Bacteria selective inhibition

For example, Escherichia coli have six PBP. PBP-la and -lb, which are transpepfidases, are involved in the synthesis of peptidoglycan. PBP-2 is necessary for supporting the rodshaped form of bacteria. Selective inhibition of this enzyme causes production of other non-rod-shaped forms of bacteria, which eventually undergo lysis. PBP-3 is necessary to form the partition during division. Selective inhibition of this enzyme leads to the formation of a fibrous form of bacteria containing many units of rod-shaped bacteria unable to separate one from another, which results in their death. Various beta-lactam antibiotics have a selective affinity to one or a few PBP. Inactivation of certain PBP (PBP-la, -lb, -2, or -3) causes cell death. Unlike these, inactivaition of low-molecular PBP (PBP-4, -5, and -6) is not lethal to bacteria. 

Antibiotics are toxic water-solubie compounds produced by molds or bacteria which inhibit the growth of other microorganisms. For an antibiotic to be useful in medicine it should have a high order of selective toxicity to microorganisms which are pathogenic to man. Al-... 

II cleaves the two complementary strands of DNA four base pairs apart and the resulting 5 -phosphoryl groups become covalently linked to a pair of tyrosine groups, one in each half of the dimeric topoisomerase II enzyme. Several groups of drugs are known that selectively inhibit topoisomerases in bacteria (quino-lones) or mammalian cells (etoposide, tenoposide). Quinolones are used to treat bacterial infections inhibitors of mammalian topoisomerases are cytostatic drugs used for the treatment of cancer. 

MANY ANTIBIOTICS WORK BECAUSE THEY SELECTIVELY INHIBIT PROTEIN SYNTHESIS IN BACTERIA... 

Enyzme catalysis is thus essential for all life. Hence the selective inhibition of critical enzymes of infectious organisms (e.g., viruses, bacteria, and multicellular parasites) is an attractive means of chemotherapeutic intervention for infectious diseases. This strategy is well represented in modem medicine, with a significant portion of antiviral, antibiotic, and antiparasitic drugs in clinical use today deriving their therapeutic efficacy through selective enzyme inhibition (see Table 1.1 for some examples). 

Disinfectants do not afford selective inhibition of bacteria O viruses, or fungi O O... 

Both sulfonamides and trimethoprim (not a sulfonamide) sequentially interfere with folic acid synthesis by bacteria. Folic acid functions as a coenzyme in the transfer of one-carbon units required for the synthesis of thymidine, purines, and some amino acids and consists of three components a pteridine moiety, PABA, and glutamate (Fig. 44.1). The sulfonamides, as structural analogues, competitively block PABA incorporation sulfonamides inhibit the enzyme dihydropteroate synthase, which is necessary for PABA to be incorporated into dihydropteroic acid, an intermediate compound in the formation of folinic acid. Since the sulfonamides reversibly block the synthesis of folic acid, they are bacteriostatic drugs. Humans cannot synthesize folic acid and must acquire it in the diet thus, the sulfonamides selectively inhibit microbial growth. 

Trimethoprim is a pyrimidine derivative (diaminopyrimidine) related to antimalarial drug pyrimethamine, which selectively inhibits bacterial dihydrofolate reductase, necessary for the conversion of dihydrofolate to tetrahydrofolic acid. Sulfonamides act by inhibiting the incorporation of PABA into dihydrofolate by bacteria. A combination of... 

Antiseptics and disinfectants are non-antibiotic biocides used to kill microorganisms or inhibit their growth. Structures are given in Figure 16.8 and biodegradation data are summarized in Table 16.4 for selected substances. Since these substances are intended to kill bacteria or inhibit their growth, published biodegradation data must... 

The results pointed out that these alkaloids possessed the highest antibacterial activity against K. pneumoniae and A. baumannii at 8 ig/mf concentration (Table 2), whereas they were moderately active to the rest of the bacteria. However, all the alkaloids tested were highly effective against C. albicans in a comparable manner to KET in the antifungal screening. Conversely, a selective inhibition was observed towards PI-3 virus by these alkaloids, while they were entirely unsuccessful on inhibition of HSV (Table 3). 

One classical and early example of selective inhibition of DNA biosynthesis is shown in Fig. 3 for the anitbiotic, mitomycin C29 A concentration of 0.1 pg/ml (3 x 10 7 M) completely inhibited DNA synthesis in E. coli B, while RNA synthesis, protein synthesis and growth meaning turbidity, i.e. cell mass increase, continued. However, after the experimental period of only 90 min, the number of viable bacteria had decreased by 85 per cent. By that time, bacterial filaments were visible under the microscope. 

Enzymes in the aaRS family are a promising target for the development of novel antibiotics (17). Selective inhibition of just one essential aaRS would be lethal to the pathogen. The best example is mupirocin, a commercially marketed IleRS inhibitor. Mupirocin, also known as pseudomonic acid, originally was isolated from Pseudomonas fluorescens and is used as a topical antibiotic against gram-positive bacteria, particularly Staphylococcus aureus. It binds directly to the first lysine of the conserved KMSKS sequence in the amino acylation active site (18). 

Inhibition of folic acid synthesis in susceptible microorganisms and ultimately the synthesis of nucleic acids. By competing with para-aminobenzoic acid (PABA) for the enzyme dihydropteroate synthetase, sulphonamides prevent the incorporation of PABA into dihydrofolate, while trimethoprin, by selectively inhibiting dihydrofolate reductase, prevents the reduction of dihydrofolate to tetrahydrofolate (folic acid). Animal cells, unlike bacteria, utilize exogenous sources of folic acid. Pyrimethamine inhibits protozoal dihydrofolate reductase, but is less selective for the microbial enzyme and therefore more toxic than trimethoprim to mammalian species. 

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