Correlates of childhood caries: A study in Qatar.

BACKGROUND: The prevalance of dental caries in children in Qatar is high, which necessitates preventive efforts. AIM: To identify the sociodemographic and behavioural correlates of dental caries in the primary dentition of children 4- to 8-year-olds in Qatar. DESIGN: Weighted data from the Qatar Child Oral Health Survey 2017 were analysed for caries prevalence (dmft>0) and experience (dmft). Sociodemographic and behavioural variables were also drawn from the survey. RESULTS AND CONCLUSION: Among the 1154 children, caries prevalence was 69.3% (95%CI [63.4, 74.5]) and experience at 3.8 dmft (95%CI [3.3, 4.2]). The prevalence ratio (PR) 0.82 (0.72, 0.94) was lower among younger than in older children; those for non-Qatari nationality Arabic PR 0.91 (0.82, 1.00) and Other PR 0.75 (0.57, 0.99) than for Qatari nationality; those attending international kindergartens/schools PR 0.89 (0.80, 0.99) than independent schools; and whose parents had university-level education PR 0.85 (0.75,0.95) than did not. Caries prevalence was lower among those toothbrushing by age 3 years PR 0.88 (0.80,0.99) than later; children with low/intermediate sugar exposures PR 0.85 (0.74,0.97) and 0.89 (0.79,1.00) than those with high exposures; children with a dental check-up PR 0.68 (0.53,0.87) than those without; and children who drank bottled water with some fluoride PR 0.89 (0.80,0.99) than those who did not. Findings were similar for dmft. In conclusion caries prevalence varied but was high across sociodemographic correlates indicating vulnerablity. Interventions focusing on behaviours - such as toothbrushing, reducing sugar intake, check-up and encouraging intake of water with fluoride - are needed.

Bacterial natural transformation by highly fragmented and damaged DNA.

DNA molecules are continuously released through decomposition of organic matter and are ubiquitous in most environments. Such DNA becomes fragmented and damaged (often <100 bp) and may persist in the environment for more than half a million years. Fragmented DNA is recognized as nutrient source for microbes, but not as potential substrate for bacterial evolution. Here, we show that fragmented DNA molecules (≥ 20 bp) that additionally may contain abasic sites, cross-links, or miscoding lesions are acquired by the environmental bacterium Acinetobacter baylyi through natural transformation. With uptake of DNA from a 43,000-y-old woolly mammoth bone, we further demonstrate that such natural transformation events include ancient DNA molecules. We find that the DNA recombination is RecA recombinase independent and is directly linked to DNA replication. We show that the adjacent nucleotide variations generated by uptake of short DNA fragments escape mismatch repair. Moreover, double-nucleotide polymorphisms appear more common among genomes of transformable than nontransformable bacteria. Our findings reveal that short and damaged, including truly ancient, DNA molecules, which are present in large quantities in the environment, can be acquired by bacteria through natural transformation. Our findings open for the possibility that natural genetic exchange can occur with DNA up to several hundreds of thousands years old.

A double kill gene cassette for the positive selection of transforming non-selective DNA segments in Acinetobacter baylyi BD413.

Natural transformation has been widely used for the monitoring of DNA in biological and environmental samples. These assays depended on selectable traits on the tested DNA. We have now developed a transformation assay system in which recombinational removal of a cassette with two conditional kill genes (hok and sacB) from the recipient genome provides positive selection for non-selective DNA. The cassette was integrated into the Acinetobacter baylyi BD413 chromosome within trpE and was flanked by two segments of non-selective test DNA, which in this study were from a T-DNA construct previously used to generate a transgenic potato. Genes for tetracycline and spectinomycin/streptomycin resistance located at the sides of the cassette allowed to maintain selection pressure against spontaneous loss of the cassette. Plasmid DNA containing the T-DNA gave transformation frequencies ranging linearly from 10(-4) per recipient (at 1 mug DNA ml(-1)) down to 10(-7) (1 ng DNA ml(-1)) by selecting for survivors after activation of both kill functions. Transformation depended on the two flanking homologous segments for recombinational exchange. DNA of the transgenic potato also gave positive scores in spite of the about 10(5)-fold dilution of T-DNA by potato DNA. False positives having a spontaneous deletion of hok and sacB occurred at a frequency of 1.8x10(-9) per cell but could be distinguished by PCR from real transformants. Thus, the system is suitable for detection of transformation frequencies down to about 10(-9). Hok and sacB as well as the regulatory system used (LacI-lac operator and T5 promoter) are known to function in many organisms suggesting wide applicability of the cassette for positive selection.

Globalization in the dental practice: a perspective from down under.

Dental education and practice in Australia and New Zealand are described by a dental dean who has practiced in South Africa, Canada, and Australia. Education is based on the English model, being a five-year program with entry from high school. Variations are being attempted on this approach, with an increasing number of dental students entering with advanced education, multiple degree alternatives, and combinations of auxiliaries including hygienists, therapists, and prosthetists. Dental boards do not examine dental graduates for licensure or actively investigate substandard skill levels or compromised practitioners. Practice is open to dentists trained in other countries based on service in needy areas and a two-part examination process. Specialty licensure is obtained based on examination by the national Royal Australasian College of Dental Surgeons and advanced education normally leads to a degree, including an additional doctoral degree. The most challenging issues facing oral health in Australia and New Zealand remain workforce shortages, especially in remote rural areas, and the cost of dental education.

Canadian dental students' perceptions of their learning environment and psychological functioning over time.

A cohort of dental students (N=28) at the University of Manitoba was followed throughout their entire dental education program to explore changes in their perceptions of the learning environment over time. Aspects of the students'psychological functioning, including common psychological symptoms, self-esteem, and coping strategies, were also evaluated to assess changes in these factors over time. A battery of instruments consisting of the Learning Environment Survey (LES), the Symptom Questionnaire (SQ), the Ways of Coping Checklist (WCCL), and the State Self-Esteem Scale (SSES) was administered at the beginning, midpoint, and end of each academic year throughout the four-year dental education program. Results indicated that there was a minor positive recalibration of student perceptions in the areas of course relevance and opportunities for outside interests during the first months of year one. Apart from this, perceptions of dental school as a seldom-to-occasionally positive learning environment were maintained over the entire dental education program. In terms of psychological functioning over time, students reported decreases in their levels of problem-focused coping and self-esteem, increased use of avoidance and wishful thinking as coping strategies, and more anxiety, depression, and hostility at various points. Some implications of these findings for dental education are discussed.

Transfer of plastid DNA from tobacco to the soil bacterium Acinetobacter sp. by natural transformation.

Acquisition of new genetic information by horizontal gene transfer is a major mechanism of genetic adaptation and evolution in prokaryotes. Naturally transformable cells of Acinetobacter sp. were exposed to plant DNA from leaf and root tissue of transplastomic tobacco. With the aadA gene (resistance against spectinomycin and streptomycin) as anchor sequence, the transfer of segments of the tobacco plastid DNA to Acinetobacter by homology-facilitated illegitimate recombination occurred at a frequency of 1.2 x 10(-7) per cell, which was about 0.1% of the frequency of fully homologous transfers. Without anchor sequence, transfer was not detected (

Spread of recombinant DNA by roots and pollen of transgenic potato plants, identified by highly specific biomonitoring using natural transformation of an Acinetobacter sp.

Transgenic potato plants with the nptII gene coding for neomycin phosphotransferase (kanamycin resistance) as a selection marker were examined for the spread of recombinant DNA into the environment. We used the recombinant fusion of nptII with the tg4 terminator for a novel biomonitoring technique. This depended on natural transformation of Acinetobacter sp. strain BD413 cells having in their genomes a terminally truncated nptII gene (nptII'; kanamycin sensitivity) followed by the tg4 terminator. Integration of the recombinant fusion DNA by homologous recombination in nptII' and tg4 restored nptII, leading to kanamycin-resistant transformants. DNA of the transgenic potato was detectable with high sensitivity, while no transformants were obtained with the DNA of other transgenic plants harboring nptII in different genetic contexts. The recombinant DNA was frequently found in rhizosphere extracts of transgenic potato plants from field plots. In a series of field plot and greenhouse experiments we identified two sources of this DNA: spread by roots during plant growth and by pollen during flowering. Both sources also contributed to the spread of the transgene into the rhizospheres of nontransgenic plants in the vicinity. The longest persistence of transforming DNA in field soil was observed with soil from a potato field in 1997 sampled in the following year in April and then stored moist at 4 degrees C in the dark for 4 years prior to extract preparation and transformation. In this study natural transformation is used as a reliable laboratory technique to detect recombinant DNA but is not used for monitoring horizontal gene transfer in the environment.

1.1 Student selection and the influence of their clinical and academic environment on learning.

Student selection and recruitment play a vital role in the successful outcome of dental education. To identify key issues and practices in selection and recruitment, the group assessed current processes, philosophies and practices from a range of different educational systems, although it was not possible to gather data from all countries or continents within the timeframe provided. Furthermore, the group explored the effect of the educational learning environment on the successful outcome of teaching dental students. It is clear that a wide variety of practices and philosophies exist and are used in different parts of the world. Measuring the success of any given process used for student selection remains a challenge. In some parts of the world, certain practices have become an integral part of the tertiary educational system, and have been applied in a similar way by many or all of the dental schools in that country. In other countries, methods vary from one dental school to another, often reflecting differences in the structure and philosophy of the educational system. There was great variation in the combinations of selection criteria used and in student recruitment strategies. However, it was clear that there was much to be gained by learning from the experiences of other dental schools in student selection. Lessons learned, best practices and philosophies used and supporting value systems proved to be very helpful for benchmarking the processes used. In the discussion of student selection, a number of important questions were raised which deserve further thought and reflection both in the ongoing debate and as part of the ever-changing world of dental education. Important new matters that require more debate and research include: a) ethical issues, including the nature of funding from the student perspective, and the concern that in some regions dentistry may become a profession only for the elite or wealthy students. b) Health standards of students entering dental school. c) How realistic is the applicant's sense of dentistry as a profession? d) How accurate is the students' sense of their career opportunities and the employment market upon graduation? Finally, the over-arching question remains, how valid, reliable and predictable are existing selection practices? Will it be practical and meaningful to standardize methods used, or will exchanging ideas as part of this global debate assist the thought process of dental leaders to improve selection practices by learning from the experiences of other schools in different parts of the world? The processes of open debate, sharing ideas and opinions and identifying sound practices across the globe is a powerful catalyst for developing innovative answers to the complex problems posed by student selection and recruitment. A 'virtual' global process with wide input from as many dental schools as possible should improve the efficacy of student selection, and allow dental educators to identify the 'potential' of prospective students and predict more accurately dental student outcomes. The debate that we have started will certainly contribute to providing a knowledge base which dental educators will be able to draw on when reviewing selection processes in their own schools.

Integration of foreign DNA during natural transformation of Acinetobacter sp. by homology-facilitated illegitimate recombination.

The active uptake of extracellular DNA and its genomic integration is termed natural transformation and constitutes a major horizontal gene-transfer mechanism in prokaryotes. Chromosomal DNA transferred within a species can be integrated effectively by homologous recombination, whereas foreign DNA with low or no sequence homology would rely on illegitimate recombination events, which are rare. By using the nptII(+) gene (kanamycin resistance) as selectable marker, we found that the integration of foreign DNA into the genome of the Gram-negative Acinetobacter sp. BD413 during transformation indeed was at least 10(9)-fold lower than that of homologous DNA. However, integration of foreign DNA increased at least 10(5)-fold when it was linked on one side to a piece of DNA homologous to the recipient genome. Analysis of foreign DNA integration sites revealed short stretches of sequence identity (3-8 bp) between donor and recipient DNA, indicating illegitimate recombination events. These findings suggest that homologous DNA served as a recombinational anchor facilitating illegitimate recombination acting on the same molecule. Homologous stretches down to 183 nucleotides served as anchors. Transformation with heteroduplex DNA having different nucleotide sequence tags in the strands indicated that strands entered the cytoplasm 3' to 5' and that strands with either polarity were integrated by homologous recombination. The process led to the genomic integration of thousands of foreign nucleotides and often was accompanied by deletion of a roughly corresponding length of recipient DNA. Homology-facilitated illegitimate recombination would explain the introgression of DNA in prokaryotic genomes without the help of mobile genetic elements.

Establishment of introduced antagonistic bacteria in the rhizosphere of transgenic potatoes and their effect on the bacterial community.

In a field release experiment, rifampicin resistant mutants of two antagonistic plant-associated bacteria were used for seed tuber inoculation of transgenic T4 lysozyme expressing potatoes, transgenic control potatoes and non-transgenic parental potatoes. The T4 lysozyme tolerant Pseudomonas putida QC14-3-8 was originally isolated from the tuber surface (geocaulosphere) of T4 lysozyme producing plants and showed in vitro antibacterial activity to the bacterial pathogen Erwinia carotovora ssp. atroseptica. The T4 lysozyme sensitive Serratia grimesii L16-3-3 was originally isolated from the rhizosphere of parental potatoes and showed in vitro antagonism toward the plant pathogenic fungus Verticillium dahliae. The establishment of the inoculated bacteria in the rhizosphere and geocaulosphere of the different plant lines was monitored over one growing season to assess the effect of T4 lysozyme produced by transgenic potato plants on the survival of both inoculants. Both introduced isolates were able to colonize the rhizo- and geocaulosphere of transgenic plants and non-transgenic parental plants, and established in the rhizosphere at levels of ca. log(10) 5 colony forming units g(-1) fresh weight of root. During flowering of plants, significantly more colony counts of the T4 lysozyme tolerant P. putida were recovered from transgenic T4 lysozyme plants than from the transgenic control and the parental line. At this time, the highest level of T4 lysozyme (% of total soluble protein) was detected. Effects of the inoculants on the indigenous microbial community were monitored by analysis of PCR-amplified fragments of the 16S rRNA genes of the whole bacterial community after separation by denaturing gradient gel electrophoresis (DGGE). At any sampling time, the DGGE pattern of rhizosphere and geocaulosphere communities did not show differences between the inoculated and non-inoculated potatoes. Neither of the introduced strains became a dominant member of the bacterial community. This work was the first approach to assess the establishment of plant growth promoting rhizobacteria and potential biocontrol agents on transgenic plants.