Resistance mechanisms isolated

The presence of a specific resistance mechanism in a bacterial isolate does not necessarily implicate that this isolate is resistant in clinical terms. However, an isolate expressing a resistance mechanism possibly will be eliminated less easily as compared to a susceptible one. In clinical practice, resistance mechanisms will be rarely identified. Usually the sensitivity of isolates will be determined and reported to the clinician by using the interpretive criteria which is sensitive, intermediate or resistant. Some bacteria harbouring resistance... 

Extracts of plants have been used as insecticides by humans since before the time of the Romans. Some of these extracts have yielded compounds useful as sources (e.g., pyrethrins, rotenoids, alkaloids), others as models (e.g., pyrethrins, physostigmine) of commercial insecticides. Recent technological advances which facilitate the isolation and identification of the bioactive constituents of plants should ensure the continued usefulness of plant compounds in commercial insect control, both as sources and models of new insect control agents and also as components in host plant resistance mechanisms. The focus in this paper will be on several classes of compounds, including limonoids, chromenes, ellagitannins, and methyl ketones, which were found to be components of the natural defenses of both wild and cultivated plants and which may be useful in commercial insect control. 

Influenza virus resistant to oseltamivir has not been found in naturally acquired isolates but has been isolated from influenza patients who have undergone treatment with this drug. These resistant strains contain mutations in the active site of neuraminidase and are generally less virulent and infective than nonresistant virus. In vitro passage of influenza virus in the presence of oseltamivir carboxylate can produce mutations in hemagglutinin that decrease the overall dependence of viral replication on neuraminidase however, the clinical relevance of this resistance mechanism is unknown. 

In conclusion, the activity of FQ is due to more than one route (Fig. 31). Due to its physicochemical properties, FQ could specifically target the lipid site of hemozoin formation. Its mechanism of action should be in part similar to that of CQ, based on the inhibition of hemozoin formation. Upon the specific (acidic and oxidizing) DV conditions, production of radical oxygen species (ROS) by FQ should be sufficient to promote significant damage on membranes of the parasite DV. The strong activity of FQ on CQ-resistant clones and isolates of P. falciparum suggests a fundamental difference in interaction with resistance mechanisms of the parasite. 

Cositecan (Karenitecin , BNP 1350) 54 (BioNumerik and ASKA Pharmaceutical) is currently being evaluated in a Phase III trial for the treatment of patients with advanced ovarian cancer who have become resistant to platinum and taxane drugs.110 Cositecan 54,111 114 which is also being evaluated against solid tumours in a Phase I trial, is an orally bioavailable, lipophilic 7-[2-(tri-methylsilyl)ethyl] derivative of camptothecin 55 which is less sensitive to both common and camptothecin-specific resistance mechanisms. Camptothecin 55 was first isolated in 1958 from Camptotheca acuminata (Nyssaceae) and its structure was reported in 1966.115 117 Camptothecin 55 was later shown to be a topoisomerase I inhibitor two camptothecin derivatives, topotecan and iri-notecan, are approved for chemotherapy use. 

DMI resistance may be governed by different resistance mechanisms co-existing in the same isolate. Molecular detection tools can help to find low frequencies of mutated individuals in populations. However, since resistance to DMIs may be a combined effect of several mechanisms, the molecular results have to be treated with care and bioassays may be always needed for verification. 

In the last case the strain was identical to eight MRSA isolates obtained from hospitals in the New York City metropolitan area, and all eight isolates, but not control isolates, could be transformed in vitro to develop intermediate resistance to vancomycin. Both the presence of glyco-peptides and environmental factors, as demonstrated by increased resistance of S. aureus to antibiotics in the presence of prosthetic material in animals, can exert selective pressure to develop new resistance mechanisms (93-95). 

Mirels, L.F., and Stevens, D.A. (2002) Resistance mechanisms in dinical isolates of Candida albicans. Antimicrobial Agents and Chemotherapy, 46, 1704-1713. 

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