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The below mentioned article provides notes on drug resistance.
Drug resistance is a major problem for successful treatment of an infectious bacterial disease. Bacteria acquire drug resistance and spread within its population. However, the mechanism of drug resistance in two different bacteria differs for a single class of drug.
In addition, resistance may arise spontaneously and selected. Moreover, mutants are not formed by direct exposure to a drug. When pathogens check the entry of a drug inside their cell envelope, they become resistant to those drugs. For example penicillin G cannot penetrate the outer membrane of Gram-negative bacteria; therefore, these are resistant to penicillin G.
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Secondly, bacteria pump the drags outside their cell envelope after drugs have entered the cell. For example, some pathogens have plasma membrane translocases that expel drugs outside the envelope. These transport proteins are called multi-drug resistance pumps.
In addition, many bacteria resist the drags by chemical modification. For example, P-lactam ring of many penicillins is hydrolysed by the enzyme penicillinase. Resistance in bacteria may also arise through using alternate pathway to bypass the sequence inhibited by the agent, or increase the production of the target metabolites.
Drag-resistance in bacteria arises through the drag-resistance genes present on bacterial chromosome and plasmids. The plasmids conferring drag resistance are called resistance plasmids (R plasmids). Plasmid associated genes are known to confer resistance to chloramphenicol, penicillins, cephalosporins, aminoglycosides, erythromycin, tetracyclines, sulfonamides, etc.
The plasmid resistance genes are transferred to progeny cells through genetic recombination i.e. conjugation, transformation and transduction. Efforts can be made to discourage the emergence of drug resistance.
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Drugs can be given in high amount to kill susceptible and mutant bacteria. Two drugs can be given simultaneously in a hope that any of two will destroy the pathogen. Thirdly, new antibiotics must be used time to time.
Example of some of antimicrobial drugs is given in Table 23.4:
