Effect of Methacryloyloxydecyl Dihydrogen Phosphate–Containing Silane and Adhesive Used Alone or in Combination on the Bond Strength and Chemical Interaction With Zirconia Ceramics Under Thermal Aging

Clinical Relevance

Achieving durable bonding to zirconia is fundamental for the application of a methacryloyloxydecyl dihydrogen phosphate (MDP)–containing silane solution or an MDP-containing silane solution associated with an MDP-containing universal adhesive.

SUMMARY

Objectives: To evaluate the effect of a methacryloyloxydecyl dihydrogen phosphate (MDP)–containing silane coupling agent and universal adhesive, used alone or in combination, on the microshear bond strength (μSBS) to zirconia after 24 hours of water storage (24h) and after 10,000 thermocycles (TC), complemented with chemical analysis of the surface to establish the presence of MDP on the surface of the zirconia after bonding procedures.

Methods and Materials: Thirty computer-aided design/computed-aided manufacturing blocks of zirconia were cut into four sections (6×6×6 mm) and sintered. Zirconia sections (n=96) were assigned to 24 groups according to three factors: 1) silane (no silane, Monobond S [MBS], Monobond P [MB+]), 2) adhesive + resin cement (no adhesive + Enforce [ENF], no adhesive + RelyX Ultimate [REX], Prime&Bond Elect + Enforce [PBE/ENF], Scotchbond Universal + RelyX Ultimate [SBU/REX]), and 3) thermocycling (no thermocycling [24h], 10,000 thermocycles [TC]). Upon silane/adhesive application, cylinder-shaped matrices were filled with resin cement and light cured. Specimens were tested in μSBS (1.0 mm/min) after 24h or TC. The μSBS data were analyzed using twoway ANOVA and Tukey’s post hoc test (α=0.05). In addition, micro-Raman spectroscopy was used to analyze the zirconia surface for immediate chemical interaction analysis (n=24).

Results: For the 24h condition, PBE/ENF resulted in lower mean μSBS than both groups with silane without PBE (MBS and MB+ groups; p<0.001). SBU alone or MB+ alone and MB+ associated with SBU showed the highest mean μSBS (p<0.001). For the TC condition, all groups showed a significant decrease in mean μSBS compared with those of 24h (p<0.001), with the exception of MB+ associated to SBU (p>0.05). However, the application of MB+ alone or MB+ associated to SBU resulted in higher mean μSBS (p<0.001) after TC than the remaining TC groups. In terms of chemical interaction, only the SBU groups, alone or combined with both of the silane agents, were associated with the methacrylate groups after rinsing.

Conclusions: The results of the current study support the use of an MDP-containing silane solution or an MDP-containing silane solution associated with an MDP-containing universal adhesive for bonding to air-abraded zirconia, as a more stable bonding after thermocycling.

Isolation of a novel intertypic recombinant human mastadenovirus B2 from two unrelated bone marrow transplant recipients

Human adenoviruses (HAdV) are well-known opportunistic pathogens of immunocompromised adult and pediatric patients but specific associations between HAdV species or individual HAdV types and disease are poorly understood.

In this study we report the isolation of a novel HAdV-B2 genotype from two unrelated immunocompromised patients, both recipients of a hematopoietic cell transplant. In both patients, the course of HAdV infection is consistent with a scenario of reactivation of a latent virus rather than a primary opportunistic infection.

Archived HAdV PCR-positive plasma, urine, and stool specimens were processed for virus isolation and detailed molecular characterization. Virus isolates were recovered from patient 1 from PCR-positive urine specimens obtained at days 103 and 116 after transplant in association with gross hematuria, and from a stool specimen obtained 138 days after transplant in association with diarrhea. An isolate was recovered from patient 2 from a PCR-positive urine specimen. Hexon and fiber gene amplification and sequencing were carried out for initial molecular typing, identifying the isolates as an intertypic recombinant with a HAdV-11-like hexon gene and a HAdV-77-like fiber gene. Comprehensive restriction fragment length polymorphism (RFLP) analysis was performed on viral DNA purified from urine and stool isolates, and next generation whole genome sequencing was carried out on purified viral genomic DNA. The genomes of the two isolated strains are 99.5% identical and represent the same RFLP genomic variant. The identified virus is a novel HAdV-B2 genotype designated HAdV-78 exhibiting a HAdV-11-like penton base, a HAdV-11-like hexon and a HAdV-77-like fiber (P11H11F77).

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A novel HAdV-B2 type was isolated from 2 unrelated stem cell transplant recipients.

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The two isolated strains are 99.5% identical and represent the same genomic variant.

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The virus is an intertypic recombinant P11H11F77 designated HAdV-78.

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Genotype HAdV-78 is closely related to HAdV-77 with a 99% sequence similarity.

2346. Cost Savings Associated with Implementation of Clinical Decision Support for Clostridiodes difficile Testing

Background

Clinical decision support for Clostridioides difficile infection (CDI) diagnostics reduces inappropriate testing, leading to decreased need for isolation and antibiotic use. Our institution utilized manual discontinuation by laboratory staff of CDI testing for inappropriate specimens, including formed stool and age < 1 year. We aimed to assess the financial impact of instituting a CDI best practice alert at a quaternary care children’s hospital.

Methods

A multidisciplinary team mapped inappropriate testing criteria identified from literature review with discrete fields in our electronic health record (EHR, EpicCare) to design an alert. The exclusion criteria identified included: (1) age < 1 year; (2) positive C. difficile test within past 14 days; (3) less than or equal to 3 unformed stools in past 24 hours; (4) current receipt of CDI-directed therapy; or (5) laxative use or barium exposure in prior 48 hours. 6 months of data prior to implementation were reviewed to estimate impact of the alert. At implementation, any exclusion criteria detected in the EHR at the time of order entry triggered an alert to deter CDI testing. Cost estimates for averted tests (Quick Check Complete Assay/Illumigene) included cost of test ($50), cost of isolation/personal protective equipment ($159/day), and cost of treatment with oral vancomycin in false-positives ($2250/treatment course).

Results

In a 6-month pre-implementation period, 586 tests for CDI were ordered; of which, 23% were identified by our criteria as inappropriate. During the first 3 months of alert implementation, 256 tests were ordered, of which 105 (41%) caused the alert to fire. Of those, 56 tests were not ordered, for a 22% reduction in testing. Laboratory staff continued to manually stop tests not meeting criteria, such as patient age <1 year when possible. Based on avoidance of testing, use of PPE, and 10 day antibiotic treatment for false-positives (assumed 25% by literature review), this translated to cost savings of $69,916, and an annual cost savings of $279,664.

Conclusion

Implementation of an alert for select patients using a bioinformatics algorithm reduced inappropriate CDI testing. Clinical decision support for CDI can lead to substantial cost savings for both antibiotic use and isolation precautions.

Disclosures

All authors: No reported disclosures.

1762. Genotype Prevalence and Molecular Characteristics of Human Adenovirus in Pediatric Hematopoietic Stem Cell Transplant Recipients

Background

Human adenovirus (HAdV) is a documented source of morbidity and mortality after hematopoietic cell transplant (HCT); however, there are limited data documenting HAdV species and type in this population. Understanding the molecular characteristics of HAdV could inform the development and assessment of interventions. The species and type of HAdV-positive specimens are detailed using an archived convenience sample of specimens obtained in pediatric HCT recipients.

Methods

The cohort included autologous and allogeneic HCT recipients between January 2000 and December 2013. An archived clinical repository of frozen specimens was interrogated to identify residual HAdV-positive specimens, which were sent to Lovelace Respiratory Research Institute (LRRI) to determine species and type. Medical chart review was performed to determine whether an isolate was related to HAdV disease or HAdV-attributable death.

Results

There were 547 HAdV PCR-positive clinical specimens from 87 HCT recipients. Of the 547 specimens, 289 were identified from an archived repository and sent to LRRI to determine species and type, and HAdV was successfully isolated and typed from 61 (Figure 1). Species C was the most common species (59.0%) with C2 being the most frequent type (34.4%). Of the 15 recipients with type C2, plasma was the most common specimen source (57.1%). Three recipients with C2 had this species and type detected from multiple sources (Tables 1 and 2). Among those with a typing result, type C2 also was responsible for 33.3% of all HAdV-attributed disease and 38.1% of all HAdV-attributed death.

Conclusion

Species C was the most common species to be isolated in a convenience sample of HAdV-positive clinical specimens from a single-center cohort of pediatric HCT recipients. Type C2 was most commonly associated with HAdV disease and attributable death. These results suggest HAdV species and type influence the impact of HAdV in this patient population. The findings need to be confirmed in prospective cohorts but suggest real-time molecular typing may be relevant and provide possible targets for the development of future interventions. These results must be interpreted with caution; not all clinical specimens were available for molecular typing, and it is possible C2 is easier to isolate from archived specimens.

Disclosures

All authors: No reported disclosures.

Outcomes of Human Adenovirus Infection and Disease in a Retrospective Cohort of Pediatric Hematopoietic Cell Transplant Recipients

BACKGROUND

Human adenoviruses (HAdVs) are associated with significant morbidity and death after hematopoietic cell transplantation (HCT). In this study, we sought to determine the incidence of HAdV infection among pediatric HCT recipients in the polymerase chain reaction (PCR) testing era, identify risk factors for viremia among patients undergoing HAdV surveillance, and assess the effectiveness of preemptive cidofovir.

METHODS

A single-center retrospective cohort of patients who underwent a transplant within a 10-year period was assembled. The incidence of and outcomes of patients with HAdV infection and disease were determined by PCR results and chart review. A Cox regression model was used for surveilled allogeneic HCT recipients to identify factors associated with viremia. We also used a discrete-time failure model with inverse probability treatment weights to assess the effectiveness of preemptive cidofovir for infection.

RESULTS

Among 572 HCT recipients, 76 (13.3%) had ≥1 sample that was HAdV PCR positive (3.5% of autologous HCT recipients and 19.7% of allogeneic HCT recipients). Among 191 allogeneic HCT recipients under surveillance, 58 (30.4%) had HAdV detected from any source, and 50 (26.2%) specifically had viremia. The mortality rate was higher in allogeneic HCT recipients with HAdV infection versus those without infection (25.9% vs 11.3%; P = .01). Factors associated with infection included an age of 6 to 12 years, an absolute lymphocyte count of <200 cells/μL, recent prednisone exposure, and recent bacteremia. Preemptive cidofovir was not associated with a reduced risk of infection progression (odds ratio, 0.96 [95% confidence interval, 0.30-3.05]).

CONCLUSIONS

HAdV infection is common and associated with an increased rate of death after allogeneic HCT. Using prediction models that incorporate factors associated with HAdV might help target surveillance. Preemptive cidofovir therapy was not protective in a subset of HAdV-positive patients. Larger observational or randomized investigations are necessary, because the utility of surveillance requires effective preemptive therapies.

Influence of Conditioning Time of Universal Adhesives on Adhesive Properties and Enamel-Etching Pattern

OBJECTIVES

To evaluate the effect of application protocol in resin-enamel microshear bond strength (μSBS), in situ degree of conversion, and etching pattern of three universal adhesive systems.

METHODS AND MATERIALS

Sixty-three extracted third molars were sectioned in four parts (buccal, lingual, and proximals) and divided into nine groups, according to the combination of the main factors-Adhesive (Clearfil Universal, Kuraray Noritake Dental Inc, Tokyo, Japan; Futurabond U, VOCO, Cuxhaven, Germany; and Scotchbond Universal Adhesive, 3M ESPE, St Paul, MN, USA)-and enamel treatment/application time (etch-and-rinse mode [ER], self-etch [SE] application for 20 seconds [SE20], and SE application for 40 seconds [SE40]). Specimens were stored in water (37°C/24 h) and tested at 1.0 mm/min (μSBS). The degree of conversion of the adhesives at the resin-enamel interfaces was evaluated using micro-Raman spectroscopy. The enamel-etching pattern was evaluated under a scanning electron microscope. Data were analyzed with two-way analysis of variance and Tukey test (α=0.05).

RESULTS

In general, the application of the universal adhesives in the SE40 produced μSBS and degree of conversion that were higher than in the SE20 (p<0.01) and similar to the ER mode. The deepest enamel-etching pattern was obtained in the ER mode, followed by the SE40.

CONCLUSIONS

The active and prolonged application of universal adhesives in the SE mode may be a viable alternative to increase the degree of conversion, etching pattern, and resin-enamel bond strength.

Molecular basis for the catalytic specificity of the CTX-M extended-spectrum β-lactamases

Extended-spectrum β-lactamases (ESBLs) pose a threat to public health because of their ability to confer resistance to extended-spectrum cephalosporins such as cefotaxime. The CTX-M β-lactamases are the most widespread ESBL enzymes among antibiotic resistant bacteria. Many of the active site residues are conserved between the CTX-M family and non-ESBL β-lactamases such as TEM-1, but the residues Ser237 and Arg276 are specific to the CTX-M family, suggesting that they may help to define the increased specificity for cefotaxime hydrolysis. To test this hypothesis, site-directed mutagenesis of these positions was performed in the CTX-M-14 β-lactamase. Substitutions of Ser237 and Arg276 with their TEM-1 counterparts, Ala237 and Asn276, had a modest effect on cefotaxime hydrolysis, as did removal of the Arg276 side chain in an R276A mutant. The S237A:R276N and S237A:R276A double mutants, however, exhibited 29- and 14-fold losses in catalytic efficiency for cefotaxime hydrolysis, respectively, while the catalytic efficiency for benzylpenicillin hydrolysis was unchanged. Therefore, together, the Ser237 and Arg276 residues are important contributors to the cefotaximase substrate profile of the enzyme. High-resolution crystal structures of the CTX-M-14 S70G, S70G:S237A, and S70G:S237A:R276A variants alone and in complex with cefotaxime show that residues Ser237 and Arg276 in the wild-type enzyme promote the expansion of the active site to accommodate cefotaxime and favor a conformation of cefotaxime that allows optimal contacts between the enzyme and substrate. The conservation of these residues, linked to their effects on structure and catalysis, imply that their coevolution is an important specificity determinant in the CTX-M family.

The five near-iron transporter (NEAT) domain anthrax hemophore, IsdX2, scavenges heme from hemoglobin and transfers heme to the surface protein IsdC

Pathogenic bacteria require iron to replicate inside mammalian hosts. Recent studies indicate that heme acquisition in Gram-positive bacteria is mediated by proteins containing one or more near-iron transporter (NEAT) domains. Bacillus anthracis is a spore-forming, Gram-positive pathogen and the causative agent of anthrax disease. The rapid, extensive, and efficient replication of B. anthracis in host tissues makes this pathogen an excellent model organism for the study of bacterial heme acquisition. B. anthracis secretes two NEAT hemophores, IsdX1 and IsdX2. IsdX1 contains a single NEAT domain, whereas IsdX2 has five, a novel property among hemophores. To understand the functional significance of harboring multiple, non-identical NEAT domains, we purified each individual NEAT domain of IsdX2 as a GST fusion and analyzed the specific function of each domain as it relates to heme acquisition and transport. NEAT domains 1, 3, 4, and 5 all bind heme, with domain 5 having the highest affinity. All NEATs associate with hemoglobin, but only NEAT1 and -5 can extract heme from hemoglobin, seemingly by a specific and active process. NEAT1, -3, and -4 transfer heme to IsdC, a cell wall-anchored anthrax NEAT protein. These results indicate that IsdX2 has all the features required to acquire heme from the host and transport heme to the bacterial cell wall. Additionally, these results suggest that IsdX2 may accelerate iron import rates by acting as a "heme sponge" that enhances B. anthracis replication in iron-starved environments.

Determination of the amino acid sequence requirements for catalysis by the highly proficient orotidine monophosphate decarboxylase

Orotidine 5'-monophosphate decarboxylase (ODCase) catalyzes the decarboxylation of orotidine 5'-monophosphate to uridine 5'-monophosphate during pyrimidine nucleotide biosynthesis. This enzyme is one of the most proficient known, exhibiting a rate enhancement of over 17 orders of magnitude over the uncatalyzed rate. An interesting question is whether the high proficiency of ODCase is associated with a highly optimized sequence of active site residues. This question was addressed by randomizing 24 residue positions in and around the active site of the E. coli ODCase (pyrF) by site-directed mutagenesis. The libraries of mutants were selected for function from a multicopy plasmid or by single-copy replacement at the pyrF locus on the E. coli chromosome. Stringent sequence requirements for function were found for the mutants expressed from the chromosomal pyrF locus. Six positions were not tolerant of substitutions and several others accepted very limited substitutions. In contrast, all positions could be substituted to some extent when the library mutants were expressed from a multicopy plasmid. For the conserved quartet of charged residues Lys44-Asp71-Lys73-Asp76, a cysteine substitution was found to provide function at positions 71 and 76. A lower pK(a) for both cysteine mutants supports a mechanism whereby the thiolate group of cysteine substitutes for the negatively charged aspartate side chain. The partial function mutants such as D71C and D76C exhibit reduced catalytic efficiency relative to wild type but nevertheless provide a rate enhancement of 15 orders of magnitude over the uncatalyzed rate indicating the catalytic proficiency of the enzyme is robust and tolerant of mutation.

Inhibition of cytoplasmic mRNA stress granule formation by a viral proteinase

Mammalian cells form dynamic cytoplasmic mRNA stress granules (SGs) in response to environmental stresses including viral infections. SGs are involved in regulating host mRNA function and metabolism, although their precise role during viral infection is unknown. SGs are thought to assemble based on functions of the RNA-binding proteins TIA-1/TIAR or Ras-GAP SH3 domain-binding protein (G3BP). Here, we investigated the relationship between a prototypical plus-strand RNA virus and SGs. Early during poliovirus infection, SG formation is induced, but as infection proceeds this ability is lost, and SGs disperse. Infection resulted in cleavage of G3BP, but not TIA-1 or TIAR, by poliovirus 3C proteinase. Expression of a cleavage-resistant G3BP restored SG formation during poliovirus infection and significantly inhibited virus replication. These results elucidate a mechanism for viral interference with mRNP metabolism and gene regulation and support a critical role of G3BP in SG formation and restriction of virus replication.

Subtle genetic changes enhance virulence of methicillin resistant and sensitive Staphylococcus aureus

Background

Community acquired (CA) methicillin-resistant Staphylococcus aureus (MRSA) increasingly causes disease worldwide. USA300 has emerged as the predominant clone causing superficial and invasive infections in children and adults in the USA. Epidemiological studies suggest that USA300 is more virulent than other CA-MRSA. The genetic determinants that render virulence and dominance to USA300 remain unclear.

Results

We sequenced the genomes of two pediatric USA300 isolates: one CA-MRSA and one CA-methicillin susceptible (MSSA), isolated at Texas Children's Hospital in Houston. DNA sequencing was performed by Sanger dideoxy whole genome shotgun (WGS) and 454 Life Sciences pyrosequencing strategies. The sequence of the USA300 MRSA strain was rigorously annotated. In USA300-MRSA 2658 chromosomal open reading frames were predicted and 3.1 and 27 kilobase (kb) plasmids were identified. USA300-MSSA contained a 20 kb plasmid with some homology to the 27 kb plasmid found in USA300-MRSA. Two regions found in US300-MRSA were absent in USA300-MSSA. One of these carried the arginine deiminase operon that appears to have been acquired from S. epidermidis. The USA300 sequence was aligned with other sequenced S. aureus genomes and regions unique to USA300 MRSA were identified.

Conclusion

USA300-MRSA is highly similar to other MRSA strains based on whole genome alignments and gene content, indicating that the differences in pathogenesis are due to subtle changes rather than to large-scale acquisition of virulence factor genes. The USA300 Houston isolate differs from another sequenced USA300 strain isolate, derived from a patient in San Francisco, in plasmid content and a number of sequence polymorphisms. Such differences will provide new insights into the evolution of pathogens.

Identification of a glycosylated Ehrlichia canis 19-kilodalton major immunoreactive protein with a species-specific serine-rich glycopeptide epitope

Ehrlichia canis has a small subset of major immunoreactive proteins that includes a 19-kDa protein that elicits an early Ehrlichia-specific antibody response in infected dogs. We report herein the identification and molecular characterization of this highly conserved 19-kDa major immunoreactive glycoprotein (gp19) ortholog of the Ehrlichia chaffeensis variable-length PCR target (VLPT) protein. E. canis gp19 has substantial carboxyl-terminal amino acid homology (59%) with E. chaffeensis VLPT and the same chromosomal location; however, the E. chaffeensis VLPT gene (594 bp) has tandem repeats that are not present in the E. canis gp19 gene (414 bp). Consistent with other ehrlichial glycoproteins, the gp19 protein exhibited a larger-than-predicted mass (approximately 3 kDa), O-linked glycosylation sites were predicted in an amino-terminal serine/threonine/glutamate (STE)-rich patch (26 amino acids), carbohydrate was detected on the recombinant gp19 protein, and the neutral sugars glucose and galactose were detected on the recombinant amino-terminal polypeptide. E. canis gp19 composition consists of five predominant amino acids, cysteine, glutamate, tyrosine, serine, and threonine, concentrated in the STE-rich patch and a carboxyl-terminal domain predominated by cysteine and tyrosine (55%). The amino-terminal STE-rich patch contained a major species-specific antibody epitope strongly recognized by serum from an E. canis-infected dog. The recombinant glycopeptide epitope was substantially more reactive with antibody than the synthetic (nonglycosylated) peptide, and periodate treatment of the recombinant glycopeptide epitope reduced its immunoreactivity, demonstrating the importance of a carbohydrate immunodeterminant(s). The gp19 protein was present on reticulate and dense-cored cells, and it was found extracellularly in the fibrillar matrix and associated with the morula membrane, the host cell cytoplasm, and the nucleus.

Effect of protein synthesis inhibitors on synexin levels and secretory response in bovine adrenal medullary chromaffin cells

The effects of the protein synthesis inhibitors actinomycin D and cycloheximide on the cellular content of the calcium binding protein synexin, and on the secretory response of cultured bovine adrenal medullary chromaffin cells were determined. Both protein synthesis inhibitors produced a slow decrease in the cellular synexin content. The synexin level was reduced by 50% after 133 h of incubation in the presence of 2 micrograms/ml actinomycin D or 5 micrograms/ml cycloheximide. However, this was partly due to an artefactual stabilization of synexin, since metabolic labelling of synexin with [35S]methionine showed that the half-time of degradation was only 40 h. The secretory response of chromaffin cells was quickly diminished in the presence of protein synthesis inhibitors. Catecholamine secretion induced by membrane depolarization or barium stimulation of intact cells, or by calcium stimulation of digitonin-permeabilized cells was decreased by 77-82% after 24 h of incubation in the presence of 5 micrograms/ml cycloheximide. These results suggest that, in addition to synexin, at least one or more proteins with a shorter half-time of degradation than synexin are involved in the secretory response of adrenal chromaffin cells.