MECHANISM OF ANTIBACTERIAL RESISTANCE
The frequency of bacterial aminoglycoside resistance encountered in clinical practice has remained nearly constant over the past 2 decades. Of the three recog-nized mechanisms of resistance that occur in aerobic gram-negative bacteria, plasmid-mediated expression of enzymes that acetylate, adenylate, or phosphorylate the aminoglycosides is the most important. Ring one is the primary target of these enzymes.
Two other common mechanisms of resistance are known. Some cases of resistance of aerobic gram-negative bacilli to streptomycin are due to mutations in the proteins of the bacterial ribosomes. Streptococci, staphylococci, and Pseudomonadaceae resist aminogly-cosides as a result of decreased transport of the amino-glycosides into the bacterial cytosol.
Anaerobes also are resistant to aminoglycosides be-cause of decreased transport into the bacterial cytosol. Combining an aminoglycoside with an antibiotic that disrupts the bacterial cell wall can overcome this natu-ral resistance.
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