Clinical impact of multidrug-resistant bacterial infections in patients with cirrhosis.

Aim: Recently, the emergency of multidrug-resistant organisms (MDRO) has complicated the management of bacterial infections (BI) in cirrhosis. We aimed to assess their clinical impact on patients with decompensated cirrhosis. Methods: A retrospective study included consecutive cirrhotic patients hospitalized for acute decompensation (AD) between January 2010 and December 2019. Results: A total of 518 AD admissions in 219 patients were included, with 260 BI episodes (50.2%). MDRO prevalence was 38.2% of the total isolates. Recent antibiotic use (OR = 4.91), nosocomial infection (OR = 2.95), and healthcare-associated infection (OR = 3.45) were their main risk factors. MDROs were associated with empiric treatment failure (OR = 23.42), a higher prevalence of sepsis (OR = 4.93), ACLF (OR = 3.42) and mortality. Conclusion: The clinical impact of MDROs was pejorative, with an increased risk of empiric treatment failure, organ failure and death.

In recent years, an increasing spread of multidrug-resistant bacteria had been observed worldwide. The emergence of these strains could represent a major problem in fragile patients such as cirrhotic patients. Over 10 years, our study analyzed the bacteriological profile of cirrhotic patient infections. The multidrug-resistant bacteria prevalence was 38.2%. Exposure to healthcare facilities and recent antibiotic use, were their main risk factors. These strains had a negative impact with an increased risk of treatment failure and death.

New Study Alert! Significant prevalence and negative clinical impact of multidrug-resistant organism (MDRO) infections in patients with cirrhosis. Main risk factors: recent antibiotic use and exposure to healthcare facilities. #cirrhosis #bacterialinfection #antibiotherapy #resistance.

Respiratory Microbiome Disruption and Risk for Ventilator-Associated Lower Respiratory Tract Infection.

BACKGROUND: Ventilator-associated lower respiratory tract infection (VA-LRTI) is common among critically ill patients and has been associated with increased morbidity and mortality. In acute critical illness, respiratory microbiome disruption indices (MDIs) have been shown to predict risk for VA-LRTI, but their utility beyond the first days of critical illness is unknown. We sought to characterize how MDIs previously shown to predict VA-LRTI at initiation of mechanical ventilation change with prolonged mechanical ventilation, and if they remain associated with VA-LRTI risk. METHODS: We developed a cohort of 83 subjects admitted to a long-term acute care hospital due to their prolonged dependence on mechanical ventilation; performed dense, longitudinal sampling of the lower respiratory tract, collecting 1066 specimens; and characterized the lower respiratory microbiome by 16S rRNA sequencing as well as total bacterial abundance by 16S rRNA quantitative polymerase chain reaction. RESULTS: Cross-sectional MDIs, including low Shannon diversity and high total bacterial abundance, were associated with risk for VA-LRTI, but associations had wide posterior credible intervals. Persistent lower respiratory microbiome disruption showed a more robust association with VA-LRTI risk, with each day of (base e) Shannon diversity <2.0 associated with a VA-LRTI odds ratio of 1.36 (95% credible interval, 1.10-1.72). The observed association was consistent across multiple clinical definitions of VA-LRTI. CONCLUSIONS: Cross-sectional MDIs have limited ability to discriminate VA-LRTI risk during prolonged mechanical ventilation, but persistent lower respiratory tract microbiome disruption, best characterized by consecutive days with low Shannon diversity, may identify a population at high risk for infection and may help target infection-prevention interventions.

Quantifying the Impact of Nasopharyngeal Specimen Quality on Severe Acute Respiratory Syndrome Coronavirus 2 Test Performance.

BACKGROUND: The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) reverse-transcription polymerase chain reaction (RT-PCR) cycle threshold (Ct) has been used to estimate quantitative viral load, with the goal of targeting isolation precautions for individuals with coronavirus disease 2019 (COVID-19) and guiding public health interventions. However, variability in specimen quality can alter the Ct values obtained from SARS-CoV-2 clinical assays. We sought to define how variable nasopharyngeal (NP) swab quality impacts clinical SARS-CoV-2 test sensitivity. METHODS: We performed amplification of a human gene target (ß-actin) in parallel with a clinical RT-PCR targeting the SARS-CoV-2 ORF1ab gene for 1282 NP specimens collected from patients with clinical concern for COVID-19. We evaluated the relationship between NP specimen quality, characterized by late Ct values for the human gene target ß-actin Ct, and the probability of SARS-CoV-2 detection via logistic regression, as well as the linear relationship between SARS-CoV-2 and ß-actin Ct. RESULTS: Low-quality NP swabs are less likely to detect SARS-CoV-2 (odds ratio, 0.607 [95% credible interval {CrI}, .487-.753]). We observed a positive linear relationship between SARS-CoV-2 and ß-actin Ct values (slope, 0.181 [95% CrI, .097-.264]), consistent with a reduction in detection of 0.181 cycles for each additional cycle of the ß-actin target. COVID-19 disease severity was not associated with ß-actin Ct values. CONCLUSIONS: Variability in NP specimen quality significantly impacts the performance of clinical SARS-CoV-2 assays, and caution should be taken when interpreting quantitative SARS-CoV-2 Ct results. If unrecognized, low-quality NP specimens, which are characterized by a low level of amplifiable human DNA target, may limit the successful application of SARS-CoV-2 Ct values to direct infection control and public health interventions.

Before the Bullets Fly: The Physician's Role in Preventing Firearm Injury.

Firearm injury is a disease that is disproportionately prevalent in the United States. When a bullet hits a human being, it brings together multiple structural determinants of health into one acute, life-changing event. Firearm injury can lead to long-term mental and physical challenges for individuals, families, and communities. Despite the impact of this disease, physicians often underestimate their role in not only treating but also preventing firearm injury. Physicians can intervene through screening, counseling, community engagement, and advocacy, and can mobilize the health care systems they serve to engage with injury prevention. Physicians also play a key role in expanding the knowledge base on firearm injury through much-needed research on the epidemiology, context, and outcomes of firearm injury. When we treat firearm injury as a disease, we can develop and implement interventions from the clinic to the statehouse that can curb profound harms. This work and these opportunities belong not only to emergency physicians and trauma surgeons, but to all fields that evaluate and assess patients over the life course.

Subglottic suction frequency and adverse ventilator-associated events during critical illness.

OBJECTIVE: Tracheal intubation and mechanical ventilation provide essential support for patients with respiratory failure, but the course of mechanical ventilation may be complicated by adverse ventilator-associated events (VAEs), which may or may not be associated with infection. We sought to understand how the frequency of subglottic suction, an indicator of the quantity of sputum produced by ventilated patients, relates to the onset of all VAEs and infection-associated VAEs. DESIGN: We performed a case-crossover study including 87 patients with VAEs, and we evaluated 848 days in the pre-VAE period at risk for a VAE. SETTING AND PARTICIPANTS: Critically ill patients were recruited from the medical intensive care unit of an academic medical center. METHODS: We used the number of as-needed subglottic suctioning events performed per calendar day to quantify sputum production, and we compared the immediate pre-VAE period to the preceding period. We used CDC surveillance definitions for VAE and to categorize whether events were infection associated or not. RESULTS: Sputum quantity measured by subglottic suction frequency is greater in the period immediately prior to VAE than in the preceding period. However, it does not discriminate well between infection-associated VAEs and VAEs without associated infection. CONCLUSIONS: Subglottic suction frequency may serve as a valuable marker of sputum quantity, and it is associated with risk of a VAE. However, our results require validation in a broader population of mechanically ventilated patients and intensive care settings.

Increased Firearm Injury During the COVID-19 Pandemic: A Hidden Urban Burden.

BACKGROUND: Public health measures were instituted to reduce COVID-19 spread. A decrease in total emergency department volume followed, but the impact on injury is unknown. With lockdown and social distancing potentially increasing domicile discord, we hypothesized that intentional injury increased during COVID-19, driven primarily by an increase in penetrating trauma. STUDY DESIGN: A retrospective review of acute adult patient care in an urban Level I trauma center assessed injury patterns. Presenting patient characteristics and diagnoses from 6 weeks pre to 10 weeks post statewide stay-at-home orders (March 16, 2020) were compared, as well as with 2015-2019. Subsets were defined by intentionality (intentional vs nonintentional) and mechanism of injury (blunt vs penetrating). Fisher exact and Wilcoxon tests were used to compare proportions and means. RESULTS: There were 357 trauma patients that presented pre stay-at-home order and 480 that presented post stay-at-home order. Pre and post groups demonstrated differences in sex (35.6% vs 27.9% female; p = 0.02), age (47.4 ± 22.1 years vs 42 ± 20.3 years; p = 0.009), and race (1.4% vs 2.3% Asian; 63.3% vs 68.3% Black; 30.5% vs 22.3% White; and 4.8% vs 7.1% other; p = 0.03). Post stay-at-home order mechanism of injury revealed more intentional injury (p = 0.0008). Decreases in nonintentional trauma after adoption of social isolation paralleled declines in daily emergency department visits. Compared with earlier years, 2020 demonstrated a significantly greater proportion of intentional violent injury during the peripandemic months, especially from firearms. CONCLUSIONS: Unprecedented social isolation policies to address COVID-19 were associated with increased intentional injury, especially gun violence. Meanwhile, emergency department and nonintentional trauma visits decreased. Pandemic-related public health measures should embrace intentional injury prevention and management strategies.

Impact of Nasopharyngeal Specimen Quality on SARS-CoV-2 Test Sensitivity.

BACKGROUND: The SARS-CoV-2 reverse-transcription polymerase chain reaction (RT-PCR) cycle of threshold (Ct) has been used to estimate quantitative viral load, with the goal of targeting isolation precautions for individuals with COVID-19 and guiding public health interventions. However, variability in specimen quality can alter the Ct values obtained from SARS-CoV-2 clinical assays. We sought to define how variable nasopharyngeal (NP) swab quality impacts clinical SARS-CoV-2 test sensitivity. METHODS: We performed amplification of a human gene target (ß-actin) in parallel with a clinical RT-PCR targeting the SARS-CoV-2 ORF1ab gene for 1311 NP specimens collected from patients with clinical concern for COVID-19. We evaluated the relationship between NP specimen quality, characterized by high Ct values for the human gene target ß-actin Ct, and the probability of SARS-CoV-2 detection via logistic regression, as well as the linear relationship between SARS-CoV-2 and ß-actin Ct. RESULTS: Low quality NP swabs are less likely to detect SARS-CoV-2 (odds ratio 0.654, 95%CI 0.523 to 0.802). We observed a positive linear relationship between SARS-CoV-2 and ß-actin Ct values (slope 0.169, 95%CI 0.092 to 0.247). COVID-19 disease severity was not associated with ß-actin Ct values. CONCLUSIONS: Variability in NP specimen quality accounts for significant differences in the sensitivity of clinical SARS-CoV-2 assays. If unrecognized, low quality NP specimens, which are characterized by a low level of amplifiable human DNA target, may limit the application of SARS-CoV-2 Ct values to direct infection control and public health interventions.

Symptomatic relapse and long-term sequelae of COVID-19 in a previously healthy 30-year-old man.

Much has been reported on the clinical course of severe COVID-19, but less is known about the natural history and sequalae of mildly symptomatic cases and the prospects of reinfection or recurrence of symptoms. We report a case of a patient with mildly symptomatic PCR-confirmed COVID-19 who, after being symptom-free for 2 weeks, redeveloped symptoms and was found to be PCR-positive again >4 weeks from original testing. Surprisingly, IgG and IgM antibody testing was negative 2 months after reinfection. Although no negative testing was performed between the two symptomatic bouts, this case raises the possibility of reinfection after controlling the virus and highlights the long period with which a patient can shed virus and experience symptoms after initial infection. Characterising variations in clinical symptoms and length of viral shedding after improvement is essential for informing recommendations on patients safely resuming contact with others.

Does Anemia Have a Potential Effect on Type 2 Hepatorenal Syndrome?

Background/Aims. Hepatorenal syndrome (HRS) is a form of functional renal failure arising in advanced cirrhosis and is characterized by a poor survival rate. Anemia is frequently observed during the clinical course of cirrhosis. Our study aimed to investigate the hematologic findings in patients with cirrhosis to determine the effects of anemia on renal functions in type 2 HRS and if it was a potential aggravating factor. Materials and Methods. This prospective study, in which all consecutive patients with cirrhosis were enrolled, was performed at a tertiary-level hospital (Military Hospital of Tunis) from January 2019 to June 2019. A total of 9 patients with HRS fulfilled the type 2 HRS diagnostic criteria, and 41 patients with cirrhosis without HRS were included. All data regarding patients were obtained from the medical record. Demographic data, routine hemograms, biochemical, and urinary test results were collected. Models of end-stage liver disease (MELD) and Child-Turcotte-Pugh (CTP) scores were calculated. Results. The most common etiology of cirrhosis was viral hepatitis (66%). According to the CTP score, 23 patients were in the CTP-A stage, 13 in the CTP-B stage, and 14 patients were in the CTP-C stage. Patients with type 2 HRS had significantly lower hemoglobin levels compared with non-HRS stable cirrhosis patients. As hemoglobin levels decreased, renal function worsened on patients with type 2 HRS. Patients with lower hemoglobin levels had poor prognosis and survival compared with patients with higher hemoglobin levels. Logistic regression analysis showed that lower hemoglobin levels and higher MELD and CTP scores were statistically significant for an onset of type 2 HRS. Conclusion. Renal dysfunction is a frequent complication in patients with end-stage chronic liver disease. The role of anemia in aggravating HRS in patients with cirrhosis is explained by hypoxia that can lead to microcirculatory renal ischemia. Other studies are required to determine if anemia is a precipitant factor for HRS or not.

Deep Learning Based on MR Imaging for Predicting Outcome of Uterine Fibroid Embolization.

PURPOSE: To develop and validate a deep learning model based on routine magnetic resonance (MR) imaging obtained before uterine fibroid embolization to predict procedure outcome. MATERIALS AND METHODS: Clinical data were collected on patients treated with uterine fibroid embolization at the Hospital of the University of Pennsylvania from 2007 to 2018. Fibroids for each patient were manually segmented by an abdominal radiologist on a T1-weighted contrast-enhanced (T1C) sequence and a T2-weighted sequence of MR imaging obtained before and after embolization. A residual convolutional neural network (ResNet) model to predict clinical outcome was trained using MR imaging obtained before the procedure. RESULTS: Inclusion criteria were met by 727 fibroids in 409 patients. At clinical follow-up, 85.6% (n = 350) of 409 patients (590 of 727 fibroids; 81.1%) experienced symptom resolution or improvement, and 14.4% (n = 59) of 409 patients (137 of 727 fibroids; 18.9%) had no improvement or worsening symptoms. The T1C trained model achieved a test accuracy of 0.847 (95% confidence interval [CI], 0.745-0.914), sensitivity of 0.932 (95% CI, 0.833-0.978), and specificity of 0.462 (95% CI, 0.232-0.709). In comparison, the average of 4 radiologists achieved a test accuracy of 0.722 (95% CI, 0.609-0.813), sensitivity of 0.852 (95% CI, 0.737-0.923), and specificity of 0.135 (95% CI, 0.021-0.415). CONCLUSIONS: This study demonstrates that deep learning based on a ResNet model achieves good accuracy in predicting outcome of uterine fibroid embolization. If further validated, the model may help clinicians better identify patients who can most benefit from this therapy and aid clinical decision making.

Characterization of Recurrences Following Second Breast-Conserving Surgery with Intraoperative Radiotherapy.

BACKGROUND: Breast-conserving surgery with breast re-irradiation is an emerging technique in the treatment of selected cases of locally recurrent breast cancer. Further information is needed to characterize factors that may select for an appropriate patient population for this treatment approach. METHODS: We report herein a single-institution retrospective analysis of patients with ipsilateral breast cancer recurrence treated with a second breast-conserving therapy with intraoperative radiotherapy. Patient records were reviewed to analyze toxicity, further recurrence, and characteristics of recurrent patients following this treatment approach. RESULTS: We included 57 patients in the analysis. At median follow-up of 24.5 months, ipsilateral breast tumor recurrence occurred in six patients (11%), four of which localized to the quadrant of the initial recurrent disease and two of which recurred elsewhere in the treated breast. Locoregional control was 89%, and disease-free survival was 81%. Only one patient was found to have grade 3 or greater toxicity. CONCLUSION: A second breast-conserving surgery with intraoperative radiotherapy is tolerable with acceptable toxicity for patients with locally recurrent disease refusing mastectomy. Prospective clinical trials are needed to define the subset of patients who may be appropriate for this treatment approach as an alternative to mastectomy.

Designing Higher Resolution Self-Assembled 3D DNA Crystals via Strand Terminus Modifications.

DNA tensegrity triangles self-assemble into rhombohedral three-dimensional crystals via sticky ended cohesion. Crystals containing two-nucleotide (nt) sticky ends (GA:TC) have been reported previously, and those crystals diffracted to 4.9 Å at beamline NSLS-I-X25. Here, we analyze the effect of varying sticky end lengths and sequences as well as the impact of 5'- and 3'-phosphates on crystal formation and resolution. Tensegrity triangle motifs having 1-, 2-, 3-, and 4-nt sticky ends all form crystals. X-ray diffraction data from the same beamline reveal that the crystal resolution for a 1-nt sticky end (G:C) and a 3-nt sticky end (GAT:ATC) were 3.4 and 4.2 Å, respectively. Resolutions were determined from complete data sets in each case. We also conducted trials that examined every possible combination of 1-nucleotide and 2-nucleotide sticky-ended phosphorylated strands and successfully crystallized all 16 possible combinations of strands. We observed the position of the 5'-phosphate on either the crossover (1), helical (2), or central strand (3) affected the resolution of the self-assembled crystals for the 2-turn monomer (3.0 Å for 1-2P-3P) and 2-turn dimer sticky ended (4.1 Å for 1-2-3P) systems. We have also examined the impact of the identity of the base flanking the sticky ends as well as the use of 3'-phosphate. We conclude that crystal resolution is not a simple consequence of the thermodynamics of the direct nucleotide pairing interactions involved in molecular cohesion in this system.

Core versus specialty rotations do not affect students' surgical development.

BACKGROUND: Research is scarce on how the diversity of surgical rotations affects students. We sought to assess the effect of core rotations compared to specialty rotations on students' development. METHODS: Students were given a suturing workshop at the beginning of their surgical clerkship along with a questionnaire. They performed both a simple and a complex suturing task at the beginning and end of the 2-month clerkship. The students were divided into 2 groups based on their surgical rotations. Technical skill and exam scores were compared. RESULTS: Thirty-eight students were included in the study. Objective scores increased for the simple task (14.2, standard deviation 4.5 vs 16.4, standard deviation 4.2, P = .04) and the complex task (12.9, standard deviation 5.3 vs 16.5, standard deviation 4.1, P < .01). Times decreased for the simple task (5.1, standard deviation 1.8 vs 4.1, standard deviation 1.3, min, P < .01) and the complex task (7.9, standard deviation 2.7 vs 6.3, standard deviation 1.5, min, P < .01). Using multivariate analysis, we found that reported hours in the operating room per week and previous hands-on experience affected proficiency of the simple suturing task only. Sixteen students had predominantly core surgical rotations. When compared to the 22 students with more specialty rotations, the only difference was gender (87.5% male vs 50.0% male, P = 0.02). There was no significant difference in the completion times (P = .96, .82), the objective scores (P = .06, .120), the written exam scores (P = .57), or the oral exam scores (P = .89). CONCLUSION: In this small study, it was found that the type of students' rotations does not affect surgical skill or knowledge acquisition.

Association of TNF-α-308 Polymorphism with Susceptibility to Autoimmune Hepatitis in Tunisians.

Autoimmune hepatitis (AIH) is a chronic hepatitis of unknown etiology and several proinflammatory cytokines are implicated in its pathogenesis. The association of TNF-α gene polymorphism with AIH onset is not fully elucidated especially in the Tunisian population. The aim of this study was to determine the association of TNF-α (-308 G > A) polymorphism with AIH susceptibility and with TNF-α expression or clinical manifestations of AIH. A total of 50 AIH patients and 150 controls were included. Evaluation of TNF-α polymorphism was performed by ARMS PCR method. A significantly higher frequence of the AA genotype was found in AIH patients compared to controls (34 vs. 8%, p = 0.00002, OR 5.88). The frequency of the A-allele was significantly higher in patients with AIH compared to controls (55 vs. 37.3%, p = 0.002, OR 2.05). The G-allele was significantly more frequent in healthy controls compared to AIH patients [43 vs. 61.3%, p = 0.001, OR 0.47 (0.3-0.75)]. There was a positive correlation between the A/A genotype and a higher serum expression of TNF-α. The TNF*A allele confer susceptibility to AIH in the Tunisian patients and is associated with increased production of TNF-α. Anti-TNF antibodies could be an alternative to the use of corticotherapy and may avoid the exacerbated immune response in AIH.

Self-Assembly of 3D DNA Crystals Containing a Torsionally Stressed Component.

There is an increasing appreciation for structural diversity of DNA that is of interest to both DNA nanotechnology and basic biology. Here, we have explored how DNA responds to torsional stress by building on a previously reported two-turn DNA tensegrity triangle and demonstrating that we could introduce an extra nucleotide pair (np) into the original sequence without affecting assembly and crystallization. The extra np imposes a significant torsional stress, which is accommodated by global changes throughout the B-DNA duplex and the DNA lattice. The work reveals a near-atomic structure of naked DNA under a torsional stress of approximately 14%, and thus provides an example of DNA distortions that occur without a requirement for either an external energy source or the free energy available from protein or drug binding.

Genome-wide association of IL-28B with response to pegylated interferon-alpha and ribavirin therapy for chronic hepatitis C in a Tunisian population.

BACKGROUND:   A polymorphism upstream of interleukin (IL)-28B was recently identified to be associated with a 2-fold difference in sustained virologic response (SVR) to pegylated interferon-alpha and ribavirin therapy in a large cohort of treatment-naive, adherent patients with chronic hepatitis C (CHC) virus genotype 1 (HCV-1) infection. AIM: We sought to confirm the polymorphism's clinical relevance by intention-to-treat analysis evaluating on-treatment virologic response and SVR. METHODS: We perform a prospective study in gastroenterology unitof tunis'military hospital in collaboration with immunology unit, military center of blood transfusion and laboratory of biochemistry of childrens' hospital of Tunis. HCV patients were genotyped as CC, CT or TT at the polymorphic site rs12979860 and TT, TG or GG at the polymorphic site rs8099917. Viral kinetics and rates of rapid virologic response (RVR, week 4) and SVR were compared by IL-28B type in a tunisian population. RESULTS: 154 patients including 80 healthy blood donors(sexratio: 1, mean age: 40.35 ±10.15 years) and 74 patients treated for CHC (39 men and 35 women; mean age = 51.7± 9.4 years) were enrolled. 35.6% of patients were genotyped as CC at the polymorphic site rs12979860 and 69.1% as TT at the polymorphic site rs8099917. The CC IL-28B type at rs12979860 was associated with a greater likelihood of SVR (77% vs 31.9%; p<0.001; OR: 7.11 [2.37-21.35]) compared with CT and TT. The CC IL-28B type at rs12979860 wasn't associated with improved of rapid virologic response (RVR). In a multivariate logistic regression model, the rs12979860 CC genotype predicted SVR (p<0.001; OR: 7.11 IC95% [2.37-21.35]). The TT IL-28B type at rs 8099917 wasn't associated with improved RVR and SVR compared with TG and GG. CONCLUSION: In treatment-naive HCV patients treated with pegylated interferon and ribavirin, a polymorphism upstream CC at the site rs12979860 of IL-28B is associated with increased sustained virologic response and effectively predicts treatment outcome.

Construction and Structure Determination of a Three-Dimensional DNA Crystal.

Structural DNA nanotechnology combines branched DNA junctions with sticky-ended cohesion to create self-assembling macromolecular architectures. One of the key goals of structural DNA nanotechnology is to construct three-dimensional (3D) crystalline lattices. Here we present a new DNA motif and a strategy that has led to the assembly of a 3D lattice. We have determined the X-ray crystal structures of two related constructs to 3.1 Å resolution using bromine-derivatized crystals. The motif we used employs a five-nucleotide repeating sequence that weaves through a series of two-turn DNA duplexes. The duplexes are tied into a layered structure that is organized and dictated by a concert of four-arm junctions; these in turn assemble into continuous arrays facilitated by sequence-specific sticky-ended cohesion. The 3D X-ray structure of these DNA crystals holds promise for the design of new structural motifs to create programmable 3D DNA lattices with atomic spatial resolution. The two arrays differ by the use of four or six repeats of the five-nucleotide units in the repeating but statistically disordered central strand. In addition, we report a 2D rhombuslike array formed from similar components.

Stabilisation of self-assembled DNA crystals by triplex-directed photo-cross-linking.

The tensegrity triangle is a robust DNA motif that can self-assemble to generate macroscopic three-dimensional crystals. However, the stability of these crystals is dependent on the high ionic conditions used for crystal growth. Here we demonstrate that a triplex-forming oligonucleotide can be used to direct the specific intercalation, and subsequent photo-cross-linking, of 4,5',8-trimethylpsoralen to single or multiple loci within or between the tiles of the crystal. Cross-linking between the tiles of the crystal improves their thermal stability. Such an approach is likely to facilitate the removal of crystals from their mother liquor and may prove useful for applications that require greater crystal stability.