When a microbe is present in very small numbers, what must be done before it can be isolated with the streak plate method?
Which level of biosafety (BSL) is appropriate for handling organisms that present a moderate risk of infection?
Which type of culture media is best for the growth of most chemoheterotrophic organisms?
Which of the following statements regarding biofilms is false?
Fortunately, biofilms are not an issue that impacts human health.
Regarding chemical requirements for growth, which element is essential for the synthesis of thiamine and biotin?
Aerobic bacteria that have developed (or retain) the ability to continue growing in the absence of molecular oxygen (O2) are called:
Which of the following classes of microorganisms would have an optimum growth rate at 62°C?
What causes a bacterial culture to enter the stationary phase?
harmful changes in pH
During which phases of the bacterial growth curve are there no changes in the number of living cells?
lag phase and stationary phase
During which phases of bacterial growth are there logarithmic changes in population growth?
Log phase and death phase
Regarding the serial dilution method, a direct measure of microbial growth, how many bacterial cells per milliliter (ml) of sample can be calculated from 71 colonies on a plate of 1:10,000 dilution?
7.1 x 10^5
Regarding turbidity, an indirect method of estimating bacterial numbers, what is the minimum number of cells per milliliter that must be present to allow the suspension to be read on a spectrophotometer?
1 x 10^7
Salts and sugars work to preserve foods by creating a
The term facultative anaerobe refers to an organism that
uses oxygen or grows without oxygen
Which of the following is an advantage of the standard plate count?
Determines the number viable cells
Which of the following is an advantage of the direct microscopic count?
Requires no incubation time
Which of the following is NOT used to determine metabolic activity?
Most bacteria grow best at pH
A culture medium on which only gram-positive organisms grow and a yellow halo surrounds Staphylococcus aureus colonies is called a(n)
selective and differential medium
A culture medium consisting of agar, human blood, and beef heart is a
During which growth phase will gram-positive bacteria be most susceptible to penicillin?
Which of the following is the best definition of generation time?
length of time needed for a cell to divide (double in size)
Which of the following is NOT a direct method to measure microbial growth?
Which of the following is an organic growth factor?
Which of the following is an example of a metabolic activity that could be used to measure microbial growth?
Patients with indwelling catheters are susceptible to infections because
biofilms develop on catheters
Bacteria are said to exhibit logarithmic, or exponential, growth. What does that mean about the growth rate of bacterial populations?
Since each and every bacterial cell is capable of reproduction, the size of a bacterial population increases by a power of two. In effect, the larger a population gets, the faster is grows
Which of the following statements describes what is happening in the cell during the stationary phase?
The number of cells that are dividing equals the number of cells that are dying.
Why are multiple serial dilutions plated when using the direct method?
To ensure that one dilution results in a plate with a countable number of colony-forming units (cfu)
Why must a new pipette be used for each dilution when plating a serial dilution?
To make sure organisms from the previous dilution are not carried over into the next dilution
What does a spectrophotometer directly measure?
Absorbance of light
Bacterial growth measures increases in the size of a(n) _____________, while the growth of a multicellular organism refers to an increase in the size of a(n) _____________.
population; individual organism
Which of the following statements describes what is happening in the cell during the lag phase?
The cells are adjusting to their new environment; cellular metabolism is accelerated.
Which of the following statements describes what is happening in the cell during the logarithmic (log) phase?
Cells are undergoing binary fission, resulting in an exponential increase in the population size.
The depletion of essential metabolites and accumulation of toxic metabolic waste products results in the beginning of the _________________ phase.
Bacterial generation times are typically measured using which units of time?
What is the difference between the direct and indirect methods of determining generation time with a growth curve?
In the direct method, the cells are enumerated by determining colony-forming units on a Petri dish; in the indirect method, the cell numbers are approximated using a spectrophotometer.
Which of the following factors may affect the generation time?
Temperature, growth media, and bacterial species are all examples of factors that can affect generation time.
Which of the following associations is INCORRECT regarding anaerobic respiration?
Lactic acid and ethanol are typical end-products of bacterial anaerobic respiration.
(Lactic acid and ethanol are typical end-products of bacterial fermentation.)
Which of the following statements regarding microbial control is false?
Canned food in supermarkets is completely sterile.
The destruction of vegetative pathogens on living tissue is known as which of the following?
Regarding environmental influences that affect the rate of microbial death, which of the following is an accurate statement?
heat is more affective under acidic conditions
What action of microbial control agents causes cellular contents to leak into the surrounding medium?
damage to either lipids or proteins in the plasma membrane
The minimal length of time for all bacteria in a particular liquid culture to be killed at a given temperature is defined as the:
thermal death time (TDT)
Which of the following physical methods to control microbial growth works via the mechanism of protein denaturation?
boiling or flowing steam
Which of the following statements does not correctly support or describe the results of the disk-diffusion experiment shown in this figure?
The results indicate that quaternary ammonium compounds are effective against the selected gram-negative and gram-positive organisms, albeit more effective against gram-negative bacteria
By definition, a tincture contains alcohol. Why would a tincture of an antiseptic be more effective than an aqueous solution?
alcohol denatures proteins and causes lipid dissolution
Glutaraldehyde is not/does not:
an excellent/fast acting sporicide
Chlorhexidine, frequently used for microbial control on skin and mucous membranes, is an example of which type of disinfectant?
Which of the following chemical agents is fairly effective against endospores and mycobacteria?
Which of the following correctly lists, in increasing order, the resistance of microorganisms to chemical biocides?
gram-positive bacteria, fungi, endospore, prion
Which of the following is the best method to sterilize heat-labile solutions?
Which of the following best describes the pattern of microbial death?
cells in a population die at a constant rate
Which of the following substances can sterilize?
Which of the following substances is used for surgical hand scrubs?
Place the following surfactants in order from the most effective to the least effective antimicrobial activity:
1-Soap; 2-Acid-anionic detergent; 3-Quats.
The antimicrobial activity of chlorine is due to which of the following?
the formation of hypochlorous acid
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