Antibiotic resistance 6, chapter

As carriers of antibiotic resistance (Chapter 3, Part 4) the emergence of antibiotic-resistant strains has had serious repercussions in the application of antibiotic therapy, and has seriously increased the danger of nosicomial infections. 

Plasmids are relatively small, circular pieces of double-stranded extrachromosomal DNA. They are capable of autonomous replication and encode for many auxiliary functions that are not usually necessary for bacterial growth. One such function of great significance is that of antibiotic resistance (Chapter 13). Plasmids may also transfer readily from one organism to another, and between species, thereby increasing the spread of resistance. 

Just as the excision of temperate viral DNA from the host chromosome could be inaccurate, and lead to additions and deletions from the sequence, so too can the F-factor gather chromosomal DNA as the host cells change from Hfr to F+. In such instances the plasmid that is formed will transfer not only itself but also this additional DNA into recipient cells. This is particularly significant because the unassociated plasmid can replicate autonomously from the chromosome to achieve a high copy number. It can also be transferred simultaneously to many recipient bacteria. If the transported DNA encoded a mechanism of antibiotic resistance (Chapter 13) it would not be difficult to imagine how whole populations could rapidly acquire the resistance characteristics. 

For many years, it was thought that binary fission was the only method of reproduction in bacteria, but it is now known that there are three methods of reproduction in which genetic exchange can occur between pairs of cells, and thus a form of sexual reproduction is exhibited. These processes are transformation, conjugation and transduction. Further details ofthese processes as they affect antibiotic resistance will be found in Chapter 9. 

Professor, Department of Medical Microbiology, University of Manitoba, Coordinator-Antibiotic Resistance Program, Department of Medicine, Health Sciences Centre, Microbiology Health Sciences Centre, Winnipeg, Canada Chapter 107... 

Antibiotic-resistant bacteria cause life-threatening infections in hospitals and society in general. There is a vital requirement to develop new antimicrobial agents, but this task involves extensive scientific trials. This chapter reviewed broad-spectrum polymeric antimicrobials, which are not susceptible to current resistance, and mechanisms of bacteria to mimic the antimicrobial action of natural HDP, which exert their effect by permeabilising the bacterial cytoplasmic membrane. Most cationic antimicrobial polymers appear to work in a manner similar to membrane-active AMP, such as magainin. The design and synthesis of different polymers, such as methacrylate-based copolymers, PPE, polynorbornene by-products, amphiphilc arylamide polymers and large polymers, have been studied as biomimetic polymers in different applications. 

Substituted derivatives of tetracyclines for which ribosomal or export-based resistance has not been exhibited. N.N-dimethylgly-cylamido derivatives of minocycline and 6-demethyl-6-deoxytc-itacycline are potent, new wide-spectrum antibiotics see Chapter 21. 

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