In Vitro models of Infections: the postantibiotic and sub-MIC effects in vitro and in vivo

1. In Vitro models of Infections:the postantibiotic and sub-MIC effects in vitro and in vivo Inga Odenholt, MD., Ph.D. Department of Infectious Diseases University hospital Malmö Sweden

3. Pharmacodynamic parameters • Postantibiotic effect (PAE) • In vitro • In vivo • Postfungal effect (PAFE) • Postantibiotic sub-MIC effect (PA SME) • In vitro • In vivo

4. Pharmacodynamic parameters • Post MIC effect (PME) • Postantibiotic leucocyte enhancement (PALE) • Sub-MIC effect (SME)

5. The postantibiotic effect in vitro

6. Postantibiotic effect; PAE in vitro Definition: • Suppression of bacterial growth after short exposure of organisms to antibiotics PAE=T-C T= The time required for the exposed culture to increase one log10 above the count observed immediately after drug removal C= The corresponding time for the unexposed control

8. Postantibiotic effectin vitro The PAE is dependent on: • Type of antibiotic • Type of bacterial species • Concentration of the antibiotic • Duration of exposure • Size of the inoculum • Growth phase of the organism

9. PAE against Gram-positive bacteria Antibioticshours • Penicillins 1-2 • Cephalosporins 1-2 • Carbapenems 1-2 • Quinolones 1-3 • Proteinsythesis inhibitors 3-5

10. PAE against Gram-negative bacteria Antibioticshours • Penicillins 0 • Cephalosporins 0 • Carbapenems (1) • Quinolones 1-3 • Proteinsythesis inhibitors 3-8 • Aminoglycosides 2-4

11. PAE against P. aeruginosa Antibiotics hours • Penicillins 0 • Cephalosporins 0 • Carbapenems 1-2 • Quinolones 1-2 • Aminoglycosides 2-3

15. PAE in vitro Methods • 1. Viable counts • Methodological pitfalls • • may overestimate killing • • negative PAEs are common with ß-lactams • and gram-negatives due to forming of filaments • similar inocula of the control and the pre- • exposed culture are desirable

17. PAE in vitro Methods 2. Optical density Methodological pitfalls • killing cannot be measured due to a detection limit of 106 cfu/ml • control curves at different inocula and viable counts after drug removal are necessary to be performed to ensure that PAE culture and control are at the same inoculum

19. PAE in vitro Methods 3. ATP measurement Methodological pitfalls • bactericidal activity is underestimated due to dead but intact (not lysed) bacteria still containing intracellular ATP • PAE is overestimated due to falsely elevated ATP content

21. PAE in vitro Methods 4. Morphology • Phase contrast microscopy • the time it takes for the bacteria to revert to 90% bacilli • Ultrastructural changes -the changes in structure correlates well with the PAE measured with viable counting 3H-thymidine incorporation 5. -correlates well with the PAE measured with viable counting

22. The postantibiotic effect in vivo

23. Postantibiotic effect in vivo Definition PAE= T-C • T= the time required for the counts of cfu in thighs of treated mice to increase one log10 above the count closest to but not less than the time M • C= the time required for the counts of cfu in thighs of untreated mice to increase one log10 above the count at time zero • M= the time serum concentration exceeds the MIC

25. PAE in vivo • Observed in several animal models • In vitro data are predictive of in vivo results except that in vivo PAE are usually longer due to the effect of sub-MICs and/or the effect of neutrophils • The major unexplained discordant results are for ß-lactams and streptococci

26. PAE in vivoAnimal models • Thigh infections in mice • Pneumonia model in mice • Infected treads in mice • Infected tissue cages in rabbits • Meningitis model in rabbits • Endocarditis model in rats

27. Mechanisms of PAE • -lactam antibiotics. At least for S. pyogenes and penicillin it has been shown that PAE stands for the time it takes for the bacteria to resynthesize new PBPs

28. Mechanisms of PAE • Erythromycin and clarithromycin: 50S ribosomal subunits were reduced during 90 min and protein synthesis during 4 h (PAE) due to prolonged binding of the antibiotics to 50S.

29. Mechanisms of PAE • Aminoglycosides: Binding of sublethal amounts of drug enough to disrupt DNA, RNA and protein synthesis. The time it takes to resynthesize these proteins. With a half-life of >2.5 h, the PAE disappears, reflecting a sufficient time for the repair mechanism to be restored.

30. Postfungal effect

31. PAFE assay • Removal of the drug: 3 washes with saline solution and centrifugation for 10 minutes after each wash. • Colony count determination: CFU of the exposed and control within same range. • Incubation in a spectrophotometer reader at 37 C for 48 h. • Growth: automatically monitored: OD changes at 10 minutes intervals.

32. Three points in the growth curve of the controls and the exposure were analyzed: Data analysis OD0:the time-point of the first significant increase in OD. OD20: the time-point where the OD reached 20% of the maximum of growth curve. OD50: the time-point where the OD reached 50% of the maximum of growth curve.

33. Control Exposed OD50 PAFE OD20 OD0 Results Mean and 95% confidencial interval of the ODx for the exposed and the corresponding controls of each species at each point in the growth curve are calculated. PAFE=T-C (t) • T: time of the exposed • C: time of the control Presence of PAFE: Lower limit of the 95% CI of ODx of exposure > the upper limit of the 95% CI of the ODx of the corresponding control for each strain.

34. PAFE of Amphotericin B PAFE after 4h incubation with the drug at a concentration of 4 x MIC (Number of strains with presence of PAFE) A. fumigatus A. ustus A. terreus A. nidulans OD 9.94 (3/3) 3.94 (2/3) 2.53 (2/3) N.P. (0/3) 0 OD 8.86(3/3) N.P. (0/3) N.P.(0/3) 2.23 (2/3) 20 OD 5.32 (3/3) 3.62 (1/3) 2.03 (2/3) N.P. (0/3) 50 PAFE after 2h incubation with the drug at a concentration of 4 x MIC A. fumigatus A. ustus A. terreus A. nidulans OD 4.05 (3/3) 1.00 (2/3) 0.64 (1/3) 1.67 (1/3) 0 OD 4.84 (2/3) N.P. (0/3) 0.84 (1/3) N.P. (0/3) 20 OD 2.95 (1/3) N.P. (0/3) N.P. (0/3) N.P. (0/3) 50 Significant PAFE: Lower 95% CI (exposed) >Upper 95% CI (control). N.P.: No PAFE

35. PAFE on different conditions PAFE: concentration and time dependent

36. PAFE for Itraconazole Incubation period: 4, 2 and 1h Drug concentrations: 50, 20, 10, 4, 1 and 0.25 times the MIC No PAFE was observed for all the strains

37. I. Conclusion • The method developed seems to be useful to measure PAFE in moulds • OD0 was superior to OD20 or OD50: • Least variation, reproducible • Shortest incubation period: economic • Maximum growth measurements not required

38. II. Conclusion For AMB: • PAFE was dose and exposure time dependent • No PAFE was observed after 1 h exposure at any concentration of AMB • No PAFE was observed at 0.25 x MIC for AMB • A. fumigatus displayed the longest PAFE For ITZ: • No PAFE was present at any concentration and exposure period

39. The postantibiotic sub-MIC effect in vitro

40. Postantibiotic sub-MIC effect; PA SME Definition • The effect of subinhibitory antibiotic concentrations on bacteria previously exposed to suprainhibitory concentrations PA SME= TPA-C • TPA=the time it takes for the cultures previously exposed to antibiotics and thereafter to sub-MICs to increase by one log10 above the counts observed immediately after washing. • C=corresponding time for the unexposed control

44. The postantibiotic sub-MIC effect in vivo

45. PAE ( PASME) in vivo of amikacin against K. pneumoniae in a thigh-infection model in mice PAE • Normal mice (half-life 19 min) 5.5 h • Uremic mice (half-life 98 min) 14.6 h

48. Post-MIC effect (PME)

50. Post-MIC effect; PME Definition • The effect of sub-MICs on bacteria previously exposed to a constant decreasing antibiotic concentration PME=Tpme-C • Tpme= The time for the counts in cfu of the exposed culture to increase one log10 above the count observed at the MIC level • C= the time for an unexposed control to increase one log10