Some Mechanisms of Resistance to Antibiotics
• Drug resistance due to altered targets
- Alteration in the target enzyme, DNA gyrase, has resulted in resistance to fluoroquinolones.
• Drug resistance due to decreased accumulation
- ß-Lactams enter gram-negative cells through porin channels. Enterobacter is largely resistant to cephalosporins by producing ß-lactamases. However, resistant organisms may also have altered porin channels through which cephalosporins do not pass.
- Tetracycline was effective against gynecologic infection due to Bacteroides but now these organisms are resistant due to the presence of plasmid-mediated protein that promotes efflux of the drug.
• Drug resistance due to enzymatic inactivation
- ß-Lactamases (penicillinases) destroy antibiotic with the ß-lactam nucleus. Neisseria gonorrhoeae is now largely resistant to penicillin because of penicillinase activity.
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