Questions For Exercise 1

 

 

 1.     What is meant by the "ubiquity" of microorganisms?

           Microbes have global distribution and some are found in practically all

         environments.

 

 2.     What two precautions are necessary in lab because of the ubiquity of

         microbes? using aseptic technique in all transfers and minimizing exposure of

          cultures to prevent contamination

 

 3.     Aseptic technique is used to prevent  infection       and  contamination.

 

 4.     What are pathogens? microbes that cause disease

 

 5.     List two benefits derived from the microbes that live within and upon our

         bodies. prevent colonization by pathogens & produce vitamins we absorb and use

 

 6.     How are bacterial colonies formed?

         by division of an isolated bacterium & continued division of cell produced

 

 7.     How can different species of bacteria be distinguished by examining their

         colonies?  by color, shape and texture of colonies                                                           

 8.     How can growths of molds be distinguished from bacterial colonies?

           produce wooly growths called mycelia rather than solid colonies

 

 9.     Is the amount of growth on the agar plate an exact representation of the

         microbes present in the environment sampled?  Explain.

           no, probably some microbes present that are unable to grow on growth medium

          used

 

10.     Which area(s) appeared to contain the greatest number of microbes? 

          Explain why.  table and mouth; with time surfaces accumulate many microbes

          and mouth provides warmth, nutrients and moisture for microbial growth

 

11.     Account for the lack of growth on the cough plate.

            microbes inhaled stick to lining of respiratory passageways and are removed

 

12.     What effect did washing have on the growth obtained from the fingers?

            should have removed some microbes resulting in less growth

 

13.     What types of microbes were isolated from the air in the laboratory?

            bacteria and molds

 

14.          37 ^oC would be the optimum incubation temperature for those microbes

          isolated from the mouth.

 

15.     Why are petri plates inverted during incubation?     

            prevents moisture from accumulating on the top, and water dripping on

           microbial growths spreading them on surface

 

Questions for Exercise 2

 

 Questions For Exercise 3                       

 

 

   1.     Give the scientific term for the three major shapes of bacteria and briefly

         describe each.

 

  a.  bacilli – rods or cylinders

 

  b.  cocci - spherical

 

  c.  spirilla – rigid spirals

 

 2.     List the steps involved in aseptic transfer of bacteria.

         a.  sterilize transfer loop & its filament by passing it through flame until it glows orange

         b.  remove cap from culture tube & pass mouth of tube through flame

         c.  use sterile loop to remove sample from culture in tube

         d.  pass mouth of tube through flame & replace its cap

         e.  use microbes collected on loop

         f.  sterilize transfer loop & filament as before

 

 3.     What is a smear? thin suspension of microbes on microscope slide

 

 4.     Briefly explain how a suspension of bacteria is heat fixed.

   It is passed through the flame slowly three times.

 

 5.     What happens during fixing? Microbes are killed and attached to the slide.

 

 6.     What is the term for the two types of ions that comprise a dye?

           chromogen is ion that imparts color and auxochrome is colorless ion that   

          combines with chromogen to form salt

 7.     Explain the difference between acidic and basic dyes.

           acidic dyes have negative (anionic) chromogens; basic dyes have positive

          (cationic) chromogens

 

 8.     Are basic or acidic dyes used most often in staining microbes?

           basic dyes

 

 9.     What type of chemical reaction occurs during positive staining?

           ionic attraction and bonding

 

 10.         b     dyes are used in the simple stain.

    a. acidic

    b. basic

    c. neutral

 

 11.    List three characteristics of bacteria that can be determined by examining

          a simple stain.

 

           a.  shape

 

   b.  size

 

          c.  arrangement of cells

 

 

12.     Why are the microbes not stained in the negative stain?

            negative chromogens are repelled by negative groups on & in bacteria

 

13.     List two advantages of the negative staining technique.

            a.  enhanced contrast

            b.  actual shape not changed by heating

 

14.     How can spirochetes be differentiated from spirilla ?

            spirochetes are longer and have more coils

 

15.     Why should a person examine the edge of a stain rather than the center of

          it? microbes are farther apart and individual microbes can be

          seen and examined

 

16.     What is the purpose of wiping the surface of the lab desk with Lysol

          solution before and after each lab?

          to kill microbes accumulating  since last lab that  might contaminate cultures & 

          those accidently left behind that might cause infection in other people

 

 17.     In the   b    stain the bacteria are not fixed.

   a. simple

   b. negative

   c. differential

 

 

Questions for Exercise 4

 

 

1.         b    The two dyes used in a differential stain are:

        a.  acidic                                                                                   d.  both a & b

        b.  basic                                                                                    e.  both b & c

        c.  neutral

 

2.     List two major uses for differential stains.

 

 a.  to improve contrast between different parts of microbes

 

 b.  grouping and identifying microbes

 

 

3.     List the two most commonly used differential stains.

 

 a.  Gram stain

 

 b.  acid-fast stain

 

 

4.     What is the function of the decolorizer in a differential stain?

         To remove primary dye from some microbes or areas of a single microbe

 

5.     List the decolorizer in the following stains:

 

 a.  Gram stain – 95% ethyl alcohol

 

 b.  acid-fast stain – acid alcohol

 

 c. spore stain - water

 

 

6.     What is a mordant? chemical that enhances the microbe’s attraction for the dye

 

7.      Gram’s iodine     is the mordant used in the Gram stain.

 

 

 

8.     In the space below, explain what happens in each step to gram-positive

        cells and gram-negative cells:

 

                                      gram-positive                       gram-negative

 

  crystal violet       colored blue               colored blue__                

 

  iodine                forms CV-I complex       forms CV-I complex          

 

  95%ET OH      CV_I remains (blue)       CV-I removed (colorless)    

 

  safranin            cells remain blue             cells_stained red                 

 

 9.     Why are Gram-positive bacteria unaffected by the safranin?

            the CV-I complex is still attached to groups to which safranin can bind

 

10.     Explain the difference in the cell wall structure between Gram+ and Gram-  

          bacteria.  Gram–positive have cell walls containing peptidoglycan that retain  

                           the CV-I complex;  Gram-negative bacteria have cell walls containing

                           many lipids that are dissolved by the decolorizer removing the CV-I complex

 

11.     Why is the smear heated during the initial step in the acid-fast stain?

            to facilitate penetration of waxy cell walls of acid fast bacteria by the dye

  

 

 

 12.     Explain what happens in each step of the acid-fast stain below:

 

   acid-fast                                nonacid-fast

 

    carbolfuchsin           stained red                    _stained_red    _-__              

 

    acid alcohol              remain red_____            _dye_removed (colorless)     

 

    methylene blue      remain red                         stained blue                            

 

 

13.     What property causes acid-fast bacteria to retain the primary stain?

            waxy cell walls containing mycolic acids

       

14.     List the medically important genus of acid-fast bacteria.

            Mycobacterium

 

 

15.     List two genera of bacteria which produce endospores.

    a.  Bacillus     

  

           b.  Clostridium

 

 

16.     What color do endospores stain?  green

 

17.                  survival               is the function of endospores.

 

 

18.     What are flagella?  long filamentous projections on surface of some microbes

 

 

19.     What is the difference between amphitrichous (polar) and peritrichous 

           flagella?  peritrichous flagella are located all around surface of bacteria; polar   

           flagella are located only at ends of bacteria

 

20.                   motility                      is the function of flagella.

 

21.       poly-betahydroxybutyrate              is the lipid commonly stored by bacteria.

 

22.     What color do the lipid granules stored by bacteria stain?  dark purple

 

23.       inhibiting phagocytosis    is the primary function of the capsule in  

            pathogenic bacteria.

 

24.     What is the color of the capsule in the capsule stain?  white

 

 

  Questions For Exercise 5

 

 

 

1.     What is a culture medium?  nutrient suspension used to cultivate microbes

 

2.     Explain what is meant by the following terms:

 

 a.  chemically defined medium - supplies minimal nutritional requirements for 

      some microbes and contains mainly salts & sugars

   

 

 b.  complex medium – contains one or more complex organic nutrients 

 

 

 c.  enriched medium – contains complex medium plus plant or animal extract

 

 

3.     Classify  the following media as chemically defined, complex, or

        enriched:

 

 a.  minimal agar – chemically defined

 

 

 b.  glucose agar – chemically defined

 

 

 c.  peptone agar - complex

 

 

 d.  yeast extract agar - enriched

 

 

4.     Which of the media listed in #3 contains the least nutrients?  Which

         contains the most nutrients?  least - Minimal agar; most - yeast extract agar

 

 

5.     What specific nutrient(s) are supplied by peptone and yeast extract?

          peptone – organic nitrogen and organic carbon

         yeast extract – B vitamins

         

6.     What is agar and how is it used in microbiological media?  

          polysaccharide from red algae used as a solidifying agent

 

7.     For what purpose are enriched media used? cultivation of fastidious 

        heterotrophs

 

8.     What is an autotroph? organism that can grow with CO₂ as its only carbon 

        source

 

 

9.     What is a heterotroph? organism that requires one or more organic

         molecules to provide its carbon

 

 

10.     Are most bacteria autotrophs or heterotrophs? hetrotrophs

 

 

11.     List the six ingredients added to water to make glucose agar and give the

          nutritional requirement(s) provided by each.

 

    a.  MgSO₄ – magnesium and sulfur

 

    b.  NaCl – sodium & chlorine

 

    c.  NH₄H₂PO₄ – nitrogen & phosphorus

 

    d.  K₂HPO₄ – potassium & phosphorus

 

    e.  glucose – organic carbon

 

    f.  agar – none ( solidifying agent)

 

12.     Why didn't any of the three species grow on the minimal agar? It contained  

          no organic carbon and all were heterotrophs.

 

13.     Which of the three species is the most fastidious? Streptococcus lactis

 

14.     Which of the three species is the least fastidious?  E coli

 

15.     What is a buffer? solution that maintains a constant pH

  

           a.  What is the buffer system in the minimal agar? phosphate buffer

 

 

    b.  What molecules act as a buffer system in the peptone agar?

          phosphates and amino acids

 

 

 

 

16.     What is a selective medium? contains chemicals that inhibit growth of

           some microbes allowing growth and isolation of others