Today’s talk

1. Today’s talk • Dimensions of AB resistance • History of AB resistance • Biology of AB resistance • Biology of antibiotic action and measurement • Genetics • Biochemistry • Selection • Some guiding questions and concepts

2. Dimensions of Antibiotic Resistance • Bacterial species • Type of transmission: hospital or community • Antibiotic • Genetic mechanism of resistance: how does the bug get the genes to be resistant? • Biochemical mechanism of resistance: what does the bug do to be resistant? • Mechanisms of selection for resistance • Individuals • Populations • Study design to assess these mechanisms

3. History of Antimicrobial Resistance

4. Early principles: Paul Ehrlich • The therapia sterilisans magna consists in this, that by means of one or at most two injections the body is freed from the parasites…. Here, therefore, the old therapeutic remedy is applicable …. frapper fort et frapper vite • A further advantage of combined therapy is, that under the influence of two different medicines the danger of rendering the parasites immune to arsenic, which naturally would be a very great obstacle in connexion with further treatment, is apparently greatly minimized.

5. Mening GC ADD DHTS All Gram negs S. aureus ADD ß- LACTAMASE ADD PBP S. pneumo PHOSPORYLATE METHYLATE RIBOSOME E.coli GC, H. flu MRSA VRE ? VMRSA ACETYLATE EFFLUX QMRSA ADD DHFR ADD ß-LACTAMASE Kleb E.coli ADENYLATE Pseud ADD PBP MUTATE 1930 1940 1950 1960 1970 1980 1990 2000 Sulfa Penicillin Strept Tetra Chlora Erythro Oxa/amp/ceph Vanco Genta Trimethoprim 3rd gen cephalosporins Fluroquinolones Carbapenems ESBLs AmpCs

6. Resistance comes fast J. Davies 1997

7. ICU Patients Non-ICU Patients Resistance increases quickly P. aeruginosa resistant to imipenem P. aeruginosa resistant to quinolones K. pneumoniae non-susceptible to 3rd cephalosporins Source: NNIS DATA Clinics Chest Med. 20:303-315

8. ICU Patients Non-ICU Patients Resistance goes up quickly (2) Methicillin-resistant Coagulase-negative Staph Methicillin-resistant S. aureus Vancomycin-Resistant enterococci Source: NNIS DATA Clinics Chest Med. 20:303-315

9. Still growing: Resistance inStreptococcus pneumoniae in US G Doern et al., Clin Inf Dis. 2005

10. Geographic variation in antibiotic resistance H. Goossens et al. 2005 Lancet

11. Proportion Penicillin Resistant State Geographic Variation Resistancein 1999

12. The Tragedy of The Commons

13. Resistance goes down slowly, if at all 39% R 45% R V Enne et al., Lancet 2001

14. Resistance goes down slowly, if at all Hennessy et al. 2002, CID ~30% decline in prescribing after initial intervention ~25% after expanded

15. But in hospitals, changes can move faster Dunkle et al. Amer J Med 1981

16. Biology of Antimicrobial Resistance

17. How do antibiotics kill? • Static v. cidal • Bacteriostatic: prevent cell division (e.g. by preventing protein synthesis) • Bactericidal: kill bacteria directly • Cidal drugs often kill only dividing bugs • Cell wall synthesis inhibitors • Others • This makes treatment of latent infection especially difficult (TB)

18. Antibiotics and the immune system • Immune responses required to kill alongside bactriostatic drugs • Also for many bactericidal drugs: phenotypic resistance Wiuff et al. AAC 2005

19. S. aureus GNR (E. coli, Klebsiella Enterobacter) Enterococcus faecium “Normal” Flora S. pneumoniae H. influenzae N. meningitidis

20. Normal flora: Consequences • Treatment exerts selection on “innocent bystanders” • Most of the harm done by use of a drug may be on species OTHER than the target of treatment • Optimal dosing for treatment ≠ optimal to prevent resistance • Most of the exposure of a given species to a given drug may be due to treatment of OTHER infections

21. Broth microdilution Etest Measuring resistance: Minimal Inhibitory Concentration (MIC)

22. MIC is a simplification Regoes et al. AAC 2004

23. Subpopulations Depends on in vitro conditions: pH, etc – not necessarily same as in vivo One parameter summary of the curve Ignores physiologic variation Limitations of MIC Regoes et al. AAC 2004

24. Biological Aspects of Resistance • Genetics: how is drug resistance coded? • And how can it move from one bug to another? • Think of: floppy disk, memory stick, punch card • Biochemistry/mechanism: what does a bug do to become resistant? • Think of: iTunes, RealPlayer, Microsoft Media Player • How resistance is selected: how do we increase the frequency of resistant bugs? • Block that metaphor!

25. Intrinsic resistance • All members of a species are resistant, and have been since before clinical use • Tuberculosis and penicillin: naturally encodes beta-lactamase • Vancomycin-producing species and vancomycin: alters its cell wall to be insensitive (same as resistance in targets!) • Don’t activate prodrug • Isoniazid or pyrazinamide and non-mycobacteria: not chemically altered to become active

26. Mutation Plasmid transfer Transformation Genetic Mechanisms of Resistance Acquisition

27. Implications • Mutation: easy to get a resistant strain in almost any patient: mutation frequencies ~10-7 – 10-10 • Unless multiple mutations are required to confer resistance! • Examples: Tuberculosis, HIV • Other mechanisms • Very complex mechanisms of resistance can evolve, because they can move as a block from one bug to the next • Can even transfer from one species to another • Emergence of a resistant bug in a single host is unlikely, unless a mix of resistant bugs and sensitive bugs is present

28. Epidemic Plasmids Courtesy Tom O’Brien, BWH

29. System for combining resistance (and other) genes Can take up new genes via integrase and add them to the “package” Often on transposons or plasmids Integrons www.mmb.usyd.edu.au/coleman/

30. Reduced permeability Efflux Degradation Detoxification Target alteration: enzyme Target alteration: mutation Target amplification Inactivate the activator of the prodrug Biochemical mechanisms

31. Mechanisms: their consequences • Most mechanisms are quite specific to one drug or class of drugs • Enzymes to alter drug or target • Target changes or amplification • A few mechanisms confer resistance to more than one class of drug • Efflux pump: “MDR transporter”

32. Mechanisms • High-level resistance: completely resistant to any achievable concentration • Partial resistance: small change in MIC

33. Mechanisms of selection

34. How Antimicrobial Use Increases Resistance: Mechanisms • “Acquired” Resistance: selection within host • Patient infected with a susceptible organism • Treatment selects a resistant variant Rx Emerg Inf Dis 2002 8:347

35. Rx How Antimicrobial Use Increases Resistance: Mechanisms • “Primary” Resistance: Selection in host population • Patient infected with a resistant organism • Competitive mechanism: Treatment selects by reducing transmission of susceptible infections

36. Rx How Antimicrobial Use Increases Resistance: Mechanisms • Increasing susceptibility to colonization • Patient carries a “normal flora” • Treatment increases susceptibility to colonization by opening ecologic niche

37. Rx Rx Rx Summary of Mechanisms of Selection of Resistance by Abx

38. Is antibiotic use harmful to individuals?

39. Dental fillings installed and removed from experimental monkeys Co-selection Summers 1993 AAC

40. Concepts and questions • Antibiotic resistance is interesting: how bad is it? • How can we measure the costs? Compared to what?

41. What can we do to/for an individual patient to prevent resistant infections?

42. Why have some kinds of drug resistance increased fast, others slowly or not at all?

43. What can we do to the population as a whole to reduce the risk of reistant infections?

44. In what circumstances does doing what is best for the patient • Increase the burden of resistance in the community? • Reduce the burden of resistance in the community? • Both but on different time scales?

45. What would happen if we stopped using antibiotics tomorrow? • To disease? • To resistance?