Modes of Resistance

3 Structure-Activity Reiationship (SAR) and Structure-Toxicity Reiationship (STR) (Domaiaga, 1994 Domaiaga and Hagen, 2003  

1 Controls potency Gene toxicity and theophyline interactions 

2 No sidechain or small group, because of proximity to gyrase binding No side effects 

3-4 Germane for gyrase binding Metal chelation site 

5 Controls potency for gram (-f) Influences gene toxicity and 

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Kelly, S.T. and G.E. Coats (1999). Mode of resistance of triazine-resistant annual bluegrass (Poa annua). Weed Technol., 13 747-752. 

A further mode of /S-lactam resistance is due to an alteration in the PBP s structure, resulting in ineffective binding of the antibiotic. Notable examples of this mode of resistance include methicillin-resistant Staphylococcus aureus (MRSA) and penicillin-resistant Streptococcus pneumoniae. 

The elucidation of the primary site and biochemical mode of action of inhibitors is often difficult and not necessarily associated with the mechanism of resistance in field isolates. Nevertheless, information on the mechanism of resistance can provide evidence to determine the site of action. Therefore, the classification of fungicides is based on crossresistance reactions rather than chemical similarities of structures or proposed modes of action (Table 1). Based on available information in the literature, three categories of inhibitor classes can be made Classes with known mode of action and known mechanism of resistance, classes with proposed mode of action and unknown mode of resistance but wide-spread field resistance, and classes in which resistance is claimed to occur in the field but both mode of action and resistance are not known. 

Microbial resistance can occur by the gradual selection of resistant mutants or more usually by R-factor j transmission between bacteria, Table V-l-2 summarizes the common modes of resistance exhibited by microorganisms against the various classes of antimicrobial agents. 

The mechanisms of action of penicillins, the bacterial modes of resistance to penicillins, the penicillin subgroups, their biodisposition, and adverse affects are provided. The subgroups discussed are the penicillins that are p-lactamase susceptible with a narrow spectrum of activity, p-lactamase-resistant penicillins having a very narrow spectrum of activity, and J3-lactamase—susceptible penicillins with a i wider spectrum of activity. The common penicillins and their susceptible organisms are listed for each I subgroup. 

Table VIII-1-3. Modes of Resistance to Anticancer Drugs...

Table VIII-1-3 summarizes the modes of resistance developed by cancers toward specific anticancer j drugs. j...

We are blessed, in the past number of years, with a better and better understanding of the modes of action and the modes of resistance to herbicides. This is especially true of the photosystem II inhibiting herbicides (1 but also of the dinitroanilines such as trifluralin (2) and particularly with the herbicides affecting amino acid... 

Identify the genetic control and biochemical mode of resistance. 

Vial, H. J., and Calas, M. (2001). Inhibitors of phospholipid metabolism. In "Antimalarial Chemotherapy, Mechanisms of Action, Modes of Resistance and New Directions in Drug Development" (Rosenthal, ed.), pp. 347-365. Humana, Totowa, NJ. 

Endou, K., Matsuoka, M., and Nakajima, Y. (1987). A mode of resistance to macrolide antibiotics Regarding Staphylococcus aureus that does not show MLS-coresistance. J. Pharmacobio. 

Bergers G, Hanahan D. Modes of resistance to anti-angiogenic therapy. Nature Reviews Cancer 2008 8 592-603. 

Controlled larval feeding and oviposition tests (Table I) showed that a major mode of resistance to tobacco budworms in TI 1112,1-35, TI 1024, and NFT is ovipositional non-preference (antixenosis). The budworm resistance observed with TI 165 and TI 1396 appears to result from larval antibiosis (5,6,9). 

Because of their high activity, only small amounts would be needed to block the advance of the fungus through the root. Further research is needed to determine if this is a viable mode of resistance and to search for other chemicals that may be responsible for the observed black shank resistance of certain tobacco varieties. 

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