chapter 6 of micro

A 0.1 ml sample of a log phase culture contains 10,000 bacterial cells/ml. It is added to 9.9 ml of fresh culture medium broth. Assume a generation time of 30 minutes, and no limiting nutrients. How many bacteria will be present in the entire broth culture after five hours?

1.02 × 106

Alkalinophiles can survive in water up to pH (11.5/10/7.0).

11.5

A microbiologist inoculates a flask of broth to a concentration of 100 bacterial cells per ml. The generation time of the species is 1 hour, and there is no lag phase. How long will it be before the culture contains more than 6,000 cells per ml?

6 hours

Explain how temperature and pH levels can influence microbial infections in the human body.

All microbes have particular ranges of temperature and pH within which they thrive. When the temperature or pH of their environment falls outside this range, their growth is inhibited, and they may even die as a result of the adverse conditions. Therefore, only those microbes whose pH and temperature requirements match those conditions found in the human body will be able to grow and reproduce there. For example, because the temperature of the human body is 37°C, only mesophiles can reproduce there. In addition, the pH of most tissues and fluids in the body is 6.5-7.5, which matches the pH requirements of neutrophiles. Therefore, it is not surprising that most human pathogens are mesophiles and neutrophiles. However, this is not always the case. Some microbes have adapted to environments that would otherwise be extremely hostile to most microbes. A good example is the bacterium Helicobacter pylori, which is able to live in the extremely acidic conditions of the stomach by secreting substances that help to neutralize the acid. The result is an infection that can lead to stomach ulcers.

A pure culture is composed of cells that arise from a single (CFU/inoculum/sample).

CFU

Which of the following statements is CORRECT regarding Figure 6.1?

Cells are alive but not reproducing during the stage represented by A.

Explain the similarities and differences between direct and indirect methods of measuring microbial growth, and give examples of each.

Direct methods of measuring microbial growth involve quantifying the number of microbes in a specimen through actual counting of cells in a microscope or cytometer, or counting the numbers of colonies produced from the plating of a specimen. The advantage of these techniques lies in their usefulness for counting very large and very small populations of bacteria. Indirect methods, by contrast, seek to quantify cells by measuring some characteristic related to the number of cells present. For example, spectrophotometry measures the amount of light transmitted through a culture; the less light that is transmitted, the more cells are present. The amount of light transmitted gives an approximation of the number of cells present. Indirect methods are useful for quantifying microbes, such as filamentous microbes, that are hard to count directly. Both direct and indirect methods seek to arrive at an approximation of the actual number of cells present. Because that number is changing even during the measurement process, neither technique can give an exact number of cells.

A Coulter counter is used to obtain pure cultures.

FALSE

A majority of prokaryotes are capable of carrying out nitrogen fixation.

FALSE

Agar is a useful compound in the microbiology lab because it is an excellent nutrient for bacteria.

FALSE

Photoheterotrophs use carbon dioxide as their sole carbon source.

FALSE

The only effective way to store bacterial cultures for short periods of time is to arrest their metabolism by freezing.

FALSE

The events of binary fission are - the cell doubles in size -the DNA is replicated -the cell forms a septum -the cell separates from its offspring The CORRECT order of these events is

II, I, III, IV.

A (Coulter/Petroff-Hauser chamber/spectrophotometer) counter is used to count cells on a light microscope.

Petroff-Hauser chamber

Molecular methods of detecting microorganisms reveal that the number of bacterial species in nature exceeds previous estimates by several orders of magnitude. In human mouths, for example, it is estimated that 500-700 microbial species are normally present. Explain why previous estimates were low.

Previous estimates of microbial diversity were largely based on the ability to detect microbes in samples handled in a typical laboratory setting. In most cases, laboratory conditions represent a narrow range of growth parameters, including temperature range, oxygen and other gas levels, and spectrum of nutrients. Even in cases where attempts are made to simulate the normal conditions for microbes (e.g., providing a high-pressure environment for organisms collected from a hyperbaric environment), microorganisms must frequently tolerate fluctuations in the growth environment or even exposure to extremely adverse conditions for short periods of time. Organisms that are intolerant of significant fluctuation in their environmental requirements do not survive transport to the lab to be measured or cultured. As a consequence, only the relatively few microbes that are versatile in their nutrient requirements and can tolerate fluctuations in their growth environment have been observed or isolated in the laboratory. This, in turn, resulted in misleadingly low estimates of microbial diversity.

Why is refrigeration a considered short-term method of storing bacteria?

Refrigeration slows metabolism but does not stop it.

Enrichment culturing may require use of controlled environmental conditions.

TRUE

Quorum sensing produces changes in gene expression.

TRUE

Serial dilution can be used in combination with pour plates as a method for isolating pure cultures.

TRUE

Streak plates are a useful way to obtain CFUs.

TRUE

Thermoduric mesophiles are often responsible for spoilage of improperly canned foods.

TRUE

A new prokaryote is recovered from a remote saline hot spring. Design a set of experiments to determine whether the organism is thermophilic or thermoduric, halophilic or halotolerant.

The experimental design should include a control in which the organism is grown in the salt conditions and at the temperature it was recovered from. One set of samples should be cultured at the same salt concentration but varying the temperatures. Another set of samples should be cultured at the temperature of the hot spring but varying the salt concentration. One culture should be grown at the lowest temperature and salt concentration used in the two experimental sets. Bacterial growth is most reliably measured using the viable plate count method (assuming the organism can be grown on plates). Alternatively, bacterial numbers may be determined using a cell counter. An excellent answer will describe the organism which can be expected to grow under the various conditions (thermophilic halophile, thermophilic halotolerant, thermoduric halophile, and so forth).

Compare and contrast the streak-plate method of isolation with the pour-plate method of isolation.

The streak-plate and the pour-plate methods of bacterial isolation are both used to produce pure cultures of bacteria from specimens. Both techniques involve the use of agar-based growth media contained in Petri plates. Additionally, both techniques involve the use of dilutions as a means of isolating single cells or groups of cells that then grow into isolated colonies. However, there are several significant differences between the two techniques. The main difference is the way in which the specimen is diluted. In the streak-plate method, the specimen is diluted by use of an inoculating loop that spreads organisms over the surface of the agar. Thus, colonies appear only on the agar surface. In the pour-plate method, however, dilutions of the specimen are made in tubes of broth and then each dilution is added to melted agar, which is then poured into Petri dishes. Thus, microbes are mixed throughout the agar, and colonies will appear both in and on the medium.

An aquatic microbe that can grow only near the surface of the water is probably which of the following?

a phototroph

Which of the following organisms would be most likely to contaminate a jar of pickles?

an acidophile

Some organisms use vitamins as (oxidizers/antioxidants/peroxidases) to be able to live as aerobes.

antioxidants

A microorganism grows in the lab on medium containing mineral salts but no organic compounds. The organism is likely to be a(n)

autotroph.

A(n) ________ is a complex community of various types of microbes that adhere to surfaces.

biofilm

MacConkey agar plates represent ________ medium.

both a differential and a selective

A capnophile is a microorganism that thrives in conditions of high

carbon dioxide levels.

Some organisms use (carotenoids/catalase/peroxidase) to prevent the damage of singlet oxygen.

carotenoids

Culturing of intracellular parasites generally requires (enrichment/cell culture/low oxygen) conditions.

cell culture

Organisms that require organic sources of carbon and energy are called (autotrophs /chemoautotrophs/chemoheterotrophs /).

chemoheterotrophs

A ________ is used in industrial microbiology to produce microbial products that are only synthesized during log phase growth.

chemostat

An organism that gains energy from redox reactions involving inorganic and organic chemicals is a(n)

chemotroph.

An axenic culture is one which

contains only a pure culture.

A laboratory recipe lists sucrose, an ammonia compound, calcium salts and a buffer as the ingredients for a microbiologic medium. These are added to water and autoclaved. What type of medium does this protocol produce?

defined broth

Blood agar plates are an example of ________ medium.

differential

Organisms that can grow with or without oxygen present are

either facultative anaerobes or aerotolerant anaerobes.

A fastidious organism might be grown on which of the following types of media?

enriched media

Joan wants to discover a microbe capable of degrading an environmental contaminant. Which of the following culturing methods would be most effective for isolation of such an organism?

enrichment culture

Creating conditions in the laboratory that promote the growth of some microbes while inhibiting the growth of others is called

enrichment culturing.

The ________ of a population is the time it takes for the cells to double in number.

generation time

At temperatures higher than the maximum growth temperature for an organism

hydrogen bonds are broken, proteins are denatured, and membranes become too fluid.

A microorganism found living under conditions of high ________ is a barophile.

hydrostatic pressure

Obligate anaerobes may be cultured in the laboratory

in a reducing medium.

An epidemiologist is investigating a new disease and observes what appear to be bacteria inside tissue cells in clinical samples from victims. The scientist wants to try to isolate the bacteria in the lab. What culture conditions are most likely to be successful?

inoculation of cell cultures

A(n) (culture/specimen/inoculum) is a sample of microorganisms introduced into a growth medium.

inoculum

A sample placed into fresh medium is initially in the (lag/log/stationary) phase of microbial growth in most instances.

lag

When cells are metabolically active but not dividing, they are in the ________ phase.

lag

A(n) (autotroph/lithotroph/organotroph) uses inorganic molecules as electron donors.

lithotroph

The generation time of bacterial cells is shortest during the ________ phase.

log

During which growth phase are bacteria more susceptible to antimicrobial drugs?

log phase

The growth of bacterial cultures is best described as

logarithmic growth.

The preferred method for long term storage of bacteria is (freezing/refrigeration/lyophilization).

lyophilization

A growth curve plots the (concentration/number/percentage) of viable organisms in a growing population over time.

number

A(n) ________ organism require(s) oxygen for growth. A) anaerobic

obligate aerobic

A microbe that grows only at the bottom of a tube of thioglycollate medium is probably a(n)

obligate anaerobe.

Reducing medium is used to isolate ________ microbes.

obligate anaerobic

Nitrogen is a growth-limiting nutrient for many organisms because

only a few microbes can extract it from the atmosphere, but all organisms require it for amino acid and nucleotide synthesis.

The (maximum/optimum/selective) growth temperature is the temperature at which an organism exhibits the highest growth rate.

optimum

The use of salt and sugar in preserving various types of foods is an application of which of the following concepts?

osmotic pressure

Microaerophiles are microbes that grow best at low

oxygen levels.

A cell that uses an organic carbon source and obtains energy from light would be called a

photoheterotroph.

CFUs (colony forming units) are the source for

pure cultures.

In the process of ________, microbes detect the presence and density of other microbes and modify their metabolic activity in response.

quorum sensing

The carotenoid pigments of some phototrophs interact with ________ to reduce its toxicity.

singlet oxygen (1O2)

A (Coulter counter/cytometer/spectrophotometer) can measure changes in the turbidity of a bacterial culture.

spectrophotometer

Rates of cell production and cell death are approximately equal during the ________ phase of growth.

stationary

The absence of ________ leaves obligate anaerobes susceptible to killing by oxygen.

superoxide dismutase

A clinical sample from a mucus membrane is usually collected as a (biopsy/needle/swab) specimen.

swab

A clinical sample labeled as "sputum" was collected from

the lungs.

Ted heats some food just to boiling, and stores some of it immediately in a container which he places in the refrigerator. A week later he takes the food out and finds it has spoiled. The microbes that spoiled the food are probably ________ organisms.

thermoduric

Which of the following is an indirect method for estimating the number of microbes in a sample?

turbidity

The ________ method provides an estimate of the CFUs (colony-forming units) in a sample.

viable plate-count