Psychrophiles are bacteria that grow best at very cold temperatures, between 0°C and 15°C.
Correct Answer: Between 0 and 15°C
The human body temperature is approximately 37°C. This temperature falls within the range of mesophiles.
Correct Answer: None of the choices
The minimum growth temperature is the lowest temperature at which an organism grows. For example, the minimum growth temperature for a thermophile is 45°C. If you place a thermophilic bacterium in an environment below this temperature, there will be no growth.
Correct Answer: The lowest temperature at which an organism will grow
The optimal growth temperature is the temperature at which the highest rate of growth occurs.
Correct Answer: The temperature at which the highest rate of growth occurs
Acidophilic bacteria grow best in acidic conditions, below pH 7.
Correct Answer: pH 2.0
The death phase occurs when the population begins to decrease.
Correct Answer: D
During the stationary phase, the number of cells produced equals the number of cells that die so the total cell number is nearly constant.
Correct Answer: C
Exponential growth begins when the total number of bacteria doubles at fixed intervals because the bacteria are dividing by binary fission. This starts at point A.
Correct Answer: A
The cell count doubles every 10 min.
Correct Answer: 10 minutes
A bacterium that uses oxygen for metabolism but shifts to anaerobic metabolism when oxygen is no longer available is a facultative anaerobe.
Correct Answer: Uses oxygen but can grow without it
Having oxygen as the final acceptor in the electron transport chain can produce oxygen free radicals and hydrogen peroxide, which are toxic and are dealt with by superoxide dismutase and catalase respectively.
Correct Answer: Aerobe
Laundry detergent and nutrient broth are not chemically defined.
Catalase splits hydrogen peroxide to water and oxygen:
2H2O2 + H2O = 2H2O + O2
Peroxidase uses H+ ions to convert hydrogen peroxide to water (oxygen is not produced).
Correct Answer: Catalase
Obligate anaerobes cannot survive in the presence of oxygen
Correct Answer: An obligate anaerobe
Differential media use specific ingredients to differentiate between organisms. A selective medium is one that contains ingredients that prohibit the growth of some organisms while fostering the growth of others. Mannitol salt agar is both selective and differential: its high salt concentration (7.5%) selects for Staphylococcus species while inhibiting the growth of other bacteria while the mannitol sugar permits differentiation between species of Staphylococcus.
Correct Answer: Both selective and differential
Like mannitol salt agar, eosin methylene blue is both selective and differential. When grown on EMB agar, colonies of E. coli have a bright and easily identifiable green sheen, created as the E. coli ferment lactose. Other enteric bacteria do not ferment lactose in the same way and so don’t look green when grown on EMB. This makes E. coli easily distinguishable from colonies of other enteric organisms.
Correct Answer: Differentiates organisms by lactose fermentation
Blood agar is used to differentiate between organisms on the basis of hemolysis of red blood cells. Gamma hemolysis shows no destruction of red blood cells around the bacterial growth, alpha hemolysis shows incomplete hemolysis of red blood cells, and beta hemolysis causes complete destruction of red blood cells.
Correct Answer: No destruction of red blood cells
The death phase represents a continuous decline in the number of dividing cells and is inversely parallel to the log phase. Because of this relationship, the death phase is sometimes called the logarithmic decline phase.
Correct Answer: Death
Measuring biomass is an indirect measurement and can be correlated with cell number.
Correct Answer: Indirect
Viable cell count is a direct method used to determine the number of live bacteria in a sample.
Correct Answer: Direct
Microscopic count is a direct method and counts both living and dead cells.
Turbidity is a rapid and routinely used indirect method and requires correlation with plate count at one time.
Correct Answer: Indirect
Plate count is a slow but simple direct method where colonies on a plate are counted by hand.
Acid production is an indirect method using titration to measure acid production and pH to detect bacterial growth.