Mastering Microbiology Ch 6

A broth medium has been inoculated, and microbial numbers will be counted periodically to generate a bacterial growth curve. At 2 hours after inoculation, the culture has progressed through lag phase and is now in log phase. At this point, the population size is 1 million cells. The generation time is 30 minutes. Assuming the continuation of log growth, how many cells would there be at 2 hours of growth in log phase?

16 million

You have identified the causative agent of the illnesses as Listeria monocytogenes and have laboratory data to support your conclusion. Now you will need to determine the bacterial load of the pathogen within the samples collected. You'd like to know whether the illness is caused by a low level exposure (low bacterial numbers) or a high level of exposure (high bacterial numbers). You will use serial dilutions and plate counts to quantify the number of bacteria in your sample. By using a "serial 10" dilution method, each new tube of diluted bacteria will be 10 times more diluted than the previous tube. A 1 mL sample of each of these dilutions can then be plated, and the resulting colony forming units counted to yield an estimate of the number of bacteria in your sample. You count 50 colony-forming units on the fourth plate that corresponds to the 10-4 dilution tube. How many bacteria would you estimate to be in the original sample?

5 x 105 bacteria per mL

A chemostat is continuous culture system that is designed to promote and prolong exponential growth and prevent bacteria from entering stationary phase. How might this work?

Chemostats provide a continued source of fresh nutrients and remove wastes and dead bacterial cells.

The Lake of the Ozarks is a human-made lake, so it collects runoff from coal strip-mining, fertilizers, resort wastewaters, and septic drainages. The average lake temperature is between 10∘C and 21∘C. Consider the physical requirements for growth and multiplication that would allow fecal coliforms to "blossom" in the Lake of the Ozarks. Which of the following would accurately describe these organisms? Check all that apply.

Facultative halophiles Psychrophiles Mesophiles

In addition to physical requirements, bacterial growth and multiplication also entails chemical requirements. Which of the following statements would accurately describe chemical requirements and conditions associated with growth in the Lake of the Ozarks environment? Select all of the following statements that are true regarding fecal coliforms in the Lake of the Ozarks.

Fecal coliforms will need to acquire trace elements for growth in the lake environment. Fecal coliforms will likely contain enzymes to counteract toxic oxygen forms. The lake environment will support the growth of facultative anaerobes.

After a period of rapid growth (log phase), bacterial growth rates will slow and enter the stationary phase. The number of viable cells no longer increases, but instead stays constant. In this activity you will indicate the statements that correctly describe what is happening during stationary phase. Select each statement that accurately describes what is happening to bacterial cultures during stationary phase.

Harmful waste products may be accumulating. The cells are likely running out of nutrients. The number of cells that are dying is balanced by the number of new cells that are being formed.

Most types of bacteria have specific metabolic oxygen requirements. Whether a bacterium requires oxygen or not has a large effect on its physiology. For example, aerobic bacteria, which require oxygen for their metabolic processes, must be able to counter the highly reactive oxygen species such as singlet oxygen (1O2) or a superoxide radical (O2−) that result from reactions within the cell. Bacteria that lack this capability are generally considered anaerobic. Since anaerobic bacteria utilize molecules other than oxygen as their final electron acceptor, they must possess adaptations to facilitate their survival in environments without oxygen. A majority of bacterial species lie somewhere in between these two polar opposites in that they are facultative anaerobes or able to utilize oxygen but also capable of surviving without it. Some particularly specialized facultative anaerobes are microaerophilic and grow only in low concentrations of oxygen. What are the enzymes and their reactions that allow bacteria to grow in the presence of oxygen? Which of the following statements correctly summarizes the enzymatic reactions to reactive oxygen species? Choose the most correct statement.

Superoxide dismutase detoxifies superoxides and converts them into hydrogen peroxide and oxygen. Catalase then converts the hydrogen peroxide into water and oxygen.

When bacteria are inoculated into a new sterile nutrient broth, their numbers don't begin to increase immediately. Instead, there is a lag phase that may last for an hour or even several days. Why don't bacterial numbers increase immediately?

The bacteria must adjust to the nutrient content in the new medium, synthesizing necessary amino acids, growth factors, and enzymes.

After your confirmation that the causative agent for the illnesses was Listeria monocytogenes, the patients were put on the appropriate antibiotic treatments and recovered well. Weeks later, you read in the paper that the local health department visited the ice cream manufacturing plant and found a machine that was contaminated with Listeria. The company had complained that the machines were sanitized according to health code specifications but the bacteria were still present after cleaning. The health department's investigation concluded that the machine was harboring mixed bacterial biofilms that allowed the bacteria to survive the chemicals used in the sanitization process. Since biofilms are formed by bacterial cells using quorum sensing to initiate the adherence and formation of the biofilm as a means to partial control and adapt to changes in their environment, the health department has determined that the mix of bacteria, which included Listeria, allowed the bacteria to survive sanitization by neutralizing or diminishing the effectiveness of the chemical compounds. What aspects of biofilm formation and the interaction of bacteria within the biofilm would allow for the survival of the bacteria in the presence of the sanitizing solutions?

The matrix of the biofilm aids in retention of nutrients and sequestration of the bacteria from environmental stresses such as chemical sanitizers. Formation of a biofilm may allow for the survival of the bacteria that are at the base of the biofilm, farthest away from any chemicals found within the environment. Quorum sensing within the biofilm allows bacteria to respond to other bacteria and alter their enzyme expression.

the figure, which line best depicts a facultative anaerobe in the absence of O2?

b

Bacteria naturally prefer company instead of solitude for growth. Examples of this kind of communal growth pattern can be found everywhere, from surfaces of the teeth and the intestines, to the surface of a slimy rock in the lake, to the thick floc that clogs water pipes. These examples of communal bacterial growth are known by what name?

biofilm

Sampling lake water for microscopic organisms is not as easy as it sounds when you want to both count and identify species. In a given water sample, your bacteria of choice can be rare or difficult to culture, particularly given the mixture of bacteria in a biofilm. Which of the following culture media would be best for growing fecal coliforms when they are relatively less abundant than other bacteria in the lake?

enrichment culture medium

Cultures of the Lake of the Ozarks water samples were grown on enrichment media for identification. However, these organisms are present to some degree in all samples. An important question from a clinical perspective is whether or not there is a significant increase in the fecal coliform populations that would put people's health at risk. If you were part of the team investigating this outbreak, how would you best enumerate the fecal coliform threat?

filtration count culture

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

group 2

Which of the following elements is NOT correctly matched with its cellular function?

phosphorus used for production of carbohydrates.

This activity asks you to consider various methods of counting or estimating the size of bacterial populations and to select the method that will provide the most accurate data for plotting a bacterial growth curve. Which of the following methods would be most appropriate for gathering data to plot a bacterial growth curve throughout the four phases?

plate count

Agars can be used to select for growth of certain types of bacteria and then allow for you to identify the different bacteria that can grow on the plate. These agars may be considered both selective and differential. Is the above statement true or false? Choose which.

true