The Enterics

1.

What are the 4 main groups of enterics?

Explanation
The correct answer is Enterobacteriaceae, Vibrionaceae, Pseudomonadaceae, and Bacteroidaceae. These four groups are the main classifications of enteric bacteria. Enterobacteriaceae includes common pathogens such as Escherichia coli and Salmonella. Vibrionaceae consists of bacteria like Vibrio cholerae, which causes cholera. Pseudomonadaceae includes Pseudomonas aeruginosa, a common cause of hospital-acquired infections. Bacteroidaceae includes Bacteroides fragilis, which is a normal inhabitant of the human gastrointestinal tract. These groups are important in clinical microbiology and have unique characteristics and clinical significance.

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2.

The enterics...

A.

Are gram negatives that are part of the normal intestinal flora or cause GI disease.
B.

Are gram positives that are part of the normal intestinal flora or cause GI disease.
C.

Have the ability to ferment lactose and produce H2S
D.

Have O, K, H antigen

Correct Answer
A. Are gram negatives that are part of the normal intestinal flora or cause GI disease.

Explanation
c) Escherichia coli and most of Enterobacteriaceae ferment lactose but Salmonella, Shigella and Pseudomonas aeruginosa do not!!
d) All have O antigen (LPS), but K(capsule) and H (flagella/motile) antigen are only present on some.

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3.

Which of these DOES ferment lactose? (meaning it converts lactose to gas and acid which can be visualized with a pH dye)

A.

E. coli
B.

Salmonella
C.

Shigella
D.

Pseudomonas aeruginosa

Correct Answer
A. E. coli

Explanation
E. coli is capable of fermenting lactose, converting it into gas and acid, which can be visualized with a pH dye.

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4.

What is not true about EMB agar?

A.

Methelene blue inhibits gram-positive bacteria
B.

Lactose fermenters become deep purple to black
C.

Bile salts inhibit gram- positive bacteria
D.

E. coli takes on a metallic green sheen in this medium.
E.

Lactose fermenters become pink-purple
F.

A and b
G.

B and c
H.

C and e
I.

A and e

Correct Answer
H. C and e

Explanation
The given correct answer is "c and e". This means that the statements "Bile salts inhibit gram-positive bacteria" and "lactose fermenters become pink-purple" are not true about EMB agar. EMB agar actually contains bile salts, which inhibit the growth of gram-positive bacteria. Additionally, lactose fermenters on EMB agar produce colonies that are typically deep purple to black in color, not pink-purple.

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5.

What is not true about MacConkey agar?

A.

Bile salts in the medium inhibit gram- positive growth
B.

Methelene blue in the medium inhibits gram- positive growth
C.

Lactose fermenters take on a metallic green sheen
D.

Lactose fermenters take on a pink-purple color
E.

A and c
F.

B and d
G.

A and d
H.

B and c

Correct Answer
H. B and c

Explanation
The statement "methelene blue in the medium inhibits gram-positive growth" is not true about MacConkey agar. MacConkey agar contains bile salts which inhibit the growth of gram-positive bacteria, not methylene blue. Additionally, lactose fermenters on MacConkey agar take on a pink-purple color, not a metallic green sheen. Therefore, the correct answer is b and c.

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6.

What are the 3 surface antigens that the enterics may have and what do they stand for?

A.

O (the external most part of LPS), K (capsule that is just inside the O antigen), and J (invasion toxin)
B.

A (lipid A of LPS) , K (capsule just outside of the LPS), H (flagella so on motile enterics)
C.

O (outermost part of LPS), K (capsule just outside the O antigen), H (flagella on motile bacteria)
D.

A (lipid A of LPS), K (capsule just inside the LPS), J (invasion toxin)

Correct Answer
C. O (outermost part of LPS), K (capsule just outside the O antigen), H (flagella on motile bacteria)

Explanation
The correct answer is O (outermost part of LPS), K (capsule just outside the O antigen), H (flagella on motile bacteria). The O antigen is the outermost part of the lipopolysaccharide (LPS) in the cell wall of enteric bacteria. The K antigen refers to the capsule that is located just outside the O antigen. The H antigen represents the flagella found on motile bacteria. These surface antigens play important roles in the identification and classification of enteric bacteria.

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7.

Which is not a correct description/ example of the diarrhea that can be caused by enterics depending on the depth of invasion?

A.

Invasion of the intestinal epithelial cells: virulence factors for invasion and binding present. TOxins destroy the cells and there is a systemic immune response that causes local WBC infiltration (pus in stool) and fever. Cell death - RBC in stool. ex) Enteroinvasive Escherichia coli, Shigella, Salmonella enteritidis
B.

Invasion of the lymph nodes and blood stream: systemic symp. of fever, headache, wbc elevation; also abd cramps ad r and w blood cells in the stool. ex) Salmonella typhi, Yersinia enterocolitica, Campylobacter jejuni
C.

Invasion of the intestinal epithelial cells: virulence factors for invasion and binding present. TOxins destroy the cells and there is a systemic immune response that causes local WBC infiltration (pus in stool) and fever. No RBC in stool. ex) Enterohemorragic Escherichia coli, Salmonella enteritidis
D.

No cell invasion: Bact bind to the intest epithelial cells but do not enter the cell. Diarrhea caused by release of exotoxin (enterotoxin)which cause electrolyte and fluid loss from intest epithelial cells = watery diarrhea without systemic symptoms. ex) Enterotoxigenic E. coli and vibrio cholera

Correct Answer
C. Invasion of the intestinal epithelial cells: virulence factors for invasion and binding present. TOxins destroy the cells and there is a systemic immune response that causes local WBC infiltration (pus in stool) and fever. No RBC in stool. ex) Enterohemorragic Escherichia coli, Salmonella enteritidis

Explanation
This answer is correct because it accurately describes the characteristics of enterohemorrhagic Escherichia coli and Salmonella enteritidis infections. These enterics invade the intestinal epithelial cells using virulence factors, leading to the destruction of cells and a systemic immune response. This immune response causes local white blood cell infiltration, resulting in the presence of pus in the stool and fever. However, there is no presence of red blood cells in the stool in these infections.

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8.

Family Enterobacteriaceae includes all of the folllowing except:

A.

E. coli
B.

Klebsiella
C.

Proteus mirabilis
D.

Enterobacter
E.

Serratia
F.

Shigella
G.

Salmonella
H.

Campylobacter jejuni
I.

Yersinia enterocolitica

Correct Answer
H. Campylobacter jejuni

Explanation
The family Enterobacteriaceae includes various genera of bacteria that are commonly found in the intestines of humans and animals. These bacteria are gram-negative, facultative anaerobes, and are often associated with gastrointestinal infections. E. coli, Klebsiella, Proteus mirabilis, Enterobacter, Serratia, Shigella, Salmonella, and Yersinia enterocolitica are all members of the Enterobacteriaceae family. However, Campylobacter jejuni is not a member of this family. Campylobacter jejuni is a curved, gram-negative bacterium that is a common cause of foodborne illness, specifically causing gastroenteritis in humans. It belongs to the Campylobacteraceae family, not Enterobacteriaceae.

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