Question 1

A physician suspects his patient has Helicobacter pylori. To confirm the diagnosis, he will submit a

Accepted Answer

Gastric biopsy is the most accurate method for diagnosing Helicobacter pylori infection.

Question 2

Which of the following scenarios indicates the potential for the isolation of Vibrio vulnificus?

Accepted Answer

Vibrio vulnificus is a bacterium that is commonly associated with marine environments. Scenario A, involving a fish hook injury on the hand acquired in the Gulf of Mexico, indicates potential exposure to marine bacteria, including Vibrio vulnificus, especially in warm seawater.

Question 3

Alkaline peptone water is an ideal transportation medium for

Accepted Answer

Alkaline peptone water is specifically designed to support the growth of Vibrio species, including Vibrio cholerae, by providing an alkaline environment that inhibits the growth of competing bacteria.

Question 4

The pathogenesis of Vibrio cholerae is related to its ability to

Accepted Answer

Vibrio cholerae causes disease primarily through the production of a powerful enterotoxin called cholera toxin, which leads to severe diarrhea.

Question 5

Which of the following environments or atmospheres is required for the isolation of a gram-negative rod that is a stool pathogen and oxidase positive, catalase positive, and able to hydrolyze hippurate?

Accepted Answer

The organism described is likely Campylobacter jejuni, which is a gram-negative rod, oxidase positive, catalase positive, and hydrolyzes hippurate. It requires a capnophilic and microaerophilic environment for optimal growth.

Question 6

Which of the following oxidase-positive, gram-negative rods can be differentiated from Vibrio cholerae based on its inability to grow on thiosulfate citrate bile salts agar?

Accepted Answer

The answer of Which of the following oxidase-positive, gram-negative rods...

Question 7

Which of the following tests can be used to rapidly identify Helicobacter pylori?

Accepted Answer

Urease test is used to rapidly identify Helicobacter pylori because this bacterium produces a large amount of urease, which hydrolyzes urea to produce ammonia and carbon dioxide, a distinctive reaction that can be detected quickly.

Question 8

All of the following tests can be used to differentiate Aeromonas hydrophila and Plesiomonas shigelloides except

Accepted Answer

Both Aeromonas hydrophila and Plesiomonas shigelloides are indole positive, so the indole test cannot be used to differentiate between them.

Question 9

Aeromonas hydrophila, Plesiomonas shigelloides, and Chromobacterium violaceum share all of the following characteristics except

Accepted Answer

Aeromonas hydrophila and Plesiomonas shigelloides are indole positive, but Chromobacterium violaceum is typically indole negative.

Question 10

Small comma-shaped, oxidase-positive, gram-negative rods that are susceptible to O/129 and string test positive is characteristic for an organism that

Accepted Answer

The description matches Vibrio cholerae, which is known for causing rice water stools in cholera.

Question 11

Which of the following Vibrio species does not require saline for growth?

Accepted Answer

V. cholerae does not require saline for growth, unlike other Vibrio species mentioned, which typically require a saline environment to thrive.

Question 12

Campylobacter jejuni is unique in that it will grow, with the appropriate atmosphere, at

Accepted Answer

Campylobacter jejuni is a thermophilic bacterium that can grow at a wide range of temperatures, from 4°C to 42°C.

Question 13

A gram-negative rod is isolated from the bronchial aspirate of an individual who inhaled a minnow while swimming at Lake of the Ozarks in central Missouri. The organism is oxidase positive. Which of the following organism identifications is least likely for this isolate?

Accepted Answer

E. coli is a gram-negative rod but is oxidase negative, making it the least likely option among those listed, which are all oxidase positive.

Question 14

A dark pigmented colony is isolated from the leg wound of a fisherman from Florida. The gram-negative rod grows on sheep blood and MacConkey agars. The organism provides the following reactions:
$\begin{array}{lll}\text {TSI: K/ A } &\text {Indole: no color change }&\text {Lysine: no color change}\
\text {1 \% NaCL  : no growth}&\text { Arginine: purple}&\text {Ornithine: no color change}\
\text {DNase: pink halo around the area of organism inoculum}
\end{array}$
The microbiologist cannot read the oxidase reaction due to the dark pigment. What can he do to help achieve a valid oxidase reaction?

Accepted Answer

The answer of A dark pigmented colony is isolated from...

Question 15

A 22-year-old male has recently adopted an Akita puppy that develops diarrhea soon after he takes it home. He soon develops bloody diarrhea and visits his physician. The doctor submits a stool for routine culture and ova and parasite examination. The O & P examination was negative. The routine culture reveals no Salmonella, Shigella, or verotoxin producing E. coli. On special medium, at a unique temperature and atmosphere, a slightly spreading, gray, flat colony is observed. A Gram stain of the colony provides gram-negative rods that appear "S" shaped. Which of the following tests can be used to screen and presumptively identify this stool pathogen?

Accepted Answer

The answer of A 22-year-old male has recently adopted an...

Question 16

Helicobacter pylori is easily identified from a gastric biopsy based on which of the following tests?

Accepted Answer

Helicobacter pylori is urease positive, and the urease test is commonly used to identify it from gastric biopsies.

Question 17

A stool culture reveals an oxidase-positive, non-lactose fermenting colony. A suspension of the organism was made in sterile distilled water and used to inoculate a commercial identification strip that did not demonstrate any positive reactions after incubation. The microbiologist then set up traditional biochemical tube tests and the results were still negative. What is the next step in the identification process?

Accepted Answer

The organism is oxidase-positive and non-lactose fermenting, which suggests that it may be a member of the family Vibrionaceae. Halophiles are a group of bacteria that can tolerate high salt concentrations, and many members of the Vibrionaceae are halophilic. Therefore, performing halotolerance testing would be the next logical step in the identification process.

Question 18

If you suspect an isolate to be Vibrio spp., which of the following tests would you be least likely use as part of the identification scheme due to its low sensitivity and specificity?

Accepted Answer

The string test is less reliable due to its low sensitivity and specificity compared to other tests like O1 and O139 antisera, O/129 susceptibility, and TCBS growth, which are more commonly used for identifying Vibrio spp.

Question 19

Each of the following tests can be used to monitor the effectiveness of therapy against Helicobacter pylori except

Accepted Answer

Serology is not useful for monitoring the effectiveness of therapy against Helicobacter pylori because it can remain positive for a long time after successful eradication, reflecting past exposure rather than current infection. Gastric biopsy and urea breath test are useful for assessing current infection status and thus the effectiveness of therapy.

Question 20

Which of the following individuals could potentially have the worst outcome if his or her described infection is due to Vibrio vulnificus?

Accepted Answer

Vibrio vulnificus is particularly dangerous for individuals with compromised immune systems, such as liver transplant recipients. In such cases, the infection can lead to septicemia, which has a high mortality rate.

Quiz 23: Vibrio, Aeromonas, Plesiomonas, Campylobacter, Helicobacter, and Chromobacterium