A longitudinal ethnographic study of hospital staff attitudes and experiences of change in nutrition care.

BACKGROUND: Change promotes quality in healthcare, yet adopting change can be challenging. Understanding how change in nutrition care is adopted may support better design and implementation of interventions that aim to address inadequate food intake in hospital. The present study followed the process of change in a healthcare organisation, exploring staff attitudes, beliefs and experiences of the implementation of a mealtime intervention. METHODS: In total, 103 h of fieldwork were conducted in this longitudinal ethnographic study over a 4-month period. Over 170 staff participated, with data captured using observation, interviews and focus groups. Data were analysed using an inductive, thematic approach, informed by implementation theory. RESULTS: Attitudes and experiences of change in nutrition care are described by three themes: (i) staff recognised the inevitability of change; (ii) staff cooperated with the intervention, recognising potential value in the intervention to support patient care, where increased awareness of their mealtime behaviours supported adopting practice changes; and (iii) some staff were able to reflect on their practice after implementing the intervention, whereas others could not. A model illustrating the interconnectedness of factors influencing implementation emerged from the research, guiding future nutrition care intervention design and supporting change. CONCLUSIONS: The requirement to address the underlying perceptions of staff about the need to change should not be underestimated. Increased efforts to market the change message to specific staff groups and physical behavioural reinforcement strategies are needed. Nutrition care in the future should focus on helping staff feel positive about making practice changes.

Evaluation of isavuconazole MIC strips for susceptibility testing of Aspergillus and Scedosporium species.

Isavuconazole is a new triazole with an expanded-spectrum and potent activity against moulds and yeasts. It has been authorized for use in adults for the treatment of invasive aspergillosis and for mucormycosis. The only commercially available isavuconazole susceptibility test is the minimum inhibitory concentration (MIC) strip isavuconazole test. The objective of this study was to assess the in vitro activity of isavuconazole using gradient concentration MIC strips, compared with the EUCAST broth microdilution reference method. A total of 147 clinically relevant fungal isolates comprising 120 Aspergillus sp. and 27 Scedosporium apiospermum complex were tested for susceptibility to isavuconazole using the EUCAST broth microdilution method and by the MIC strip isavuconazole test. The percent essential agreement between the two methods was calculated within a 1-fold dilution. The geometric means for the MICs using the EUCAST reference methods and the strip test were respectively: 0.60 mg/l and 0.65 mg/l for A. fumigatus, 0.70 mg/l and 0.77 mg/l for A. flavus, 1.50 mg/l and 1.25 mg/l for A. niger, 0.41 mg/l and 0.38 mg/l for A. terreus, 1.22 mg/l and 1.08 mg/l for S. apiospermum complex. The isavuconazole MIC strips showed good agreement with the EUCAST reference method. Isavuconazole MIC strips could be useful for susceptibility testing of Aspergillus sp. and S. apiospermum complex.

Exploring approaches to dietetic assessment of a common task across different universities through assessment moderation.

BACKGROUND: Assessment presents one of the greatest challenges to evaluating health professional trainee performance, as a result of the subjectivity of judgements and variability in assessor standards. The present study aimed to test a moderation procedure for assessment across four independent universities and explore approaches to assessment and the factors that influence assessment decisions. METHODS: Assessment tasks designed independently by each of the four universities to assess student readiness for placement were chosen for the present study. Each university provided four student performance recordings for moderation. Eight different academic assessors viewed the student performances and assessed them using the corresponding university assessment instrument. Assessment results were collated and presented back to the assessors, together with the original university assessment results. Results were discussed with assessors to explore variations. The discussion was recorded, transcribed, thematically analysed and presented back to all assessors to achieve consensus on the emerging major learnings. RESULTS: Although there were differences in absolute scores, there was consistency (12 out of 16 performances) in overall judgement decisions regarding placement readiness. Proficient communication skills were considered a key factor when determining placement readiness. The discussion revealed: (i) assessment instruments; (ii) assessor factors; and (iii) the subjectivity of judgement as the major factors influencing assessment. CONCLUSIONS: Assessment moderation is a useful method for improving the quality of assessment decisions by sharing understanding and aligning standards of performance.

A cross-sectional study exploring the different roles of individual and group assessment methods in assessing public health nutrition competence.

BACKGROUND: Competency in the practice of public health is essential for dietitians, yet little is known about credible and dependable assessment in this field. The present study aimed to investigate the role of individual and group assessment tasks as elements of a public health nutrition competency-based assessment system. METHODS: Assessment performance data from 158 dietetics students (three group tasks and one individual task) who had completed a practical placement learning experience in a public health nutrition setting were examined using nonparametric techniques. All 158 students were deemed individually 'competent' on completion of the placement. RESULTS: The median mark was significantly lower for the individual compared to the group task, with a greater range of marks achieved in the individual assessment. There was a weak relationship between individual and group marks for the whole cohort (n = 158) (Spearman's rho correlation coefficient = 0.193, P = 0.015). Bland-Altman analysis showed that the mean (SD) agreement between the two assessment tasks was -5.9 (17.7) marks. Systematic bias between the two tasks was also demonstrated, indicating that students with the lowest average mark of the two assessments scored lower on the individual assessment task compared to their group task and those who had a higher average mark scored higher on the individual group assessment compared to their group task. CONCLUSIONS: Student performance in public health differs between individual and group assessment. Individual assessment appears to differentiate between students, yet group work is essential for the development of teamwork skills. Both should be considered in the judgement of public health nutrition competency.

Work-based assessment: qualitative perspectives of novice nutrition and dietetics educators.

BACKGROUND: The assessment of competence for health professionals including nutrition and dietetics professionals in work-based settings is challenging. The present study aimed to explore the experiences of educators involved in the assessment of nutrition and dietetics students in the practice setting and to identify barriers and enablers to effective assessment. METHODS: A qualitative research approach using in-depth interviews was employed with a convenience sample of inexperienced dietitian assessors. Interviews explored assessment practices and challenges. Data were analysed using a thematic approach within a phenomenological framework. Twelve relatively inexperienced practice educators were purposefully sampled to take part in the present study. RESULTS: Three themes emerged from these data. (i) Student learning and thus assessment is hindered by a number of barriers, including workload demands and case-mix. Some workplaces are challenged to provide appropriate learning opportunities and environment. Adequate support for placement educators from the university, managers and their peers and planning are enablers to effective assessment. (ii) The role of the assessor and their relationship with students impacts on competence assessment. (iii) There is a lack of clarity in the tasks and responsibilities of competency-based assessment. CONCLUSIONS: The present study provides perspectives on barriers and enablers to effective assessment. It highlights the importance of reflective practice and feedback in assessment practices that are synonymous with evidence from other disciplines, which can be used to better support a work-based competency assessment of student performance.

'What do doctors think they need to know about nutrition?'-a qualitative study of doctors with formal nutrition training.

BACKGROUND: Doctors are on the frontline of patient care and in an ideal position to provide nutritional advice, yet can feel ill-equipped to do so. The aim of this study was to explore the nutrition knowledge, skills and practice required for nutrition-competent medical graduates, and their role in providing nutrition advice and care, from the perspective of doctors with formal nutrition training. METHODOLOGY: We conducted an exploratory qualitative research study. A purposive sample of 12 medical doctors and students with formal nutrition training across Australia participated in in-depth semi structured interviews. Data were analysed thematically. RESULTS: There were four main themes identified: 1. Identifying the role of doctors in nutrition care; 2. Understanding the interrelatedness of the social determinants of health and nutrition status is key; 3. Optimising nutrition care through multidisciplinary collaboration; and 4. Providing evidence-based nutrition care. CONCLUSION: This exploratory study suggests that doctors consider that nutrition competent medical graduates require skills in referring to dietitians, an understanding and application of the social determinants of health, and practise applying multidisciplinary and evidence-based nutrition care.

An evaluation of a public health nutrition workforce development intervention for the nutrition and dietetics workforce.

BACKGROUND: Workforce development is a key element for building the capacity to effectively address priority population nutrition issues. On-the-job learning and mentoring have been proposed as strategies for practice improvement in public health nutrition; however, there is limited evidence for their effectiveness. METHODS: An evaluation of a mentoring circle workforce development intervention was undertaken. Thirty-two novice public health nutritionists participated in one of three mentoring circles for 2 h, every 6 weeks, over a 7-month period. Pre- and post-intervention qualitative (questionnaire, interview, mentor diary) and quantitative (competence, time working in public health nutrition) data were collected. RESULTS: The novice public health nutritionists explained the intervention facilitated sharing of ideas and strategies and promoted reflective practice. They articulated the important attributes of the mentor in the intervention as having experience in and a passion for public health, facilitating a trusting relationship and providing effective feedback. Participants reported a gain in competency and had an overall mean increase in self-reported competence of 15% (range 3-48% change; P < 0.05) across a broad range of competency elements. Many participants described re-orienting their practice towards population prevention, with quantifiable increases in work time allocated to preventive work post-intervention. CONCLUSIONS: Mentoring supported service re-orientation and competency development in public health nutrition. The nature of the group learning environment and the role and qualities of the mentor were important elements contributing to the interventions effects. Mentoring circles offer a potentially effective strategy for workforce development in nutrition and dietetics.

Listening styles of undergraduate health students.

BACKGROUND: Concerns about poor communication in the medical and other healthcare professions are common in the empirical literature, with studies showing direct relationships between practitioners' effective listening and patients' satisfaction and less risk of litigation. Furthermore, people do not simply listen or not listen, rather they adopt particular listening styles, making the understanding and investigation of practitioner communication a complex topic. The objective of this study was to identify the listening styles of undergraduate health science students enrolled at one Australian university. METHODS: A cross-sectional study using a paper-based version of the Listening Styles Profile (LSP-16) was administered to a cohort of students enrolled in undergraduate education programs in eight different health disciplines: emergency health (paramedics), nursing, midwifery, occupational therapy, physiotherapy, nursing/emergency health dual degree, health science and nutrition and dietetics. The LSP-16 is a validated and reliable scale that assesses participants' preferences for each of four distinct listening style constructs. There were 1459 health students eligible for inclusion in the study. Ethics approval was granted. RESULTS: A total of 860 students participated in the study (response rate of 58%), of whom 87.2% (n=750) were female. Across the group, a strong preference was shown for the People Listening Style (LS), which is a listening style characterised by a concern for people's feelings and emotions. Otherwise, an unexpected amount of homogeneity in preferred listening style was found within the group of health science students. Female students reported a slightly stronger preference for the People LS, whereas males reported slightly stronger preferences for the Action LS and Content LS. There were no statistical differences in preference for LS by students' age or year level of undergraduate enrolment. CONCLUSION: The health professional student participants of this study reported a preference for a range of listening styles, which is appropriate for many healthcare settings. However, a strong preference for the People LS and a moderate preference for the Content LS were evident. This study should be replicated with practicing professionals to establish if the demands of the workplace affect practitioners' listening style(s).

Duchenne muscular dystrophy: preliminary experience with sacubitril-valsartan in patients with asymptomatic left ventricular dysfunction.

OBJECTIVE: Duchenne muscular dystrophy (DMD) is an inherited X-linked recessive neuromuscular disease caused by mutations of the dystrophin gene, leading to early and progressive muscle deterioration and dilated cardiomyopathy. The aim of this investigation was to assess whether treatment with sacubitril/valsartan (S/V) is well tolerated and may have beneficial effects in DMD patients with left ventricle (LV) dysfunction. PATIENTS AND METHODS: We administered S/V to 3 DMD patients (19-29 yeard old) with LV ejection fraction <35% at echocardiography but no symptoms of heart failure. All patients were on optimal medical therapy. S/V was initiated at a very low dose of 12/13 mg/die, after withdrawal of angiotensin-converting enzyme inhibitor therapy, and slowly titrated to the dose of 49/51 mg twice daily or the maximally tolerated dose. Clinical and echocardiographic follow-up was performed after 3, 6 and 12 months. RESULTS: At baseline, the LV ejection fraction was 32±1%. A significant improvement of LV ejection fraction was observed at 3 months (44.0±6.0%; p<0.05), which was maintained at 6 (45.7±5.0%) and 12 (43.3±3.2%) months (p<0.05 for both). No relevant side effects were reported throughout the period of the study. CONCLUSIONS: Our preliminary data suggest that, in DMD patients with reduced LV ejection fraction, S/V is safe and may improve LV function.

Adoption Factors Related to Electronic Vaccine Record in the Public Primary Care Network of Buenos Aires City.

The Electronic Health Record used in the public primary care network of Buenos Aires City has a specific module for the vaccines registration. The present study explores the factors of EHR adoption by nurses. We found 5 barriers and one facilitator for adoption. Barriers are related with organize the flow of patients especially during vaccine campaigns, adapt the work stations and integrate the records with the vaccine central program.

Terahertz generation in nitrides due to transit-time resonance assisted by optical phonon emission.

The conditions for THz radiation generation caused by electron transit-time resonance in momentum and real spaces under optical phonon emission are analyzed for nitride-based materials and their structures. It is shown that such a mechanism provides a unique possibility to realize sub-THz and THz radiation generation at the border between the electro-optical and electronic techniques by using two alternative approaches: (i) amplification of transverse electromagnetic waves in 3D bulk materials and 2D quantum wells, and (ii) longitudinal current-field instabilities in sub-micron and micron n(+)nn(+) diodes. Estimations of frequency regions, output power and efficiency of the generation demonstrate that nitrides are promising materials for THz radiation generation.

Terahertz oscillations in ultra-thin n-In(0.53)Ga(0.47)As ungated channels.

Using a self-consistent Monte Carlo simulator we investigate the spectrum of voltage fluctuations of an n-type InGaAs two-terminal layer of variable thickness W in the range 1-100 nm and variable length L in the range 0.01-10 µm embedded in an external dielectric medium. Calculations are performed at T = 300 K for different dopings and in the presence of an external bias of increasing strength. When the bias is well below the threshold for the Gunn effect the spectrum peaks at the plasma oscillations of the electron gas. For W≥100 nm and carrier concentrations of 10(17)-10(18) cm(-3) the peaks are in good agreement with the standard three-dimensional (3D) expression of the plasma frequency. For W≤10 nm the results exhibit a plasma frequency that depends on the length of the layer, thus implying that the oscillation mode is dispersive. The corresponding frequency covers a wide range of values 0.1-10 THz and is in agreement with the two-dimensional (2D) expression of the plasma frequency obtained for a collisionless regime within the in-plane approximation for the electric field. A region of cross-over between the 2D and 3D behaviours of the plasma frequency is shown for W>10 nm. When the bias is above the threshold for the Gunn effect, we observe the washing out of the plasma peak and the onset of a frequency peak associated with the transit time of the Gunn domain located in the sub-terahertz frequency region.

Optimising the effectiveness of diabetes education in an East Asian population.

AIM: To explore the collective patterns of learning behaviours and preferences of Chinese people during diabetes education. The study was carried out across three countries and aimed to identify strategies that could be used to tailor diabetes education to Chinese people. METHODS: A case study approach was undertaken in three countries (Australia, China and Singapore) using participant observations and qualitative interviews. Purposive sampling was used to select field sites before a snowball technique was employed to identify relevant interviewees. Thematic analysis with pattern matching was used for data analysis. RESULTS: A total of 39 participant observations and 22 interviews were conducted. Chinese people with diabetes were observed seeking advice and recommendations from health professionals. When told clearly what to do, they strived for full compliance. They tended to be submissive during diabetes education and were not likely to raise concerns, negotiate or participate in making medical decisions. They appeared to prefer prescriptive concrete instructions rather than more flexible conceptual education and to believe that behavioural change should be achieved by individual willpower and determination, resulting in an 'all-or-nothing' approach. Regular repeated information sessions were reported to establish rapport and trust. CONCLUSIONS: For diabetes education to be culturally modified for Chinese people, there is a need to consider their unique philosophies and behaviours during education to support lifestyle changes. Building trust from the early stages of education was achieved by encouraging rapport through the provision of clear and precise instructions. This should be done before engaging in an open discussion of implementation strategies. Once the trust is built, healthy behaviour change may follow.

Attributes of the complete dental record: a Delphi approach to standards.

BACKGROUND: Adherence to the Dental Board of Australia Guidelines on dental records is not universal and remediation of deficient practise requires clarity in the practical application of standards. The aim of this research is to clarify practical requirements of dental record keeping in New South Wales. METHODS: Seventeen experts were invited to participate in an electronically administered series of Delphi questionnaires. Concepts were refined until consensus was reached. RESULTS: Two rounds were required to achieve a satisfactory level of consensus (>80%). A high level of consensus was obtained across the two rounds, with 72% and 86% agreement on propositions in the first and second rounds, respectively. Consensus criteria were established in 14 domains to establish attributes of the complete dental record (ACDR). CONCLUSIONS: The ACDR may supplement existing national guidelines and are likely to be useful in a remediation context in which clear, unambiguous expectations for conduct are paramount.

Managing User Needs During the EHR Implementation in Buenos Aires City: The HelpDesk Role.

Enablement, guidance, and proactive preparation for a new IT system implementation has proven to be a smart way to prepare people to embrace change. These activities are closely related to change management approaches which seek to help people understand and adopt specific behaviors. That being said, investing in such activities becomes the cornerstone of the success of the project. Leading IT companies around the world include in their strategy for new services and offering deployments, a proactive HelpDesk service. This not only helps build long lasting/trusted relationships between end users and IT sectors but also helps reduce cost and maximizes the Return of Investment. A streamlined process and easy to use/fluent communication channel between parties are powerful risk management/Quality Assurance and Continuous Improvement tools. In this paper, we address the example of a HelpDesk support team implementation of a city-scaled Electronic Health Records implementation.

Trends in child and adolescent obesity prevalence in economically advanced countries according to socioeconomic position: a systematic review.

Recent obesity trends in children and adolescents suggest a plateau. However, it is unclear whether such trends have been experienced across socioeconomic groups. We analysed whether recent trends in child and adolescent overweight and obesity differ by socioeconomic position (SEP) across economically advanced countries. Eligible studies reported overweight and obesity prevalence in children and/or adolescents (2-18 years), for at least two time points since 1990, stratified by SEP. Socioeconomic differences in trends in child and adolescent overweight and obesity over time were analysed. Differences in trends between SEP groups were observed across a majority of studies. Over half the studies indicated increasing prevalence among low SEP children and adolescents compared to a third of studies among children and adolescents with a high SEP. Around half the studies indicated widening socioeconomic inequalities in overweight and obesity. Since 2000 a majority of studies demonstrated no change or a decrease in prevalence among both high and low SEP groups. However around 40% of studies indicated widening of socioeconomic inequalities post-2000. While our study provides grounds for optimism, socioeconomic inequalities in overweight and obesity continue to widen. These findings highlight the need for greater consideration of different population groups when implementing obesity interventions.

The expression of metalloproteinase-2, -9, and -14 and of tissue inhibitors-1 and -2 is developmentally modulated during osteogenesis in vitro, the mature osteoblastic phenotype expressing metalloproteinase-14.

During osteogenesis, in vitro, of tibial-derived rat osteoblasts (ROB) and derived clones, changes occur in the interactions of mature osteoblasts with the endogenous extracellular matrix (ECM) and these culminate in the formation of tridimensional nodules, which become sites of mineral deposition. We investigated if these changes might be mediated by remodeling of ECM, and we focused our study on the neutral metalloproteinases (MMPs), known agents of matrix remodeling, and on their tissue inhibitors (TIMPs). We report that during in vitro differentiation, osteoblasts express the secreted MMP-2 and -9 and the membrane gelatinase MMP-14. These, along with the tissue inhibitors TIMP-1 and -2, are developmentally regulated according to the maturation stage of osteoblasts. Their levels change in a similar association with osteoblast phenotypic maturation in different populations of ROB, which take different times to complete osteogenesis in vitro. MMP-14 expression coincides in both cell populations with the mature osteoblastic phenotype and is localized in the cells forming nodules. MMP-2 and -9 are expressed diffusely in the osteoblast population. Developmentally associated changes in the activation of MMP-2 are detected, associated in their timing with the expression of MMP-14 in both populations of ROB, and MMP-14 activates pro-MMP-2 in vitro. Expression of messenger RNAs (mRNAs) for the three MMPs increases up to the time of nodule formation. At this stage, TIMP-1 mRNA levels are lowest. TIMP-2 mRNA decreases throughout osteogenesis. In situ hybridization in 7-day-old rat tibias shows the strongest expression of MMP-14 among osteogenic cells, in lining osteoblasts on the newly formed trabeculae under the growth plate, and on the endosteal surface of cortical bone. Our data support the concept that the developmentally regulated expression of MMP-14 triggers localized proteolysis within the osteogenic population, concomitant in vitro to nodule formation.

Rat tibial osteoblasts III: propagation in vitro is accompanied by enhancement of osteoblast phenotype.

Postproliferative confluent cultures of primary rat tibial osteoblasts (ROB), cultured in medium supplemented with ascorbic acid and beta-glycerophosphate (AS-bGP, differentiation medium) express, in sequence, specific bone markers which identify a succession of maturation stages, and eventually form mineralized noduli. We report an investigation on the effect of extensive proliferation in vitro in unsupplemented medium on the osteogenic potential of mass cultures of ROB. The growth rates of the populations, derived from two independent primary cultures, was constant throughout 110 cumulative population doublings (CPD) in culture. Propagated cells maintained features similar to osteoblasts in primary cultures with respect to serum and anchorage dependence for growth and to the chemokinetic effect on endothelial cells exerted by their conditioned media (CM). Propagated populations, set at confluence in differentiation medium, were tested for the expression of early [alkaline phosphatase (AP)] and late [osteocalcin (OC); bone sialoprotein (BSP); 45Ca incorporation and mineralization] osteogenic markers. We observed an increase, parallel to the increase in CPD, in both the level of maximal expression of AP (enzyme/microgram cellular DNA) and in the frequency of nodules, reaching five- to sixfold (at 78 CPD) and eightfold (at 60 CPD), respectively, the levels of primary cultures. AP expression (enzyme and mRNA) persisted during mineralization and 45Ca incorporation. The time required by propagated cultures for the formation of nodules decreased with increase of CPD, and was reduced to less than one third at 87 CDP. Nodules became mineralized over a similar lapse of time as in primary cultures and were positive by histochemistry for BSP and OC. We also obtained osteogenic clones from two independent cultures after 72 CPD. 90% of these showed an osteoblast phenotype, expressing AP and forming nodules positive for OC and BSP, which mineralized. Timing of formation and frequency of nodules/plated cells in clones was similar to that found in propagated cultures of equivalent CPD. In summary, propagated ROB populations and derived clones showed enhanced osteoblast phenotype, possibly due to an increase in osteogenic cells and enrichment of proliferating mature osteoblasts, consequent to extended propagation in culture.

Nitric oxide and salt sensitivity.

Studies in laboratory animals suggest that altered nitric oxide (NO) production may be associated with salt sensitivity. In this investigation we determined whether the endogenous NO production was altered in salt-sensitive human subjects when salt intake was changed. Salt sensitivity was assessed from the magnitude of the blood pressure (BP) lowering obtained when the salt intake was reduced from high to a low intake. The combined urinary excretion of nitrites and nitrates, the major metabolites of NO, was employed as an index of endogenous NO production. Salt-sensitive subjects (n = 23) were older, heavier, and had greater waist-to-hip ratios and higher baseline BP than salt-resistant individuals (n = 25). In salt-sensitive subjects, mean blood pressure (MBP) decreased 11.8+/-0.7 mm Hg, and NO metabolite excretion increased from 823+/-102 to 1530+/-148 mmol/24 h, when salt intake was reduced from 316 to 28 micromol/day. NO metabolite excretion was 45% lower during high salt (0.66+/-0.1 micromol/mg creatinine) than during low salt intake (1.12+/-0.1 micromol/mg creatinine) (P < .001). In contrast, when salt intake was reduced, salt-resistant subjects exhibited no significant mean changes in BP or NO metabolite excretion. During low salt intake, NO metabolite excretion (micromol/ day) was significantly higher in salt-sensitive individuals. The magnitude of decrease of systolic blood pressure, diastolic blood pressure, or MBP induced by reducing salt intake was not related to the increase in urinary excretion of NO metabolite levels (r2 = 0.009; P = .66). In summary, to the extent that urinary NO metabolite levels reflect the activity of the endogenous NO system, our results support the view that salt sensitivity may in part be determined by an inability to increase or to sustain NO production in response to high salt. Insufficient NO production during high salt may in turn lead to altered pressure-natriuresis relationships and to an increase in BP. The possibility that the increase in BP induced by high salt intake in salt-sensitive individuals could be the key factor in reducing NO metabolite levels can not be ruled out.

Specific interactions between DNA left-handed supercoils and actinomycin D.

The interactions between the natural cyclopentapeptide antibiotic actinomycin D (ACT) and circular pBR322 DNA have been studied by freezing the topological state of the DNA in the complex by topoisomerase I reaction. Both supercoiled and relaxed DNAs, in the complexes at low antibiotic/DNA base-pair ratios, showed a dramatic decrease in linking number that cannot be explained by taking into account only the generally accepted unwinding of 28 degrees for each ACT molecule bound. Recent results derived from the crystallographic analysis of the complex between GpC and ACT suggest that ACT could mediate non-covalent cross-links between distant sections of DNA. Bridges between ACT and different sections of the pBR322 double helix could also explain our results. Two-dimensional gel electrophoresis of ACT-relaxed pBR322 DNA complexes reveals that all supercoils induced by ACT are negative. Two models of the complexes which correspond to the stabilization of DNA crossing by one or two molecules of ACT are proposed. In both cases the ability of ACT to stabilize only DNA left-handed supercoils is derived from the chirality of ACT, when it interacts with DNA.