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Resistance to antibiotics

Resistance to antibiotics. Intrinsic resistance (examples) penG does not enter gram negative bacteria well why? doesn’t penetrate--ampicillin does rifampin doesn’t kill fungi why? doesn’t get in---weaken barrier with amphotericin and then it does

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Resistance to antibiotics

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  1. Resistance to antibiotics • Intrinsic resistance (examples) • penG does not enter gram negative bacteria well • why? doesn’t penetrate--ampicillin does • rifampin doesn’t kill fungi • why? doesn’t get in---weaken barrier with amphotericin and then it does • isoniazid does not kill bugs that don’t require synthesis of mycolic acids • Environmental resistance • e.g. sulfonamide resistance if high purines, methionine, thymidine available (such as in an abscess) • e.g. aminoglycosides not effective in anaerobic environment • Acquired Resistance • genetic changes, plasmids with new genes

  2. 2006 Antibiogram Harborview/UW

  3. Acquired Drug Resistance • 1. enzymatic inactivation (b-lactams, aminoglyc. chloramph)

  4. Bacteria keep up with big pharma in the b-lactam antibiotic arms race bacteria can often express more than one -lactamase

  5. Inactivation of aminoglycosides by acetylation, phosphorylation, and adenylation in drug-resistant organisms

  6. Acquired Drug Resistance • 1. enzymatic inactivation (b-lactams, aminoglyc. chloramph) • 2. rapid efflux of drug out of cell (tetracyclines,ciprofloxacin)

  7. Drug export systems in Gram +

  8. Acquired Drug Resistance • 1. enzymatic inactivation (b-lactams, aminoglyc. chloramph) • 2. rapid efflux of drug out of cell (tetracyclines,ciprofloxacin) • 3. decreased conversion to active form (isoniazid) • 4. increased concentration of antagonist/competitor (sulfonamide resistance with increased PABA synthesis). • 5. altered amount of receptor (trimethoprim-DHFR amplification) • 6. altered structure of target to reduce binding (methicillin resistance, vancomycin resistance, ciprofloxacin res.)

  9. Vancomycin resistance: mechanism

  10. Vancomycin resistance: mechanism

  11. Resistance can be transferred between bacteria • phage transduction • transposable elements • plasmid transfer during conjugation • plasmids can contain multiple resistance genes • transfer can occur between non-pathogen and pathogens

  12. Plasmid-mediated drug resistance tetracycline chloramphenicol sulfonamide aminoglycoside

  13. Problems with Antibiotic resistance • more than 50% of antibiotics used in domestic animals for sub-therapeutic effect: breeding ground for resistance There are 7.5 billion chickens, 292 million turkeys, 109 million cattle and 92 million pigs in the United States.

  14. Antibiotics given to pigs as of 2000

  15. “KFC does not purchase poultry treated nontherapeutically with medically important antibiotics.” – Letter to “Keep Antibiotics Working,” August 28, 2002 • McDonald’s ‘We’ve listened to the concerns, studied the issue, and the bottom line was we thought it was the right thing to do to discontinue the use of [fluoroquinolone antibiotics] in poultry,’ said Walt Riker, spokesman for Oak Brook-based McDonald’s. – Walt Riker, McDonald’s, “Chickens Fed With Antibiotics McGone,” Chicago Sun-Times, February 12, 2002

  16. Prospects for new antibiotics? • new antibiotic development slowed in 80’s/90’s • selective drugs have lower market value • 5-15 yr time frame to get new drugs to physicians • recent increase in new antibiotic development is encouraging

  17. active against Strep pneumoniae

  18. Plasmid Mediated Quinolone Resistance (PMQR) • First reported in a strain of K. pneumoniae • QnrA protein – 218 aa protein • Protects DNA gyrase and topoisomerase IV from the inhibitory activity of quinolones--exact mechanism is not known yet • Qnr proteins • QnrA2 – K. oxytoca (China) • QnrB - E. coli, K. pneumoniae, E. cloacae, C. koseri (USA and India) - 40% aa identity with QnrA • QnrS – S. flexneri (Japan) - 59% aa identity with QnrA • The presence of other mechanisms of resistance may increase plasmid-mediated quinolone resistance

  19. PREVALENCE OF PLASMID-MEDIATED RESISTANCE TO QUINOLONES IN Escherichia coli • 1% QnrA+ isolates among ciprofloxacin-resistant E.coli from different countries [AAC (2003) 47:559] • 11% QnrA+ isolates among ciprofloxacin-resistant K. pneumoniae and 0% in E.coli from USA [AAC (2004) 48: 1295] • 7.7% QnrA+ isolates among ciprofloxacin-resistant E. coli in Shanghai (China) [AAC (2003) 47: 2242] • 0.4% QnrA+ isolates among nalidixic acid- resistant Escherichia coli (France) [AAC (2005) 49: 3091]

  20. TB drug development • no new TB drugs in past 40 years • multi-drug resistant TB prevalent • Johnson & Johnson • R207910 • targets mycobacterium ATP synthetase

  21. b-Lactam Antibiotic development • spectrum of action • resistance to b-lactamase • specificb-lactamase inhibitors

  22. Ampicillin R Penicillin G Amoxicillin Methicillin Dicloxacillin

  23. Penicillinase resistant -methicillin -dicloxacillin narrow spectrum resistant b-lactam antibiotics-1

  24. Methicillin resistance • caused by unique peptidyl transferase that does not bind b-lactams • had been largely confined to hospital acquired infections • more recently--outbreaks in athletic teams, iv drug users, school children, gay community, general population • 900 cases in LA county jails (2002) Structure of PBP2a

  25. A m i n o p e n i c i lli n s gra m n e gat i ve s e nsi t i ve am pi c il l in amox i c illi n A n t ip s e u d omo n a l gra m n e gat i ve in c l u di ng s e nsi t i ve t i ca r c ill i n ps e u domo n a s p i p e r ac ill i n b-lactam antibiotics-1 - la ct ama s e G r ou p S p e c t r um b s e n s it ivi t y Na t u r al p e ni c il l ins n arro w s p e ct r u m s e nsi t i ve Pe n G/ Pe n V gra m po si t i ve Pe ni c ill i n a s e r e sis ta n t n arro w s p e ct r u m r es i st an t m e t h i ci l lin d i cl oxac il l in

  26. Cephalosporins Brody’s Human Pharmacology

  27. b-lactam antibiotics-2 - la ct ama s e G r ou p S p e c t r um b s e n s it ivi t y C e p h a l o s po r i ns b roa d s p e ct r u m var i a bl e c e fac l o r c e ft ri axon e

  28. Newer b-lactams • aztreonam (monobactam) • gram- specific • resistant to b-lactamase • Carbapenems: imipenem, meropenem • broad spectrum (gram+,gram-) • resistant to b-lactamase • penetrates CSF • imipenem a substrate for dehydropeptidase I in kidney, meropenem is not Brenner

  29. b-lactamase inhibitors

  30. b-lactamase inhibitors • Clavulanic acid (suicide inhibitor for most lactamases) • little antibiotic action on its own • combine with amoxicillin to get Augmentin (oral activity) • combine with ticarcillin to get Timentin • Sulbactam (similar inhibitor) • combine with ampicillin to get Unasyn (given iv or im)

  31. Activity of available b-lactamase inhibitors against clinically important b-lactamases

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