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
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.