The document discusses postantibiotic effects (PAE) and sub-minimum inhibitory concentration (sub-MIC) effects of antibiotics in vitro and in vivo. It defines PAE as the suppression of bacterial growth after brief antibiotic exposure. PAE depends on antibiotic type, bacteria, concentration, and exposure duration. It is longer for Gram-positives than Gram-negatives. Sub-MICs can prolong PAE and cause sub-MIC effects, suppressing bacterial growth. Prolonged PAE and sub-MIC effects indicate antibiotics may be effective at lower doses or longer intervals than expected based solely on in vitro MICs.

1. The postantibiotic and sub-MIC
The postantibiotic and sub-MIC
effects in vitro and in vivo
effects in vitro and in vivo
Inga Odenholt, MD., Ph.D.
Department of Infectious Diseases
University hospital
Malmö
Sweden

2. The postantibiotic effect in vitro
The postantibiotic effect in vitro

3. Postantibiotic effect;
Postantibiotic effect;
PAE in vitro
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

4. Postantibiotic effect
9
8
7
log10 cfu/mL
2.3 h
Control
6
PAE
5
4
3
0
2
4
6
8
10
12
h
Odenholt et al. SJID, 1988

5. Postantibiotic effect
Postantibiotic effect
in vitro
in 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

6. PAE against Gram-positive bacteria
Antibiotics
• Penicillins
• Cephalosporins
• Carbapenems
• Quinolones
• Proteinsythesis inhibitors
hours
1-2
1-2
1-2
1-3
3-5

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

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

9. The PAE at different concentrations against E. coli
8
7
6
hours
5
Rifampicin
4
Tetracykline
Cefamandole
3
2
1
0
0,5
1
2
4
xMIC
8
16
32
Craig & Gudmundsson, 1991

10. PAE at different exposure times against S. aureus
6
5
PAE (h)
4
Penicillin
Erythromycin
3
2
1
0
0
2
4
6
8
10
12hours

11. Effect on inoculum size on the PAE
120
100
Min
80
10 9 cfu/mL
10 7 cfu/mL
60
10 5 cfu/mL
10 3 cfu/mL
40
20
0
1
Ciprofloxacin
2
Tobramycin

12. PAE in vitro
PAE in vitro
Methods
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 preexposed culture are desirable

13. Postantibiotic effect
9
8
7
log10 cfu/mL
2.3 h
Control
6
PAE
5
4
3
0
2
4
6
8
10
12
h
Odenholt et al. SJID, 1988

14. PAE in vitro
PAE in vitro
Methods
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

15. PAE in vitro
PAE in vitro
Methods
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

16. PAE measured with ATP
-7
log10 M bacterial ATP
-8
-9
Control
PAE
Dilution
-10
-11
0
1
2
3
4
5
6
7
8
9
h

17. PAE in vitro
PAE in vitro
Methods
Methods
Morphology
4.
• 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
5. 3H-thymidine incorporation
-correlates well with the PAE measured with
viable counting

18. Control related effective
Control related effective
regrowth time (CERT)
regrowth time (CERT)

19. CERT
CERT
• Definition
CERT=T-C
T=the time required for resumption of
logarithmic growth and increase of one
log10 to occur over the preexposed inoculum
of the test tube

20. Calculation of CERT with bioluminescence
3
1.3 h
2
ATP log10 M
6h
1
PAE=4,7 h
Control
PAE
0
-1
-2
h
-2
-1
0
1
2
3
4
5
6
7

21. Calculation of CERT using viable counts
3
1.6 h
2
log10 cfu/mL
1
0
PAE=-0.3 h
Control
PAE
-1
1.3 h
-2
-3
-4
-2
-1
0
1
2
3
4
5
6
7
h

22. The postantibiotic effect in vivo
The postantibiotic effect in vivo

23. Postantibiotic effect in vivo
Postantibiotic effect in vivo
Definition
PAE= T-C-M
• 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

24. The postantibiotic effect of gentamicin against K. pneumoniae in vivo
10
9
8
log10 cfu/mL
7
6
5
4
Control
PAE
3
T>MIC
2
1
0
-2
0
2
4
6
8
10
12
Fantin et al. JAC, 1990
14
h

25. PAE in vivo
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 vivo
PAE in vivo
Animal models
Animal 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
Mechanisms of PAE
• β-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
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
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. The postantibiotic sub-MIC
The postantibiotic sub-MIC
effect in vitro
effect in vitro

31. Postantibiotic sub-MIC
Postantibiotic sub-MIC
effect; PA SME
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

32. PA SME of telithromycin against H. influenzae
10
9
8
log10 cfu/mL
7
6
5
PAE
0.1xMIC
4
0.2xMIC
0.3xMIC
Control
3
2
1
0
3
6
9
12
15
18
21
24
h

33. The postantibiotic sub-MIC
The postantibiotic sub-MIC
effect in vivo
effect in vivo

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

35. The PAE and PA SME of piperacillin against S. aureus in vivo
9,00
8,50
8,00
log10 cfu/mL
7,50
7,00
Control
PAE
PA SME
6,50
6,00
5,50
Penicillinase
5,00
4,50
T>MIC
4,00
h
-2
0
2
4
6
8
10
Oshida et al. JAC, 1990

36. Post-MIC effect (PME)
Post-MIC effect (PME)

37. Post-MIC effect; PME
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

38. The post-MIC effect of benzylpenicillin against S. pneumoniae (PcR)
10
9
8
log10 cfu/mL
7
MIC
10mg/l
100 mg/l
Control
6
5
4
PME at 10 mg/l 12.9-2.3= 10.6
3
PME at 100 mg/l 7.5-2.3= 5.2
2
1
0
2
4 MIC
6
8
10
12
14
16
18
20
22
24 h

39. Mechanism of PA SME?
Mechanism of PA SME?
• The PAE of ß-lactam antibiotics seems to
represent the time necessary to synthesize
new PBPs. When bacteria in the PA-phase
are exposed to sub-MICs, most PBPs are
still inactivated and only a small amount of
the drug is needed to prolong the inhibition
of cell multiplication until a critical number
of free PBPs are once more available

40. Postantibiotic leucocyte
Postantibiotic leucocyte
enhancement
enhancement

41. Postantibiotic leucocyte
Postantibiotic leucocyte
enhancement; PALE
enhancement; PALE
• Bacteria pretreated with antibiotics for a
brief period of time show increased
susceptibility to intracellular killing and
phagocytosis
• In general, antibiotics that produce the
longest PAEs exhibit maximal PALEs

42. Sub-MIC effects
Sub-MIC effects

43. The SME of P&G kinolon against S. pneumoniae
9
8
log10 cfu/mL
7
6
Control
0.1xMIC
0.2xMIC
0.3xMIC
5
4
3
2
h
0
3
6
9
12
15
18
21
24

44. Sub-MIC effects; SME
Sub-MIC effects; SME
Definition
• The effect of subinhibitory antibiotic
concentrations on bacteria not previously
exposed to suprainhibitory concentrations
SME= Ts-C
•Ts=the time it takes for the cultures exposed to
sub-MICs to increase by one log10 above the counts
observed immediately after washing
•C=corresponding time for the unexposed control

45. Sub-MIC effects
Sub-MIC effects
• The minimum antibiotic concentrations that
produces a structural change in bacteria seen
by light or electron microscopy
• The minimum antibiotic concentration that
produces a one log10 decrease in the bacterial
population compared to the control
• Loss or change of bacterial toxins

46. Sub-MIC effects
Sub-MIC effects
• Loss of surface antigens resulting in
decreased adhesion
• Increased rates of phagocytic ingestion
and killing
• Increased chemotaxsis and opsonization

47. Mechanism of sub-MIC
Mechanism of sub-MIC
effects
effects
• SME probably tests the distribution of
antibiotic susceptibility in the bacterial
population, in which there are
subpopulations that are inhibited by
concentrations less than the MIC. The
SME would therefore represent the time
it takes for the population with the
higher MIC to become dominant

48. Implications
Implications
• The combined effects of supra- and subinhibitory
concentrations seem to be more important for
dosing regimens then PAE itself.
• A long PA SME/PME indicate that longer dosing
intervals may be used even for antibiotics, which
are dependent on the T>MIC for efficacy