PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “resistance evolution”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 487 records · Page 27Linked to original sources
PubMed2003

Economics versus alleles: balancing integrated pest management and insect resistance management for rotation-resistant western corn rootworm (Coleoptera: Chrysomelidae).

Western corn rootworm, Diabrotica virgifera virgifera LeConte, has overcome crop rotation in several areas of the central United States. We expanded a simple model of adult behavior and population genetics to explain how rotation resistance may have developed and to study ways to manage the western corn rootworm in a landscape of corn, soybean, and winter wheat where evolution of resistance may occur. We modeled six alternative management strategies over a 15-yr time horizon, as well as a strategy involving a 2-yr rotation of corn and soybean in 85% of the landscape, to investigate their effectiveness from both a biological and economic perspective. Generally, resistance to crop rotation evolves in fewer than 15 yr, and the rate of evolution increases as the level of rotated landscape (selection pressure) increases. When resistance is recessive, all six alternative strategies were effective at preventing evolution of rotation resistance. The two most successful strategies were the use of transgenic rotated corn in a 2-yr rotation and a 3-yr rotation of corn, soybean, and wheat with unattractive wheat (for oviposition) preceding corn. Results were most sensitive to increases in the initial allele frequency and modifications of the density-dependent survival function. Economically, three alternative strategies were robust solutions to the problem, if technology fees were not too high. Repellant soybean, attractive rotated corn, and transgenic rotated corn, all in 2-yr rotations, were economically valuable approaches. However, even the currently common 2-yr rotation was economical when resistance was recessive and the actual costs of resistance would not be paid until far in the future.

Agriculture↗
PubMed1982

Towards an alternative evolution model.

Lamarck and Darwin agreed on the inconstancy of species and on the exclusive gradualism of evolution (nature does not jump). Darwinism, revived as neo-Darwinism, was almost generally accepted from about 1930 till 1960. In the sixties the evolutionary importance of selection has been called in question by the neutralists. The traditional conception of the gene is disarranged by recent molecular-biological findings. Owing to the increasing confusion about the concept of genotype, this concept is reconsidered. The idea of the genotype as a cluster of genes is replaced by a cybernetical interpretation of the genotype. As nature does jump, exclusive gradualism is dismissed. Saltatory evolution is a natural phenomenon, provided by a sudden collapse of the thresholds which resist against evolution. The fossil record and the taxonomic system call for a macromutational interpretation. As Lamarck and Darwin overlooked the resistance of evolutionary thresholds, an alternative evolution model is needed, the first to be constructed on a palaeontological and taxonomic basis.

Animals↗
PubMed2026

Genetic architecture and evolution of stripe rust resistance uncovered using diverse panels of wheat lines and North American Puccinia striiformis f. sp. tritici isolates.

Screening global wheat germplasm with a diverse collection of pathogen races expands the catalog of novel Yr loci and identifies new sources of broad-spectrum resistance against evolving Pst populations. Newly emerging highly virulent races of Puccinia striiformis f. sp. tritici (Pst) often defeat deployed resistance genes (Yr), highlighting the need for novel sources of durable resistance. A global diversity panel of 377 spring wheat (Triticum aestivum L.) lines was screened for all-stage resistance (ASR) against a panel of diverse 20 Pst isolates at the seedling stage and for adult-plant-stage resistance (APR) against natural mix of field races. Genome-wide association mapping identified 77 unique Yr loci. Of these, 34 overlapped with the previously mapped 1150 Yr loci, confirming the robustness of our GWAS results, while 43 were likely novel. Comparison of the nine adult-plant-stage Yr loci mapped in our study with known APR genes identified only one overlap, with Yr29. Except for Yr29, APR genes Yr18 and Yr36 were detected at low frequencies, indicating that resistance in our panel may arise from less characterized or novel sources. Two wheat lines, lacking widely effective Yr5 and Yr15 alleles, exhibited resistance to all 20 Pst races at the seedling stage and natural field races at the adult stage, suggesting that they may carry novel, broad-spectrum ASR alleles. Wheat improvement had no effect on the frequency of ASR alleles but resulted in a threefold increase in the frequency of APR alleles, suggesting that the latter were subjected to more consistent breeding selection over time. Our findings underscore the value of combined screening of diverse germplasm with diverse pathogen races to identify novel sources of broad-spectrum resistance for breeding stripe rust resistant cultivars.

Triticum↗
PubMed1991

Evolution of Staphylococcus aureus resistance to erythromycin in Denmark, 1959 to 1988: comparison with erythromycin-susceptible strains.

Between 1959 and 1988, all Staphylococcus aureus strains (15 168 patients) isolated from blood in Denmark have been collected, investigated and stored, and clinical data has been obtained. Erythromycin resistance was found in 4.9% of these strains. The frequency of erythromycin resistance peaked at 25% in 1966, due to the spread in hospitals of multiresistant strains of the 83A complex. When these strains dominated, an increased mortality rate was seen in patients infected with erythromycin-resistant S. aureus. In contrast to most countries, erythromycin resistance in S. aureus declined to less than 5% in 1971, continued to fall to 1.3% in 1983, and has increased slowly to 2.4% in 1988. The decline was only due to a decrease of multiresistant strains. Erythromycin-resistant strains isolated in recent years are predominantly resistant only to penicillin and erythromycin and belong to many different phage type patterns. In Denmark, inducible resistance has occurred at a stable high frequency of approximately 90% of the erythromycin-resistant strains during the last 30 years. Erythromycin-resistant strains isolated today, however, have higher minimum inhibitory concentrations, and are rarely resistant to spectinomycin, in contrast to the strains isolated in the first half of the observation period.

Denmark↗
PubMed1991

Evolution of Staphylococcus aureus resistance to erythromycin in Denmark, 1959 to 1988: correlations between characteristics of erythromycin-resistant bacteraemia strains.

In an attempt to characterize erythromycin-resistant Staphylococcus aureus we present the intricate relationships between the following factors: phage type, period of isolation, antibiogram, minimum inhibitory concentration (MIC) to erythromycin, inducible or constitutive resistance, spectinomycin susceptibility, hospital- or community-acquired infection, and mortality rate. We studied 718 cases of bacteraemia with erythromycin-resistant S. aureus, occurring between 1959 and 1988. Central factors were phage type pattern, period of isolation, and antibiogram. Between 1959 and 1973 the majority of the erythromycin-resistant strains were multiresistant and belonged to the 83A complex and the related group III. They were mainly inducibly resistant, spectinomycin resistant, and had intermediate MICs (1-4 mg l-1) to erythromycin. The majority of these strains came from hospital-acquired infections and still exist today, although in decreased numbers. By contrast, erythromycin-resistant S. aureus isolated in recent years are usually co-resistant only to penicillin and more rarely also to tetracycline. These strains have inducible resistance, are spectinomycin susceptible, and have a high erythromycin MIC. They are isolated both from hospital- and community-acquired infections. Strains with constitutive resistance to macrolides occurred at a stable low level (13%) during the whole observation period and always had high MICs to erythromycin. The mortality rate among patients with S. aureus bacteraemia due to an erythromycin-resistant strain was only associated with the year of infection and decreased from 61% in the first 15-year period to 40% in the subsequent 15 years.

Bacteriophage Typing↗
PubMed2001

Experimental studies on the evolution of antimony-resistant phenotype during the in vitro life cycle of Leishmania infantum: implications for the spread of chemoresistance in endemic areas.

Pentavalent antimonial unresponsiveness is an emerging problem in endemic areas and information on factors which could modulate the transmission of drug-resistant phenotypes and parasites during life cycle are warranted. Using axenic amastigotes resistant to potassium antimonyl tartrate (Sb(III)) we investigated the modulation of antimonyl resistance during the in vitro life cycle. We assessed: (i) the stability of the drug-resistant phenotype during the in vitro life cycle; (ii) the transmission of drug-resistant clones when mixed with a wild-type clone at different susceptible/chemoresistant ratios (50/50,90/10,10/90) after one or two in vitro life cycles. We demonstrate that: (i) mutants which were 12,28,35 and 44 fold more resistant to Sb(III)-antimonial than their parental wild-type, were Glucantime Sb(V)-resistant when growing in THP-1 cells; (ii) the drug-resistant phenotype was partially retained during long-term in vitro culture (3 months) in drug free medium; (iii) the antimonyl-resistant phenotype was retained after one or more in vitro life cycles. However, when drug-resistant parasites were mixed with susceptible, mutants could not be detected in the resulting population, after one or two in vitro life cycles, whatever the initial wild-type/chemoresistant ratio. These results could be explained by the lower capacity of drug-resistant amastigotes to undergo the amastigote-promastigote differentiation process, leading probably to their sequential elimination during life cycle. Taken together, these observations demonstrate that different factors could modulate the transmission of Leishmania drug resistance during the parasite's life cycle.

Animals↗
PubMedDate not supplied

The evolution of multiple drug resistance in malaria parasites.

Forces determining the rate of spread of drug resistance in malaria were explored using a genetics transmission model which took account of the strong population structure of these parasites. The rate of change of frequency of drug resistant mutants in the parasite population is primarily a function of the proportion of hosts treated with drugs, and parasite transmission rates. With high transmission rates, selection by drugs is more effective than with lower rates because the resistant mutant passes on more copies of itself to the next generation of hosts. Thus reducing transmission rates, either at the overall population level or from drug-treated individuals, should be effective in curbing the spread of resistance. An exception to this is when 2 unlinked genes act jointly (not independently) to confer resistance, when the prevailing transmission rate is already low, drug use is minimal, and resistance genes are rare. Reductions in fitness of the mutant in the absence of drugs (i.e., a fitness cost to resistance) and the degree of epistasis and the mode of gene action of the drugs do not alter these conclusions.

Animals↗
PubMed2000

[Evolution of drug-resistant Mycobacterium tuberculosis in the province of Castellón. 1992-1998].

OBJECTIVES: To determine the frequency of resistant Mycobacterium tuberculosis and the risk factors associated with resistance in the province of Castellón (Spain). MATERIAL AND METHODS: This prospective study of M. tuberculosis sensitivity applied Canetti's method of proportions to all strains isolated in Castellón (n = 532) from January 1992 through December 1998 (7 years); 461 cases were new. RESULTS: The overall frequency of resistant strains was 4.7% (25/532), of which 3.9% (18/461) were instances of primary resistance and 11.1% (7/63) were of secondary resistance. Three percent were resistant to isoniazid, 1.87% to rifampicin, 1.87% to streptomycin and 0.56% to ethambutol. Multiple drug resistance was found in 0.2% (1/461) of the new cases and 1.1% (6/532) overall. The presence of resistant M. tuberculosis was associated with a history of antituberculous treatment (OR = 3.14; p = 0.017) and the presence of one or more risk factors for tuberculosis (OR = 3.32; p = 0.066). CONCLUSIONS: The overall rates of resistant M. tuberculosis and multiple drug resistance are low in the province of Castellón; however resistance is associated with higher mortality such that controlling some preventable risk factors might reduce the frequency of resistance.

Adolescent↗
PubMed1999

Resistance to fusidic acid.

Resistance to fusidic acid is determined by a number of mechanisms. The best described are alterations in elongation factor G, which appear in natural mutants that are harboured at low rates in normal populations of staphylococci (10(6) to 10(8)). Altered drug permeability has also been described, and appears to be plasmid-borne. Binding by chloramphenicol acetyltransferase type I and efflux are other described mechanisms of resistance whose prevalence is unclear. A large number of studies have examined rates of fusidic acid resistance in staphylococci. Most show low levels of resistance. Studies where high levels of resistance have been seen are from areas of the hospital where cross infection is common. Rates of resistance have tended to be slightly higher in methicillin-resistant strains of Staphylococcus aureus. Studies on the evolution of resistance have shown no major trends to the emergence of resistance. In one case this is despite increasing use of both systemic and topical fusidic acid over more than 24 years. Selection for resistant variants during treatment was recognised early in vitro and in vivo. However, evidence suggests that it does not occur at high frequency in clinical practice. Nevertheless, accumulated experience is that fusidic acid in combination with other agents results in less resistance emergence.

Animals↗
PubMed2006

Inheritance of resistance to the Cry1Ab Bacillus thuringiensis toxin in Ostrinia nubilalis (Lepidoptera: Crambidae).

Laboratory selection with Cry1Ab, the predominant Bacillus thuringiensis (Bt) toxin in transgenic corn, Zea mays L., produced >1000-fold resistance in two laboratory strains of European corn borer, Ostrinia nubilalis (Hübner). We tested the offspring of various crosses to determine the mode of inheritance of resistance to Cry1Ab. Patterns of inheritance of resistance were similar in the two resistant strains. The progeny of reciprocal F1 crosses (resistant male x susceptible female and vice versa) responded alike in bioassays, indicating autosomal inheritance. The median lethal concentrations (LC50 values) of F1 were intermediate between the resistant and susceptible parents, indicating approximately additive inheritance. However, the dominance of resistance increased as the concentration of Cry1Ab decreased. Analysis of progeny from backcrosses (F1 x susceptible strain) suggests that resistance was controlled by more than one locus. In particular, the fit of observed to expected mortality improved as the number of putative loci increased from 1 to 10. The polygenic nature of resistance in these two laboratory strains suggests that major genes for resistance to Cry1Ab were not common in the founding populations of O. nubilalis. A low initial frequency of major genes for Cry1Ab resistance might be an important factor in delaying evolution of resistance to Bt corn in this pest.

Animals↗
PubMed2001

The evolution of methicillin-resistant Staphylococcus aureus in Canadian hospitals: 5 years of national surveillance.

BACKGROUND: To better understand the epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) in Canadian hospitals, surveillance has been conducted in sentinel hospitals across the country since 1995. We report the results of the first 5 years of the program. METHODS: For each newly identified inpatient with MRSA, medical records were reviewed for demographic and clinical data. Isolates were subjected to susceptibility testing and molecular typing by pulsed-field gel electrophoresis. RESULTS: A total of 4507 patients infected or colonized with MRSA were identified between January 1995 and December 1999. The rate of MRSA increased each year from a mean of 0.95 per 100 S. aureus isolates in 1995 to 5.97 per 100 isolates in 1999 (0.46 per 1000 admissions in 1995 to 4.12 per 1000 admissions in 1999) (p < 0.05). Most of the increase in MRSA occurred in Ontario, Quebec and the western provinces. Of the 3009 cases for which the site of MRSA acquisition could be determined, 86% were acquired in a hospital, 8% were acquired in a long-term care facility and 6% were acquired in the community. A total of 1603 patients (36%) were infected with MRSA. The most common sites of infection were skin or soft tissue (25% of MRSA infections), pulmonary tissues (24%) and surgical sites (23%); 13% of the patients were bacteremic. An epidemiologic link with a previously identified MRSA patient was suspected in 53% of the cases. Molecular typing indicated that most (81%) of the isolates could be classified as related to 1 of the 4 Canadian epidemic strains of MRSA. INTERPRETATION: There has been a significant increase in the rate of isolating MRSA in many Canadian hospitals, related to the transmission of a relatively small number of MRSA strains.

Adolescent↗