Micro final

• Microbes


  A virus or living organism that requires a microscope to be seen
• Microbes


  • Can be unicellular or multicellular
  • Every microbe contains a genome and has the capacity to reproduce
  • Ubiquitous: present nearly everywhere
• Pathogens are less than 1% of the total number of microbial species on the planet
• Normal microflora


  Commensal microorganisms that compete with harmful organisms for nutrients and space, preventing colonization by pathogenic organisms
• Three domains of life


  • Bacteria (prokaryotic)
  • Archaea (prokaryotic)
  • Eukaryota (eukaryotic)
• Bacteria and archaea have evolved independently of one another, even though they are both prokaryotic
• Nucleoid region


  Contains condensed DNA throughout cytoplasm and is not delineated by a membrane, compared to a nucleus which is well-defined and delimited by a nuclear membrane
• Transcription and translation in prokaryotes


  Occur simultaneously and on the same mRNA for cytoplasmic proteins, allowing for short generation time
• SRP (signal recognition particle)


  Binds to growing peptide and brings it to the membrane, where they are translated
• DNA as a molecular clock


  The changes in DNA overtime can determine evolutionary relationships
• Genes with high similarity = short evolutionary distance, genes with less similarity = more time to diverge
• Endosymbiont hypothesis


  Eukaryotic organelles evolved from prokaryotic microbes through endosymbiosis
• Vertical gene transfer


  Transmission of an entire genome from parent to offspring, genes passed to next generation (hereditary)

  
• Horizontal gene transfer


  Acquisition of a piece of DNA from another cell, passed to same generation (not hereditary), passed to same or different species

  
• Horizontal gene transfer creates fuzzy boundaries between microbial species because it obscures monophyletic distinctions
• Pangenome


  Whole genome, including core genes (information genes found in all species), accessory genes (dispensable and unique, novel to HGT)
• rRNA sequences


  Helpful for prokaryotic taxonomy because it is highly conserved, not helpful because HGT creates a "mosaic" of DNA that is sequenced from multiple species
• Metagenomics


  Study of total genomic DNA obtained directly from environmental sample, such as soil, sea water, etc., without culturing microbes in the laboratory, used for unculturable organisms
• Polyphasic approach


  Genotype, chemotype, phenotype to determine classification, used for culturable organisms
• Current definition of "microbial species"

  95% similarity of DNA sequence and shared ecotype (habitat or metabolism)
• 16sRNA sequence


  "Molecular clock", highly conserved because function of ribosomes is confined
• Vaccines


  Medical tool used to promote immunity against infection by specific microbes
• Types of vaccines


  • Live-attenuated
  • Inactivated
  • Toxoid
  • Subunit
  • Nucleic acid
• Live-attenuated vaccine


  Contain living virus/bacteria that is weakened (so it does not cause serious disease), work very well because they are the closest thing to natural infection, bind and enter cell but cannot replicate because it is weakened
• Inactivated vaccine


  Made with a killed/inactivated infectious microbe, less effective in eliciting immunity, require multiple doses to build up immunity, cannot bind and enter cell
• Toxoid vaccine


  Weakened bacterial toxoids rather than whole microbe, B-cells produce antibodies that recognize true toxin and can hamper its action
• Subunit vaccine


  Contain only a part of a microbe, usually the antigen, not great because they take a long time to make, and spike proteins are frequently mutating
• Nucleic acid vaccine


  Introduce stabilized mRNA to encode viral antigen protein via lipid droplet, allow for fast turnaround for spike protein mutants
• Herd immunity


  Protection of people who are not immune to a contagious disease by having a certain percentage of the population vaccinated, the immune cannot spread the disease, slowing or stopping the chain of transmission, generally 2/3 of population must be vaccinated to protect the vulnerable population, more contagious disease= more % of population must be vaccinated
• Antimicrobials


  Medicines that kill or stop the growth of microbes
• Antibiotics


  Antimicrobial medicines that specifically work to inhibit bacterial infections
• Koch's postulates


  1. Microbe is found in all cases of the disease but absent from healthy

  2. Microbe is isolated from diseased and grown in pure culture

  3. Microbe is introduced to healthy host, disease occurs

  4. Same strain of microbe is obtained from newly diseased host

  Used for determining if there is causation between microbe and disease, fail when patient is asymptomatic, can't grow pure culture, no animal model
• Components of bacterial cell envelope


  • Inner cell membrane
  • Teichoic acid
  • Capsule
  • Periplasmic space
  • Outer membrane
  • Lipopolysaccharide (LPS)
  • Porins
  • Arabinogalactan
  • Mycolic acid
  • Lipoid capsule
  • No peptidoglycan / cell wall

  
• Teichoic acid


  Traps cations, acts as bacteriophage receptors
• Capsule


  Allows bacteria to evade host immune system, allows bacteria to stick to other bacteria or host cells (adhesion)
• Periplasmic space


  Space between inner and outer cell membranes, contains degradative enzymes and chemoreceptors

  
• Outer membrane


  Connected to peptidoglycan layer by lipoproteins, contains LPS, porins, surface proteins

  
• Lipopolysaccharide (LPS)


  Core polysaccharides provide structure and stability, O-polysaccharide acts as antigen to distinguish between gram negative species, Lipid A is endotoxin released when cell walls of dead bacteria break down
• Porins


  Channels permitting passage of nucleotides, disaccharides, amino acids
• Arabinogalactan


  Found above periplasmic space