Microbiology 223: Chapter 1 Homework

Which of the following are limitations of antibiotics?

1. Antibiotics are not effective in treating viral infections 2. Antibiotics may be toxic 3. Treatment with antibiotics can lead to the emergence of resistant strains

Louis Pasteur conducted an experiment to disprove the theory of spontaneous generation. An overview of this experiment is summarized in this figure. Based on this information, match each component in the experiment with its purpose in this experiment.

1. Beef broth: provided a nutritious environment to support microbial growth. 2. Bunsen burner (flame): provided heat that destroyed microorganisms already present in the beef broth. 3. Flask with S-shaped neck: provided the physical conditions for trapping airborne contaminants and preventing microorganisms from entering the flask. 4. Air: provided a source of potential external microbial contaminants.

Which of the following conclusions can be drawn from Pasteur's experiment involving the flasks with S-shaped necks?

1. Microbes can be blocked from accessing favorable growth environments. 2. Microorganisms can be present in nonliving matter, such as air, liquids, and solids. 3. Microbial life can be destroyed by heat. 4. Pasteur's observations support the theory of biogenesis.

Pasteur's experiments and observations provided the basis for developing aseptic techniques that prevent the introduction of unwanted microorganisms into controlled environments. Given what you have learned from the design of Pasteur's experiment, which of the following scenarios would be considered an aseptic technique?

1. Wearing gloves when handling sterile laboratory equipment. 2. Using a Bunsen burner (flame) to heat wire inoculating loop prior to use. 3. Taking steps to prevent contaminants from entering sterile solutions.

Part complete Staphylococcus aureus (remember that an organism's scientific name can also be written with the genus name abbreviated—in this case, S. aureus) is a bacterium, one of the groups of microorganisms. Although the different groups of microorganisms share some similarities, there are several important differences that distinguish each group.

Bacteria: 1. Derive nutrition from organic or inorganic sources or conduct photosynthesis. 2. Have cell walls that contain peptidoglycan. Archaea: 1. Not typically associated with human disease. 2. Found in extreme environments. Fungi 1. Eukaryotic 2. Can be unicellular or multicellular. Viruses 1. Cannot survive outside a host cell 2. Can be seen only with an electron microscope

The tests for these uncommon pathogens are similar to the ones that have already been performed for the common viruses, but in this case, you will try to identify the DNA or proteins of specific viruses that are not often seen in clinics or hospitals in that area of the country. Each region of the country has certain viral pathogens that are spread throughout the human population that live in that area. When one of these viruses spreads to a new area, we consider it to be "emerging" in this new population of people. Some detective work and deductions will be required. By applying the scientific method, you can focus and refine your list of possible viral pathogens to experimentally test for. You'll begin your investigation by reviewing the patient's history and symptoms and formulating a hypothesis for possible causative agents. Based on what you know of the scientific method, what would you like to do next?

Design and run some tests or experiments.

S. aureus has been isolated from George's infected wound. To satisfy Koch's postulates, what would George's doctor need to do with the isolated S. aureus?

Inject the S. aureus into an animal, observe whether the animal gets an infection similar to George's, and isolate the same strain of S. aureus from the infection

Further characterization of the S. aureus isolated from George's wound reveals that the strain is MRSA. Why is George's doctor concerned that MRSA has been identified as the causative agent of George's infection?

MRSA is transmissible.

Part complete In this activity, you will predict which scenarios would most likely produce growth if Pasteur's S-shaped neck flasks were cut at various points along the curve. The S-shaped necks of Pasteur's flasks provided an ideal system for testing the role of airborne contaminants in introducing microorganisms in nonliving matter. As Pasteur demonstrated through his experiments, the top curve in the S-shaped neck prevented airborne microorganisms from entering the flask, and, as a result, contaminants collected in the bottom portion of the S-shaped curve. In this figure, four scenarios are proposed (as indicated by arrows) in which the S-shaped neck is broken at different points. Identify the scenario(s) in which airborne microbial contamination of the sterile beef broth is most likely to occur.

Scenario A: break near the mouth of the flask. Scenario B: break before the first curve in the S-shaped neck

For each of the following statements, determine whether it refers to the theory of spontaneous generation or to biogenesis.

Spontaneous Generation: 1. Life can arise spontaneously from nonliving matter. 2. Living cells can arise from nonliving matter under favorable conditions. 3. Vital Forces in nonliving matter can lead to new life. Biogenesis: 1. Living cells can arise only from preexisting living cells. 2. Life can arise as a result of microorganisms present in nonliving matter. 3. Microorganisms present in nonliving matter can lead to new microorganisms.

In 1861, Pasteur conducted his now-famous experiments using flasks with long necks bent into an S-shape. Imagine that you are a scientist working in Pasteur's lab at this time. You decide to tip the flasks so that broth enters the long S-shaped neck. You then return the flask to its upright position. Predict the most likely outcome of tipping one of Pasteur's S-necked flasks.

The broth would become contaminated with microbes because they were trapped in the neck.

One of the first set of experiments to refute spontaneous generation was done in 1688 by Francesco Redi. Which of the following statements regarding Francesco Redi's experiments is true?

The results of his experiment demonstrated that living organisms are derived from other living organisms.

In the late 1800s, a researcher by the name of Robert Koch developed a series of postulates (guidelines) that can be used to prove that a given pathogen is the true cause of a disease. Koch's Postulates 1. The suspected causative agent must be found in every case of the disease and be absent from healthy hosts. 2. The agent must be isolated and grown outside the host. 3. When the agent is introduced to a healthy, susceptible host, the host must get the disease. 4. The same agent must be found in the diseased experimental host. Which of the following steps does NOT follow one of Koch's postulates?

You give a patient an antibiotic to treat an infection.

You have successfully completed the experiments and analyzed your results. Your analysis has allowed you to refine you hypothesis and remove all but one virus strain from your list of possible causative agents. With your success at identifying the viral pathogen, you will now need to begin the long process of characterization, the studying of all aspects of an organism to determine whether this virus is truly new or has been isolated and identified before. The characterization will begin with studying the genome of this pathogen. Sequencing machines will determine the order of the nucleic acids that make up the viral genome, and computers will be able to analyze this sequence to determine the genes available for this virus. What is the area of biology that studies the nucleic acid makeup of an organism?

genetics