1. Why don’t antibiotics work for viral infections?
Bacterial vs. Viral Infections
Why don’t antibiotics work for viral infections?
MicrobeLibrary.org; © Jean-Yves Sgro, University of Wisconsin
Polio Virus
Streptococcus
Life Sciences-HHMI Outreach. Copyright 2008 President and Fellows of Harvard College.

2. Bacterial Infections Viral Infections
Can you think of some illnesses caused by viruses or bacteria?
Bacterial Infections Viral Infections
strep throat
gastroenteritis
cholera
tuberculosis
food poisoning
botulism
gangrene
necrotizing fasciitis
boils, abscesses
pneumonia
acne
meningitis
ulcers
the flu
colds
AIDS
hepatitis
chicken pox
gastroenteritis
measles
mumps
E. Bola
pneumonia
West Nile
cervical cancer
Life Sciences-HHMI Outreach. Copyright 2008 President and Fellows of Harvard College.

3. Sample Bacterial Illness: Strep Throat
en.wikipedia.org/wiki/Strep_throat
infectious agent: Streptococcus pyogenes
- spherical bacteria usually found in pairs or chains
most sore throats are actually caused by viruses and are NOT considered strep throat (~15-35% are strep throat)
symptoms: sudden, severe sore throat, fever over 101°F,
swollen tonsils and lymph nodes, white or yellow spots on the
back of a bright red throat
Life Sciences-HHMI Outreach. Copyright 2008 President and Fellows of Harvard College.

4. Sample Bacterial Illness: Strep Throat
en.wikipedia.org/wiki/Strep_throat
diagnosed with a throat culture and detection of strep-specific molecules
treated with antibiotics, usually penicillin for 10 days
Life Sciences-HHMI Outreach. Copyright 2008 President and Fellows of Harvard College.

5. Viral Illness: The Common Cold
symptoms: sore throat, runny nose, nasal congestion, cough
prevalance: 3 colds/ person/ year
incubation period 2-5 days
no cure for the common cold (or the flu)
Life Sciences-HHMI Outreach. Copyright 2008 President and Fellows of Harvard College.

6. basic structural properties of bacteria and viruses
Should you ask for an antibiotic when you have a cold or the flu?
To understand why antibiotics DO NOT work for viruses, you should understand:
how antibiotics work
basic structural properties of bacteria and viruses
Life Sciences-HHMI Outreach. Copyright 2008 President and Fellows of Harvard College.

7. Structure of a Bacterial Cell
Cell Wall
-for protection and giving structure to the cell
Ribosomes
-site of protein synthesis (translation)
Life Sciences-HHMI Outreach. Copyright 2008 President and Fellows of Harvard College.

8. Properties of Viruses Basic Structure
single stranded OR double stranded RNA or DNA
protein shell capsid
some have a lipid bilayer with embedded proteins
Adapted from:
Host Cell
Influenza
Life Sciences-HHMI Outreach. Copyright 2008 President and Fellows of Harvard College.

9. Properties of Viruses Virus Life Cycle virus attaches to host cell
virus enters cell via endocytosis
capsid degraded
host transcribes viral DNA
host ribosomes translate viral RNA
new viruses assemble
Host Cell
Adapted from:
Life Sciences-HHMI Outreach. Copyright 2008 President and Fellows of Harvard College.

10. Antibiotic Treatment of Bacterial Infections
antibiotics kill bacteria or prevent bacteria from dividing
antibiotics are produced naturally by bacteria and fungi
antibiotics are mass produced by growing huge cultures of the source microbe
Why might microbes produce antibiotics in nature?
to prevent the growth of microbe competitors
Staphyloccocus aureus
antibiotic
Life Sciences-HHMI Outreach. Copyright 2008 President and Fellows of Harvard College.

11. Antibiotics: Mechanisms of Action
Inhibition of Bacterial Protein Synthesis
- some antibiotics bind to the large or small subunit of the bacterial ribosome
Examples: neomycin, streptomycin, azithromycin, erythromycin, tetracycline
Life Sciences-HHMI Outreach. Copyright 2008 President and Fellows of Harvard College.

12. Antibiotics: Mechanisms of Action
Inhibition of Cell Wall Synthesis
-some antibiotics prevent peptidoglycan formation
Examples: vancomycin, amoxicillin, ampicillin, penicillin
Life Sciences-HHMI Outreach. Copyright 2008 President and Fellows of Harvard College.