Question 1

At present, the most accurate indicator of evolutionary relatedness among organisms is the

Accepted Answer

The sequence of the ribosomal small subunit RNA is considered the most accurate indicator of evolutionary relatedness among organisms. This is because the sequence of this RNA is highly conserved and relatively slow to evolve, making it useful for tracing evolutionary history. Differences in the sequence of this RNA can also be used to determine the degree of relatedness between organisms.

Question 2

Researchers studying the rigidity and flexibility of the cell envelope used chemotaxis to measure the ability of microbes to squeeze through tight spaces. E. coli, a gram-negative bacterium, was able to traverse narrower channels than B. subtilis, a gram-positive microbe, even though both cells are the same size when grown without restriction. E. coli has the more flexible cell envelope because

Accepted Answer

E. coli, being gram-negative, has a thinner peptidoglycan layer compared to the thicker peptidoglycan layer in gram-positive bacteria like B. subtilis, resulting in a more flexible cell envelope.

Question 3

Archaea have been found in many microenvironments in the human body.Which of the following microenvironments is most likely to fit with the designation of Archaea as "extremophiles?"

Accepted Answer

Archaea are known for thriving in extreme conditions, such as high temperature, extreme pH, high salt concentrations, and anaerobic environments. The gingiva and gut are both anaerobic environments, which makes them the most likely microenvironments for Archaea to be considered "extremophiles." The other options do not involve extreme conditions that are typically associated with Archaea.

Question 4

You have found a mutant of Streptococcus pneumoniae that has lost the ability to produce a capsule.If you inject this strain into a population of healthy mice, what prediction can you make about the consequences?

Accepted Answer

The capsule produced by Streptococcus pneumoniae is an important virulence factor that helps the bacterium evade the host's immune system. It also protects the bacterium from phagocytosis. Without the capsule, the bacterium is more susceptible to phagocytosis and therefore less virulent. Therefore, the mice are likely to remain healthy because the mutant strain is less likely to cause a severe infection.

Question 5

A patient has a serious respiratory infection.A sputum sample yielded a bacterium that did not have any peptidoglycan.You hypothesize that the identity of this microbe could possibly be ______.

Accepted Answer

Mycoplasma pneumoniae is known for lacking a cell wall, including peptidoglycan. This makes it resistant to certain antibiotics that target the cell wall, and is also a characteristic used to identify this bacterium.

Question 6

You apply the acid-fast stain method to a patient's specimen, an aspirate from the lungs.Microscopic examination reveals a large number of bright pink-red bacillus-shaped bacteria in the smear.Which statement is true?

Accepted Answer

The acid-fast stain method is used to detect acid-fast bacteria like Mycobacterium tuberculosis which causes tuberculosis. The presence of a large number of pink-red bacillus-shaped bacteria suggests the presence of M. tuberculosis in the patient's specimen, indicating a possible tuberculosis infection.

Question 7

If you observe rod-shaped, pink cells on a slide that had just been Gram stained, you can assume that their cell envelope contains endotoxin.
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Accepted Answer

Gram-negative bacteria have a cell envelope that contains endotoxin in their outer membrane, which is released upon cell lysis and can cause an immune response in the host. Rod-shaped, pink cells are indicative of Gram-negative bacteria, so it can be assumed that their cell envelope contains endotoxin.

Question 8

Which of the following is mismatched?

Accepted Answer

Tenericutes have no cell walls, not waxy or acid-fast ones.

Question 9

E. coli has been isolated and cultured from three different individuals. Upon biochemical testing of these three cultures, you find that there are differences in some reactions. What is the best explanation of these differences?

Accepted Answer

It is normal genetic variation seen among strains of E. coli. E. coli is known for its genetic diversity, and different strains can have varying biochemical reactions.

Question 10

A research laboratory that identifies the subspecies of bacterial isolates from a recent Salmonella epidemic would refer to Bergey's Manual of ______ Bacteriology for guidance in identification.

Accepted Answer

Bergey's Manual of Systematic Bacteriology is the standard reference for the identification and classification of bacteria.

Question 11

The process of sporangium formation and endospore maturation requires 6-8 hours.What is most likely to result if the temperature of the environment was raised to 100°C about 2 hours after the process started?

Accepted Answer

Raising the temperature to 100°C after 2 hours of sporangium formation and endospore maturation will likely denature the proteins and disrupt the process of endospore maturation. The endospore requires several hours to become fully heat resistant, and raising the temperature at such an early stage would prevent it from forming properly. Therefore, the best choice is E, which states that the endospore would not form properly because it is not yet heat resistant.

Question 12

In which situation would a bacterium most likely have cytoplasmic inclusions?

Accepted Answer

Cytoplasmic inclusions are storage materials found in bacteria, often accumulating when nutrients are abundant, allowing the cell to store excess nutrients for future use.

Question 13

A clinical laboratory that identifies the bacterial agents that cause human disease would refer to Bergey's Manual of ______ Bacteriology for guidance in identification.

Accepted Answer

Bergey's Manual of Determinative Bacteriology is used for the identification of bacterial species based on their physical and biochemical characteristics. It is commonly used by clinical laboratories as a reference for identifying human pathogens. Systematic and evolutionary bacteriology deal with the classification and evolution of bacteria rather than their identification, while classical bacteriology refers to the early history of microbiology and is not commonly used in modern laboratory settings.

Question 14

You need to determine if a pure culture of bacteria is gram-positive or gram-negative, but you've just spilled your only solution of crystal violet so you can't do a Gram stain.You decide to try a lysozyme treatment on a sample of each culture and then examine the samples under the microscope.The expected result is

Accepted Answer

Lysozyme is an enzyme that breaks down the peptidoglycan layer in the cell wall of bacteria, causing them to lyse. Gram-negative bacteria have a thinner peptidoglycan layer compared to gram-positive bacteria, which makes them more resistant to lysozyme treatment. Therefore, gram-negative bacteria will be less affected by the lysozyme treatment, while gram-positive bacteria will be lysed and appear as debris. Thus, the expected result is that gram-positives will lyse and appear as debris, while gram-negatives will be unaffected.

Question 15

You've just isolated a new bacterium in pure culture, and you culture it on a general purpose medium where its cells have a coccobacillus morphology.When you examine the cells after culturing on a variety of differential media, you find that in some cases, the cells appear as coccobacillus, but in others, they can be filamentous, cocci, or club-shaped.The best explanation for this observation is that

Accepted Answer

The observation that the cells can have various shapes (coccobacillus, filamentous, cocci, or club-shaped) suggests that the bacterium is pleomorphic, meaning it can change its shape under different conditions.

Question 16

Serological analysis for bacterial identification typically involves using

Accepted Answer

Serological analysis involves the use of specific antibodies to identify bacterial antigens. This is done through techniques such as ELISA or agglutination tests. Microscopic analysis, base concentration determination, enzyme identification, and colony appearance analysis are other methods for bacterial identification but these are not typically used in serological analysis.

Question 17

You've just isolated a new bacterium in pure culture, and you culture it on a general purpose medium where its cells have a rod-shape (bacillus) morphology.In addition to culturing it on solid media, you inoculate a slide to grow it as a biofilm.When you use confocal microscopy to image the biofilm, you observe that there are several cellular morphologies, ranging from coccus to coccobacillus to long bacillus.The best explanation for this observation is that

Accepted Answer

The microenvironments within a biofilm can promote structural variation in bacterial cells, leading to different morphologies. This phenomenon is known as phenotypic heterogeneity or biofilm diversity. Therefore, it is expected to observe different bacterial cell shapes in a biofilm culture of the same species. The other options, such as a faulty microscope, impure culture, and inappropriate incubation conditions, are less likely explanations for this observation.

Question 18

A new drug is found to act by blocking the incorporation of subunits into sterol molecules for the cell membrane.Which statement is true?

Accepted Answer

This drug would only affect bacteria with sterols in their cell membrane, such as mycoplasmas. However, most bacteria, including many pathogenic species, do not have sterols in their cell membrane and would be unaffected by this drug. Therefore, it would not be a broad-spectrum antibiotic.

Question 19

You have made a smear of a bacterial culture and have performed the Gram stain on it.Looking at the organism under the microscope, you notice that the cells do not seem to be the dark blue-purple of a gram-positive reaction, but instead are light purple.Your staining procedure was performed correctly.What is your best explanation as to why the bacteria have stained this way?

Accepted Answer

The light purple staining suggests that the bacterial cells did not retain the crystal violet dye during the staining process, which indicates that the cells have a thinner peptidoglycan layer in their cell wall. This is often characteristic of gram-negative bacteria, which have an additional outer membrane that can interfere with the uptake of the crystal violet stain.

Question 20

Which of the following bacteria is not closely related to the others?

Accepted Answer

Salmonella bongori is a distinct species from the other options, which are subspecies of Salmonella enterica.

Quiz 4: Bacteria and Archaea