02.01 Bacteria

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Included In This Lesson



  1. Bacteria- synonomous with the term prokaryote. Bacteria are single-celled organisms that have been around for about 3.8 billion years. It is estimated that there are 1 trillion different bacteria species on Earth as and 99.99% have yet to be discovered.
    1. Bacterial structure-
      1. All Bacterial cells have
        1. Cell membranes- control what enters and leaves cell
        2. Cytoplasm-structure and support
        3. Free-floating Ribosomes- where proteins are made
        4. Free-floating DNA and RNA- store and transmit genetic information
      2. Some Bacterial cells have
        1. Cell walls-for protection. Made with or without peptidoglycan
        2. Flagella- for motility
        3. Cilia- for motility
        4. Pili (pilus)- attachment
    2. Bacterial organization
      1. Rods- a.k.a Bacillus-Rod-shaped or Bacilliform bacteria
        1. Diplobacilli
          1. Single rods ex. Bacillus cereus
          2. Double rods ex. Coxiella burneti
        2. Streptobacilli-Chains of rod shaped bacteria
          1.  ex. Streptobacillus moniliformis
      2. Cocci-single sphere-shaped bacteria
        1. Diplococci- arranged in pairs of cocci
          1. ex. Streptococcus pneumonia
        2. Streptoococci- cocci arranged in chains
          1. ex. Streptococcus pyogenes
        3. Staphlococci- Cocci arraged in clusters like grapes
          1. ex. Staphylococcus aureus
      3. Spiral- curved bacteria
        1. Vibrio- look like a comma
          1. ex. Vibrio cholerae
        2. Spirilla- have rigid spiral structure usually have flaglella
          1. ex.Helicobacter pylori
        3. Spirochetes- have helical shape with flexible body that can move like flagellum
            1. ex. Leptospira interrogans
    3. Staph vs Strep
        1. Things they have in common
          1. Shape- both are Cocci (sphere)
          2. anaerobic
          3. gram-positive
          4. antibiotic-resistant forms exist
          5. pathogenic
        2. How they differ
          1. Their formation-strep divide on one axis to form pairs or chains, staph divide on multiple axes to form clusters
          2. Ability to produce catalase- staph = yes, strep = no
          3. Media for growth- strep needs enriched media, staph does not
          4. Where it is found in humans- Staph on the skin, strep in the respiratory tract
    4. Bacterial Growth-
      1. Steps of binary fission
        1. DNA replicates
        2. Each copy attaches to the cell membrane
        3. Cell pulls apart/divides
      2. Phases of growth
        1. Lag phase-adapting to conditions- not dividing
        2. Log phase- logarithmic or exponential growth phase, cells divide and rate of population doubles (assuming no limits)
        3. Stationary phase- some grow-limiting factor stunts growth.
        4. Death phase- bacteria die due to a lack of resources.
    5. Controlling Microbial growth-
      1. Kill or inhibit bacterial growth by
        1. sterilization with heat
          1. ex. autoclave, boiling, pasteurization
        2. Low temp- refrigerate or freeze to slow microbial growth
        3. Drying- dehydration often kills microbes
        4. Irradiation-destroys DNA
        5. Filtration- physical separation of cells
        6. Chemical treatments-formaldehyde, ozone
        7. Antimicrobial agents- antiseptics, disinfectants (i.e. bleach)
        8. Preservatives
        9. Antibiotics
    6. Bacterial Testing
      1. Stains-used to ID type of bacteria
        1. ex Gram staining. If bacteria stains pink- Gram-negative (has thin peptidoglycan wall)or purple- Gram-positive (has thick peptidoglycan cell wall)
      2. Agars- a jelly-like substance made from red algae and used to grow certain types of bacteria pending nutrient additions.
      3. Broths-different broths for growing certain bacteria that might contain a specific metabolite in order to ID based on metabolic pathways.
      4. Cultures-allows bacteria grow in a broth (Luria broth), stab cultures or on an agar plate (using Petri dishes) usually for diagnostics, identification or research.
      5. Sensitivity- a test done to determine a bacteria’s sensitivity to an antibiotic.


Today we’re going to be talking about Bacteria.

The word bacteria is synonymous with the term prokaryote. These are single-celled organisms that do not have a nucleus. One what to remember this is pro rhymes with no. These are believed to be the oldest forms of life on earth, dating back about 3.8 billion years. There are about 1 trillion varieties on Earth and only about .01% have been discovered.

All bacteria contain a cell membrane, the gate-keeper organelle, cytoplasm for structure and internal support, ribosomes for making protein and free-floating genetic material known as DNA and RNA.

Bacteria are organized by their shape There are 3 main shape types. the first ones listed here are the Rods. Rod shaped bacteria  aka bacillus or bacilliform bacteria are one common form. There are diplobacilli that are either single rods or double rods and streptobacilli that exist as chains of rod shaped bacteria.

The second main shape are the cocci. These are single sphere shaped bacteria. Included in this are the diplococci which are pairs of cocci, streptococci that are arranged in chains of cocci and staphlococci that are cocci arranged in clusters likes grapes.

The third main bacteria shape are spirals. Vibrio are bacteria that are curved like a comma. Spirilla have a rigid spiral structure and usually have flagella. And the spirochetes which have a helical shape whose body moves and flexes like a flagellum.
Two of the most verbalized types of bacteria are the staphs and the streps.  While different they do have some things in common. Both are cocci shaped and are gram positive (Will get to this in a minute). They are both anaerobic meaning they live well without oxygen present. They are spoken of a lot because of their pathogenicity meaning they are disease-causing. and both have evolved strains that have become antibiotic resistant.
These two “popular” bacteria types also have differences. They way they form for example. Strep divide on one axis to form pairs or chains, staph divide on multiple axes to form clusters. Staph can make catalase an enzyme that can break down hydrogen peroxide, strep cannot.  To grow strep you need enriched media, not for staph though. And location, location, location. Staph infects the skin and strep infects the respiratory tract.

Bacteria growth occurs through binary fission which basically means that the Dna copies itself, those copies attach to the membrane and then the cell divides. this happens easy and fast. Initial growth is known as the lag phase, where the bacterial gets acclimated to its new environment. Once asjusted it reaches lag phase where it is dividing exponentially, once it reaches the carrying capacity of its environment it hits the stationary phase and if resouces become limited it hits the death phase.  Of course man has found ways to inhibit or prevent bacterial growth. Changing temp is one way. high heat kills so we can autoclave, sterilize or pasteurize to kill bacteria. Life doesn’t bode well without water, so drying areas will inhibit bacteriaa growth. Gamma rays that pack a punch can penetrate bacteria and kill it. One of the ways we clean our drinking water is by filtering out bacteria. Chemicals such as chlorine and fluorine can kill bacteria. Antiseptics like mouthwash or preservatives in food can inhibit bacterial growth and of course, the ever abused antibiotic can somewhat still kill bacteria.
Bacterial testing helps us identify, trat and research bacterial strains. One way is staining bacterial. Gram staining tells us whether a bacteria has a thin or thick cell wall. Different Agars and broth are used to grow and ID certain types of bacteria. bacterial cultures are grown for food, diagnostics, and research. And sensitivity testing on bacteria can be done to see how effective an antibiotic may be on a particular strain.

So in review, bacteria are single-celled prokaryotes and have no nucleus. They come in 3 main shapes bacillus, cocci and spirals. Bacteria grow quickly via binary fission and do through different growth phases in a lifetime. There are many different ways to kill or inhibit bacterial growth as well as many ways to grow bacteria to test, identify and research.

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