Eliminating Algorithmic Racial Bias in Clinical Decision Support Algorithms: Use Cases from the Veterans Health Administration

The Veterans Health Administration uses equity- and evidence-based principles to examine, correct, and eliminate use of potentially biased clinical equations and predictive models. We discuss the processes, successes, challenges, and next steps in four examples. We detail elimination of the race modifier for estimated kidney function and discuss steps to achieve more equitable pulmonary function testing measurement. We detail the use of equity lenses in two predictive clinical modeling tools: Stratification Tool for Opioid Risk Mitigation (STORM) and Care Assessment Need (CAN) predictive models. We conclude with consideration of ways to advance racial health equity in clinical decision support algorithms.

Development and validation of a standardized blood culture contamination definition and metric dashboard for a large health care system

OBJECTIVES

Blood culture contamination is a major problem in health care, with significant impacts on both patient safety and cost. Initiatives to reduce blood culture contamination require a reliable, consistent metric to track the success of interventions. The objective of our project was to establish a standardized definition of blood culture contamination suitable for use in a Veterans Health Administration (VHA) national data query, then to validate this definition and query. A secondary objective was to construct a national VHA data dashboard to display the data from this query that could be used in VHA quality improvement projects aimed at reducing blood culture contamination.

METHODS

A VHA microbiology expert work group was formed to generate a standardized definition and oversee the validation studies. The standardized definition was used to generate data for calendar year 2021 using a Structured Query Language data query. Twelve VHA hospital microbiology laboratories compared the data from the query against their own locally derived contamination data and recorded those data in a data collection worksheet that all sites used. Data were collated and presented to the work group.

RESULTS

More than 50,000 blood culture accessions were in the validation data set, with more than 1,200 contamination events. The overall blood culture contamination rate for the 12 facilities participating was 2.56% with local definitions and data and 2.43% with the standardized definitions and data query. The main differences noted between the 2 data sets were deemed to be issues in local definitions. The query and definition were then converted into a national data dashboard that all VHA facilities can now access.

CONCLUSIONS

A standardized definition for blood culture contamination and a national data query were validated for enterprise-wide VHA use. To our knowledge, this represents the first reported standardized, validated, and automated approach for calculating and tracking blood culture contamination. This tool will be key in quality initiatives aimed at reducing contamination events in VHA.

Increased carbapenemase testing following implementation of national VA guidelines for carbapenem-resistant Enterobacterales (CRE)

OBJECTIVE

To describe national trends in testing and detection of carbapenemases produced by carbapenem-resistant Enterobacterales (CRE) and associate testing with culture and facility characteristics.

DESIGN

Retrospective cohort study.

SETTING

Department of Veterans' Affairs medical centers (VAMCs).

PARTICIPANTS

Patients seen at VAMCs between 2013 and 2018 with cultures positive for CRE, defined by national VA guidelines.

INTERVENTIONS

Microbiology and clinical data were extracted from national VA data sets. Carbapenemase testing was summarized using descriptive statistics. Characteristics associated with carbapenemase testing were assessed with bivariate analyses.

RESULTS

Of 5,778 standard cultures that grew CRE, 1,905 (33.0%) had evidence of molecular or phenotypic carbapenemase testing and 1,603 (84.1%) of these had carbapenemases detected. Among these cultures confirmed as carbapenemase-producing CRE, 1,053 (65.7%) had molecular testing for ≥1 gene. Almost all testing included KPC (n = 1,047, 99.4%), with KPC detected in 914 of 1,047 (87.3%) cultures. Testing and detection of other enzymes was less frequent. Carbapenemase testing increased over the study period from 23.5% of CRE cultures in 2013 to 58.9% in 2018. The South US Census region (38.6%) and the Northeast (37.2%) region had the highest proportion of CRE cultures with carbapenemase testing. High complexity (vs low) and urban (vs rural) facilities were significantly associated with carbapenemase testing (P < .0001).

CONCLUSIONS

Between 2013 and 2018, carbapenemase testing and detection increased in the VA, largely reflecting increased testing and detection of KPC. Surveillance of other carbapenemases is important due to global spread and increasing antibiotic resistance. Efforts supporting the expansion of carbapenemase testing to low-complexity, rural healthcare facilities and standardization of reporting of carbapenemase testing are needed.

National Kidney Foundation Laboratory Engagement Working Group Recommendations for Implementing the CKD-EPI 2021 Race-Free Equations for Estimated Glomerular Filtration Rate: Practical Guidance for Clinical Laboratories

Recognizing that race is a social and not a biological construct, healthcare professionals and the public have called for removal of race in clinical algorithms. In response, the National Kidney Foundation and the American Society of Nephrology created the Task Force on Reassessing the Inclusion of Race in Diagnosing Kidney Diseases to examine the issue and provide recommendations. The final report from the Task Force recommends calculating estimated glomerular filtration rate (eGFR) without a race coefficient using the recently published CKD-EPI 2021 creatinine and creatinine-cystatin C equations. The Task Force recommends immediately replacing older eGFRcr equations (MDRD Study and CKD-EPI 2009) with the new CKD-EPI 2021 equation. In a 2019 survey by the College of American Pathologists, 23% of 6200 laboratories reporting eGFRcr used an incorrect equation that is not suitable for use with standardized creatinine measurements, 34% used the CKD-EPI 2009 equation and 43% used the MDRD Study 2006 equation re-expressed for standardized creatinine measurement. Rapid transition to using the CKD-EPI 2021 equation is an opportunity for laboratories to standardize to a single equation to eliminate differences in eGFRcr due to different equations used by different laboratories, and to report eGFR without use of race. We provide guidance to laboratories for implementing the CKD-EPI 2021 equations for both eGFRcr and eGFRcr-cys.

VA-Wide, Multicenter Verification Study of the Cepheid Xpert SARS-CoV-2 Assay

Early in the Severe Acute Respiratory Syndrome Coronavirus 2 pandemic, there was a progressive increase in diagnostic demands that developed within a relatively short period of time. On February 4, 2020, the Secretary of Health and Human Services issued the Emergency Use Authorization for in vitro diagnostics assays for the Severe Acute Respiratory Syndrome Coronavirus 2 virus. Subsequently, multiple assays were approved under the Emergency Use Authorization, including the Cepheid Xpert SARS-CoV-2 assay. Presented here is a description of the nationally coordinated verification study of the Cepheid assay that was performed within the Veteran’s Affairs Health System. This coordinated study helped to expedite the verification process for a majority of the Veteran’s Affairs system labs, preserved precious system resources, and highlighted the power of a national medical system in response to an emergency.

493. Laboratory Evaluation and Epidemiology of Carbapenemase-Producing Carbapenem-Resistant Enterobacteriaceae in Department of Veterans Affairs, 2017

Background

Carbapenemase-producing (CP)-carbapenem-resistant Enterobacteriaceae (CRE) pose a major threat to public health and are a priority target of national prevention and control efforts including within Department of Veterans Affairs (VA). The laboratory evaluation and epidemiology of CRE in VA is uncertain.

Methods

Using data from the Veterans Health Administration Corporate Data Warehouse, we identified all Veterans with ≥1 CRE result obtained during 2017 and reviewed their electronic health record. Two case definitions were used: (1) 2015 CDC CRE (Enterobacteriaceae resistant to any carbapenem or with documented carbapenemase production) and (2) 2017 VA CP-CRE (E. coli, Klebsiella spp., and Enterobacter spp. resistant to imipenem, meropenem, or doripenem or with documented carbapenemase production). Patients harboring carbapenemase-producers detected by rectal screening tests only were included. We reviewed patient charts whose isolates met both CRE definitions, extracting detailed microbiologic and travel data for the first positive 2017 result.

Results

We identified 904 unique Veterans with CRE; 577 (64%) patients had results meeting both CRE case definitions while 327 (36%) had results meeting CDC CRE criteria only (Figure 1). Of the 458 patients with clinical isolates meeting both case definitions, urine specimens predominated (64%) and were associated with the lowest crude 90-day mortality (16%); mortality was highest amongst patients with respiratory tract cultures (40%) and bloodstream isolates (34%) (Figure 2). Nearly half (48%) of VA CP-CRE were tested for carbapenemases (76% in-house; 24% send-out); of these, 75%tested positive with 78% being a KPC, 1% NDM, and 21% unspecified (Figure 3). Additionally, all 119 CRE carriers with an identified gene had KPC. Only 7 patients (1%) had documented overseas travel.

Conclusion

Currently the incidence of CP-CRE in the nation’s largest healthcare system is low relative to other problem pathogens such as MRSA and Clostridioides difficile but is associated with a high crude mortality especially with respiratory and bloodstream isolates. KPC comprised almost all carbapenemases identified. This provides an initial, granular snapshot of CRE in VA to serve as a roadmap for ongoing CP-CRE prevention and control.

Disclosures

All authors: No reported disclosures.

Laboratory practices for identification and reporting of carbapenem-resistant Enterobacteriaceae in Department of Veterans Affairs facilities

Laboratory identification of carbapenem-resistant Enterobacteriaceae (CRE) is a key step in controlling its spread. Our survey showed that most Veterans Affairs laboratories follow VA guidelines for initial CRE identification, whereas 55.0% use PCR to confirm carbapenemase production. Most respondents were knowledgeable about CRE guidelines. Barriers included staffing, training, and financial resources.

2161. Pilot Implementation of a Nationwide Automated Multidrug-Resistant Organism Tracking and Alert System in Veterans Affairs

Background

Regional spread of multidrug-resistant organisms (MDROs), including carbapenem-resistant Enterobacteriaceae (CRE), can occur when carriers present unbeknownst to healthcare facilities and thereby delay appropriate infection control interventions. Herein, we describe pilot implementation of a novel national system that automatically alerts local facility staff to newly admitted patients with any history of CRE or methicillin-resistant Staphylococcus aureus (MRSA) in VA.

Methods

From December 2016 to November 2017, we implemented the alert system in 10 VA medical centers. The system continually monitors the VA Corporate Data Warehouse for new facility admissions nationwide among patients with archived CRE and MRSA data. When such admissions occur, an alert is emailed to Infection Prevention personnel at the local facility. During implementation, we upgraded to a faster, more accurate report, “MDRO Tracker”, that provided alerts within 4 hours of admission. We evaluated system utility in three ways: (1) assessing user data and feedback; (2) comparing a dataset identifying all unique patients harboring CRE and MRSA to the subset of patients whose most recent positive result was identified at a different VA facility; and (3) enrolling a convenience sample of CRE and MRSA patients to validate system accuracy and assess whether the new system or existing infrastructure identified the MDRO first. IRB approval was obtained at each site.

Results

The number of users increased over time and are shown in Figure 1. User feedback data are shown in Figure 2; 71/256 (28%) responses indicated that alert data were new and/or timely. Of all CRE- and MRSA-positive patients identified during the study period, 11/101 (11%) and 214/2,390 (9%), respectively, had positive MDRO results originating from a different VA facility. Of the 61 CRE and 1,720 MRSA patients enrolled by research staff, 21% (n = 13) of CRE and 7% (n = 71) of MRSA cases were first identified by the automated system.

Conclusion

This pilot implementation of a novel automated MDRO alert system shows feasibility and potential for substantial utility of such a system. Further refinement and expanded β-testing of the system is underway.

Disclosures

M. A. Gelman, Cepheid: Speaker, Speaking Fee.

Using Focused Laboratory Management and Quality Improvement Projects to Enhance Resident Training and Foster Scholarship

Training in patient safety, quality, and management is widely recognized as an important element of graduate medical education. These concepts have been intertwined in pathology graduate medical education for many years, although training programs face challenges in creating explicit learning opportunities in these fields. Tangibly involving pathology residents in management and quality improvement projects has the potential to teach and reinforce key concepts and further fulfill Accreditation Council for Graduate Medical Education goals for pursuing projects related to patient safety and quality improvement. In this report, we present our experience at a pathology residency program (University of Iowa) in engaging pathology residents in projects related to practical issues of laboratory management, process improvement, and informatics. In this program, at least 1 management/quality improvement project, typically performed during a clinical chemistry/management rotation, was required and ideally resulted in a journal publication. The residency program also initiated a monthly management/informatics series for pathology externs, residents, and fellows that covers a wide range of topics. Since 2010, all pathology residents at the University of Iowa have completed at least 1 management/quality improvement project. Many of the projects involved aspects of laboratory test utilization, with some projects focused on other areas such as human resources, informatics, or process improvement. Since 2012, 31 peer-reviewed journal articles involving effort from 26 residents have been published. Multiple projects resulted in changes in ongoing practice, particularly within the hospital electronic health record. Focused management/quality improvement projects involving pathology residents can result in both meaningful quality improvement and scholarly output.

The Veteran-Initiated Electronic Care Coordination: A Multisite Initiative to Promote and Evaluate Consumer-Mediated Health Information Exchange

INTRODUCTION

Information continuity is critical to person-centered care when patients receive care from multiple healthcare systems. Patients can access their electronic health record data through patient portals to facilitate information exchange. This pilot was developed to improve care continuity for rural Veterans by (1) promoting the use of the Department of Veterans Affairs (VA) patient portal to share health information with non-VA providers, and (2) evaluating the impact of health information sharing at a community appointment.

MATERIALS AND METHODS

Veterans from nine VA healthcare systems were trained to access and share their VA Continuity of Care Document (CCD) with their non-VA providers. Patients and non-VA providers completed surveys on their experiences.

RESULTS

Participants (n = 620) were primarily older, white, and Vietnam era Veterans. After training, 78% reported the CCD would help them be more involved in their healthcare and 86% planned to share it regularly with non-VA providers. Veterans (n = 256) then attended 277 community appointments. Provider responses from these appointments (n = 133) indicated they were confident in the accuracy of the information (97%) and wanted to continue to receive the CCD (96%). Ninety percent of providers reported the CCD improved their ability to have an accurate medication list and helped them make medication treatment decisions. Fifty percent reported they did not order a laboratory test or another procedure because of information available in the CCD.

CONCLUSIONS

This pilot demonstrates feasibility and value of patient access to a CCD to facilitate information sharing between VA and non-VA providers. Outreach and targeted education are needed to promote consumer-mediated health information exchange.

Patient Education for Consumer-Mediated HIE. A Pilot Randomized Controlled Trial of the Department of Veterans Affairs Blue Button

OBJECTIVES

Consumer-mediated health information exchange (HIE) is one of the three types of HIE designated by the Office of the National Coordinator. HIE is intended to improve the quality of care while reducing cost, yet empirical support for this claim is mixed. Future research should identify the contexts whereby HIE is most effective.

METHODS

This study was conducted as a pilot two-arm randomized controlled trial. In the intervention arm, 27 veterans were taught how to generate a Continuity of Care Document (CCD) within the Blue Button feature of their VA patient portal and were then asked to share it with their community non-VA provider. In the attention control condition, 25 Veterans were taught how to look up health information on the Internet. The impact of this training on the next non-VA medical visit was examined.

RESULTS

Nineteen (90%) veterans in the intervention arm shared their CCD with their non-VA provider as compared with 2 (17%) in the attention control arm (p<0.001). Both veterans and non-VA providers indicated high satisfaction with the CCD. Comparison of medical records between the VA and non-VA providers did not indicate improved medication reconciliation (p=0.72). If veterans shared their CCD prior to their non-VA providers ordering laboratory tests, the number of duplicate laboratories was significantly reduced (p=0.02).

CONCLUSIONS

In this pilot randomized controlled trial, training 52 veterans to share their CCD was feasible and accepted by both patients and providers. Sharing this document appeared to reduce duplicate laboratory draws, but did not have an impact on documented medication list concordance.

Pathology Milestones: Assessing Clinical Competency by Committee

All Accreditation Council for Graduate Medical Education accredited pathology residency training programs are now required to evaluate residents using the new Pathology Milestones assessment tool. Similar to implementation of the 6 Accreditation Council for Graduate Medical Education competencies a decade ago, there have been challenges in implementation of the new milestones for many residency programs. The pathology department at the University of Iowa has implemented a process that divides the labor of the task in rating residents while also maintaining consistency in the process. The process is described in detail, and some initial trends in milestone evaluation are described and discussed. Our experience indicates that thoughtful implementation of the Pathology Milestones can provide programs with valuable information that can inform curricular changes.

Identification and deletion of Tft1, a predicted glycosyltransferase necessary for cell wall β-1,3;1,4-glucan synthesis in Aspergillus fumigatus

Aspergillus fumigatus is an environmental mold that causes severe, often fatal invasive infections in immunocompromised patients. The search for new antifungal drug targets is critical, and the synthesis of the cell wall represents a potential area to find such a target. Embedded within the main β-1,3-glucan core of the A. fumigatus cell wall is a mixed linkage, β-D-(1,3;1,4)-glucan. The role of this molecule or how it is synthesized is unknown, though it comprises 10% of the glucans within the wall. While this is not a well-studied molecule in fungi, it has been studied in plants. Using the sequences of two plant mixed linkage glucan synthases, a single ortholog was identified in A. fumigatus (Tft1). A strain lacking this enzyme (tft1Δ) was generated along with revertant strains containing the native gene under the control of either the native or a strongly expressing promoter. Immunofluorescence staining with an antibody against β-(1,3;1,4)-glucan and biochemical quantification of this polysaccharide in the tft1Δ strain demonstrated complete loss of this molecule. Reintroduction of the gene into the knockout strain yielded reappearance in amounts that correlated with expected expression of the gene. The loss of Tft1 and mixed linkage glucan yielded no in vitro growth phenotype. However, there was a modest increase in virulence for the tft1Δ strain in a wax worm model. While the precise roles for β-(1,3;1,4)-glucan within A. fumigatus cell wall are still uncertain, it is clear that Tft1 plays a pivotal role in the biosynthesis of this cell wall polysaccharide.

Increasing colorectal cancer screening in an overdue population: participation and cost impacts of adding telephone calls to a FIT mailing program

Many people who live in rural areas face distance barriers to colonoscopy. Our previous study demonstrated the utility of mailing fecal immunochemical tests (FIT) to average risk patients overdue for colorectal cancer (CRC screening). The aims of this study were to determine if introductory and reminder telephone calls would increase the proportion of returned FITs as well as to compare costs. Average risk patients overdue for CRC screening received a high intensity intervention (HII), which included an introductory telephone call to see if they were interested in taking a FIT prior to mailing the test out and reminder phone calls if the FIT was not returned. This HII group was compared to our previous low intensity intervention (LII) where a FIT was mailed to a similar group of veterans with no telephone contact. While a higher proportion of eligible respondents returned FITs in the LII (92 vs. 45 %), there was a much higher proportion of FITs returned out of those mailed in the HII (85 vs. 14 %). The fewer wasted FITs in the HII led to it having lower cost per FIT returned ($27.43 vs. $44.86). Given that either intervention is a feasible approach for patients overdue for CRC screening, health care providers should consider offering FITs using a home-based mailing program along with other evidence-based CRC screening options to average risk patients. Factors such as location, patient population, FIT cost and reimbursement, and personnel costs need to be considered when deciding the most effective way to implement FIT screening.

Evaluation of a home-based colorectal cancer screening intervention in a rural state

PURPOSE

Distance from health care facilities can be a barrier to colorectal cancer (CRC) screening, especially for colonoscopy. Alternatively, an improved at-home stool-based screening tool, the fecal immunochemical test (FIT), requires only a single sample and has a better sensitivity-specificity balance compared to traditional guaiac fecal occult blood tests. Our objective was to determine if FITs mailed to asymptomatic, average-risk patients overdue for screening resulted in higher screening rates versus mailing educational materials alone or no intervention (ie, usual care).

METHODS

Veterans ages 51-64, asymptomatic, at average risk for CRC, overdue for screening and in a veterans administration (VA) catchment area covering a large rural population were randomly assigned to 3 groups: (1) education only (Ed) group: mailed CRC educational materials and a survey of screening history and preferences (N = 499); (2) FIT group: mailed the FIT, plus educational materials and survey (N = 500); and (3) usual care (UC) group: received no mailings (N = 500).

FINDINGS

At 6 months postintervention, 21% of the FIT group had received CRC screening by any method compared to 6% of the Ed group (and 6% of the UC group) (P < .0001). Of the 105 respondents from the FIT group, 71 (68%) were eligible to take the FIT. Of those, 64 (90%) completed the FIT and 8 (12%) tested positive.

CONCLUSIONS

This low-intensity intervention of mailing FITs to average risk patients overdue for screening resulted in a significantly higher screening rate than educational materials alone or usual care, and may be of particular interest in rural areas.

Unusual galactofuranose modification of a capsule polysaccharide in the pathogenic yeast Cryptococcus neoformans

Galactofuranose (Galf) is the five-membered ring form of galactose. Although it is absent from mammalian glycans, it occurs as a structural and antigenic component of important cell surface molecules in a variety of microbes, ranging from bacteria to parasites and fungi. One such organism is Cryptococcus neoformans, a pathogenic yeast that causes lethal meningoencephalitis in immunocompromised individuals, particularly AIDS patients. C. neoformans is unique among fungal pathogens in bearing a complex polysaccharide capsule, a critical virulence factor reported to include Galf. Notably, how Galf modification contributes to the structure and function of the cryptococcal capsule is not known. We have determined that Galf is β1,2-linked to an unusual tetrasubstituted galactopyranose of the glucuronoxylomannogalactan (GXMGal) capsule polysaccharide. This discovery fills a longstanding gap in our understanding of a major polymer of the cryptococcal capsule. We also engineered a C. neoformans strain that lacks UDP-galactopyranose mutase; this enzyme forms UDP-Galf, the nucleotide sugar donor required for Galf addition. Mutase activity was required for the incorporation of Galf into glucuronoxylomannogalactan but was dispensable for vegetative growth, cell integrity, and virulence in a mouse model.

A novel xylosylphosphotransferase activity discovered in Cryptococcus neoformans

Cryptococcus neoformans is a fungal pathogen that causes serious disease in immunocompromised individuals. The organism produces a distinctive polysaccharide capsule that is necessary for its virulence, a predominantly polysaccharide cell wall, and a variety of protein- and lipid-linked glycans. The glycan synthetic pathways of this pathogen are of great interest. Here we report the detection of a novel glycosylphosphotransferase activity in C. neoformans, identification of the corresponding gene, and characterization of the encoded protein. The observed activity is specific for UDP-xylose as a donor and for mannose acceptors and forms a xylose-alpha-1-phosphate-6-mannose linkage. This is the first report of a xylosylphosphotransferase activity in any system.

The structure of Cryptococcus neoformans galactoxylomannan contains beta-D-glucuronic acid

The structure of galactoxylomannan, a capsular polysaccharide from the opportunistic yeast Cryptococcus neoformans, was re-examined by NMR spectroscopy and GC-MS. The residue that is 3-linked to the side chain galactose and was previously assigned as beta-D-xylose [Vaishnav, V. V.; Bacon, B. E.; O'Neill, M.; Cherniak, R. Carbohydr. Res.1998, 306, 315-330] was determined to be beta-D-glucuronic acid. A revised structure for this polymer is presented, along with a proposal that this compound be termed glucuronoxylomannogalactan (GXMGal).

Cryptococcal xylosyltransferase 1 (Cxt1p) from Cryptococcus neoformans plays a direct role in the synthesis of capsule polysaccharides

The opportunistic yeast Cryptococcus neoformans causes serious disease in humans and expresses a prominent polysaccharide capsule that is required for its virulence. Little is known about how this capsule is synthesized. We previously identified a beta1,2-xylosyltransferase (Cxt1p) with in vitro enzymatic activity appropriate for involvement in capsule synthesis. Here, we investigate C. neoformans strains in which the corresponding gene has been deleted (cxt1Delta). Loss of CXT1 does not affect in vitro growth of the mutant cells or the general morphology of their capsules. However, NMR structural analysis of the two main capsule polysaccharides, glucuronoxylomannan (GXM) and galactoxylomannan (GalXM), showed that both were missing beta1,2-xylose residues. There was an approximately 30% reduction in the abundance of this residue in GXM in mutant compared with wild-type strains, and mutant GalXM was almost completely devoid of beta1,2-linked xylose. The GalXM from the mutant strain was also missing a beta1,3-linked xylose residue. Furthermore, deletion of CXT1 led to attenuation of cryptococcal growth in a mouse model of infection, suggesting that the affected xylose residues are important for normal host-pathogen interactions. Cxt1p is the first glycosyltransferase with a defined role in C. neoformans capsule biosynthesis, and cxt1Delta is the only strain identified to date with structural alterations of the capsule polysaccharide GalXM.

Diagnostic performance of a new automated heterophile antibody test in adults and children

Epstein-Barr virus serologic profiles were obtained from 618 patients using an automated platform, including the new BioPlex heterophile assay. When compared with 2 IgM viral capsid antigen (VCA) assays and a predicate heterophile assay, the BioPlex heterophile assay was more likely to be associated with serologic patterns of acute infection.

A beta-1,2-xylosyltransferase from Cryptococcus neoformans defines a new family of glycosyltransferases

Cryptococcus neoformans is an opportunistic fungal pathogen characterized by a prominent polysaccharide capsule that envelops the cell. Although this capsule is dispensable for in vitro growth, its presence is essential for virulence. The capsule is primarily made of two xylose-containing polysaccharides, glucuronoxylomannan and galactoxylomannan. There are likely to be multiple xylosyltransferases (XTs) involved in capsule synthesis, and the activities of these enzymes are potentially important for cryptococcal virulence. A beta-1,2-xylosyltransferase with specificity appropriate for capsule synthesis was purified approximately 3000-fold from C. neoformans, and the corresponding gene was identified and cloned. This sequence conferred XT activity when expressed in Saccharomyces cerevisiae, which lacks endogenous XT activity. The gene, termed CXT1 for cryptococcal xylosyltransferase 1, encodes a 79-kDa type II membrane protein with an N-linked glycosylation site and two DXD motifs. These latter motifs are believed to coordinate divalent cation binding in the activity of glycosyltransferases. Site-directed mutagenesis of one DXD motif abolished Cxt1p activity, even though this activity does not depend on the addition of a divalent cation. This may indicate a novel catalytic mechanism for glycosyl transfer. Five homologs of Cxt1p were found in the genome sequence of C. neoformans and 34 within the sequences of other fungi, although none were found in other organisms. Many of the homologous proteins are similar in size to Cxt1p, and all are conserved with respect to the essential DXD motif. These proteins represent a new family of glycosyltransferases, found exclusively within the fungal kingdom.

Evaluation of a multiplexed bead assay for assessment of Epstein-Barr virus immunologic status

Currently, serological assays using either indirect immunofluorescence assay or enzyme-linked immunosorbent assay (ELISA) are performed to evaluate the status of Epstein-Barr virus (EBV) infection in humans. Although these methods are reliable, they are limited to testing an antibody response to a single viral antigen per reaction, thus necessitating a panel of assays to complete the evaluation. In contrast, a new bead-based method (BioPlex 2200; Bio-Rad Laboratories, Hercules, Calif.) can analyze the humoral response to multiple antigens in a single tube. This approach potentially reduces overall cost, turnaround time, and sample volume. The aim of this study was to evaluate the multiplexed EBV serologic assays performed on the BioPlex 2200 platform compared to results of conventional heterophile and ELISA-based assays. A total of 167 nonconsecutive, stored serum samples from adult and pediatric patients submitted for EBV serologic studies were used in the evaluation. Concordance between results generated by the BioPlex 2200 system and conventional assays was calculated. The anti-EA-D assay had the lowest concordance at 91%. The BioPlex 2200 system showed 97% agreement with conventional heterophile and anti-nuclear antigen assays and 92% agreement with the anti-VCA IgG and immunoglobulin M assays. Agreement between the BioPlex 2200 system and conventional testing was 92% with respect to categorization of acute versus nonacute EBV disease. The correlation between these two systems with regard to assignment into one of four categories of EBV status was also good (82%). In summary, there is excellent correlation between contemporary EBV serologic testing and the BioPlex 2200 system.

UDP-glucose dehydrogenase plays multiple roles in the biology of the pathogenic fungus Cryptococcus neoformans

Cryptococcus neoformans is a pathogenic fungus surrounded by an elaborate polysaccharide capsule that is strictly required for its virulence in humans and other mammals. Nearly half of the sugar residues in the capsule are derived from UDP-glucuronic acid or its metabolites. To examine the role of these nucleotide sugars in C. neoformans, the gene encoding UDP-glucose dehydrogenase was disrupted. Mass spectrometry analysis of nucleotide sugar pools showed that the resulting mutant lacked both UDP-glucuronic acid and its downstream product, UDP-xylose, thus confirming the effect of the knockout and indicating that an alternate pathway for UDP-glucuronic acid production was not used. The mutant was dramatically affected by the lack of specific sugar donors, demonstrating altered cell integrity, temperature sensitivity, lack of growth in an animal model of cryptococcosis, and morphological defects. Additionally, the polysaccharide capsule could not be detected on the mutant cells, although the possibility remains that abbreviated forms of capsule components are made, possibly without proper surface display. The capsule defect is largely independent of the other observed changes, as cells that are acapsular because of mutations in other genes show lack of virulence but do not exhibit alterations in cell integrity, temperature sensitivity, or cellular morphology. All of the observed alterations were reversed by correction of the gene disruption.

Biosynthesis of d-arabinose in Mycobacterium smegmatis: specific labeling from d-glucose

d-Arabinose is a major sugar in the cell wall polysaccharides of Mycobacterium tuberculosis and other mycobacterial species. The reactions involved in the biosynthesis and activation of d-arabinose represent excellent potential sites for drug intervention since d-arabinose is not found in mammalian cells, and the cell wall arabinomannan and/or arabinogalactan appear to be essential for cell survival. Since the pathway involved in conversion of d-glucose to d-arabinose is unknown, we incubated cells of Mycobacterium smegmatis individually with [1-(14)C]glucose, [3,4-(14)C]glucose, and [6-(14)C]glucose and compared the specific activities of the cell wall-bound arabinose. Although the specific activity of the arabinose was about 25% lower with [6-(14)C]glucose than with other labels, there did not appear to be selective loss of either carbon 1 or carbon 6, suggesting that arabinose was not formed by loss of carbon 1 of glucose via the oxidative step of the pentose phosphate pathway, or by loss of carbon 6 in the uronic acid pathway. Similar labeling patterns were observed with ribose isolated from the nucleic acid fraction. Since these results suggested an unusual pathway of pentose formation, labeling studies were also done with [1-(13)C]glucose, [2-(13)C]glucose, and [6-(13)C]glucose and the cell wall arabinose was examined by NMR analysis. This method allows one to determine the relative (13)C content in each carbon of the arabinose. The labeling patterns suggested that the most likely pathway was condensation of carbons 1 and 2 of fructose 6-phosphate produced by the transaldolase reaction with carbons 4, 5, and 6 (i.e., glyceraldehyde 3-phosphate) formed by fructose-1,6 bisphosphate aldolase. Cell-free enzyme extracts of M. smegmatis were incubated with ribose 5-phosphate, xylulose 5-phosphate, and d-arabinose 5-phosphate under a variety of experimental conditions. Although the ribose 5-phosphate and xylulose 5-phosphate were converted to other pentoses and hexoses, no arabinose 5-phosphate (or free arabinose) was detected in any of these reactions. In addition, these enzyme extracts did not convert arabinose 5-phosphate to any other pentose or hexose. In addition, incubation of [(14)C]glucose 6-phosphate and various nucleoside triphosphates (ATP, CTP, GTP, TTP, and UTP) with cytosolic or membrane fractions from the mycobacterial cells did not result in formation of a nucleotide form of arabinose, although other radioactive sugars including rhamnose and galactose were found in the nucleotide fraction. Furthermore, no radioactive arabinose was found in the nucleotide fraction isolated from M. smegmatis cells grown in [(3)H]glucose, nor was arabinose detected in a large-scale extraction of the sugar nucleotide fraction from 300 g of cells. The logical conclusion from these studies is that d-arabinose is probably produced from d-ribose by epimerization of carbon 2 of the ribose moiety of polyprenylphosphate-ribose to form polyprenylphosphate-arabinose, which is then used as the precursor for formation of arabinosyl polymers.