Clinical Micriobiology HW#2

Microbiology Animation: Enzymes: Competitive Inhibition

1. How does a competitive inhibitor slow enzyme catalysis? They compete with the substrate for the enzyme's active site

2. What enables competitive inhibitors to bind to a specific enzyme? Competitive inhibitors have structures that resemble the enzyme’s substrate.

3. If high amounts of sulfanilamide are in the presence of an enzyme whose substrate is PABA, what outcome is expected? The enzyme will stop functioning.

4. Which of the following statements regarding competitive inhibitors is true? Competitive inhibitors decrease the rate of enzyme activity.

CHAPTER 5

1. An enzyme, citrate synthase, in the Krebs cycle is inhibited by ATP. This is an example of all of the following EXCEPT: competitive inhibition

**An enzyme, citrate synthase, in the Krebs cycle is inhibited by ATP. This is an example of all of the following: feedback inhibition, allosteric inhibition, noncompetitive inhibition

2. The use of enzymes is necessary to increase the activation energy requirements of a chemical reaction. FALSE

3. Once an enzyme has converted substrates into products, the active site reverts back to its original form. TRUE

 

CHAPTER 6

1. In the figure, which line best depicts an obligate anaerobe in the presence of O2?

                           Letter C

2. Most bacteria grow best at pH: pH 7

3. Assume you inoculated 100 cells into 100 ml of nutrient broth. You then inoculated 100 cells of the same species into 200 ml of nutrient broth. After incubation for 4 hours, you should have: The same number of cells in both.

4. Agar is used as a solidifying agent in microbiological media since few bacteria can degrade it. TRUE

Chapter 7
1. Prior to drawing blood for a blood donation, the nurse will scrub the arm with a Betadine solution. This form of antimicrobial control would be called: Antisepsis

**Antisepsis is the destruction of vegetative pathogens on living tissue.

2. Which of the following disinfectants acts by disrupting the plasma membrane? Bisphenols

3. A disk-diffusion test using Staphylococcus gave the following results:

Disinfectant Zone of inhibition (mm)

A 0

B 2.5

C 10

D 5

In the table, which compound was bactericidal? The answer cannot be determined.

Chapter 5 Reading 9

1. Microbes are often identified using biochemical tests that detect specific enzymes of metabolic pathways. E. coli typically ferments lactose, whereas Shigella does not. If a pure culture of each bacterium was placed in a tube containing lactose as the only food source, and a chemical indicator changed color after a pH change, what would the tubes look like after the bacteria were incubated?

The tube with E. coli would indicate a pH change, and the Shigella tube would indicate no change.

**This biochemical test is used to differentiate E. coli, which produces lactase and ferments the sugar (thereby producing acids), from Shigella, which does not produce lactase.

 Chapter 6

1. In the figure, which line shows the growth of an obligate aerobe incubated anaerobically?

                       Letter C

2. If cells are grown in media containing amino acids labeled with radioactive nitrogen (¹⁵N), most of the radioactivity will be found in the cells': DNA and proteins

3. Most pathogenic bacteria are thermophiles. FALSE

Interactive Microbiology: Biofilms and Quorum Sensing

1. The sorting bins below show sequential stages of biofilm development. Match the text-based conditions and properties below to the biofilm development stage it best describes.

Biofilm development stage:

1) initial attachment

2) rapid bacterial growth and division

3) additional bacteria species joining biofilm; quorum sensing starting to change gene        expression; autoinducer threshold reached; matrix beginning to form; water channels    forming

4) protection from outside chemicals; free-floating bacteria

2. Quorum sensing affects biofilm development through control of: Gene expression

**Quorum sensing is the process by which bacteria sense the density of nearby microorganisms. Bacteria respond to changes in this density of neighboring cells though changes in gene expression. These changes in gene expression lead to particular characteristics of the biofilm: matrix formation, water channels, and cooperative relationships with other bacterial species.

3. Which of the following best describes the effect of autoinducers as their concentration increases around bacterial cells? They alter bacterial gene expression.

**Autoinducers are signaling molecules that bacteria use for quorum sensing. As the concentration of autoinducers increases, more and more bacterial receptors are activated. At some threshold level, the activated receptors cause changes in bacterial gene expression. These changes contribute to biofilm development, and may trigger increased virulence.
4. The area around and above the biofilm shown below is filled with an antibiotic. Of the four cells labeled in the biofilm, which would be exposed to the LOWEST concentration of antibiotics?
                Cell 4

**Antibiotic molecules move into a biofilm by diffusion. Cells near the surface of the biofilm or near a water channel are exposed to the highest concentrations of antibiotic. The matrix surrounding deeper layers of the biofilm acts as a barrier to antibiotic diffusion. The concentration of antibiotics therefore decreases as one goes deeper into the biofilm. Cells near the surface are easily killed off, but those in the deeper layers, like Cell 4, are less affected. This is one of the reasons biofilms are so hard to completely remove with antibiotic treatment.

 

Interactive Microbiology: Biofilms and Quorum Sensing (Scientific Thinking)

1. You are working in a research lab trying to determine which mixtures of bacterial species can form biofilms. To determine this, you perform a bacterial growth study looking at the number of viable bacteria cells remaining after treatment with penicillin (an antibiotic). You know that all your mixtures of bacteria are susceptible to penicillin when they do not grow as a biofilm. You include a control mixture in your study that you know does not form biofilms. Three different experimental mixtures (Groups 1, 2, and 3) and your control were grown at the same density of cells (12,000 cells per dish). You treat all groups with the same dose of penicillin for 10 hours. You count the number of viable cells 6 hours and 48 hours after the treatment ends. The graph below shows the data from this experiment.

 

Which of the bacterial mixtures(s) grow as a biofilm? Group 2

The matrix produced by bacteria that grow in a biofilm can slow down the diffusion of antibiotics into the biofilm. Cells deep in the biofilm are therefore protected against the antibiotic. A substantial number of Group 2 cells died off during the penicillin treatment, but these were only cells at the surface of the biofilm. Cells at the bottom of the biofilm survived and were able to re-establish the colony over the next 36 hours.

CHAPTER 7

1. Any process that destroys the non-spore forming contaminants on inanimate objects is sterilization. FALSE

2. Which of the following does NOT achieve sterilization? Pasteurization 

3. All of the following are effective for destroying prions EXCEPT: Boiling

**All of the following are effective for destroying prions:

          incineration

          NaOH + autoclaving at 134 degree C

          proteases