Direct count of total cells can be performed using a hemocytometer or a Petroff-Hausser counting chamber.
Missing Word
hemocytometer
Hemocytometers and Petroff-Hausser counting chambers are specialized slides with grids that allow for direct microscopic counting of cells in a known volume. This method provides a quick estimate of cell density, although it does not distinguish between live and dead cells.
Question 2
The plate count method allows direct count of total cells growing on solid medium.
Missing Word
plate count
The plate count method involves diluting a sample and plating it onto a solid medium, allowing viable cells to form colonies that can be counted. Each colony ideally arises from a single cell, providing an estimate of the number of colony-forming units (CFUs) in the original sample.
Question 3
A statistical estimate of the number of live cells in a liquid is usually done by most probable number.
Missing Word
most probable number
The most probable number (MPN) method is a statistical approach used to estimate the concentration of viable microorganisms in a sample by observing the presence or absence of growth in a series of dilutions. It is particularly useful for samples with low cell densities or when cells cannot grow on solid media.
Question 4
For this indirect method of estimating the growth of a culture, you measure turbidity using a spectrophotometer.
Missing Word
turbidity
Turbidity, or cloudiness, of a culture is directly related to cell density; a spectrophotometer measures the amount of light that passes through the culture. Increased cell growth results in increased turbidity and decreased light transmission, providing an indirect measure of cell concentration.
Question 5
Active growth of a culture may be estimated indirectly by measuring the following products of cell metabolism: ATP or acid from fermentation.
Missing Word
ATP
Active growth of a culture leads to the production of metabolic byproducts such as ATP (energy currency) or acids (from fermentation). Measuring these products provides an indirect assessment of the culture's metabolic activity and, by extension, its growth rate.
Question 6
A bacterium that thrives in a soda lake where the average pH is 10.5 can be classified as a(n) alkaliphile.
Missing Word
alkaliphile
Alkaliphiles are microorganisms that thrive in alkaline environments with high pH levels, typically above pH 9. Their enzymes and cellular structures are adapted to function optimally under these conditions, which would be detrimental to neutrophilic organisms.
Question 7
Lactobacillus acidophilus grows best at pH 4.5. It is considered a(n) acidophile.
Missing Word
acidophile
Acidophiles are organisms that thrive in acidic environments. Lactobacillus acidophilus's optimal growth at pH 4.5 directly aligns with the definition of an acidophile, indicating its adaptation to acidic conditions.
Question 8
A bacterium that thrives in the Great Salt Lake but not in fresh water is probably a halophile.
Missing Word
halophile
Halophiles require high salt concentrations for growth. The Great Salt Lake's high salinity provides the necessary environment for a halophile to thrive, while fresh water lacks the required salt concentration.
Question 9
Bacteria isolated from the bottom of the ocean need high atmospheric pressures to survive. They are barophiles.
Missing Word
barophiles
Barophiles, also known as piezophiles, require high pressure to grow. Bacteria from the ocean depths are adapted to the extreme pressure found there, making them barophiles.
Question 10
Staphylococcus aureus can be grown on multipurpose growth medium or on mannitol salt agar that contains 7.5% NaCl. The bacterium is halotolerant.
Missing Word
halotolerant
Halotolerant organisms can tolerate high salt concentrations but do not require them for growth. Staphylococcus aureus's ability to grow in both standard media and high-salt media demonstrates its halotolerance.
Question 11
Blood agar contains many unspecified nutrients, supports the growth of a large number of bacteria, and allows differentiation of bacteria according to hemolysis (breakdown of blood). The medium is complex and differential.
Missing Word
complex
Complex media contain ingredients of unknown chemical composition, while differential media allow for the visual distinction of different microbial species based on their metabolic activities. Blood agar fits both criteria, as it contains unspecified nutrients and allows for differentiation based on hemolysis.
Question 12
Rogosa agar contains yeast extract. The pH is adjusted to 5.2 and discourages the growth of many microorganisms; however, all the colonies look similar. The medium is complex and selective.
Missing Word
complex
Complex media contain ingredients of unknown chemical composition, while selective media inhibit the growth of some microorganisms while allowing others to grow. Rogosa agar's yeast extract makes it complex, and its low pH selectively inhibits many microorganisms.