal transfer functions. Although 3D images are not required for diagnosis, they aid both radiologists and referring clinicians by demonstrating anatomic relationships and the extent of disease, particularly for vessels oriented in the z axis. Three-dimensional imaging of the vasculature and airway structures has many advantages, including the potential to obviate invasive procedures such as angiography and bronchoscopy. Clinical applications of volume rendering of spiral CT data include cardiovascular imaging (aorta, pulmonary vasculature, and venous abnormalities), staging of thoracic neoplasms (mediastinal and pulmonary masses), tracheobronchial imaging, and imaging of chest wall disease.

Portal venous system thrombosis: helical CT angiography before transjugular intrahepatic portosystemic shunt creation

PURPOSE

To evaluate the utility of helical computed tomographic (CT) angiography for depiction of thrombi in the portal venous system in patients under consideration for transjugular intrahepatic portosystemic shunt (TIPS) creation.

MATERIALS AND METHODS

Contrast material-enhanced helical CT was performed before TIPS creation in 25 patients. Axial, multiplanar, and three-dimensional images were evaluated to determine whether thrombus was present in the portal system and whether TIPS creation was contraindicated. CT findings were confirmed at visceral angiography (n = 3), direct portography (n = 20), or duplex ultrasonography (n = 2).

RESULTS

Ten (40%) of 25 patients, including 10 (56%) of 18 patients with refractory variceal hemorrhage, had thrombus in the portal venous system. Helical CT scans depicted thrombus in nine (90%) of 10 patients (95% confidence interval = 0.71, 1.00) and in 16 (94%) of 17 vessels (95% confidence interval = 0.83, 1.00), including the portal vein (eight of eight patients), splenic vein (three of four patients), and superior mesenteric vein (five of five patients). TIPS creation was canceled in four (16%) patients on the basis of CT findings.

CONCLUSION

Thrombi in the portal venous system are common in patients with refractory variceal hemorrhage. Helical CT angiography is sensitive and specific for portal venous system thrombosis and can provide information that alters treatment in these patients.

Three-dimensional CT stereoscopic visualization of renal masses: impact on diagnosis and patient treatment

OBJECTIVE

The objective of this study was to determine whether three-dimensional reconstruction with stereoscopic display of helical CT data sets and CT angiography are useful in the examination of patients with known or suspected renal masses.

CONCLUSION

Volume-rendering techniques applied to helical CT data sets coupled with three-dimensional stereoscopic imaging provide a complete examination of patients with known or suspected renal masses. Such information can help guide patient treatment and provide a single preoperative study when nephron-sparing surgery or total nephrectomy is considered.

Automatic liver segmentation technique for three-dimensional visualization of CT data

PURPOSE

To develop a system for automatic segmentation of the liver from computed tomographic (CT) scans of the abdomen for three-dimensional volume-rendering displays.

MATERIALS AND METHODS

An automated liver segmentation system was developed, which combined domain knowledge with analysis of a global histogram, morphologic operators, and the parametrically deformable contour model. Boundaries of the thresholded liver volume were modified section-by-section by exploiting information from adjacent sections. These boundaries were refined by optimization of the parametrically deformable contour model. Volume-rendered images were created by using the boundaries to exclude tissues outside the liver. The system was tested on CT data sets from 10 cases of potentially resectable hepatic neoplasm.

RESULTS

Of the 401 sections in the 10 cases, 53 sections (13.2%) required user modifications during segmentation. The utility of the three-dimensional-rendered images with use of these liver boundaries was judged by a radiologist as being comparable to that of three-dimensional images created with manual editing. Twenty-eight of the sections were deemed imperfect by the radiologist and might need further modifications.

CONCLUSION

An effective technique for automatic segmentation of the liver from CT images has been developed. This technique promises to save time and simplify the creation of three-dimensional liver images by minimizing operator intervention.

CT angiography with volume rendering: advantages and applications in splanchnic vascular imaging

The authors compared volume rendering with maximum intensity projection (MIP) and shaded surface display as a technique for generating three-dimensional (3D) images of the vasculature from spiral computed tomography (CT) data sets. In four patients with pathologic splanchnic vasculature, the advantages of volume-rendered display are illustrated for depiction of 3D vascular anatomy, vascular and visceral interrelationships, variant vasculature, tumor encasement, and hepatic tumor localization for presurgical planning.

Fraction 1 capsular antigen (F1) purification from Yersinia pestis CO92 and from an Escherichia coli recombinant strain and efficacy against lethal plague challenge

As a first step in formulating an improved plague vaccine, we developed a simple purification strategy that produced high yields of pure cell-associated and culture supernatant-derived fraction 1 capsular antigen (F1) from both avirulent Yersinia pestis C092 (Pgm- Lcr-) and an Escherichia coli F1-producing recombinant strain. Cell-associated F1 was partially purified by sequential ammonium sulfate precipitations of a sodium chloride extract of acetone-dried bacteria harvested from broth cultures. Cell-free F1 was precipitated directly from culture supernatants with a single application of 30% ammonium sulfate. By exploiting the aggregative property of F1, large quantities of purified high-molecular-weight F1 species from both cell extracts and supernatants were isolated in the void volume of a preparative gel filtration column. Highly purified, endotoxin-free F1, combined with two different adjuvants, induced very high F1 titers in mice and protected them against either subcutaneous (70 to 100% survival) or aerosol (65 to 84% survival) challenge with virulent organisms. This protection was independent of the source of the antigen and the adjuvant used. F1-induced protection against both subcutaneous and aerosol challenge was also significantly better than that conferred by immunization with the licensed killed whole-cell vaccine. Our results indicate that F1 antigen represents a major protective component of previously studied crude capsule preparations, and immunity to F1 antigen provides a primary means for the host to overcome plague infection by either the subcutaneous or respiratory route.

Skeletal 3-D CT: advantages of volume rendering over surface rendering

Both surface rendering and volume rendering have been extensively applied to CT data for 3-D visualization of skeletal pathology. The review illustrates potential limitations of each technique by directly comparing 3-D images of bone pathology created using volume rendering and surface rendering. Surface rendering show gross 3-D relationships most effectively, but suffer from more stairstep artifacts and fail to effectively display lesions hidden behind overlying bone or located beneath the bone cortex. Volume-rendering algorithms effectively show subcortical lesions, minimally displaced fractures, and hidden areas of interest with few artifacts. Volume algorithms show 3-D relationships with varying degrees of success depending on the degree of surface shading and opacity. While surface rendering creates more three-dimensionally realistic images of the bone surface, it may be of limited clinical utility due to numerous artifacts and the inability to show subcortical pathology. Volume rendering is a flexible 3-D technique that effectively displays a variety of skeletal pathology with few artifacts.

Relationship between virulence and immunity as revealed in recent studies of the F1 capsule of Yersinia pestis

Yersinia pestis, the causative agent of plague, possesses multiple virulence determinants encoded on its three plasmids and on its chromosome. We evaluated the role of the protein capsule F1 in virulence an immunity against plague. Strains lacking F1, either those that are naturally occurring or those with genetically defined nonpolar mutations in the structural gene, retained their virulence for mice and nonhuman primates. However, both active immunization with F1, from either a recombinant vector or Y. pestis, and passive immunization with F1 monoclonal antibody protected mice from experimental infection with wild-type F1-positive organisms. These results suggest that protective immunogens like F1 need not be essential for virulence. The rare isolation of virulent F1-negative organisms from F1-immunized animals infected with F1-positive strains supports this conclusion and also suggests that, in addition to F1, an optimal vaccine against plague should include essential virulence factors as immunogens.

Phase variation of Enterococcus faecalis pAD1 conjugation functions relates to changes in iteron sequence region

pAD1 (60 kb) is a conjugative, hemolysin/bacteriocin plasmid in Enterococcus faecalis. It confers a mating response to the peptide sex pheromone cAD1 produced by recipient (plasmid-free) cells, leading to highly efficient plasmid transfer in broth matings. Control of the physiological response to cAD1 can been overridden by a reversible phase variation event at frequencies on the order of 10(-4) to 10(-3) per cell per generation (L. T. Pontius and D. B. Clewell, Plasmid 26:172-185, 1991). The variant forms are designated Dryc and Dry+, which reflects the colony morphologies of cells whose conjugation functions are switched on and off, respectively. Here we show that Dryc variants exhibit a structural change in a region between repA and repB that contains two clusters of 8-bp iterons. The change involved a 31- or 32-bp increase in size of this region. In three or four independent variants examined, one of the iteron clusters increased in size from 13 to 17 iterons. When iteron DNA was placed on a multicopy plasmid and introduced into a wild-type pAD1 derivative, the Dryc phenotype was generated. Since traA, a key negative regulator of conjugation, bears several centrally located iteron-like sequences with the same orientation, we speculate that the protein(s) that normally binds iterons (possibly RepA and/or RepB) blocks traA transcription in Dryc variants.

Three-dimensional spiral CT during arterial portography: comparison of three rendering techniques

The three most common techniques for three-dimensional reconstruction are surface rendering, maximum-intensity projection (MIP), and volume rendering. Surface-rendering algorithms model objects as collections of geometric primitives that are displayed with surface shading. The MIP algorithm renders an image by selecting the voxel with the maximum intensity signal along a line extended from the viewer's eye through the data volume. Volume-rendering algorithms sum the weighted contributions of all voxels along the line. Each technique has advantages and shortcomings that must be considered during selection of one for a specific clinical problem and during interpretation of the resulting images. With surface rendering, sharp-edged, clear three-dimensional reconstruction can be completed on modest computer systems; however, overlapping structures cannot be visualized and artifacts are a problem. MIP is computationally a fast technique, but it does not allow depiction of overlapping structures, and its images are three-dimensionally ambiguous unless depth cues are provided. Both surface rendering and MIP use less than 10% of the image data. In contrast, volume rendering uses nearly all of the data, allows demonstration of overlapping structures, and engenders few artifacts, but it requires substantially more computer power than the other techniques.

Construction of recombination-deficient strains of Streptococcus gordonii by disruption of the recA gene

Degenerate oligonucleotide primers were used in a polymerase chain reaction (PCR) to amplify a region of the recA sequence of Streptococcus gordonii Challis. The resulting PCR fragment was cloned into the suicide vector pAM6199 and introduced into strain Challis, giving rise to recombination-deficient strains in which the recA gene was specifically inactivated.

Architecture of the vir regulons of group A streptococci parallels opacity factor phenotype and M protein class

Group A streptococci have traditionally been categorized into two broad groups based on the presence or absence of serum opacity factor (OF). Recent studies show that these two groups vary in a number of properties in addition to the OF phenotype, including sequence variations in the constant region of the antiphagocytic M protein genes, the presence or absence of immunoglobulin G Fc receptor proteins, and the presence or absence of multiple M protein-like genes situated in a tandem array. The M protein genes (emm) in OF- streptococcal strains are known to be part of a regulon of virulence-related genes controlled by the trans-acting positive regulatory gene, virR, situated just upstream of emm. In OF+ strains, however, the region adjacent to virR is occupied by an M protein-related, type IIa immunoglobulin G Fc receptor gene (fcrA), and the relative position of emm has not been determined. To further define the vir regulon in OF+ streptococci, we used the polymerase chain reaction to show that fcrA49 is situated immediately upstream of emm49 in the OF+ type 49 strain CS101. This result shows for the first time the separate identity and genetic linkage of these two genes in the vir regulon of an OF+ group A streptococcal strain and confirms our previous hypothesis that emm49 exists as the central gene in a trio of emm-like genes. Additionally, using DNA hybridizations, we found considerable sequence divergence between OF- and OF+ group A streptococci in virR and in the noncoding sequences between virR and the emm or fcrA expression site. We found, however, a high degree of sequence conservation in this region within each of the two groups of strains.

Identification of two type IIa IgG-binding proteins expressed by a single group A streptococcus

Functional heterogeneity associated with Ig-binding proteins expressed by group A streptococci is well documented. In this study we have demonstrated that treatment of group A streptococcal isolate 64/14 with CNBr resulted in the solubilization of two different sized proteins that displayed identical functional reactivity with human IgG1, IgG2, and IgG4 (characteristics of a type IIa binding protein). Monospecific polyclonal antibodies to each form of type IIa molecule were prepared and no antigenic cross-reactivity between the two m.w. forms of type IIa binding protein could be detected. The smaller m.w. protein was shown to be identical or closely related to the recombinant type IIa protein cloned from strain CS110. These studies provide further evidence for the heterogeneity of type II Ig-binding proteins expressed by pathogenic group A streptococci.

Identification of two type IIa IgG-binding proteins expressed by a single group A streptococcus

Functional heterogeneity associated with Ig-binding proteins expressed by group A streptococci is well documented. In this study we have demonstrated that treatment of group A streptococcal isolate 64/14 with CNBr resulted in the solubilization of two different sized proteins that displayed identical functional reactivity with human IgG1, IgG2, and IgG4 (characteristics of a type IIa binding protein). Monospecific polyclonal antibodies to each form of type IIa molecule were prepared and no antigenic cross-reactivity between the two m.w. forms of type IIa binding protein could be detected. The smaller m.w. protein was shown to be identical or closely related to the recombinant type IIa protein cloned from strain CS110. These studies provide further evidence for the heterogeneity of type II Ig-binding proteins expressed by pathogenic group A streptococci.

Degenerate oligonucleotide primers for enzymatic amplification of recA sequences from gram-positive bacteria and mycoplasmas

RecA protein in gram-negative bacteria, especially in Escherichia coli, has been extensively studied, but little is known about this key enzyme in other procaryotes. Described here are degenerate oligonucleotide primers that have been used to amplify by the polymerase chain reaction (PCR) recA sequences from several gram-positive bacteria and mycoplasmas. The DNA sequences of recA PCR products from Streptococcus pyogenes, Streptococcus mutans, Enterococcus faecalis, and Mycoplasma pulmonis were determined and compared. These data indicate that the M. pulmonis recA gene has diverged significantly from recA genes of other eubacteria. It should be possible to use cloned recA PCR products to construct recA mutants, thereby providing the means of elucidating homologous genetic recombination and DNA repair activities in these organisms.

Isolated DNA repeat region from fcrA76, the Fc-binding protein gene from an M-type 76 strain of group A streptococci, encodes a protein with Fc-binding activity

The DNA repeat region of fcrA76, the gene encoding a group A streptococcal Fc-binding protein, was subcloned in-frame into an Escherichia coli plasmid expression vector. The expressed protein product displayed the same Fc-binding properties as the full-length Fc-binding protein expressed from fcrA76. The affinity-purified, full-length Fc-binding protein was found to compete with staphylococcal protein A or streptococcal protein G for binding to beads coated with human IgG. These results are consistent with earlier studies suggesting that the binding sites on human IgG for protein A, protein G and the type II Fc-binding protein from group A streptococci are located at the interface of the CH2 and CH3 domains of the Fc region.

Fc-receptor and M-protein genes of group A streptococci are products of gene duplication

The partial nucleotide sequence for an Fc-receptor gene from an M-type 76 group A streptococcus was determined. DNA sequence analysis revealed considerable sequence similarity between the Fc-receptor and M-protein genes in their proposed promoter regions, signal sequences, and 3' termini. Additional analysis indicated that the deduced Fc-receptor protein contains a proline-rich region and membrane anchor region highly similar to that of M protein. In view of these results, we postulated that Fc-receptor and M-protein genes of group A streptococci are the products of gene duplication from a common ancestral gene. It is proposed that DNA sequence similarity between these two genes may allow for extragenic homologous recombination as a means of generating antigenic diversity in these two surface proteins.

Cloning and expression of the gene for an immunoglobulin G Fc receptor protein from a group A streptococcus

DNA containing the 5' end of the M-12 structural gene was used as a probe in colony hybridizations in an attempt to clone the M-76 gene from an M-type 76 group A streptococcal strain. A single positive colony was detected, and Southern hybridization analysis of plasmid DNA isolated from this colony indicated that the insert DNA had homology to the 5' end of the M-12 structural gene. Subclones were constructed to define the limits of the M-76 gene, and sonicates of these subclones were reacted with M-76-specific antiserum in immunodiffusion. A sonicate of one subclone, JM83(pDH56), reacted strongly with the M-76-specific antiserum but also reacted with preimmune rabbit serum. Protein expressed from this subclone bound immunoglobulin from horse and pig, as well as human myeloma immunoglobulin G (IgG) representing all four subclasses and purified human IgG Fc fragments. This indicated that JM83(pDH56) expressed a protein with characteristics previously attributed to the IgG Fc receptor protein from group A streptococci. Western blot analysis indicated that the cloned IgG Fc receptor protein had a molecular weight of approximately 29,000. Binding studies showed that the Fc receptor gene is expressed by the M-type 76 strain from which it was cloned and by an M- variant.