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PubMedDate not supplied

[Cross resistance to pyrethroids in Aedes aegypti from Cuba induced by the selection with organophosphate malathion].

A strain from Aedes aegypti (L) collected in the municipality of Santiago de Cuba with low levels of resistance to malathion (1.79x) was subjected to selection pressure aimed at evaluating the evolution of the resistance to this organophosphate and its usefulness for control. After 5 generations of selection (SAN-F5) with malathion, it was not possible to increase the resistance and it was obtained a value of resistance factor (FR50) of 2.22x. None or little cross resistance to the following organophosphate insecticides was observed: fenthion, temephos and fenitrotion; however, it was found an elevated cross resistance to deltamethrin pyrethroid, with a value of 287.5x in the third generation of selection. It was also observed cross resistance to other pyrethroids (lambda-cyhalothrin, cypermethrin and ciflutrine). The mechansim of elevated esterases did not generate resistance to pyrethroids, which was corroborated through inhibition gel studies and through the calculation of the frequency in microtitering plaques. Nevertheless, there was an increase in the frequency of the glutathione-s-transferase mechanism from 0.049 in Santiago de Cuba to 0.42 in SAN-F5, which may be associated with the resistance to pyrethroids. The cross resistance to pyrethroids, mainly to deltamethrin, resulting from the selection with malathion may limit the use of these insecticides in the control unless a good strategy for their use is laid down.

Aedes↗
PubMed1988

[Course of the resistance of Staphylococcus aureus to pefloxacin. A study based on 782 strains isolated in 1985 and 1986].

We studied the evolution of the resistance of Staphylococcus aureus to pefloxacin during 1985 and 1986 in eight hospital units. The pefloxacin resistant Staphylococcus aureus, which amounted to 8.9% in 1985 reached 27% in 1986. They are found mainly among the methicillin-resistant Staphylococcus. There is no obvious relationship between this resistance and the consumption of pefloxacin in each of the units.

Drug Resistance, Microbial↗
PubMedDate not supplied

Herbicide selection of Italian ryegrass under different levels of UVB radiation.

Ultraviolet-B radiation is an environmental stress for plants and this situation could become aggravated in the next decades. In this study we used Italian ryegrass (Lolium multiflorum Lam.) as a model system to test whether an environmental stress derived from global change, such as UVB, can influence the efficacy of control procedures and evolution toward herbicide resistance. We grew three generations of Italian ryegrass plants with and without UVB light and subjected them to a series of diclofop-methyl [(+/-)-2-[4-(2,4-dichlorophenoxy) phenoxy] propanoic acid, methyl ester] doses. The effect of selection history was tested with herbicide dose response. The effect of herbicide application on plant survival and biomass varied significantly among herbicide doses and with absence or presence of UVB light. In the absence of herbicide, the decrease in individual fecundity with increasing plant density was similar under both no-UVB and UVB light treatments. Only plants growing without UVB light increased production of reproductive structures in response to the decrease in density caused by herbicide application. Our study shows that UVB light was a weak stress factor for the ryegrass plants. However, when herbicide selection pressure was high, UVB light reduced the evolution toward herbicide tolerance. When selection pressure on the parental plants was lower, the two stress factors had a synergistic effect, causing changes in herbicide efficacy that in turn had demographic and evolutionary consequences. In the field, these interactions between stress factors might be of significance for annual weeds in which seed output is a major determinant in fitness.

Biological Evolution↗
PubMed2006

Effect of a mixture of iprobenfos and malathion on the development of malathion resistance in the mosquito Culex pipiens pallens Coq.

A malathion-resistant (RM) strain of Culex pipiens pallens Coq was obtained by successively selecting a field population with malathion in the laboratory. The synergistic effect of iprobenfos on malathion toxicity and alpha-naphthyl acetate (alpha-NA) esterase assay revealed that malathion resistance in the RM strain was associated with increased alpha-NA esterase activity and the synergism was mainly due to the inhibition by iprobenfos of this activity. There was no difference in alpha-NA esterase activity between the larvae and female adults in the susceptible (S) strain, but the activity in the adults was 13-fold higher than in the larvae of the RM strain. To understand the effect of the application of a mixture of iprobenfos and malathion on the evolution of malathion resistance, an artificial strain (Syn) was generated by mixing the RM and S strains with 0.1 frequency of the malathion-resistant individuals. The offspring of the Syn strain were divided into two sub-strains, Rm and Rm+ibp, which were successively treated with, respectively, malathion alone and malathion + iprobenfos (1:2) at LC70. In the mixture, the fungicide iprobenfos acted as a synergist of malathion. After treatment for 10 generations, the resistance level to malathion was 317.4-fold for the Rm sub-strain, whereas for the Rm+ibp sub-strain it was only 38.9-fold, compared with the Syn strain. Similar results were obtained by measurement of alpha-NA esterase activity from both larvae and female adults. The alpha-NA esterase activities in larvae and female adults at F10 generation were 2.6- and 10.9-fold from the Rm+ibp sub-strain and 5.7- and 98.5-fold from the Rm sub-strain, respectively, compared with the Syn strain. The above results suggested that iprobenfos, although it cannot completely stop or prevent the onset of malathion resistance, could dramatically delay its evolution.

Animals↗
PubMed1996

Dissemination of the strA-strB streptomycin-resistance genes among commensal and pathogenic bacteria from humans, animals, and plants.

Gene transfer within bacterial communities has been recognized as a major contributor in the recent evolution of antibiotic resistance on a global scale. The linked strA-strB genes, which encode streptomycin-inactivating enzymes, are distributed worldwide and confer streptomycin resistance in at least 17 genera of gram-negative bacteria. Nucleotide sequence analyses suggest that strA-strB have been recently disseminated. In bacterial isolates from humans and animals, strA-strB are often linked with the suIII sulfonamide-resistance gene and are encoded on broad-host-range nonconjugative plasmids. In bacterial isolates from plants, strA-strB are encoded on the Tn3-type transposon Tn5393 which is generally borne on conjugative plasmids. The wide distribution of the strA-strB genes in the environment suggests that gene transfer events between human, animal, and plant-associated bacteria have occurred. Although the usage of streptomycin in clinical medicine and animal husbandry has diminished, the persistence of strA-strB in bacterial populations implies that factors other than direct antibiotic selection are involved in maintenance of these genes.

Animals↗
PubMed2001

Rapid loss of stress resistance in Drosophila melanogaster under adaptation to laboratory culture.

We investigate changes in resistance to desiccation and starvation during adaptation of Drosophila melanogaster to laboratory culture. We test the hypothesis that resistance to environmental stresses is lost under laboratory adaptation. For both traits, there was a rapid loss of resistance over a three-year period. The rapidity of the response suggested that mutation accumulation could not account for it. Rather, resistance to environmental stresses appeared to be lost as a correlated response to selection on another trait, such as early fertility, with which stress resistance is negatively genetically correlated. These results suggest that caution is needed when extrapolating from evolution of stress resistance in long-established laboratory stocks to patterns of responses and correlated responses in natural populations.

Adaptation, Physiological↗
PubMed2004

Seasonal changes of methamidophos susceptibility and biochemical properties in Plutella xylostella (Lepidoptera: Yponomeutidae) and its parasitoid Cotesia plutellae (Hymenoptera: Braconidae).

Methamidophos resistance and acetylcholinesterase (AChE) insensitivity to methamidophos, dichlorvos, and carbofuran were determined in the field populations of Plutella xylostella (L.) (Lepidoptera: Yponomeutidae) and its parasitoid Cotesia plutellae Kurdjumov (Hymenoptera: Braconidae) collected from the corresponding hosts between October 1998 and December 2003 in Fuzhou and Minhou, Fijian, China. Resistance levels to methamidophos and AChE insensitivity to the three insecticides in the two species of insects were high during autumn and spring and low during summer. Resistance to methamidophos was 15.3- and 12.6-fold higher in resistant F0 parents of P. xylostella and C. plutellae than in their susceptible F11 progeny, respectively. The bimolecular rate constant (k(i)) values of AChE to methamidophos, dichlorvos, and carbofuran were 4.6-, 6.3-, and 7.7-fold higher in F11 progeny of P. xylostella, and 3.7-, 4.5-, and 3.7-fold higher in F11 progeny of C. plutellae than those in their F0 parents, respectively. Compared with susceptible F11 progeny, the resistance ratios for methamidophos were 4.2-29.8 and 3.8-13.1 in 21 field populations of P. xylostella and C. plutellae, respectively. The k(i) values of AChE to methamidophos, dichlorvos, and carbofuran were 2.0-21.6-, 3.6-9.5-, and 2.6-9.2-fold higher in F11 progeny of P. xylostella, and 1.8-7.6-, 1.9-4.6-, and 2.2-7.6-fold higher in F11 progeny of C. plutellae than those in 21 field populations, respectively. Significant correlative variations of methamidophos resistance as well as significant correlative variations of k(i) values of AChE to insecticides between the two species of insects also were found in space and time. The k(i) values of AChE to insecticides in C. plutellae were far higher than those in P. xylostella. There were no obvious differences in the Km and Vmax of AChE between F0 parents and F11 progeny of P. xylostella and C. plutellae, respectively. But carboxylesterase activity was 1.6-fold higher in F0 parents of C. plutellae than in F11 progeny, and glutathione S-transferase activity was 1.5-fold higher in F0 parents of P. xylostella than in F11 progeny. The results suggested that the AChE insensitivity to insecticides might play the most important role in methamidophos resistance in the two species of insects. From these results, a spatial and temporal correlative evolution of methamidophos resistance and insensitive AChE was found to exist between P. xylostella and C. plutellae.

Acetylcholinesterase↗
PubMedDate not supplied

[Genetic control of tetracycline resistance in bacteria].

Modern data on prevalence, structural and functional organization of the tetracycline resistance determinants in bacteria are reviewed. The three mechanisms of the antibiotic resistance are the tetracycline efflux, the ribosomal protection and the antibiotic modification. The problems of evolution of tetracycline resistance genes are discussed.

Bacteria↗
PubMedDate not supplied

[Microbial resistance: what is to be done? Information from the panel of experts].

This document represents the recommendations of a panel of Spanish experts on antibiotic use and resistance. In a Task Force, under the auspices of the Spanish Ministry of Health and Consumer Affairs that took place in 1994 in Madrid, the members were gravely concerned about the national increase in antibiotic resistance. They analysed the development, evolution and spread of antibiotic resistance among community-acquired human bacterial pathogens in Spain, its relation with antibiotic consumption, and they proposed future surveillance strategies for monitoring the patterns of antibiotic use and consumption. Success will require a collective action among the producers (pharmaceutical industry), prescribers (doctors, veterinarians), dispensers (pharmacists), and consumers (patients). Two similar documents have been recently published by the American Society of Microbiology and the World Health Organization showing the global concern about this topic.

Anti-Bacterial Agents↗
PubMed1999

Pharmacoclinical strategy in neuroleptic resistant schizophrenic patients treated by clozapine: clinical evolution, concentration of plasma and red blood cell clozapine and desmethylclozapine, whole blood serotonin and tryptophan.

1. The aim of the study was to determine if a more rational therapeutic approach could be devised for neuroleptic resistant psychotic patients treated for months and years with clozapine. Clozapine is an atypical antipsychotic medication, but its therapeutic benefit has been limited by a high incidence of agranulocytosis and seizures. 2. The study has been performed in an open setting and included 12 patients. Some of them developed a secondary depression and were treated with fluoxetine. 3. Pharmacokinetic analysis were conducted at the same time as clinical evaluations, grading using the BPRS, the PDS, and QLS, and determinations of plasma and red blood cell clozapine and desmethylclozapine, plasma and RBC fluoxetine and norfluoxetine, whole blood serotonin and tryptophan. 4. A positive linear correlation was found only between RBC concentration and the evolution of the QLS. 5. Clozapine is efficacious both on positive and negative symptoms but its mechanism of action remains unclear. Positive symptoms disappear more quickly, sometimes followed by a post psychotic depression. Negative symptoms improve more slowly but regularly. They seem to be correlated with serotoninergic mechanisms. For whole blood 5HT, an important increase was seen about 4 weeks after Cloza administration, and then a decrease. 6. Therapeutic drug monitoring (on the same sample drawn for haematological monitoring providing) could play a useful role in the management of patients treated by clozapine: compliance, lowest dose, possible toxicity, drug interaction, lack of efficacy, relapse predictivity.

Adult↗
PubMed2006

Trends in antimicrobial resistance phenotypes in non-typhoid Salmonellae from human and poultry origins in France.

A total of 1873 strains from human origin and 4283 strains from non-human origin of Salmonella enterica serotypes Typhimurium, Enteritidis, Heidelberg, Hadar and Virchow, collected over three years 1993, 1997 and 2000, were examined in order to determine the rate of antimicrobial resistance to 12 antimicrobial drugs. The objective of the study was to describe and to compare the evolution of the main resistance types in human and non-human isolates, focusing on the poultry sector. The evolution and the rates of antimicrobial resistances for the five serotypes, with the exception of Virchow, were almost comparable in strains isolated from human and non-human sources over the period studied. The most striking result concerning single resistance was the spectacular increase of the resistance frequency to nalidixic acid for the strains belonging to serotypes Hadar and Virchow, especially in the poultry food sector (14% in 1993 vs. 72% in 2000 for Salmonella Virchow, 4% in 1993 vs. 70% in 2000 for Salmonella Hadar) and also in human isolates (24% in 1997 vs. 48% in 2000 for S. Virchow, 31% in 1997 vs. 78% in 2000 for S. Hadar). In addition to the classical resistance to ampicillin, streptomycin, sulphonamide, chloramphenicol and tetracycline (ASSuCT resistance type), which stabilized between 1997 and 2000, the emergence of a new resistance type was observed.

Animals↗
PubMed2005

Evaluation of a chemically inducible promoter for developing a within-plant refuge for resistance management.

Chemically inducible production of Bacillus thuringiensis (Bt) toxins in transgenic plants may provide considerable benefits in preventing or delaying the evolution of insect resistance to Bt crops by creating within-plant temporal refuges. We examined the effect of inducible cry1Ab expression on survival of different genotypes (RR, RS, and SS) of diamondback moth, Plutella xylostella (L.), in transgenic broccoli, Brassica oleracea L., plants transformed with a PR-1a/cry1Ab expression cassette. Spraying leaves of these plants with the inducer acibenzolar-s-methyl [= benzo (1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester] (ASM) resulted in high levels of Bt toxin, and detached leaves from fully induced plants caused 100% mortality to all instars of P. xylostella SS and RS genotypes. When plants infested with larvae were treated with ASM, only a few larvae that were nearing completion of their development were able to survive the induction process. Signal transduction from ASM-treated leaves to new plant tissue also was evaluated using a larval assay. New foliage that emerged after plants were induced remained toxic to > or = 80% of RS larvae up to the fourth new leaf. In whole plant tests, however, induced plants remained protected from larval damage for > or = 3 wk. Uninduced PR-1a/cry1Ab plants seemed to produce low levels of Bt that were undetected by an enzyme-linked immunosorbent assay but that resulted in significant fitness costs for susceptible insects. The suitability of PR-1a/cry1Ab broccoli plants for insect resistance management and the requirements of an appropriate inducible promoter are discussed.

Animals↗
PubMed2002

The 'carnivore connection'--evolutionary aspects of insulin resistance.

Insulin resistance is common and is determined by physiological (aging, physical fitness), pathological (obesity) and genetic factors. The metabolic compensatory response to insulin resistance is hyperinsulinaemia, the primary purpose of which is to maintain normal glucose tolerance. The 'carnivore connection' postulates a critical role for the quantity of dietary protein and carbohydrate and the change in the glycaemic index of dietary carbohydrate in the evolution of insulin resistance and hyperinsulinaemia. Insulin resistance offered survival and reproductive advantages during the Ice Ages which dominated human evolution, during which a high-protein low-carbohydrate diet was consumed. Following the end of the last Ice Age and the advent of agriculture, dietary carbohydrate increased. Although this resulted in a sharp increase in the quantity of carbohydrate consumed, these traditional carbohydrate foods had a low glycaemic index and produced only modest increases in plasma insulin. The industrial revolution changed the quality of dietary carbohydrate. The milling of cereals made starch more digestible and postprandial glycaemic and insulin responses increased 2-3 fold compared with coarsely ground flour or whole grains. This combination of insulin resistance and hyperinsulinaemia is a common feature of many modern day diseases. Over the last 50 y the explosion of convenience and takeaway 'fast foods' has exposed most populations to caloric intakes far in excess of daily energy requirements and the resulting obesity has been a major factor in increasing the prevalence of insulin resistance.

Biological Evolution↗
PubMed2001

In vitro evolution of the human immunodeficiency virus type 1 gag-protease region and maintenance of reverse transcriptase resistance following prolonged drug exposure.

We studied the human immunodeficiency virus type 1 phenotypic and genotypic profiles of a dual drug-resistant isolate (isolate 14aPost-DR) selected for zidovudine (ZDV) and lamivudine (3TC) resistance and then cultured in the presence of 3TC and a protease inhibitor: indinavir (IDV), ritonavir, or KNI-272. The IDV-treated virus was highly resistant to 3TC, ZDV, and IDV and accumulated protease mutations at positions M46I and V82F. A change from alanine to valine was observed in 4 of 10 clones in the P2 position of the p7-p1 Gag-protease cleavage site, linked to position M46I in the dominant viral quasispecies. Previous 3TC resistance did not impair the development of additional mutations in the protease and Gag-protease cleavage regions.

Drug Resistance, Microbial↗
PubMed2001

A recombinant virus assay using full-length envelope sequences to detect changes in HIV-1 co-receptor usage.

The clinical management of HIV-1 infection has benefited enormously from molecular characterization of drug resistance as well as determination of the viral phenotype in vitro. HIV-1 infected individuals on HAART are currently monitored for the development of drug resistance variants allowing clinicians to redesign drug regimens. An understanding of the molecular basis of the evolution of drug resistance in vivo allows the improvement of the drugs as well as in vitro evaluation of new antiviral compounds alone or in combination with those currently approved. New findings suggest that viral envelopes could be a target to inhibit infection and replication. Therefore the generation of a recombinant virus assay (RVA) to allow the phenotypic determination of drug resistance against entry inhibitors (EI) is anticipated. We constructed an env-deleted clone of HIV-1 using the molecular clone NL-4.3. PCR amplified complete envelope genes (NL-4.3, BaL, primary envelope-genes) were ligated in vitro with a deletion clone (pNL-deltaK) and PM1-cells, supporting the replication of R5- and X4-tropic viruses, were transfected. Determination of co-receptor usage of the harvested recombinant virus-swarm revealed no difference compared to the molecular clones derived individually from three different patients. These results clearly show that an envelope-based RVA is practicable to monitor HIV-co-receptor usage at a given time point. Furthermore, this assay will allow to monitor resistance development against existing and future entry inhibitors and will aid to improve the management of HIV-therapy.

Antiretroviral Therapy, Highly Active↗
PubMed2002

[Mechanisms of antibiotic resistance].

Antibiotics interfere with structural and regulatory elements of bacterial cells leading to growth arrest or cell death. Bacteria have evolved a variety of strategies to overcome the effects of antibiotics. Examples are enzymatic destruction, alteration of the target, efflux and permeability changes. Resistance towards the same substance can be mediated by several mechanisms. Efflux pumps can probably act as mediators of higher resistance development. Alteration of common targets can lead to cross-resistance against several classes of antibiotics. Genetic events, such as point mutations, transfer of plasmids and gen regulation, can mediate a rapid emergence of resistance. Therefore, substances like rifampicin should be only used in combination with other drugs. Accumulation of resistance genes under common regulatory control in integrons induces co-resistance against substances of different specificity. Detailed knowledge of resistance mechanisms, their evolution and dynamics is important for a rational use of antibiotics and other strategies against antibiotic resistance.

Anti-Bacterial Agents↗