1. Antibiotics that affect the Cell Envelope

2. Key Words Sterilization/disinfection/antisepsis Bacitracin
Antibiotic Vancomycin
Selective toxicity beta lactam
Bactericidal Penicillins
Bacteriostatic Cephalosporins
Minimal inhibitory concentration (MIC) Monobactam
Susceptibility testing Clavulinic acid
Penicillin binding proteins Penicillinase/beta lactamase
Autolysins Polymyxin B
Cycloserine Resistance

3. STERILIZATION
All killed
non-selective

4. Sterilization autoclaving ethylene oxide ultra-violet light
121oC (heat/pressure)
Heat resistant materials
ethylene oxide
Non heat resistant
usually equipment
ultra-violet light
surfaces (e.g operating rooms)
not totally effective

5. Membrane filters
pores
bacteria

6. Disinfection Liquids that kill bacteria e.g. phenol based
too toxic for skin surfaces

7. Antiseptics Topical (e.g. skin) e.g. iodine or 70% alcohol
“reduce” bacterial load

8. ANTIBIOTICS Selectively toxic for bacteria bactericidal (killing)
bacteriostatic (growth inhibition)
no harm to patient

9. Antibiotics
destroy structures
present in bacteria
not present in host

10. Antibiotics work together
with immune system

11. Minimal inhibitory concentration
lowest level stopping growth
e. g. zone of inhibition around a disk impregnated with antibiotic

12. Antibiotics that inhibit cell wall
biosynthesis are bactericidal
Without cell wall, osmotic pressure
causes bacteria to burst

13. Peptidoglycan synthesis
Cytoplasm
Cell Membrane
Cell wall
undecaprenol
sugar
amino
acid

14. Cycloserine alanine (ala) analog inhibits conversion of L-ala to D-ala
inhibits formation of D-ala-D-ala

15. Cycloserine
Analog of alanine
Cytoplasm X X
sugar
amino
acid X X

16. Bacitracin
Inhibits dephosphorylation

17. Bacitracin
Cell membrane
undecaprenol P P

18. Vancomycin
binds to D-ala-D-ala
inhibits cross-linking

19. Vancomycin
Cell wall

20. Beta lactam antibiotics
penicillins
cephalosporins
monobactams
inhibit penicillin binding proteins
stop cross-linking

21. Beta lactams
Cell wall
Penicillin binding protein

22. Cross-linking of peptidoglycan

23. STRUCTURE OF PENICILLINNH CH O N
CH3
COOH S
Site of penicillinase action.
Breakage of the  lactam ring.

24. Attached to lactam ring
penicillins
5 membered ring
cephalosporins
6 membered ring
monobactams
no second ring

25. Chemical modifications change biological activity
Early lactam antibiotics
inactive against Gram negative bacteria
no penetration of outer membrane

26. Resistance mechansims
Produce beta lactamase (penicillinase)
destroys antibiotic
modified penicillin binding proteins
don’t bind antibiotic
modified porins
no internalization of antibiotic

27. Clavulinic acid beta lactam binds strongly beta lactamases
inhibits activity

28. Polymyxin B lipid A phospholipids
binds
lipid A
phospholipids
disrupts outer membrane, Gram negative bacteria
toxic to human cells