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Lecture 9 - we will discuss the following topics:

II. Control of Microbial Growth (Chapter 7 and pp. 554-558)

A. Terminology

1. sterilization - destroy all viable cells, spores, viruses

2. disinfection - kill pathogens on inanimate surfaces

3. antisepsis - kill pathogens on living tissue

4. de-germ – mechanical removal

4. sanitization - lower # of pathogens to acceptable levels

B. How do we kill microbes?

1. Nonspecific – work against almost all microbes in the same way

a. Physical methods

b. Chemical methods

i. phenols - denature proteins, disrupt membranes

Ex.

ii. halogens - oxidation of cellular material

Exs.

iii. alcohols - denature proteins, dissolve lipid membranes

Ex.

2. Specific – specifically kill some types of microbes, others are left unharmed.

Antibiotics (pp. 554-558)

Antibiotic – a natural substance produced by one microorganism that inhibits the growth of another

a. How were antibiotics discovered?

Alexander Fleming (1928)

Penicilliumnotatum (Eukarya – fungi)

b. How do antibiotics work?

Bactericidal - kill

Bactriostatic – inhibit

Selective toxicity – no harm to host

c. Cellular Target Sites of Antibiotics – 4 - Important

cell wall synthesis

  • prevent synthesis of new peptidoglycan
  • works only on growing cells
  • selective how?
  • least toxic

Exs.penicillin, methacilllin, cephalosporin

plasma membrane integrity and/or function

  • alter permeability
  • selective how?

Eukarya –

Bacteria –

Exs.polymyxin B, nystatin

nucleic acid synthesis

  • interfere with enzymes gyrase and polymerase
  • selective how?

Ex. rifampin, quinolones like ciprofloxacin

protein synthesis

  • target 70S ribosome
  • greater toxicity – why?

Exs.tetracycline, chloramphenicol, erythromycin

3. Antibiotic Resistance

a. history

1940s -

1969 -

1980s -

1980s -

1990s and on -

b. how did we get in to this predicament?

amount manufactured -

number of prescriptions -

Antibiotic resistance can develop extremely rapidly - even in a patient receiving treatment in a hospital

Notes from clinical case:

Assignment

Read Chapter 7 and pages 554-558

Review 1, 2, 5, 7- 9

MC 1,9,10

CT 1-3

CA 3

FYI

How do you know if an antibiotic is going to work?

You should feel better within 24-48 hours of starting antibiotic treatment.

If you do not feel better:

  1. You have a viral infection and not a bacterial infection OR
  2. You have a bacterial infection but the antibiotic prescribed is not effective against the bacteria you have OR
  3. You have a bacterial infection but bacteria are resistant to the antibiotic that was prescribed

Then you should contact your doctor and let her/him know that the antibiotic is not working.

What can you do to reduce the likelihood that bacteria will become antibiotic resistant?

  1. Take the correct dosage of your antibiotic and always take the entire prescription. If you don’t, infectious bacteria that have not yet been killed off may survive, reproduce, and cause a more severe relapse, one that may not be treatable.
  2. Ask the doctor to tailor the prescription to fit your schedule so that you don’t miss a dose.
  3. Ask if you can take the antibiotic for the shortest amount of time possible.
  4. Ask the doctor to prescribe a narrow-spectrum antibiotic, one that works specifically against a few strains of bacteria, rather than a broad-spectrum antibiotic that targets more strains. The more bacteria exposed to antibiotics, the greater the chance that a strain will develop antibiotic resistance.
  5. Use the antibiotic only for the prescribed illness. Never take antibiotics that you have left over from a previous illness. Never take antibiotics that were prescribed for someone else (not even your mom).