MCB 3020, Spring 2005

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MCB 3020, Spring 2005 Microbial Growth Control
and Antibiotic Resistance
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Chapter 18 Microbial Growth Control I.
Microbial growth control II. Measuring
antimicrobial activity III. Food
preservation IV. Antimicrobial drugs V.
Antibiotic Resistance
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I. Microbial Growth Control
A. uses B. autoclave C. radiation D. filters E.
chemical agents
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I. Microbial Growth Control
Inhibition limiting microbial growth
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A. Uses
Food preservation Laboratory work Disease
prevention Disease treatment
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B. Autoclave
Machine that uses steam under pressure for
sterilization.
Items are heated to 121C for 10-15 minutes.
kills endospores
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C. Radiation
1. Ultraviolet (220 to 300 nm)
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D. Filters
Used to sterilize heat-sensitive solutions
and gasses
A pore size of 0.22 micron will remove most
bacteria.
Will it remove most viruses?
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E. Chemical Agents
Antimicrobial agents
Chemicals that kill or inhibit the growth of
microorganisms
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Bacteriostatic agents chemicals that inhibit
growth, but do not kill
frequently are inhibitors of protein synthesis
Bacteriolytic agents kill cells by lysis eg.
penicillin
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1. Disinfectants
Chemicals used to kill microbes on inanimate
objects.
Chlorine Phenolic compounds
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2. Antiseptics
Chemicals used to kill microbes on
living tissue.
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II. Measuring antimicrobial activity
A.Tube dilution assay
B. Agar diffusion assay
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A. Tube dilution assay
1. inoculate tubes containing several
concentrations of test compound with test
organism and incubate.
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1
.1
.01
.001
10
MIC
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B. Agar diffusion assay
agar plate
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III. Food preservation
A. Common spoilage organisms
B. Preservation methods
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A. Common food spoilage organisms
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B. Preservation methods
1. Pasteurization
71C, 15 sec., or 63-66C, 30 min
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5. pH control
pickling
fermented foods
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IV. Antimicrobial drugs
A. Selective toxicity
B. Growth factor analogs
C. Antibiotics D. Antivirals and antifungals
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A. Selective toxicity
Toxicity for the pathogen, but not for the host.
Something to think about What is the basis for
selective toxicity?
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B. Growth factor analogs
A substance structurally related to a growth
factor that blocks its use.
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1. Sulfanilamide
Growth factor analog structurally
related to p-aminobenzoic acid (PABA)
Inhibits microbial growth by inhibiting folate
synthesis
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H2N
COOH
H2N
SO2NH2
PABA
sulfanilamide
O
H
C
N
CH2
N
HN
N
N
R
H2N
folate
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Sulfanilamide is nontoxic to humans because we
take up folate from our diet.
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C. Antibiotics
Substances produced by microbes that kill or
inhibit the growth of microbes
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1. inhibitors of cell wall synthesis
penicillin
vancomycin
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Prevents transpeptidation in cell wall
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Erythromycin (macrolide)
macrolide ring
50S ribosomal subunit
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Tetracycline R1H, R2OH, R3CH3, R4H
Broad spectrum Target 30s ribosomal subunit
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Kanamycin (aminoglycoside)
Target 30 s ribosomal subunit
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3. inhibitors of DNA gyrase
naladixic acid
novobiocin
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Antivirals and Antifungals
A. Antivirals
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B. Antifungals
Ergosterol inhibitors
polyenes
azoles
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V. Antibiotic Resistance
A. the problem of resistance B. resistance
mechanisms C. development of resistance D.
enzymes that inactivate antibiotics
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A. The problem of resistance
Examples of drug-resistant bacteria

• Vancomycin-resistant Staphlyococcus aureus
• Penicillin-resistant Streptococcus pneumoniae
• Quinolone-resistant Salmonella enterica

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Why so much resistance?

• Overuse of antibiotics in inpatient and
  outpatient settings.
• Increased use of quinolones, tetracyclines, and
  glycopeptides in agriculture, the poultry
  industry, veterinary practice, and marine
  biology.
• Newer, implantable cardiovascular and orthopedic
  devices that necessitate prophylactic antibiotics.

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B. Resistance mechanisms
lack of target site
impermeability
chemical modification of the antibiotic
pump antibiotic out of cell
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C. Development of resistance
1. Mutation
target site modification
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R-plasmids (resistance plasmids)
Plasmids that carry antibiotic
resistance genes.
Antibiotic resistance genes usually
encode enzymes that inactivate antibiotics
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D. Enzymes that inactivate antibiotics
1. Chloramphenicol acetyltransferase
acetylates chloramphenicol
2. beta-lactamase
cleaves the beta-lactam ring
3. Tetracycline pump
pumps tetracycline out of the cell
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Interactions of antibiotics with alcohol in humans

• Antibiotics that are affected by alcohol are
  chloramphenicol, cephalosporins, metronidazole,
  and others.
• These produce "disulfiram-like" reactions.

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Disulfiram-like reactions

• Disulfiram is a drug to treat alcoholism.
• Some antibiotics cause a reaction similar to
  disulfiram reactions.
• Inactivates the enzyme aldehyde dehydrogenase.
• Causing accumulation of acetaldehyde in blood.
• Symptoms are flushed face, severe headaches,
  chest pains, shortness of breath, vomiting, and
  sweating.

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Alcohol dehydrogenase
Aldehyde dehydrogenase
X
Disulfiram
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Study objectives 1. Know how the following are
used to control microbial growth autoclaves,
radiation, filters, disinfectants,
antiseptics. Contrast cidal agents,
bacteriostatic agents,and lytic agents. Know the
examples presented in class. 2. Compare and
contrast the tube dilution assay and the agar
diffusion assay. Understand how each is
used to measure antimicrobial activity of
chemicals. 3. What is MIC? How does it
correlate with antimicrobial activity of an
inhibitor? 4. Memorize the common food spoilage
organisms covered in class. 5. Know what
pasteurization is and what types of foods are
pasteurized. 6. Memorize the food preservation
methods and examples presented in class. 7.
What is selective toxicity? Understand the basis
of selective toxicity of growth factor
analogs, antibiotics, azidothymidine, interferon,
and antiviral agents. 8. What is a growth
factor analog? 9. How does sulfanilamide
inhibit the growth of some bacteria? 10. Know the
names and targets of the antibiotics presented in
lecture. 11. Know the following antiviral
agentsrifampin, azidothymidine, interferon.
Azidothymidine inhibits reverse transcriptase.
What viruses are affected this? 12. Know the
names and target of the antifungal agents
(polyenes, azoles). 13. Why is selective toxicity
more difficult to obtain with antivirals and
antifungals?
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Study objectives 14. Give 3 examples of
antibiotic-resistant bacteria. What are
the major causes of antibiotic resistance? 15.
What are the mechanisms by which bacteria require
antibiotic resistance? What is the role
of R-plasmids in resistance? Understand
how antibiotic-inactivating enzymes work. 16.
Explain why alcohol should not be consumed while
taking some antibiotics. Why do
disulfiram-like antibiotics cause symptoms when
consumed with alcohol?