lecture 4 Antibiotics, Reid lecture and midterm practice questions.docx

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Microbiology and Immunology
Course Code
Microbiology and Immunology 2500A/B
Kelly Summers

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Lec 4 AntibioticsAntimicrobial Agentsdoesnt have to be antibioticsDisinfectants antimicrobial agents that are applied to inanimate objects floors tablesAntiseptics sufficiently nontoxic to be applied to living tissues hand sanitizersAntibiotics produced by bacteriafungi that are used by humans topically internallyAlexander FlemingDiscovered penicillin in 1928Produced from Penicillium notatum bacteriaFound colonies of staphylococci couldnt grow around a contaminating moldIt was extremely important in WWII treating injured soldiersAntibioticsRepresent our most effective therapeutic against bacterial infectionsEnables cancer chemotherapy organ transplantation all invasive surgeries Decreased the mortality rate Without antibiotics we would be susceptible to diseases infections Community pneumonia in contacts with community getting the pneumonia outside the health care settingNosocomial in health carehospital settingBacterial endocarditis infection in heart valves You would die from it before the invention of antibioticsBut a lot of people are worried that we are entering the post antibiotic era when everything becomes resistant to many antibiotics 2 major problems of AntibioticsDiminished interest from pharmaceutical companies to develop new antibiotics they bring new drugs takes a lot of time testing and money its extremely expensive to develop them and then bacteria become resistant so the developed antibiotics become uselessBacterial resistance to antibiotics always happensOrganisms spread anywhere they want because of global trafficplanes going to everywhere everyday How do antibiotics workEither kill bacteria or stop them from growingFor bacteriostatic antibiotics the immune system must take over to kill the bacteriaThere is a classic exponential phase graphtetracyclin stop bacteria from growingpenicillin kill bacteria Measuring Antibiotic ActivityMinimum inhibitory concentration MIC culture tubes with varying conc of agent Check for visible growth MIC lowest conc of agent that inhibits growth As the concentration of antibiotic increases the culture tubes become clearer There will be more bacteria in the beginning and it becomes less and less with the expose to antibiotics The lower the number the better the antibioticsBut these tests eventually make bacteria resistant to the antibioticsWhat do antibiotics targetThey target essential bacterial components things that bacteria need and it gives antibiotics specificitycell wall synthesis of bacteria protein synthesis DNARNA synthesis Folate synthesis Cell membrane alterationTargets are not present in eukaryotic cells Lactam AntibioticsPenicillin prototype Contain a lactam ringInhibit cell wall synthesis in bacteriaThe lactams bind the bacterial penicillin binding proteins PBPstranspeptidases result is no peptide crosslinksweak cell wallcell deathBut some bacteria can produce a lactamase an enzyme that destroys the ring and thus the antibiotic MethicillinContains a lactam ringChemically modified penicillinCant be cleaved by lactamasesSome bacteria can produce a different penicillinbinding protein PBP2a encoded by mecPBP2a doesnt bind methicillin or other lactams VancomycinInhibits cell wall synthesis if Gram positive bacteria doesnt work for gram negatives because it cant get through the cell membrane of the gram negativesglycopeptide antibioticLast resortvancomycin binds the peptide linkage at terminal DAlaDAla residues and inhibits transpeptidationResistance genes change these to DAlaDLac and vancomycin can no longer bindResistance encoded by the van genes Bacteria are very smartProtein synthesis inhibitorsBacteria contain 70s ribosomesEukaryotes contain 80s ribosomesMany antibiotics target bacterial ribosomes and block translation 50s inhibitors Erythromycin Chloramphenicol and 30s inhibitorsTetracycline Kanamycinif you can block the bacterias ability to make proteins they cant survivegrow They need to make proteins Folic Acid synthesis inhibitorsTrimethoprim and SulfonamidesFolic acid is a vitamin B9 for humansBacteria need this for thymidine synthesisBacteria cannot absorb folic acid so they must synthesize their own
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