Resistance-causing enzymes

D. D., Draker, K., Sears, P., et al. Design of Bifunctional Antibiotics That Target Bacterial rRNA and Inhibit Resistance-Causing Enzymes. J. Am. Chem. Soc. 2000,... 

To facilitate the discovery of safer and more active aminoglycosides, high-throughput methods are necessary. Microarray techniques enable medicinal chemists to identify weak binders to resistance-causing enzymes and tight binders to ribosomal RNA. Recently, our laboratory reported the construction of aminoglycoside microarrays to study antibiotic resistance [35, 36]. 

G. D. Wright, and C.-H. Wong, Design of bifunctional antibiotics that target bacterial rRNA and inhibit resistance-causing enzymes, J. Am. Chem. Soc., 122 (2000) 5230-5231. 

One approach to combating antibiotic resistance caused by P-lactamase is to inhibit the enzyme (see Enzyme inhibition). Effective combinations of enzyme inhibitors with P-lactam antibiotics such as penicillins or cephalosporins, result in a synergistic response, lowering the minimal inhibitory concentration (MIC) by a factor of four or more for each component. However, inhibition of P-lactamases alone is not sufficient. Pharmacokinetics, stability, ability to penetrate bacteria, cost, and other factors are also important in determining whether an inhibitor is suitable for therapeutic use. Almost any class of P-lactam is capable of producing P-lactamase inhibitors. Several reviews have been pubUshed on P-lactamase inhibitors, detection, and properties (8—15). 

P-Lactamases are enzymes that hydrolyze the P-lactam ring of P-lactamantibiotics (penicillins, cephalosporins, monobactams and carbapenems). They are the most common cause of P-lactam resistance. Most enzymes use a serine residue in the active site that attacks the P-lactam-amid carbonyl group. The covalently formed acylester is then hydrolyzed to reactivate the P-lacta-mase and liberates the inactivated antibiotic. Metallo P-lactamases use Zn(II) bound water for hydrolysis of the P-lactam bond. P-Lactamases constitute a heterogeneous group of enzymes with differences in molecular structures, in substrate preferences and in the genetic localizations of the encoding gene (Table 1). 

All -lactam antibiotics are bactericidal. They interfere with the synthesis of the bacterial wall by inhibiting the bacterial ftanspeptidase enzymes essential for the construction of peptidoglycan of the wall. Some -lactams may be inactivated by the -lactamases (penicillinases) produced by bacteria and, thus, the activity of both penicillins and cephalosporins can be determined by their ability to withstand the destructive action of -lactamases also produced by the organism for its optimal protection. Bacterial resistance caused by -lactamase production... 

Derived from kanamycin A is tnodi-fied by only two of the nine resistance modification enzymes knowr for aminoglycosides used patenter-ally for infections caused by Gram-negatives. 

Irradiation. Although no irradiation systems for pasteurization have been approved by the U.S. Food and Dmg Administration, milk can be pasteurized or sterilized by P tays produced by an electron accelerator or y-rays produced by cobalt-60. Bacteria and enzymes in milk are more resistant to irradiation than higher life forms. For pasteurization, 5000—7500 Gy (500,000—750,000 tad) are requited, and for inactivating enzymes at least 20,000 Gy (2,000,000 rad). Much lower radiation, about 70 Gy (7000 tad), causes an off-flavor. A combination of heat treatment and irradiation may prove to be the most acceptable approach. 

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