Resistance biochemical mechanisms

The basic biochemical mechanisms leading to bacterial resistance can be classified into three different categories. 

Biochemical mechanism of resistance to aminoglycosidic antibiotics, H. Umezawa, Adv. Carbohydr. Chem. Biochem., 30 (1974) 183-225. 

Biochemical mechanisms of resistance 3.5 Multidrug resistance pumps... 

The following sections describe the biochemical mechanisms of resistance to different classes of antibiotics, with the antibiotics grouped according to their mechanism of action. 

An antibiotic inhibits bacterial growth if it is able to reach the site of its action, interacts, and substantially inhibits the function of an essential component necessary for its growth. A given bacterial cell becomes resistant to an antibiotic if at least one of these steps is no longer operative. This can result from one of the following four biochemical mechanisms. 

The biochemical mechanisms of internal and acquired resistances are identical and can be explained as the result of one of the following four reasons ... 

Eastman A, Richon VM. Mechanisms of cellular resistance to platinum coordination complexes. In (McBrien DCH, Slater TF, eds) Biochemical Mechanisms of Platinum Anticancer Drugs 1986 IRL Oxford, UK pp. 91-119. 

Possible biochemical mechanisms of resistance to alkylating agents include changes in ceU DNA repair capability, increases in cell thiol content (which in turn can serve as alternative and benign targets of alkylation), decreases in ceU permeability, and increased activity of glutathione transferases. Increased metaUothionein content has been associated with tumor cell resistance to cisplatin. 

Mechanisms of Resistance. Three distinct biochemical mechanisms of resistance to tetracyclines have been identified. The energy-dependent efflux of antibiotic mediated by resistance proteins located in the bacterial... 

Pharmacologists have been attempting to define what it is about clozapine s biochemical mechanism of action that accounts for its special efficacy as well as its side effects. As discussed extensively in this chapter, SDA properties may account in part for reducing EPS, for reducing tardive dyskinesia, and perhaps even for lack of prolactin elevation SDA properties may even help explain improvement in negative symptoms of schizophrenia. However, the concept of SDA does not appear to explain the therapeutic actions of clozapine in treatment-resistant cases because clozapine is superior to other agents that share this property. 

Preston, C. and C.A. Mallory-Smith (2001). Biochemical mechanisms, inheritance, and molecular genetics of herbicide resistance in weeds. In Powles, S.B. and Shaner, D.L., eds., Herbicide Resistance and World Grains. Boca Raton, FL CRC Press, pp. 23-60. 

In a recent book devoted to biochemical mechanism of pesti-cidal action, the author states (quoting primary sources) that resistance to systemics is caused by "the high selection pressure exerted by these fungicides on the fungal population with the result that,in some circumstances only, resistant strains survive. Older fungicides seem to have been less effective as fungicides than the new compounds"(27)This means that most of the chemical protectants such as the sulfenimides left both resistant and sensitive strains and presumably, and as is usual, the sensitive population adapts better to the total environment. 

Figure 4.3. Biochemical mechanisms of resistance to (a) inorganic mercury compounds, (b) some...

Within these two broad types of resistance, several biochemical mechanisms are known, including reduced uptake, enzymatic inactivation, target site modification and enhanced efflux. The last mentioned is assuming greater importance as additional studies are undertaken. A direct link between antibiotic and biocide resistance remains to be established. 

Among the biochemical mechanisms of fungicide resistance are reduced permeability, metabolism (increased detoxification or decreased conversion to the toxic material), and reduced affinity of the target site for the toxin. 

Regardless of the nature of the original sensitizing stimulus, however, induced resistance is mediated and expressed through the endogenous genetically encoded biochemical mechanisms of the plant. 

Other mechanisms. Many other biochemical mechanisms are known or postulated to function in disease resistance in plants, e.g., silicization of cell walls, "b" or PR ("pathogenesis-related") proteins, AVF (anti-viral factors) and "phytointerferon", or superoxide anions. These mechanisms have not been investigated as extensively as the above described mechanisms, especially in cases of "induced resistance". Space does not permit their consideration in this article. 

Plants, like animals, are hosts for a substantial number of viruses, which are often transmitted by sucking insects such as aphids and bugs (Heteroptera). Resistance to viral infection can be achieved either by biochemical mechanisms that inhibit viral development and multiplication or by warding off vectors such as aphids in the first place. 

The increase in vascular resistance is the decisive factor and, in the majority of cases, is even the sole cause. It can be functional and reversible as well as structural and irreversible. Blood flow correlates directly with vessel diameter to the 4 power, i.e. small radial changes cause large changes to vessel resistance. An increase in the blood supply may favour the occurrence of portal hypertension or enhance its clinical development. The persistent interference with biochemical mechanisms which regulate the blood circulation in the liver and the impact of pathological substances may have further pathogenic effects. (23, 62, 72, 81,118, 128) (s. fig. 14.1)... 

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