Summer 2008 Workshop in Biology and Multimedia for High School Teachers.

• Summer 2008 Workshop

• in Biology and Multimedia

• for High School Teachers

Bacterial vs. Viral InfectionsWhy don’t antibiotics work for viral infections?

http://www.microbelibrary.org/microbelibrary/files/ccImages/Articleimages/simonson/Images/Streptococcus%20sobrinus%20fig1.jpgMicrobeLibrary.org; © Jean-Yves Sgro, University of Wisconsin

Polio Virus Streptococcus

Life Sciences-HHMI Outreach. Copyright 2008 President and Fellows of Harvard College.

Bacterial Infections Viral Infections

Can you think of some illnesses caused by viruses or bacteria?

• 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


Sample Bacterial Illness: 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)

en.wikipedia.org/wiki/Strep_throat

• symptoms: sudden, severe sore throat, fever over 101°F, swollen tonsils and lymph nodes, white or yellow spots on theback of a bright red throat• transmission usually by air-born bacteria

• incubation period prior to symptoms 2-5 days


http://www.microbelibrary.org/microbelibrary/files/ccImages/Articleimages/simonson/Images/Streptococcus%20sobrinus%20fig1.jpg

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


http://www.microbelibrary.org/microbelibrary/files/ccImages/Articleimages/simonson/Images/Streptococcus%20sobrinus%20fig1.jpg

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)


http://en.wikipedia.org/wiki/Image:Rhinovirus.PNG

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

• basic biosynthetic pathways of bacteria and viruses


Structure of a Bacterial Cell

http://en.wikipedia.org/wiki/Image:Average_prokaryote_cell-_en.svg

Cell Wall-maintains cell structure

-composed of peptidoglycan, a polymer of sugars and amino acids

Plasma Membrane-phospholipid bilayer surrounding cell-contains proteins that play a role in transport of ions, nutrients, and wastes

Flagella-tail-like structure used for locomotion


Structure of a Bacterial Cell

Nucleoid-region DNA is found in prokaryotesDNA-single double-stranded circular chromosome-no histone proteinsPlasmid-small circular chromosome-may carry an antibiotic resistance gene

Ribosomes-site of protein synthesis (translation)



virulence factors: molecules produced by a pathogen that aid in its survival in a host

Some Features of an Infectious Bacteria

• capsule: surrounds bacterial cell wall; protects bacteria from phagocytosis

• enzymes: break down matrix between cells allowing bacteria to spread throughout tissues

• pili: allows bacteria to attach to and invade other cells despite mucous and cell-turnover

Toxins• exotoxins: cause lysis of specific host cells

• enterotoxins: cause secretion of fluid into the small intestine leading to vomiting and diarrhea• endotoxins: cell-bound lipopolysaccharides; causes fever and inflammation



Bacterial Transcription and Translation

- occur independent of host cell• transcription occurs using a single RNA polymerase• transcription occurs in bacteria independent of a host cell• translation occurs using a bacterial ribosome consisting of a large and small subunit


Bacterial Reproduction-can occur independent of host cell

http://en.wikipedia.org/wiki/Image:Binary_fission.png

-bacterial chromosome replicates

-cell growth occurs (includes cell wall synthesis)

-cell elongates (includes cell wall synthesis) and the two chromosomes segregate

- ring forms of FtsZ fibers and closes dividing the cytoplasm in two


Properties of Viruses

Host Cell

Adapted from: http://en.wikipedia.org/wiki/Image:Virus_Replication.svg#file

Basic Structure• single stranded OR double stranded RNA or DNA • protein shell capsid• some have a lipid bilayer with embedded proteins

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Nucleic acid

Protein CapsidLipid Membrane

http://microbewiki.kenyon.edu/index.php/Image:8430_lores.jpg

Influenza


Properties of Viruses

QuickTime™ and aTIFF (Uncompressed) decompressor

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Virion

Host Cell

Host Cell Nucleus

Host Cell Ribosomes

Host cell

Golgi

Adapted from: http://en.wikipedia.org/wiki/Image:Virus_Replication.svg#file

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


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

http://en.wikipedia.org/wiki/Image:Staphylococcus_aureus_%28AB_Test%29.jpg

Why might microbes produce antibiotics in nature?

• to prevent the growth of microbe competitors

Staphyloccocus aureus

antibiotic


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.http://en.wikipedia.org/wiki/Image:Average_prokaryote_cell-_en.svg

Antibiotics: Mechanisms of ActionInhibition 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. http://en.wikipedia.org/wiki/Image:Average_prokaryote_cell-_en.svg

Summer 2008 Workshop in Biology and Multimedia for High School Teachers.

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