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• Summer 2008 Workshop • in Biology and Multimedia • for High School Teachers Bacterial vs. Viral Infections Why don’t antibiotics work for viral infections? MicrobeLibrary.org; © Jean-Yves Sgro, University of Wisconsin Polio Virus http://www.microbelibrary.org/microbelibrary/files/ccImages/Articleimages/simonson/Images/Streptococcus%20sobrinus%20fig1.jpg Streptococcus Life Sciences-HHMI Outreach. Copyright 2008 President and Fellows of Harvard College. Can you think of some illnesses caused by viruses or bacteria? Bacterial Infections Viral Infections • strep throat • the flu • gastroenteritis • colds • cholera • AIDS • tuberculosis • hepatitis • food poisoning • chicken pox • botulism • gastroenteritis • gangrene • measles • necrotizing fasciitis • mumps • boils, abscesses • E. Bola • pneumonia • pneumonia • acne • West Nile • meningitis • cervical cancer • ulcers Life Sciences-HHMI Outreach. Copyright 2008 President and Fellows of Harvard College. Sample Bacterial Illness: Strep Throat en.wikipedia.org/wiki/Strep_throat http://www.microbelibrary.org/microbelibrary/files/ccImages/Articleimages/simonson/Images/Streptococcus%20sobrinus%20fig1.jpg • 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 • transmission usually by air-born bacteria • incubation period prior to symptoms 2-5 days Life Sciences-HHMI Outreach. Copyright 2008 President and Fellows of Harvard Sample Bacterial Illness: Strep Throat en.wikipedia.org/wiki/Strep_throat http://www.microbelibrary.org/microbelibrary/files/ccImages/Articleimages/simonson/Images/Streptococcus%20sobrinus%20fig1.jpg • diagnosed with a throat culture and detection of strepspecific molecules • treated with antibiotics, usually penicillin for 10 days Life Sciences-HHMI Outreach. Copyright 2008 President and Fellows of Harvard Viral Illness: The Common Cold http://en.wikipedia.org/wiki/Image:Rhinovirus.PNG • 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 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 Life Sciences-HHMI Outreach. Copyright 2008 President and Fellows of Harvard Structure of a Bacterial Cell Cell Wall -maintains cell structure -composed of peptidoglycan, a polymer of sugars and amino acids Flagella -tail-like structure used for locomotion http://en.wikipedia.org/wiki/Image:Average_prokaryote_cell-_en.svg Plasma Membrane -phospholipid bilayer surrounding cell -contains proteins that play a role in transport of ions, nutrients, and wastes Life Sciences-HHMI Outreach. Copyright 2008 President and Fellows of Harvard Structure of a Bacterial Cell Nucleoid -region DNA is found in prokaryotes DNA -single double-stranded circular chromosome -no histone proteins Plasmid -small circular chromosome -may carry an antibiotic resistance gene http://en.wikipedia.org/wiki/Image:Average_prokaryote_cell-_en.svg Ribosomes -site of protein synthesis (translation) Life Sciences-HHMI Outreach. Copyright 2008 President and Fellows of Harvard Some Features of an Infectious Bacteria virulence factors: molecules produced by a pathogen that aid in its survival in a host • capsule: surrounds bacterial cell wall; protects bacteria from phagocytosis • pili: allows bacteria to attach to and invade other cells despite mucous and cellturnover http://en.wikipedia.org/wiki/Image:Average_prokaryote_cell-_en.svg • enzymes: break down matrix between cells allowing bacteria to spread throughout tissues 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 Life Sciences-HHMI Outreach. Copyright 2008 President and Fellows of Harvard 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 Life Sciences-HHMI Outreach. Copyright 2008 President and Fellows of Harvard Bacterial Reproduction -can occur independent of host cell -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 http://en.wikipedia.org/wiki/Image:Binary_fission.png Life Sciences-HHMI Outreach. Copyright 2008 President and Fellows of Harvard Properties of Viruses Basic Structure • single stranded OR double stranded RNA or DNA • protein shell capsid • some have a lipid bilayer with embedded proteins Life Sciences-HHMI Outreach. Copyright 2008 President and Fellows of Harvard College. Nucleic acid Protein Capsid Lipid Membrane Adapted from: http://en.wikipedia.org/wiki/Image:Virus_Replication.svg#file Influenza http://microbewiki.kenyon.edu/index.php/Image:8430_lores.jpg Host Cell Properties of Viruses Virus Life Cycle Virion • virus attaches to host cell • virus enters cell via endocytosis • capsid degraded • host transcribes viral DNA • host ribosomes translate viral RNA Host Cell Nucleus Host Cell Ribosomes QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Host cell Golgi • new viruses assemble Host Cell Adapted from: http://en.wikipedia.org/wiki/Image:Virus_Replication.svg#file Life Sciences-HHMI Outreach. Copyright 2008 President and Fellows of Harvard 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 http://en.wikipedia.org/wiki/Image:Staphylococcus_aureus_%28AB_Test%29.jpg Life Sciences-HHMI Outreach. Copyright 2008 President and Fellows of Harvard College. 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 http://en.wikipedia.org/wiki/Image:Average_prokaryote_cell-_en.svg ife Sciences-HHMI Outreach. Copyright 2008 President and Fellows of Harvard College. Antibiotics: Mechanisms of Action Inhibition of Cell Wall Synthesis -some antibiotics prevent peptidoglycan formation Examples: vancomycin, amoxicillin, ampicillin, penicillin e Sciences-HHMI Outreach. Copyright 2008 President and Fellows of Harvard College. http://en.wikipedia.org/wiki/Image:Average_prokaryote_cell-_en.svg