microbiology section 1

• Characteristics of prokaryotic cells:

  • Lack a nucleus surrounded by a complex nuclear membrane
  • Generally have a single, circular chromosome located in a nucleoid
  • Domains: Archaea and bacteria
  • Lack membrane-bound organelles
  • Not multicellular
  • Have a cell wall (envelopes cell membrane)
  • DNA loosely contained in the nucleoid region
• Characteristics of eukaryotic cells:

  • Have a nucleus surrounded by a complex nuclear membrane that contains multiple, rod-shaped chromosomes
  • Domain: eukarya
  • All plant cells and animal cells are eukaryotic
  • Larger than prokaryotic
• Prokaryotic shapes and cell arrangements:

  • Round coccus shape, bacillus rod shape, vibrio curved rod shape, coccobacillus short rod shape, spirillum spiral shape, spirochete long loose helical spiral shape
  • Coccus (single coccus), diplococcus (pair of two cocci), tetrad (grouping of four cells arranged in a square), streptococcus (chain of cocci), staphylococcus (cluster of cocci), bacillus (single rod), streptobacillus (chain of rods)
• Eukaryotic External Structure:

  • Some eukaryotic cells have cell walls providing structural stability, protection, and resistance to environmental stresses
  • Cell morphology includes various shapes like spheroid, ovoid, cuboidal, flat, lenticular, fusiform, discoidal, crescent, ring stellate, and polygonal
  • Cell wall materials: cellulose (fungi and plants), biogenic silica, calcium carbonate, agar, carrageenan (protists and algae), chitin (Fungi)
• Eukaryotic: Extracellular Matrix:

  • Cells of animals and some protozoans do not have cell walls
  • Secrete a sticky mass of carbohydrates and proteins into the spaces between adjacent cells
  • Integrin proteins interact with transmembrane proteins in the plasma membranes of eukaryotic cells lacking cell walls
  • Host cell’s extracellular matrix is where microbial pathogens attach to establish infection
• Endospores v. vegetative cells:

  • Vegetative cells are sensitive to extreme temperatures and radiation, gram-positive, with normal water content and enzymatic activity, capable of active growth and metabolism
  • Endospores are resistant to extreme conditions, dehydrated, dormant with no metabolic activity
• Gram positive v. Gram Negative:

  • Gram positive have a thick cell wall, stains purple (Ex: streptococcus)
  • Gram negative have a thin cell wall, stains red/pink, have an outer membrane containing LPS (endotoxin) (Ex: E. Coli)
• Viruses:

  • Acellular, composed of nucleic acid (RNA or DNA) and a protein coat (capsid)
  • Capsid shape varies, can be naked or enveloped
• Fungi:

  • Act as decomposers in the environment
  • Yeast (unicellular) and molds/mushrooms (multicellular)
  • Major sources of antibiotics (Ex: Penicillin)
  • Fungal cell walls made of chitin and ergosterols
• Protists:

  • Unicellular eukaryotic parasites (Ex: malaria, Giardia)
  • Algae are photosynthetic, can be unicellular or multicellular
  • Protozoa are nonphotosynthetic, motile, and unicellular
• Parasitic Helminths:

  • Two major types: Roundworms (nematoda) and flatworms (platyhelminthes), also multicellular
  • Roundworms examples: Ascaris lumbricoides, pinworm (Enterobius vermicularis), Toxocara canis, T. cati
  • Flatworms (flukes) examples: Schistosoma mansoni, S. haematobium, S. japonicum, Dracunculiasis (guinea worm disease)
• Benefits of nonpathogenic microorganisms:

  • Bacteria and archaea are unicellular prokaryotic organisms
  • Prokaryotes thrive on or within the human body, necessary for soil formation and stabilization
  • Prokaryotes capture and recycle elements like carbon and nitrogen
  • Some bacteria degrade toxic chemicals in water and soil
• Genes encoding degradatory enzymes for aromatic compounds found in oil are commonly found on plasmids
• Alcanivorax borkumensis produces surfactants that solubilize hydrophobic molecules in oil, making them more accessible to other microbes for degradation
• Gene therapy attempts to correct genetic abnormalities by introducing a nonmutated, functional gene into the patient's genome
• Nonmutated gene encodes a functional protein that the patient would otherwise be unable to produce
• Gene therapies have proven relatively ineffective, except for treatments for cystic fibrosis and adenosine deaminase deficiency
• Risks of gene therapy include triggering an unanticipated inflammatory response, infecting non-targeted cells, the modified virus causing disease, and unintentionally inactivating important genes
• Primary pathogens can cause disease regardless of the host's defenses, while opportunistic pathogens require compromised host defenses to cause disease
• Bacillus anthracis is a highly virulent pathogen responsible for anthrax
• ID50 is the number of pathogen cells or virions required to cause active infection in 50% of inoculated animals
• ID50 is the number of pathogenic cells, virions, or amount of toxin required to kill 50% of infected animals
• Adhesins are proteins or glycoproteins on the surface of pathogens that attach to receptors on host cells
• Bacteria evade phagocytosis by producing capsules, altering their surface, and using antigenic variation
• Viruses use adhesins to attach to host cells and rely on antigenic variation to avoid host immune defenses
• Fungal virulence factors include adhesins, proteases, and mycotoxins
• Protozoan parasites have unique features for attaching to host cells, such as adhesive discs and antigenic variation
• Helminths use proteases to penetrate intact skin and express glycans on their external surface to evade the immune system
• bacterial cells have an outer membrane, which contains lipopolysaccharide (LPS)
• peptidoglycan consists of glycan chains that are cross-linked by short polypeptides
• exoenzymes 


  Some pathogens produce extracellular enzymes,that enable them to invade host cells and deeper tissues
•  Many pathogens produce phospholipases that act to degrade cell membranes and cause lysis of target cells. 
• Bacterial pathogens also produce various protein-digesting enzymes, or proteases, which can be used to digest other proteins
• gram-negative bacterial pathogens release endotoxin either when the cell dies, resulting in the disintegration of the membrane, or when the bacterium undergoes binary fission
• The lipopolysaccharide (LPS) found on the outer membrane of gram-negative bacteria is called endotoxin 
•  exotoxins are protein molecules that are produced by a wide variety of living pathogenic bacteria.They cause damage to cells dependent upon receptor-mediated targeting of cells and specific mechanisms of action of the host
• biofilms are not random collections of microorganisms; rather, they are highly structured communities that provide a selective advantage to their constituent microorganisms. Ex microbial mats that grow in water
•  brightfield microscope,


  most commonly used type of microscope, is a compound microscope with two or more lenses that produce a dark image on a bright background
• electron microscope (EM),


  uses short-wavelength electron beams rather than light to increase magnification and resolution
• transmission electron microscope (TEM


   uses an electron beam from above the specimen that is focused using a magnetic lens .projected through the specimen onto a detector. Electrons pass through the specimen, and then the detector captures the image