1. Controlling Microbial Growth
Chapter 12

2. Most microbes good, but…
• where they are growing critical
• yogurt = good
• bloodstream = BAD
• Nosocomial infections
• Hygiene Hypothesis

3. Binary fission in bacteria
To control growth, we need to stop or slow down this process
Fig. 5.8

4. Cidal vs. Static

5. Control Methods

6. Physical Control
• Heat: incineration vs. steam
• Filtration
• Temperature
• Radiation
• Desiccation (oven)

7. Physical Control - Heat
• Bacteria can’t tolerate extreme temp changes
– Fever
• Protein denaturation - high fever

8. Heat
• Dry heat – incineration

9. Heat
• Dry heat - incineration
• Moist heat - boiling water/steam
– Kills most in seconds
– Pasteurization - temp & time
– What about endospores?

10. How can you get temp above boiling
water?
Temperature and the Physical Control of Microbes

11. Operation of an Autoclave

12. What types of items go in?
• Medical instruments
– Surgical
– Dental
– Piercing
• Microbial media
• Anything metal, some types of plastic

13. Physical Control
• Refrigeration/freezing - microbes still there
– cold temp slows down
– Microbes can freeze/thaw and still reproduce

14. Physical Control
• Radiation
– UV
– Ionizing

15. The Ionizing and Electromagnetic
Spectrum of Energies Fig. 5.7

16. Physical Control - radiation
• Radiation damages DNA
• UV radiation (ultraviolet light)
– UV lamps for disinfection
– Causes T-T dimers
– Cell death
– What happens in humans?

17. Mutations block
DNA processes
• TT dimer distorts DNA
• No replication
• No transcription
• High dose = death

18. Physical Control - radiation
• Ionizing radiation (solar rays, radioactive)
– 10K times more energy than UV
– ionization of water (OH- & H3O+ )
– DNA breaks apart
– Sterilize plastics, food, destroy viruses (Ebola)
– What happens to humans exposed to IR?
• Acute exposure -
• Chronic exposure -
• How do we know this???

19. Physical Control - desiccation
• All living things need water
• Dry out grains, meat, fish to preserve

20. Disinfectants/Antiseptics
• Ancient Egypt - chemicals for embalming
• 1800’s - Iodine used in medicine
• Joseph Lister - 1860’s
– Read Pasteur
– soaked instruments in phenol
– Knighted in 1912

21. Halogens
• Halogens - extremely
reactive
• Interacts with amino acids -
destroys cell membrane
• Iodine
– w/detergent
• Chlorine
– disinfect H2O

22. Alcohols
• Denature proteins
• Dry cells out
• Disrupt lipid bilayer
• No effect on
endospores& some
viruses

23. Phenolic Compounds
• highly reactive
– acidic
• denature proteins
– destroys cell membrane
• first used by Lister
– Lysol
– Trichlosan - milder
• potential for resistance?

24. Heavy Metals
• Used as disinfectants - poison
• Specific enzymes inhibited

25. Heavy Metals
• Silver
– Silver nitrate - eye
infections (gonorrhea)
• Copper
– Copper Sulfate -
swimming pools;
antifungal
• Mercury
– antiseptics, pesticides

26. Antimicrobial Chemotherapy
• Antibiotic control

27. Pre-antibiotic era
• Medicine was a gruesome business
• Civil war - more than 2/3 of all deaths due to disease, not
wounds
• Paul Erlich - early 1900s
– Arsenic compounds as syphilis treatment
– Fell out of favor b/c toxic

30. Sulfanilamide - sulfa drugs
• 1932 - “prontosil” developed by Gerhard Domagk
• Effective in treating Gram-positive bacterial infections
• Gave push to development of newer & better antibiotics
Bacteria need This
PABA to make looks like
folic acid PABA

31. Development of penicillin
• Alexander Fleming
• 1929 - Penicillium mold prevented S. aureus
growth
• Extract killed Gram-positive bacteria
• 1939 - Florey & Chain
• Mass produced in USA

32. Penicillin & derivatives
• One of the most widely used antibiotics
• Best against Gram-pos; some Gram-neg
(gonorrhea)
• ~ 10% of population allergic
• Works on rapidly dividing cells
– No effect on endospores!

33. Penicillin Derivatives

34. Penicillin Resistance
• Many bacterial species have developed resistance
• MRSA - methicillin resistant Staph. aureus

35. Streptomyces - natural antibiotic R&D
Soil bacterium - lots of genes for making
antibiotic compounds
• Aminoglycoside (streptomycin, gentamycin)
– Good if allergic to penicillin
– Inhibits protein synthesis
– Erythromycin: Zithromax, Biaxin
– Vancomycin - last resort for MDR Gram-pos

36. Broad Spectrum antibiotics
• Selective Toxicity
• Chloramphenicol first one isolated
– Effective against Gram-pos &neg, chlamydiae, some
fungi
– Nasty side effects - hemolytic (last resort)
• Tetracycline
– Very few side effects (short term) - overprescribed
– Yeast infections common
– Discoloration of teeth/stunted bones in children

37. Antibiotic Resistance
• Emerging danger
• Natural selection of resistant strains thru
overuse
– Overprescibing meds
– Used in livestock feed

38. • Take entire course of prescription
• Do not take higher dose of same
med if no improvement
• Do not take antibiotics for viral
infection

40. How bacteria become resistant:

41. Antifungal meds
• Fungal infections big problem for immune
suppressed individuals
• Antifungals - not many choices
– Nystatin, miconazole - interfere w/sterols (cell
membrane)
– Amphotericin B - used for serious internal organ
infection
– Griseofulvin - ringworm treatment

42. Antiviral meds - not antibiotics
• Antivirals target
different stages of
viral replication
– amantadine -
prevents
attachment
– acyclovir -
interferes w/viral
DNA replication