Antibiotics specific agents

Many of the antibiotics used clinically are active by their ability to inhibit protein biosynthesis in bacteria. The individual steps of protein biosynthesis all seem susceptible to disruption by specific agents. Some specific examples are listed below ... 

Bleomycin is a naturally occurring fermentation product of Streptomyces verticillus. It is a basic glycoprotein, complexed with Cu++. It intercalates between DNA base pairs, and it also chelates iron, generating oxygen radicals which further damage the DNA. It is the only cell-cycle specific agent among the antibiotics as it causes accumulation of cells in the G2 phase of the cell cycle. 

There are several reasons why public health authorities and most physicians recommend against stockpUing antibiotics. Specific antibiotics are effective only against specific infections, and we cannot predict which agents terrorists wiU use. People must take the antibiotics at the proper time after exposure for them to be effective, which means that they must know when they have been exposed. Antibiotics taken inappropriately can lead to resistant bacteria, which can put the entire community at risk. The CDC has stockpiled large amounts of antibiotics, and we wftl make these available immediately to exposed people within 12h of the recognition of an attack... 

As a result of these observations, a variety of methods have been utilized to modify antimicrobial use in an effort to combat resistance. These include the use of an antimicrobial formulary, re.striction of agents, requirement of prior approval to obtain specific agents, multidisciplinary antibiotic management teams, and the use of computerized support systems. The impact of these programs on resistance is reviewed elsewhere,and one or more of these methods is being employed in many institutions. 

Wang, G., and Taylor, D. E. (1998). Site-specific mutations in the 23S rRNA gene of Helicobacter pylori confer two types of resistance to macrolide-lincosamide-streptogramin B antibiotics. Antimicrofe Agente Chemother. 42, 1952—1958. 

Figure 12-7. Proposed sites of inhibition (0) of the respiratory chain by specific drugs, chemicals, and antibiotics. The sites that appear to support phosphorylation are indicated. BAL, dimercaprol. TTFA, an Fe-chelating agent. Complex I, NADHiubiquinone oxidoreductase complex II, succinate ubiquinone oxidoreductase complex III, ubiquinohferricytochrome c oxidoreductase complex IV, ferrocytochrome ctoxygen oxidoreductase. Other abbreviations as in Figure 12-4.

The cell walls of mycobacteria contain three structures peptidoglycan, an arabinogalactan polysaccharide and long chain hydroxy fatty acids (mycolic acids) which are all covalently linked. Additional non-covalently attached lipid components found in the wall include glycolipids, various phospholipids and waxes. The lipid-rich nature of the mycobacterial wall is responsible for the characteristic acid-fastness on staining and serves as a penetration barrier to many antibiotics. Isoniazid and ethambutol have long been known as specific antimycobacterial agents but their mechanisms of action have only recently become more clearly understood. 

In contrast to chemical agents, micro-organisms are dynamic and can adapt to situations like antibiotic or heat treatment and risks from specific micro-organisms may change over time. 

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