Question 1

Which of the following descriptions will directly facilitate identification of bacteria?

Accepted Answer

Physical characteristics of colony morphology, such as shape, texture, and size, are specific to certain bacterial species and can be used to identify them. Environmental growth temperature, atmospheric conditions, and colony color can vary among different bacterial species but may not be specific enough for identification without additional testing or analysis.

Question 2

Swarming is

Accepted Answer

Swarming is when bacterial growth appears as a hazy blanket on the surface of the agar and extends beyond the initial streak lines. This pattern is commonly seen in Proteus species of bacteria. Option A refers to bacterial colonies being crowded together, but does not necessarily imply swarming. Option B describes a different phenomenon called hemolysis, where bacteria cause the breakdown of red blood cells on a Blood Agar Plate. Option C describes a pattern of hemolysis, but not necessarily swarming.

Question 3

A microbiologist is reading stool culture plates. She sees an organism that has a dry, pink colony with a surrounding "halo" of pink on MAC. What is a good presumptive identification of this organism?

Accepted Answer

The description of a dry, pink colony with a surrounding "halo" of pink on MacConkey agar (MAC) suggests a lactose-fermenting organism, which is characteristic of Escherichia coli and some Citrobacter species. These organisms typically produce pink colonies on MAC due to lactose fermentation, which is indicative of Escherichia/Citrobacter-like organisms.

Question 4

Colonies of Bacillus anthracis are described as

Accepted Answer

Colonies of Bacillus anthracis are described as resembling "Medusa's heads" due to their irregular, filamentous projections that resemble the snakes on the mythical Medusa's head. This characteristic is used in microbiology to help identify the organism in culture.

Question 5

Colony morphology is defined as

Accepted Answer

Colony morphology refers to the observable characteristics of a colony, such as its size, shape, texture, and color. It does not include smell or constitution, and while environmental conditions can impact colony morphology, they are not inherent characteristics of the colony itself.

Question 6

The edge of the colonies is described as all the following, except

Accepted Answer

The term "glasslike" is not typically used to describe the edge of colonies in microbiology. The other options (smooth, filamentous, irregular) are common descriptors for colony edges.

Question 7

Colonies growing on the SBA have discolored the media to a green color around and under the colonies. This is consistent with which type of hemolysis?

Accepted Answer

The answer of Colonies growing on the SBA have discolored...

Question 8

Generally, microbiologists observe the colonial morphology of organisms on primary culture after how many hours of incubation?

Accepted Answer

Colonial morphology of organisms on primary culture is typically observed after 18 to 24 hours of incubation, as this time frame allows most bacteria to grow sufficiently to be visible and distinguishable.

Question 9

A microbiologist is reading stool culture plates. She sees an organism that has a large, mucoid pink colony on MAC. What is a good presumptive identification of this organism?

Accepted Answer

Klebsiella and Enterobacter are both known to produce mucoid, pink-colored colonies on MAC. This is due to production of an exopolysaccharide called colanic acid. However, further testing would be needed to confirm the exact species of organism present.

Question 10

Gamma ($\gamma$)-hemolysis is

Accepted Answer

Gamma hemolysis refers to the lack of hemolytic activity by bacteria on blood agar plates (BAP), meaning the organisms do not lyse the erythrocytes in the medium.

Question 11

Beta ($\beta$ )-hemolysis is

Accepted Answer

Beta-hemolysis is the complete clearing of erythrocytes (red blood cells) in a blood agar plate (BAP) around and under the colony. The code F1F1F1S1F1F1F10 indicates the specific type of beta-hemolysis observed.

Question 12

Alph ($\beta$)-hemolysis is

Accepted Answer

Alpha-hemolysis (α-hemolysis) is characterized by the partial lysing of erythrocytes in a blood agar plate (BAP), which results in a greenish or brownish discoloration around and under the colony, not complete clearing or no effect.

Question 13

The colonies growing on the SBA have produced a wide, deep, clear zone around and under the colonies. This is consistent with which type of hemolysis?

Accepted Answer

The answer of The colonies growing on the SBA have...

Question 14

When differentiating colony size on the culture plates, what organisms generally have the larger colonies by comparison?

Accepted Answer

Gram-negative rods generally form larger colonies on culture plates compared to other types of bacteria due to their rapid growth rate and efficient nutrient uptake mechanisms.

Question 15

When microbiologists set up a biochemical identification using a commercial system on a suspected pathogen from a culture, they must

Accepted Answer

The answer of When microbiologists set up a biochemical identification...

Question 16

The relative concentration of bacteria on culture plates is directly proportional to

Accepted Answer

The relative concentration of bacteria on culture plates is directly proportional to the concentration in which they are present in the clinical specimen, as this determines the initial number of bacteria available to grow and multiply on the plate.

Question 17

An upper respiratory specimen contains many indigenous organisms which may be time consuming, cost prohibitive, and insurmountable. What should the microbiologist do?

Accepted Answer

The best option is to differentiate potential pathogens from the "usual" inhabitants of the upper respiratory tract and direct the diagnostic workup only to potential pathogens. This approach is cost-effective, less time-consuming, and provides better patient care as it targets the most likely causative agents of disease. Working quickly with commercially available kits may not necessarily result in accurate identification of all organisms present in a sputum specimen, and working up only the gram-negative rods present in the culture may miss important pathogens. Additionally, it is important to be able to ascertain whether the results generated by a commercial or automated system correlate with the suspected organism, but this alone is not sufficient for a comprehensive diagnostic approach.

Question 18

A microbiologist is reading stool culture plates. She is looking for enteric pathogens on the MAC plate. What do they look like?

Accepted Answer

Enteric pathogens such as Salmonella and Shigella typically appear as clear, colorless colonies on MacConkey (MAC) agar because they do not ferment lactose.

Question 19

MacConkey (MAC) agar is used to

Accepted Answer

MacConkey agar is a selective and differential medium that helps to differentiate lactose fermenters (which produce acid and cause pink colonies) from lactose nonfermenters (which do not produce acid and appear colorless on the medium). It is commonly used to isolate and identify enteric bacteria, such as Escherichia coli and Salmonella typhimurium, from clinical and environmental samples.

Question 20

Plate reading is

Accepted Answer

Plate reading involves examining bacterial growth on culture media, which includes comparing the growth on different types of media. This is known as a comparative examination. It does not necessarily involve examining colonial morphology or setting up biochemical tests. The purpose of plate reading is to determine the characteristics of bacterial growth in order to identify and classify the bacteria.

Quiz 8: Use of Colony Morphology for the Presumptive Identification of Microorganisms

Which of the following descriptions will directly facilitate identification of bacteria?

Swarming is

A microbiologist is reading stool culture plates. She sees an organism that has a dry, pink colony with a surrounding "halo" of pink on MAC. What is a good presumptive identification of this organism?

Colonies of Bacillus anthracis are described as

Colony morphology is defined as

The edge of the colonies is described as all the following, except

Colonies growing on the SBA have discolored the media to a green color around and under the colonies. This is consistent with which type of hemolysis?

Generally, microbiologists observe the colonial morphology of organisms on primary culture after how many hours of incubation?

A microbiologist is reading stool culture plates. She sees an organism that has a large, mucoid pink colony on MAC. What is a good presumptive identification of this organism?

Gamma ( $\gamma$ ) -hemolysis is

Beta ( $\beta$ ) -hemolysis is

Alph ( $\beta$ ) -hemolysis is

The colonies growing on the SBA have produced a wide, deep, clear zone around and under the colonies. This is consistent with which type of hemolysis?

When differentiating colony size on the culture plates, what organisms generally have the larger colonies by comparison?

When microbiologists set up a biochemical identification using a commercial system on a suspected pathogen from a culture, they must

The relative concentration of bacteria on culture plates is directly proportional to

An upper respiratory specimen contains many indigenous organisms which may be time consuming, cost prohibitive, and insurmountable. What should the microbiologist do?

A microbiologist is reading stool culture plates. She is looking for enteric pathogens on the MAC plate. What do they look like?

MacConkey (MAC) agar is used to

Plate reading is

Quiz 8: Use of Colony Morphology for the Presumptive Identification of Microorganisms

Which of the following descriptions will directly facilitate identification of bacteria?

Swarming is

A microbiologist is reading stool culture plates. She sees an organism that has a dry, pink colony with a surrounding "halo" of pink on MAC. What is a good presumptive identification of this organism?

Colonies of Bacillus anthracis are described as

Colony morphology is defined as

The edge of the colonies is described as all the following, except

Colonies growing on the SBA have discolored the media to a green color around and under the colonies. This is consistent with which type of hemolysis?

Generally, microbiologists observe the colonial morphology of organisms on primary culture after how many hours of incubation?

A microbiologist is reading stool culture plates. She sees an organism that has a large, mucoid pink colony on MAC. What is a good presumptive identification of this organism?

Gamma ( γ\gammaγ ) -hemolysis is

Beta ( β\betaβ ) -hemolysis is

Alph ( β\betaβ ) -hemolysis is

The colonies growing on the SBA have produced a wide, deep, clear zone around and under the colonies. This is consistent with which type of hemolysis?

When differentiating colony size on the culture plates, what organisms generally have the larger colonies by comparison?

When microbiologists set up a biochemical identification using a commercial system on a suspected pathogen from a culture, they must

The relative concentration of bacteria on culture plates is directly proportional to

An upper respiratory specimen contains many indigenous organisms which may be time consuming, cost prohibitive, and insurmountable. What should the microbiologist do?

A microbiologist is reading stool culture plates. She is looking for enteric pathogens on the MAC plate. What do they look like?

MacConkey (MAC) agar is used to

Plate reading is

Gamma ( $\gamma$ ) -hemolysis is

Beta ( $\beta$ ) -hemolysis is

Alph ( $\beta$ ) -hemolysis is