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PubMed2004

Immigration and emigration of Burkholderia cepacia and Pseudomonas aeruginosa between and within mixed biofilm communities.

AIMS: To investigate the dynamics of binary culture biofilm formation through use of both the Sorbarod model of biofilm growth and the constant depth film fermenter (CDFF). METHODS AND RESULTS: Pseudo steady-state biofilm cultures of laboratory and clinical strains of Pseudomonas aeruginosa, selected on the basis of their ability to produce a Burkholderia cepacia growth-inhibitory substance, were established on Sorbarod filters and challenged with corresponding planktonic grown cultures of B. cepacia. Reverse challenges were also conducted. Both B. cepacia and P. aeruginosa were able to form steady-state monoculture biofilms after 48 h growth. When steady-state biofilms of B. cepacia NTCT 10661 were challenged with planktonically grown P. aeruginosa PAO1 known to produce a B. cepacia growth-inhibitory substance, the immigrant population was rapidly and almost completely bound to the biofilm, displacing B. cepacia. By contrast, established biofilms of P. aeruginosa PAO1 resisted immigration of B. cepacia 10661. Similar experiments conducted with a nongrowth inhibitory substance producing clinical pairing of P. aeruginosa 313113 and B. cepacia 313113 led to the formation of stable, mixed biofilm populations in both instances. Moreover, co-inoculation with these clinical isolates resulted in a stable, mixed steady-state biofilm. Similar observations were made for biofilms generated in CDFFs. In such instances following pan-swapping between two monoculture CDFFs, B. cepacia 313113 was able to integrate into an established P. aeruginosa 313113 biofilm to form a stable binary biofilm. CONCLUSIONS: Establishment of a mixed species community follows a specific sequence of inoculation that may either be due to some degree of match between co-colonizers or that P. aeruginosa predisposes uncolonized sections of the surface to permit B. cepacia colonization. SIGNIFICANCE AND IMPACT OF THE STUDY: Colonization of a surface with one bacterial species confers colonization resistance towards other species. Disinfection of a surface might well increase the probability of pathogen harbourage.

Bacteriological Techniques↗
PubMed1997

Microbial population dynamics on leaves.

Microbial population dynamics on leaves in time and space are a function of immigration, emigration, growth, and death. Insight into the relative significance of each population process to the generation of specific dynamics for individual microorganisms is necessary to understanding the ecology and life history strategy of the microorganism and to developing effective control strategies. Additionally, information on the significance of within-leaf versus extra-leaf processes to the generation of phyllosphere dynamics is important to determining the range of spatial scales over which a population should be studied. Unfortunately, such information is difficult to obtain due to the lack of effective methodologies for distinguishing these processes within phyllosphere populations. Future research efforts should focus on the quantification of immigration, emigration, growth, and death relative to the population dynamics of phyllosphere microorganisms.

Journal Article↗
PubMed1995

Return migration on the policy agenda in Sweden.

"Explicit policies on return migration are of rather recent date in most European countries, including Sweden. During the last few years a number of new policy initiatives have been taken in this field. The purpose of this paper is to examine how official Swedish policies on return migration have changed during the last 20 years. The conclusion is that Sweden has moved from a ¿non-policy' in the 1970s, much in opposition to ¿guestworker' or rotation systems, towards an active and explicit policy promoting return in the mid-1990s. The major trends in the country's immigration, emigration and return flows are also presented."

Demography↗
PubMed1986

[Turning points in demographic trends].

A method for estimating demographic turning points using spline functions is described. It involves using a nonlinear least squares method to estimate the points in time at which such turning points occur. "The method is employed for assessing turning points in the trends of the numbers of live births, deaths, marriages, immigrants, emigrants and internal migrants after the Second World War in the Netherlands. In general the trends can be described adequately by specifying three turning points after 1950." (summary in ENG)

Demography↗
PubMed1984

Demographic components of gene frequency change in free-ranging macaques on Cayo Santiago.

Gene frequency profiles from January 1973 to January 1977 for three polymorphic loci were examined in Cayo Santiago rhesus social groups. The effects of demographic components (i.e., births, deaths, immigrations, emigrations, and group fission and fusion) on total change in gene frequencies are assessed. Allelic frequencies at the carbonic anhydrase II, 6-phosphogluconate dehydrogenase, and transferrin loci were analyzed in four social groups. In the two groups that underwent fission and fusion during the study period, the timing of these processes was related to the largest short-term changes in gene frequences. However, immigration and emigration had the greatest effect on total change in gene frequency in all groups during the study period. The relative importance of births and deaths in producing gene frequency change varied among the social groups. These results suggest that the relative importance of the demographic components of gene frequency change in primate populations is determined by behavioral patterns and ecological conditions specific to the population considered.

Animals↗
PubMed1989

All about U.S. immigration statistics.

The quality of data collected by the U.S. Immigration and Naturalization Service (INS) is assessed, with a focus on differences between U.S. and U.N. definitions of immigrants, emigrants, and refugees. The author suggests that "gaps in migration data collected for the U.S. limit their usefulness for studying international migration and estimating national population change. For example, no information is collected on emigration of legal permanent residents or U.S. citizens, nor is there any direct information on the immigration of U.S. citizens. Data collected on legal immigrants are based on a legal and administrative definition that often conflicts with the demographic definition of an immigrant."

Americas↗
PubMedDate not supplied

The elderly and international migration in Canada: 1971-1986.

"This paper addresses issues of elderly immigrants in Canada within two areas: their characteristics as immigrants and their contribution to the social phenomenon of the aging of the Canadian population. The patterns of net immigration of persons aged 60 years and over are identified according to sex, age and place of origin of immigrants.... Emigration of this group is studied separately. The results of the analysis demonstrate that the elderly immigrant population displays migration patterns significantly different from that of the total immigrant population. Older immigrants participate even more extensively than their younger counterparts in the process of remigration or return migration. As a consequence, an increase of the proportion of older immigrants...does not necessarily accelerate the aging of the Canadian population." (SUMMARY IN ITA)

Adult↗
PubMed1965

Health of immigrants.

Explore the source record for details and available documents.

Emigration and Immigration↗
PubMed1965

Immigration.

Explore the source record for details and available documents.

Emigration and Immigration↗
PubMedDate not supplied

[A physician demand and supply forecast model for Nova Scotia].

RATIONALE: There is well-founded concern about the current and future availability of Health Human Resources (HHR). Demographic trends are magnifying this concern -- an ageing population will require more medical interventions at a time when the HHR workforce itself is ageing. The lengthy and costly training period for most health care workers, especially physicians, poses a real challenge that requires planning these activities well in advance. Hence, there is definite need for a good HHR forecasting model. OBJECTIVES: To present a physician forecasting model that projects the Full-Time Equivalent (FTE) demand for and supply of physicians in Nova Scotia to the year 2020 for three specialties: general practitioners, medical, and surgical. The model enables gap analysis and assessment of alternative policy options designed to close the gaps. METHODOLOGY: The methodology for estimating demand fo physician services involves three steps: (i) Establishing the FT for each physician. To this end we calculate the income of each physician using Physician Billings Data and then identify the 40th and 60th percentile income levels for each of the 40 specialties. The income levels are then used to calculate the FTE using a formula developed at Health Canada; (ii) Calculating the FTE for each service by distributing the FTE of each physician at the service level (i.e., by patient age, sex, most responsible diagnosis, and hospital status group); and (iii) Using Statistics Canada's population projections to project future demand for three broad medical disciplines: general practitioners, medical specialist, and surgical specialists. The supply side of the model employs a stock/flow approach and exploits time-series and other data for variables, such as emigration, international medical graduates (IMGs), medical school entrants, retirements, mortality, and so on, which in turn allow us to access a host of policy parameters. RESULTS: Under the status quo assumption, demand for physician services will outstrip the growth in supply for all three specialties. CONCLUSIONS: The model can simulate supply-side policy changes (e.g. more IMGs, delayed retirements) and can also reflect changes in demand (e.g. a cure for leukemia; different work intensities for physicians). The model is highly parameterized so that it can accommodate shocks that may influence the future requirements for physicians. Once a future requirement is determined, the supply model can identify the policy levers (new entrants, immigration, emigration, retirement) necessary to close the gap between demand and supply. The model is a user-friendly tool made for policy makers to formulate appropriate physician workforce planning.

Adult↗
PubMed1982

Computer predictions of New Zealand doctor numbers.

Considerable debate has been generated about "the coming crisis in medical manpower" with most current analyses predicting a large surplus of doctors in the late 1980s. However, predictions can be complex because of potential fluctuations in the input variables due to political and social factors. Variables affecting active doctor numbers include the numbers of medical students graduating each year, immigration, emigration, the proportions of males and females, age at retirement, and extent of part-time work. A computer simulation is described which enables the relative effects of these variables to be compared. It is found that adjustments in the medical school intake have a relatively small short-term effect compared with the effects of adjustments in several of the other variables, particularly immigration numbers.

Computers↗