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PubMed1995

Evolution of rifampin resistance in human immunodeficiency virus-associated tuberculosis.

Acquired rifampin resistance without preexisting isoniazid resistance is highly unusual in patients with tuberculosis. The purpose of this report is to describe and characterize that unusual pattern of acquired drug resistance in three patients with human immunodeficiency virus (HIV) infection. The patients originally had Mycobacterium tuberculosis strains that were susceptible to isoniazid and rifampin. During treatment in two patients and after completion of therapy in the remaining one, each patient developed active, rifampin-resistant, isoniazid-susceptible tuberculosis. One patient subsequently developed isoniazid resistance also. Studies on patients' M. tuberculosis isolates using IS6110 restriction fragment length polymorphism typing and rpoB gene sequencing indicated that rifampin resistance in each patient arose during therapy by an rpoB gene mutation in the original M. tuberculosis isolate. Detection of this unusual drug-resistance phenotype in three patients with HIV infection suggests that acquired rifampin resistance is somehow associated with co-infection due to HIV and tuberculosis.

AIDS-Related Opportunistic Infections↗
PubMed2005

Evolution of cadmium resistance in Daphnia magna.

A diverse laboratory population of Daphnia magna Straus was established by combining individuals from eight sources. Artificial selection for increased resistance to the acute toxic effects of cadmium was performed, and after eight generations, the average median effective concentration increased from 61 to 180 microg/L. No differences in life span, offspring production, time to first brood, number of offspring in the first brood, or intrinsic rate of population increase (r) were observed between the cadmium-adapted population and the controls under ideal conditions or under conditions of temperature or feeding ration stress, but cadmium-adapted daphnids were smaller. Control and cadmium-adapted populations were equally sensitive to copper and malathion, but the cadmium-adapted population was less sensitive to lead and more sensitive to phenol. Analysis of amplified fragment-length polymorphisms indicated a significant decrease in genetic diversity in the cadmium-adapted population. Although the evolved cadmium resistance would allow adapted populations to exist in areas where cadmium concentrations would be toxic to unadapted populations, the decreased genetic diversity, smaller size, and increased sensitivity to at least one other toxicant could reduce the probability of long-term survival even in the absence of future cadmium exposure.

Adaptation, Physiological↗
PubMed1999

Molecular epidemiology of malaria in Yaounde, Cameroon IV. Evolution of pyrimethamine resistance between 1994 and 1998.

Pyrimethamine, in combination with sulfadoxine, is currently one of the major alternative drugs used for the treatment of chloroquine-resistant Plasmodium falciparum malaria infections in Africa. The mechanism of pyrimethamine resistance has been strongly associated with a single, key point mutation in the dihydrofolate reductase-thymidylate synthase gene, resulting in the substitution of the wild-type allele Ser-108 by either Asn-108 or Thr-108. The pyrimethamine-resistant phenotype and/or genotype were determined in 273 Cameroonian clinical isolates obtained in Yaounde by in vitro assays and polymerase chain reaction-restriction fragment length polymorphism over a 5-year period. The in vitro assays showed that 42% (18 of 43) and 63% (69 of 110) of the isolates obtained in 1994-1995 and 1997-1998, respectively, were resistant to pyrimethamine (50% inhibitory concentration [IC50] > 100 nM). The polymerase chain reaction showed that 43% (55 of 127) and 59% (50 of 85) of the isolates in 1994-1995 and 1997-1998, respectively, had the mutant Asn-108 allele. The pyrimethamine-resistant genotype (Asn-108) corresponded with the pyrimethamine-resistant phenotype (IC50 > or = 100 nM) in a large majority (> 95%) of the isolates. The results of our study suggest an increasing prevalence of pyrimethamine resistance in Yaounde. Our study further suggests that pyrimethamine resistance can be monitored by a technique that can be adopted by malaria research centers in Africa.

Adolescent↗
PubMed2000

Evolution of drug resistance and interpretation of drug sensitivity test.

Though with the advent of more and more numbers of antibiotics, infection control has become easier but it has been established more resistant strains of microbes are appearing. These resistant strains are becoming major public health problem. Drug misuse is one of the factors for resistant strains. While discussing mechanisms of drug resistance, gene transfer plays an important part. Drug resistance can be prevented by taking several strategies. There are several methods for performing antibiotic sensitivity test e.g., diffusion methods and dilution methods which are discussed elaborately.

Anti-Bacterial Agents↗
PubMedDate not supplied

Evolution of antibiotic resistance of non-typhoidal salmonellae in Greece during 1990-97.

Susceptibility to 15 antibiotics was determined in 1548 non-typhoidal salmonella strains isolated in Greece from l990 to l997. The overall prevalence of resistance of both Salmonella enterica serotype Enteritidis and Salmonella enterica serotype Typhimurium increased during the first years of the study. A decrease was observed from 1996, especially for S. Enteritidis, which showed the highest overall antibiotic resistance. S. Typhimurium was the serotype with the highest multiresistance to antibiotics. The rest of the serotypes had very low resistance prevalence compared with both S. Enteritidis and Typhimurium serotypes.

Drug Resistance, Bacterial↗
PubMed2001

Evolution of antibiotic resistance of non-typhoidal salmonellae in Greece during 1990-97.

Susceptibility to 15 antibiotics was determined in 1548 non-typhoidal salmonella strains isolated in Greece from l990 to l997. The overall prevalence of resistance of both Salmonella enterica serotype Enteritidis and Salmonella enterica serotype Typhimurium increased during the first years of the study. A decrease was observed from 1996, especially for S. Enteritidis, which showed the highest overall antibiotic resistance. S. Typhimurium was the serotype with the highest multiresistance to antibiotics. The rest of the serotypes had very low resistance prevalence compared with both S. Enteritidis and Typhimurium serotypes.

Animals↗
PubMed1999

Evolution of genotypic resistance to nucleoside analogues in patients receiving protease inhibitor-containing regimens.

The prevalence of genotypic resistance to nucleoside analogues (NA) was examined using a line probe assay (LiPA, Innogenetics, Spain) and a point mutation assay to test for codon 151 polymorphism in plasma from 34 individuals who had been exposed to NA for longer than 1 year. The testing was repeated in the same population after 6 months of being on a new potent protease inhibitor (PI)-containing antiretroviral combination. Only nine (47%) of the 19 patients initially carrying the codon 41 mutation restored zidovudine wild-type (WT) virus population. Similarly, eight (33%) out of 24 carrying the codon 215 mutation restored the wild-type variant. Two subjects carrying codon 74 didanosine mutation reverted to wild-type genotype, as well as two (18%) out of 11 harbouring the codon 184 lamivudine-resistant variant. To conclude, the extent to which drug recycling might be of benefit in subjects showing a restoration of genotypic sensitivity to former drugs needs to be explored.

Acquired Immunodeficiency Syndrome↗
PubMed1991

Mechanisms involved in the evolution of progestin resistance in human breast cancer cells.

The emergence of resistant cells reduces the efficacy of many forms of drug therapy in human breast cancer. In order to understand some of the possible mechanisms by which hormonally dependent human breast cancers develop resistance to progestin therapy we have developed a human breast cancer cell line (5-RP) which is resistant to the growth inhibitory effects of progestins in culture. These cells routinely grow in 10 microM medroxyprogesterone acetate (MPA). The cell line was developed from T-47D-5 human breast cancer cells by stepwise selection in increasing concentrations of MPA. The progestin-resistant phenotype was relatively stable as assessed by the removal of MPA from the medium for varying periods of time. 5-RP cells passaged in the absence of MPA were still essentially insensitive to the growth inhibitory effects of MPA for at least 22 passages. Even at 53 passages out of the drug the 5-RP line was still less sensitive than the original T-47D-5 parent line. Transforming growth factor-alpha (TGF-alpha) and epidermal growth factor (EGF) receptor mRNA were both increased in the 5-RP line compared to the T-47D-5. Consistent with increased TGF-alpha expression, the EGF receptor measured by ligand binding was decreased. When the cells were removed from MPA, TGF-alpha expression declined gradually, but EGF-receptor mRNA levels increased, as did EGF-binding activity. These cells remained estrogen and progesterone receptor positive. Although progestins did not downregulate estrogen receptor expression, they did downregulate progesterone receptor expression in the 5-RP line. The progesterone receptor level of the 5-RP line, in the absence of MPA, was approximately 58% of that found in T-47D-5 cells, even after MPA had been removed for long periods of time. This decrease in receptor level was reflected in decreased ability to respond to progestins as assessed by the decreased ability of MPA to activate expression of both an endogenous gene (EGF receptor) as well as a transiently transfected progestin-responsive gene (MMTV-TK-CAT). Progestin resistance in the 5-RP cell line appears to be multifactorial, involving both increased growth factor expression and decreased receptor levels. It is likely, however, that these two aspects do not account entirely for the progestin-resistant phenotype and as yet other unidentified mechanisms may also be involved.

Antineoplastic Agents↗
PubMed1989

[Appearance and evolution of bacterial resistance to antibiotics].

Concomitant with antibiotic use has been the appearance of resistance bacteria which seem able to emerge as rapidly as new antibiotics are introduced. Although initially encountered in hospitals, resistant bacteria are now being detected as causes of human and animal infections and as colonizers of the gut. Moreover, resistant bacteria are isolated from the environment.

Animals↗
PubMed1986

[Evolution of the resistance of Streptococcus pneumoniae to erythromycin at the Pitié-Salpêtrière Hospital (1980-1984)].

From January 1980 to December 1984, 563 swabs for Streptococcus pneumoniae were isolated at the Pitié-Salpêtrière hospital in Paris, and of these 63 were resistant to erythromycin. The percentage of swabs resistant to erythromycin rose from 2.7% in 1980 to 19.6% in 1984 and was similar for cultures of blood, serous fluid, bronchial secretions, otolaryngological specimens and smears from the conjunction. For swabs resistant to erythromycin these belonged almost exclusively (57 out of 60 or 90%) to the serotypes 6, 14, 19 and 23; one may ask whether the rise in resistance of S. pneumoniae to erythromycin was due to a rise in the frequency of isolation of these serotypes? Between 1980 and 1984 such rise took place since the frequency of isolation of S. pneumoniae belonging to the serotypes 6, 14, 19 or 23 rose from 38% in 1980 to 50% in 1984, but the rise was not significant (p = 0.1). In fact S. pneumoniae serotypes 6, 14, 19 or 23 have become resistant is significant (p less than 0.05). Two factors should be taken into consideration when interpreting these facts. The first is the increased consumption of macrolide antibiotics which doubled overall between 1979 and 1983, both at the Pitié-Salpêtrière hospital and in the Public Assistance hospitals of Paris as well as provincial hospitals throughout France. The second factor is the strictly hospital nature of this study which may have led to an overestimation of the frequency of resistance of S. pneumoniae to erythromycin.

Cross Infection↗
PubMed1985

Evolution of methotrexate resistance of human acute lymphoblastic leukemia cells in vitro.

A human acute lymphoblastic T-cell line, MOLT-3, was fed with Roswell Park Memorial Institute Medium 1640 supplemented with 10% fetal bovine serum and antibiotics which contained increasing concentrations of methotrexate (MTX). The development of drug resistance was associated initially with progressive decrease in MTX transport. When the cells became 200-fold resistant, a rise in the dihydrofolate reductase was noted which was short-lived in the absence of the drug. A 10,000-fold increase in MTX resistance was accompanied, in addition to further decrease in MTX transport, by a 10-fold increase in the dihydrofolate reductase activity. While the purely transport-related resistant cell lines had a collateral sensitivity to lipid-soluble antifols, the sublines which had both transport- and enzyme-related MTX resistance contained a subpopulation highly resistant to these antifols. Chromosome analysis of the subline with increased dihydrofolate reductase activity showed an expanded abnormally banded region in chromosome 5.

Cell Line↗
PubMed1985

Serial studies on the evolution of chloroquine resistance in an area of East Africa receiving intermittent malaria chemosuppression.

Serial in vitro and in vivo tests for chloroquine sensitivity of Plasmodium falciparum were carried out from 1979 to 1982 in an area of E. Africa where chemosuppression with chloroquine had been attempted since 1977. Within 1(1/2) years there were signs of a decreasing drug response. Chloroquine resistance was first detected in 1981 and this increased markedly in 1982. Other contributory causes for the rise of parasite rates in children were possibly a decline in the efficiency of the drug distribution system and also immunological factors. Evidence of resistance to pyrimethamine was also found. Observations were made of the heterogeneity of the parasites' responses with emerging resistance. Implications for the future are discussed.

Child↗