Multiple Choice

Which of the following methods would be used to measure the concentration of bacterial contamination in processed peanut butter?

1. turbidity measurement
2. total plate count
3. dry weight measurement
4. direct counting of bacteria on a calibrated slide under the microscope

In which phase would you expect to observe the most endospores in a Bacillus cell culture?

1. death phase
2. lag phase
3. log phase
4. log, lag, and death phases would all have roughly the same number of endospores.

During which phase would penicillin, an antibiotic that inhibits cell-wall synthesis, be most effective?

1. death phase
2. lag phase
3. log phase
4. stationary phase

Which of the following is the best definition of generation time in a bacterium?

1. the length of time it takes to reach the log phase
2. the length of time it takes for a population of cells to double
3. the time it takes to reach stationary phase
4. the length of time of the exponential phase

What is the function of the Z ring in binary fission?

1. It controls the replication of DNA.
2. It forms a contractile ring at the septum.
3. It separates the newly synthesized DNA molecules.
4. It mediates the addition of new peptidoglycan subunits.

If a culture starts with 50 cells, how many cells will be present after five generations with no cell death?

1. 200
2. 400
3. 1600
4. 3200

Filamentous cyanobacteria often divide by which of the following?

1. budding
2. mitosis
3. fragmentation
4. formation of endospores

Which is a reason for antimicrobial resistance being higher in a biofilm than in free-floating bacterial cells?

1. The EPS allows faster diffusion of chemicals in the biofilm.
2. Cells are more metabolically active at the base of a biofilm.
3. Cells are metabolically inactive at the base of a biofilm.
4. The structure of a biofilm favors the survival of antibiotic resistant cells.

Quorum sensing is used by bacterial cells to determine which of the following?

1. the size of the population
2. the availability of nutrients
3. the speed of water flow
4. the density of the population

Which of the following statements about autoinducers is incorrect?

1. They bind directly to DNA to activate transcription.
2. They can activate the cell that secreted them.
3. N-acylated homoserine lactones are autoinducers in gram-negative cells.
4. Autoinducers may stimulate the production of virulence factors.

An inoculated thioglycolate medium culture tube shows dense growth at the surface and turbidity throughout the rest of the tube. What is your conclusion?

1. The organisms die in the presence of oxygen
2. The organisms are facultative anaerobes.
3. The organisms should be grown in an anaerobic chamber.
4. The organisms are obligate aerobes.

An inoculated thioglycolate medium culture tube is clear throughout the tube except for dense growth at the bottom of the tube. What is your conclusion?

1. The organisms are obligate anaerobes.
2. The organisms are facultative anaerobes.
3. The organisms are aerotolerant.
4. The organisms are obligate aerobes.

Pseudomonas aeruginosa is a common pathogen that infects the airways of patients with cystic fibrosis. It does not grow in the absence of oxygen. The bacterium is probably which of the following?

1. an aerotolerant anaerobe
2. an obligate aerobe
3. an obligate anaerobe
4. a facultative anaerobe

Streptococcus mutans is a major cause of cavities. It resides in the gum pockets, does not have catalase activity, and can be grown outside of an anaerobic chamber. The bacterium is probably which of the following?

1. a facultative anaerobe
2. an obligate aerobe
3. an obligate anaerobe
4. an aerotolerant anaerobe

Why do the instructions for the growth of Neisseria gonorrhoeae recommend a CO₂-enriched atmosphere?

1. It uses CO₂ as a final electron acceptor in respiration.
2. It is an obligate anaerobe.
3. It is a capnophile.
4. It fixes CO₂ through photosynthesis.

Bacteria that grow in mine drainage at pH 1–2 are probably which of the following?

1. alkaliphiles
2. acidophiles
3. neutrophiles
4. obligate anaerobes

Bacteria isolated from Lake Natron, where the water pH is close to 10, are which of the following?

1. alkaliphiles
2. facultative anaerobes
3. neutrophiles
4. obligate anaerobes

In which environment are you most likely to encounter an acidophile?

1. human blood at pH 7.2
2. a hot vent at pH 1.5
3. human intestine at pH 8.5
4. milk at pH 6.5

A soup container was forgotten in the refrigerator and shows contamination. The contaminants are probably which of the following?

1. thermophiles
2. acidophiles
3. mesophiles
4. psychrotrophs

Bacteria isolated from a hot tub at 39 °C are probably which of the following?

1. thermophiles
2. psychrotrophs
3. mesophiles
4. hyperthermophiles

In which environment are you most likely to encounter a hyperthermophile?

1. hot tub
2. warm ocean water in Florida
3. hydrothermal vent at the bottom of the ocean
4. human body

Which of the following environments would harbor psychrophiles?

1. mountain lake with a water temperature of 12 °C
2. contaminated plates left in a 35 °C incubator
3. yogurt cultured at room temperature
4. salt pond in the desert with a daytime temperature of 34 °C

Which of the following is the reason jams and dried meats often do not require refrigeration to prevent spoilage?

1. low pH
2. toxic alkaline chemicals
3. naturally occurring antibiotics
4. low water activity

Bacteria living in salt marshes are most likely which of the following?

1. acidophiles
2. barophiles
3. halotolerant
4. thermophiles

EMB agar is a medium used in the identification and isolation of pathogenic bacteria. It contains digested meat proteins as a source of organic nutrients. Two indicator dyes, eosin and methylene blue, inhibit the growth of gram-positive bacteria and distinguish between lactose fermenting and nonlactose fermenting organisms. Lactose fermenters form metallic green or deep purple colonies, whereas the nonlactose fermenters form completely colorless colonies. EMB agar is an example of which of the following?

1. a selective medium only
2. a differential medium only
3. a selective medium and a chemically defined medium
4. a selective medium, a differential medium, and a complex medium

Haemophilus influenzae must be grown on chocolate agar, which is blood agar treated with heat to release growth factors in the medium. H. influenzae is described as ________.

1. an acidophile
2. a thermophile
3. an obligate anaerobe
4. fastidious