细菌对抗生素耐药的演变（英文ppt）humans nature the causes and consequences

Evolution of Resistance to Antibiotics in Bacteria Presented by lJana Boozer lKatelin Erwin lAshley Gregory lSara Thompson HUMANS in other words, the bacteria are “resistant“ and continue to multiply in the presence of therapeutic levels of an antibiotic. Why do bacteria become resistant to antibiotics? lWhen antibiotics are used to kill the bacterial microorganisms, a few microorganisms are able to still survive, because microbes are always mutating, eventually leading to a mutation protecting itself against the antibiotic lAntibiotics that are used correctly overwhelm the harmful bacteria lOveruse of antibiotics or unnecessary use creates a selective environment lResistant bacteria has better fitness in this context lResistant strains survive and multiply. lAfter reproducing, the resistant bacteria move to another host. How humans have created the upsurge of bacterial diseases: International travel Inadequate sanitation “antibiotic paradox” How do bacteria become resistant? Bacteria can gain resistance over time through: Acquired resistance Vertical gene transfer Horizontal gene transfer Acquired Resistance lMechanisms are developed by bacteria in order to acquire resistance lEither modification of existing genetic material or acquisition of new genetic material from another source. lDevelopment of resistance through spontaneous mutation is called primary resistance. Errors in DNA synthesis during replication Occasional failures in the DNA repair systems Vertical Gene Transfer lResistant genes are developed lGenes directly transferred to progeny during DNA replication lThis is directly related to Darwins theory of evolution. Horizontal Gene Transfer (HGT) l“lateral gene transfer” lGenetic material is contained in small packets of DNA. lPackets can be transferred between individual bacteria of the same species or different species. 3 Mechanisms of HGT lTransduction lTransformation lPenicillin-resistant gonorrhea lConjugation lIn 1968, 12,500 people in Guatemala died of Shigella diarrhea epidemic. Spread of Resistant Bacteria lRapid growth of bacteria Small size Simple internal structure lMultiply rapidly New generation in as little as 20 minutes Strategies to delay widespread antibiotic resistance: lDont use antibiotics to treat viruses or viral infections. lAvoid mild doses of antibiotics over a long period of time. lWhen treating a bacterial infection with antibiotics, take all the pills. lUse a combination of drugs to treat bacterial infections lReduce/eliminate “preventive” use of antibiotics on livestock and crops. Evolutionary theory: lGiven time, heredity, and variation, any living organism will evolve when a selective pressure is introduced Benefit/Cost lBenefit In presence of antibiotics, being resistant benefits bacteria. lCost Resistant genotypes are less fit than sensitive counterparts in the absence of antibiotics Can bacteria lose their antibiotic resistance? lAntibiotic resistance traits can be lost Occurs more slowly Selective pressure is removed lBacterial population can potentially revert to a population of bacteria that responds to antibiotics. lWith more research, education of the public, and well thought out regulations, the problems can be solved. lSeveral strategies are currently used to find new antibacterial compounds and new strategies are in development and trial. Sources /evosite/relevance/IA1antibiotic s.shtml /Fdac/features/795_antibio.html /wgbh/evolution/library/10/4/l_