Microbiology Exam #2-Fall 2004

Name: __________________________

D1.	The term chemotroph refers to an organism that: a)  uses CO2 for its carbon source b)  must obtain organic compounds for its carbon needs c)  gets energy from sunlight d)  gets energy by oxidizing chemical compounds e)  does not need a carbon source

C2.	The term phototroph refers to an organism that: a)  uses CO2 for its carbon source b)  must obtain organic compounds for its carbon needs c)  gets energy from sunlight d)  gets energy by oxidizing chemical compounds e)  does not need a carbon source

E3.	A microorganism that has an optimum growth temperature of 37° C, but can survive short exposure to high temperatures is called a/an: a)  extremophile b)  thermophile c)  psychrophile d)  facultative psychrophile e)  thermoduric

B4.	A microorganism that does not have catalase or superoxide dismutase would find it difficult to live in an environment with: a)  carbon dioxide b)  oxygen c)  high salt d)  temperatures above 37° C e)  high acidity

D5.	A microaerophile: a)  grows best in an anaerobic jar b)  grows with or without oxygen c)  needs normal atmospheric levels of oxygen d)  requires a small amount of oxygen but won't grow at normal atmospheric levels e)  none of the choices are correct

C6.	The phase of the bacterial growth curve in which the rate of multiplication equals the rate of cell death is the: a)  lag phase b)  log phase c)  stationary phase d)  death phase e)  all of the choices are correct

A7.	The phase of the bacterial growth curve in which newly inoculated cells are adjusting to their new environment, metabolizing but not growing is the: a)  lag phase b)  log phase c)  stationary phase d)  death phase e)  all of the choices are correct

C8.	In the viable plate count method, a measured sample of a culture is evenly spread across an agar surface and incubated. Each _____ represents one _____ from the sample. a)  cell, cell b)  cell, colony c)  colony, cell d)  species, colony e)  generation, cell

B9.	The process that destroys or removes all microorganisms and microbial forms including bacterial endospores is: a)  disinfection b)  sterilization c)  antisepsis d)  sanitization e)  degermation

D10.	The process of using a cleansing technique to mechanically remove and reduce microorganisms and debris to safe levels is: a)  disinfection b)  sterilization c)  antisepsis d)  sanitization e)  degermation

C11.	The use of chemical agents directly on exposed body surfaces to destroy or inhibit vegetative pathogens is: a)  disinfection b)  sterilization c)  antisepsis d)  sanitization e)  degermation

D12.	Sterilization is achieved by: a)  flash pasteurization b)  hot water c)  boiling water d)  steam autoclave e)  all of the choices are correct

A13.	Dry heat: a)  is less efficient than moist heat b)  cannot sterilize c)  includes tyndallization d)  is used in devices called autoclaves e)  will sterilize at 121° C for 15 minutes

A14.	Disinfection of beverages such as apple juice, milk, and wine, is optimally achieved by: a)  pasteurization b)  chlorination c)  moist heat autoclave d)  filtration e)  boiling water

E15.	All of the following are phenols or phenolics except: a)  Lysol b)  hexachlorophene c)  triclosan d)  cresols e)  chloramines

C16.	All of the following pertain to hypochlorites except: a)  release hypochlorous acid in solution b)  cause denaturation of enzymes c)  found in iodophors d)  they belong to a class of chemical compounds called halogens e)  found in common household bleach

B17.	Iodophors include: a)  chloramines b)  Betadine c)  tincture of iodine d)  alcohols e)  chlorhexidine

D18.	Which is mismatched: a)  sodium hypochlorite – chlorine b)  iodophor – iodine c)  benzalkonium chloride – quaternary ammonium compound d)  Merthiolate – silver e)  formalin – formaldehyde

B19.	All of the following are alkylating control agents except: a)  ethylene oxide b)  iodophor c)  glutaraldehyde d)  formaldehyde e)  chlorine dioxide

A20.	The sterilizing gas used in chemiclaves is: a)  ethylene oxide b)  iodophor c)  glutaraldehyde d)  formaldehyde e)  chlorine dioxide

B21.	Salvarsan was: a)  discovered by Fleming b)  used to treat syphilis c)  formulated from the red dye prontosil d)  first discovered as a product of Penicillium notatum e)  discovered by Robert Koch

E22.	Penicillins and cephalosporins: a)  interfere with elongation of peptidoglycan b)  are metabolic analogs of PABA and block folic acid synthesis c)  attach to the 30S ribosomal subunit and disrupt protein synthesis d)  damage cell membranes e)  block peptidases that cross-link glycan molecules

B23.	Sulfonamides: a)  interfere with elongation of peptidoglycan b)  are metabolic analogs of PABA and block folic acid synthesis c)  attach to the 30S ribosomal subunit and disrupt protein synthesis d)  damage cell membranes e)  block peptidases that cross-link glycan molecules

C24.	Aminoglycosides: a)  interfere with elongation of peptidoglycan b)  are metabolic analogs of PABA and block folic acid synthesis c)  attach to the 30S ribosomal subunit and disrupt protein synthesis d)  damage cell membranes e)  block peptidases that cross-link glycan molecules

D25.	A chemical that inhibits beta-lactamase enzymes is: a)  synercid b)  penicillinase c)  aztreonam d)  clavulanic acid e)  imipenem

A26.	Which antimicrobic does not inhibit cell wall synthesis? a)  erythromycin b)  vancomycin c)  cephalosporins d)  penicillins e)  bacitracin

E27.	The cellular basis for bacterial resistance to antimicrobics include: a)  bacterial chromosomal mutations b)  synthesis of enzymes that alter drug structure c)  prevention of drug entry into the cell d)  alteration of drug receptors on cell targets e)  all of the choices are correct

D28.

A clinical microbiologist makes serial dilutions of several antimicrobics in broth, then incubates each drug dilution series with a standard amount of a patient's isolated pathogen. What is this microbiologist setting up? a)  Kirby-Bauer test b)  a standard curve c)  standard plate count d)  MIC test e)  a growth curve

29. Agree or disagree with the following statements. In either case, fully defend your position (if you agree explain why and if you disagree explain why).

1. Denitrification is an important of the nitrogen cycle.

Agree-De nitrification involves the reduction by facultative anaerobes of nitrate into nitrite, nitrous oxide, or nitrogen gas. This will eventually return nitrogen back into the atmosphere, which is the primary reservoir of nitrogen in the nitrogen cycle.

2. Because they are growing at their maximum possible growth rate, bacterial populations in log phase are the most sensitive to antimicrobial drugs that are designed to kill the bacteria.

Agree-At their maximum growth rate, bacteria are metabolizing at their fastest rate. This means that transport of molecules across the cell membrane will be happening at its maximum rate. Antimicrobics need to be transported across the membrane (and sometimes metabolized, in order to kill the bacteria.

3. Lyophillization is a commonly used sterilization method designed to kill bacteria and their endospores.

Disagree-Lyophillization, which involves rapid cooling under a vacuum dehydrates the bacteria and turns them into a stable powder that last can survive for years. This is a method for preserving bacterial cultures.

D. Cephalosporins and penicillins have different modes of action for killing bacteria.

Disagree-they are both B-lactam antibiotics that kill bacteria by interrupting cell wall sysnthesis by inhibiting the formation of the cross-links in peptidoglycan

30. (7 points) Describe how the antimicrobic drug sulfonamide kill bacteria but not a human host.

Sulfonamide is an antimetabolite that competitively inhibits the enzyme that forms folic acid. It is structurally similar to PABA which is a substrate (along with glutamine and pteridine) that the enzyme uses to form folic acid. Folic acid is a substrate in another reaction that forms the coenzymes THF. THF is necessary in the metabolic pathway that forms nucleotides and certain amino acids. Thus, sulfonamide kills bacteria by disrupting their protein and nucleic acid synthesis. Sulfonamides are selective for most bacteria because they must have this pathway to live. Humans do not have this metabolic pathway. They must obtain folic acid in their diet (they can’t make it themselves). Thus, they don’t have a metabolic pathway to be inhibited.

31. (7 points) Place the bacterial types listed below in one of the following three categories: I. can use O2 and can detoxify its toxic byproducts , II. do not use O2 but can detoxify its toxic byproducts, III. do not use O2 and cannot detoxify its toxic byproducts.

Bacterial types: obligate anaerobe (III), aerotolerant anaerobe (II), obligate aerobe (I), facultative anaerobe (I), and microaerophile (I).

List the two different processes by which facultative anaerobes can metabolize chemical compounds in the absence of O2.

Anaerobic respiration and fermentation

32. (6 points) Contrast these two methods of measuring the growth of microbial populations 1) Coulter counter and 2) measurement of cell mass by turbidity. As your are contrasting these methods include information on the following: a) how the technique works b) advantages of the techniques c) disadvantages of the techniques.

The Coulter counter is a direct method of counting bacteria. Material from a sample is drawn through a photodetector and every time a bacterium crosses the light path, it interrupts it and a count is tallied. The advantages of this process is that it is fast, not prone to counting errors, and can be used on motile organisms. The disadvantages are the expense of the equipment, training to use it, its inability to distinguish living from dead cells, and its tendency to count clusters of cells as one cell.

The turbidity technique involves using the spectrophotometer to quantitate amount of turbidity in a culture. To relate this to cell numbers, a standard curve must be made plotting cell numbers vs turbidity. This involves counting several turbid solutions by another counting method (such as the Coulter counter). The advantage of this technique is that, once the standard curve is made, it can be used to count any population that were grown under the same conditions as the standard curve by just taking an absorbance reading and plugging it into the standard curve. This is a very fast method if you have a standard curve to refer to. It is inexpensive (spectrophomtoeters are much cheaper than Coulter counters) and the instrument is much easier to use than a Coulter Counter. Like the Coulter counter, it can be used for motile organisms but does not distinguish living from dead bacteria.

33. (8 points) Describe how ultraviolet light kills bacteria. What are the limitations of this disinfection method? Describe two applications we discussed in class for the use of ultraviolet light in disinfection.

UV light is non ionizing radiation. It cause the formation of T-T dimmers in DNA (abnormal bonds between thymines on the same polynucleotide chain). T-T dimmers interfere with DNA replication and transcription. Bacterial cells have repair enzymes that can cut out T_T dimmers but when they do that they cut out the nucleotides on both the affected and complementary strands. Thus, when the nucleotides are replaced there is no template and mistakes (mutation) will likely be made. This can also kill the bacteria. UV light has poor penetrating power so its applications are limited to surface disinfection. We talked about the use of UV light in transfer hoods and the use of UV light to disinfect water during water treatment (which requires spreading the water into a very thin film before it passes through the UV light).