Vibrio species — MCQs

10 questions

A 7-year-old boy is brought to the emergency room because of severe, acute diarrhea. He is drowsy with a dull, lethargic appearance. He has sunken eyes, poor skin turgor, and dry oral mucous membranes and tongue. He has a rapid, thready pulse with a systolic blood pressure of 60 mm Hg and his respirations are 33/min. His capillary refill time is 6 sec. He has had no urine output for the past 24 hours. Which of the following is the most appropriate next step in treatment?

A 47-year-old woman presents to a local medical shelter while on a mission trip with her church to help rebuild homes after a hurricane. She has been experiencing severe nausea, vomiting, and diarrhea for the last 2 days and was feeling too fatigued to walk this morning. On presentation, her temperature is 99.2°F (37.3°C), blood pressure is 95/62 mmHg, pulse is 121/min, and respirations are 17/min. Physical exam reveals decreased skin turgor, and a stool sample reveals off-white watery stools. Gram stain reveals a gram-negative, comma-shaped organism that produces a toxin. Which of the following is consistent with the action of the toxin most likely involved in the development of this patient's symptoms?

A 25-year-old man presents to the physician with 2 days of profuse, watery diarrhea. He denies seeing blood or mucus in the stools. On further questioning, he reveals that he eats a well-balanced diet and generally prepares his meals at home. He remembers having some shellfish from a street vendor 3 days ago. He takes no medications. His past medical history is unremarkable. Which of the following mechanisms most likely accounts for this patient’s illness?

A stool sample was taken from a 19-year-old male who presented with profuse watery diarrhea. He recently returned from a trip to Central America. A microbiologist identified the causative agent as a gram-negative, oxidase-positive, comma-shaped bacteria that is able to grow well in a pH > 8. Which of the following is a mechanism of action of the toxin produced by this bacteria?

A 57-year-old HIV-positive male with a history of intravenous drug abuse presents to the emergency room complaining of arm swelling. He reports that he developed progressively worsening swelling and tenderness over the right antecubital fossa three days prior. He recently returned from a trip to Nicaragua. His past medical history is notable for an anaphylactoid reaction to vancomycin. His temperature is 101.4°F (38.6°C), blood pressure is 140/70 mmHg, pulse is 110/min, and respirations are 20/min. Physical examination reveals an erythematous, fluctuant, and tender mass overlying the right antecubital fossa. Multiple injection marks are noted across both upper extremities. He undergoes incision and drainage and is started on an antibiotic that targets the 50S ribosome. He is discharged with plans to follow up in one week. However, five days later he presents to the same emergency room complaining of abdominal cramps and watery diarrhea. Which of the following classes of pathogens is most likely responsible for this patient’s current symptoms?

A 17-year-old girl comes to the physician because of a 12-hour history of profuse watery diarrhea with flecks of mucus that started shortly after she returned from a trip to South America. She has not had any fever or nausea. Pulse is 104/min and blood pressure is 110/65 mm Hg. Physical examination shows dry mucous membranes and decreased skin turgor. Stool culture shows gram-negative, comma-shaped, flagellated bacilli. Therapy with oral rehydration solution is initiated. Which of the following is the most likely mechanism of this patient's diarrhea?

A 45-year-old woman comes to the emergency department because of abdominal cramping, vomiting, and watery diarrhea for the past 4 hours. One day ago, she went to a seafood restaurant with her family to celebrate her birthday. Three of the attendees have developed similar symptoms. The patient appears lethargic. Her temperature is 38.8°C (101.8°F). Which of the following organisms is most likely responsible for this patient's current symptoms?

A 24-year-old woman presents with 3 days of diarrhea. She was recently on vacation in Peru and admits that on her last day of the trip she enjoyed a dinner of the local food and drink. Upon return to the United States the next day, she developed abdominal cramps and watery diarrhea, occurring about 3-5 times per day. She has not noticed any blood or mucous in her stool. Vital signs are stable. On physical examination, she is well appearing in no acute distress. Which of the following is commonly associated with the likely underlying illness?

A 23-year-old man comes to the physician because of a 2-day history of profuse watery diarrhea and abdominal cramps. Four days ago, he returned from a backpacking trip across Southeast Asia. Physical examination shows dry mucous membranes and decreased skin turgor. Stool culture shows gram-negative, oxidase-positive, curved rods that have a single polar flagellum. The pathogen responsible for this patient's condition most likely has which of the following characteristics?

Q10

An 83-year-old male presents to the emergency department with altered mental status. The patient’s vitals signs are as follows: temperature is 100.7 deg F (38.2 deg C), blood pressure is 143/68 mmHg, heart rate is 102/min, and respirations are 22/min. The caretaker states that the patient is usually incontinent of urine, but she has not seen any soiled adult diapers in the past 48 hours. A foley catheter is placed with immediate return of a large volume of cloudy, pink urine. Which of the following correctly explains the expected findings from this patient’s dipstick urinalysis?

Vibrio species US Medical PG Practice Questions and MCQs

Question 1: A 7-year-old boy is brought to the emergency room because of severe, acute diarrhea. He is drowsy with a dull, lethargic appearance. He has sunken eyes, poor skin turgor, and dry oral mucous membranes and tongue. He has a rapid, thready pulse with a systolic blood pressure of 60 mm Hg and his respirations are 33/min. His capillary refill time is 6 sec. He has had no urine output for the past 24 hours. Which of the following is the most appropriate next step in treatment?

A. Start IV fluid resuscitation by administering colloid solutions
B. Provide oral rehydration therapy to correct dehydration
C. Give initial IV bolus of 2 L of Ringer’s lactate, followed by packed red cells, fresh frozen plasma, and platelets in a ratio of 1:1:1
D. Start IV fluid resuscitation with normal saline or Ringer’s lactate, along with monitoring of vitals and urine output (Correct Answer)
E. Give antidiarrheal drugs

Explanation: ***Start IV fluid resuscitation with normal saline or Ringer's lactate, along with monitoring of vitals and urine output*** - This patient presents with **severe dehydration** and **hypovolemic shock** (lethargy, sunken eyes, poor skin turgor, dry mucous membranes, rapid thready pulse, hypotension [systolic BP 60 mmHg], tachypnea, prolonged capillary refill >5 seconds, and anuria). - According to **PALS guidelines**, the immediate priority is rapid intravenous administration of **isotonic crystalloids** (normal saline or Ringer's lactate) given as **20 mL/kg boluses** over 5-20 minutes, repeated as needed based on clinical response. - Close monitoring of vital signs, mental status, perfusion (capillary refill), and urine output is essential to assess response to resuscitation and guide further fluid management. *Start IV fluid resuscitation by administering colloid solutions* - While colloids (albumin, synthetic colloids) can expand intravascular volume, **isotonic crystalloids** are preferred for initial resuscitation in severe dehydration per **WHO and PALS guidelines**. - Crystalloids are equally effective, more readily available, less expensive, and have fewer potential adverse effects compared to colloids in pediatric dehydration. - There is no proven survival benefit of colloids over crystalloids in this clinical scenario. *Provide oral rehydration therapy to correct dehydration* - **Oral rehydration therapy (ORT)** is the appropriate first-line treatment for **mild to moderate dehydration** in children who can tolerate oral intake. - However, ORT is **contraindicated** in patients with **severe dehydration** or **hypovolemic shock**, particularly those with altered mental status, inability to drink, or hemodynamic instability. - This patient's drowsiness, hypotension, and signs of shock require immediate IV resuscitation; ORT would be too slow and potentially dangerous. *Give initial IV bolus of 2 L of Ringer's lactate, followed by packed red cells, fresh frozen plasma, and platelets in a ratio of 1:1:1* - A 2-liter bolus is **excessive and dangerous** for a 7-year-old child (average weight ~23 kg); the appropriate initial bolus is **20 mL/kg** (~460 mL), which can be repeated based on response. - The **1:1:1 massive transfusion protocol** (packed RBCs, FFP, platelets) is indicated for **hemorrhagic shock** with significant blood loss, not for hypovolemic shock from dehydration. - There is no evidence of bleeding or coagulopathy in this patient; blood products are not indicated. *Give antidiarrheal drugs* - **Antidiarrheal agents** (loperamide, diphenoxylate) are **contraindicated** in young children with acute infectious diarrhea, as they can prolong illness, increase risk of complications (toxic megacolon, bacterial overgrowth), and mask serious underlying conditions. - The priority in severe dehydration is **fluid and electrolyte resuscitation**, not stopping the diarrhea. - The diarrhea typically resolves once the underlying infection is controlled and hydration is restored.

Question 2: A 47-year-old woman presents to a local medical shelter while on a mission trip with her church to help rebuild homes after a hurricane. She has been experiencing severe nausea, vomiting, and diarrhea for the last 2 days and was feeling too fatigued to walk this morning. On presentation, her temperature is 99.2°F (37.3°C), blood pressure is 95/62 mmHg, pulse is 121/min, and respirations are 17/min. Physical exam reveals decreased skin turgor, and a stool sample reveals off-white watery stools. Gram stain reveals a gram-negative, comma-shaped organism that produces a toxin. Which of the following is consistent with the action of the toxin most likely involved in the development of this patient's symptoms?

A. Decreased ribosomal activity
B. Increased membrane permeability
C. Cleavage of junctional proteins
D. Increased adenylyl cyclase activity (Correct Answer)
E. Activation of receptor tyrosine kinase

Explanation: ***Increased adenylyl cyclase activity*** - The patient's symptoms (severe nausea, vomiting, diarrhea, dehydration, **hypotension**, and **tachycardia**) along with the presence of a **gram-negative, comma-shaped organism** producing an off-white watery stool are highly suggestive of **Cholera** caused by *Vibrio cholerae*. - Cholera toxin is an **AB5 toxin** that irreversibly activates **adenylyl cyclase** in intestinal epithelial cells, leading to increased intracellular cyclic AMP (cAMP) levels. This increased cAMP then causes massive secretion of chloride and bicarbonate into the intestinal lumen, followed by water, resulting in the characteristic **"rice-water stool"**. *Decreased ribosomal activity* - This mechanism is characteristic of toxins like **Shiga toxin** (produced by *Shigella dysenteriae* and enterohemorrhagic *E. coli*) and **diphtheria toxin** (produced by *Corynebacterium diphtheriae*). - These toxins inhibit protein synthesis by inactivating the 60S ribosomal subunit, which typically leads to **cytotoxicity** rather than the profuse watery diarrhea seen in cholera. *Increased membrane permeability* - Some toxins, such as **alpha-toxin** of *Clostridium perfringens* (gas gangrene) or **pore-forming toxins**, increase membrane permeability by creating pores in cell membranes. - While this can lead to cell damage and lysis, it is not the primary mechanism by which the cholera toxin causes massive fluid secretion. *Cleavage of junctional proteins* - Toxins that cleave **tight junction proteins** (e.g., *Clostridium difficile* toxins A and B) can disrupt the intestinal barrier and lead to fluid leakage. - However, the main mechanism of cholera toxin is fluid secretion due to ion channel activation rather than direct disruption of intercellular junctions. *Activation of receptor tyrosine kinase* - Activation of **receptor tyrosine kinases** is typically involved in cell growth, differentiation, and metabolism, not directly in acute, severe secretory diarrhea. - While some bacterial toxins can modulate host signaling pathways, direct activation of receptor tyrosine kinases is not the primary mechanism of action for toxins causing cholera-like symptoms.

Question 3: A 25-year-old man presents to the physician with 2 days of profuse, watery diarrhea. He denies seeing blood or mucus in the stools. On further questioning, he reveals that he eats a well-balanced diet and generally prepares his meals at home. He remembers having some shellfish from a street vendor 3 days ago. He takes no medications. His past medical history is unremarkable. Which of the following mechanisms most likely accounts for this patient’s illness?

A. Tyrosine kinase phosphorylation
B. ADP-ribosylation of Gs protein (Correct Answer)
C. Tyrosine kinase dephosphorylation
D. Osmotic effect of intestinal contents
E. Inflammation of the gastrointestinal wall

Explanation: ***ADP-ribosylation of Gs protein*** - The patient's history of consuming **shellfish from a street vendor** and presenting with **profuse, watery diarrhea** strongly suggests **cholera**. - **Cholera toxin** works by irreversibly ADP-ribosylating the **Gs alpha subunit**, leading to constitutive activation of **adenylate cyclase** and increased intracellular **cAMP**, which causes excessive fluid and electrolyte secretion into the intestinal lumen. *Tyrosine kinase phosphorylation* - This mechanism is characteristic of signaling pathways involved in growth and differentiation, often seen with **growth factor receptors**, and is not the primary cause of acute, watery diarrhea from food poisoning. - While some bacterial toxins can affect intracellular signaling, **tyrosine kinase phosphorylation** is not the direct mechanism for the massive fluid loss seen in cholera. *Tyrosine kinase dephosphorylation* - This process typically downregulates cell signaling pathways, which would likely **decrease** cellular activity, rather than trigger the profuse secretion seen in this patient's presentation. - It is not a known mechanism for the pathogenesis of infectious diarrheal diseases such as cholera. *Osmotic effect of intestinal contents* - While **osmotic diarrhea** is characterized by the presence of non-absorbable solutes in the gut lumen, drawing water in, the history here points more to an actively secreted fluid loss. - The sheer volume and rapid onset of the diarrhea suggest an active secretory mechanism rather than simply an osmotic effect from malabsorption. *Inflammation of the gastrointestinal wall* - **Inflammatory diarrhea** typically involves blood or mucus in the stool, fever, and abdominal pain, none of which are reported by the patient. - The patient's "profuse, watery" diarrhea without blood or mucus signifies a non-inflammatory, secretory etiology often caused by toxins.

Question 4: A stool sample was taken from a 19-year-old male who presented with profuse watery diarrhea. He recently returned from a trip to Central America. A microbiologist identified the causative agent as a gram-negative, oxidase-positive, comma-shaped bacteria that is able to grow well in a pH > 8. Which of the following is a mechanism of action of the toxin produced by this bacteria?

A. Overactivation of adenylate cyclase by inhibition of Gi subunit by ADP-ribosylation
B. Inactivation of the 60S ribosomal subunit by cleaving an adenine from the 28S rRNA
C. Overactivation of guanylate cyclase
D. Overactivation of adenylate cyclase by activation of Gs subunit by ADP-ribosylation (Correct Answer)
E. Degradation of cell membranes by hydrolysis of the phospholipids

Explanation: ***Overactivation of adenylate cyclase by activation of Gs subunit by ADP-ribosylation*** - The description of the bacterium as **gram-negative, oxidase-positive, comma-shaped, growing well in pH > 8**, and causing **profuse watery diarrhea** after travel to Central America points to *Vibrio cholerae*. - **Cholera toxin** (CTX) produced by *V. cholerae* is an A-B toxin that **ADP-ribosylates the Gs α-subunit**, permanently activating **adenylate cyclase**. This leads to increased cAMP levels, causing secretion of water and electrolytes into the intestinal lumen. *Overactivation of adenylate cyclase by inhibition of Gi subunit by ADP-ribosylation* - This mechanism describes the action of **pertussis toxin** from *Bordetella pertussis*, which ADP-ribosylates and **inhibits the Gi subunit**, preventing adenylate cyclase inhibition. - While both ultimately increase cAMP, the specific target and mechanism (inhibition of Gi vs. activation of Gs) differ from cholera toxin. *Inactivation of the 60S ribosomal subunit by cleaving an adenine from the 28S rRNA* - This mechanism is characteristic of **Shiga toxin** produced by *Shigella dysenteriae* and Shiga-like toxins (verotoxins) produced by **enterohemorrhagic *E. coli*** (EHEC). - These toxins inhibit protein synthesis, leading to cell death and often bloody diarrhea and hemolytic uremic syndrome, which is not described here. *Overactivation of guanylate cyclase* - **Heat-stable enterotoxins (ST)** produced by **enterotoxigenic *E. coli*** (ETEC) activate **guanylate cyclase**, leading to increased cGMP and subsequent fluid secretion. - While ETEC can cause watery diarrhea, the bacterial characteristics provided (oxidase-positive, comma-shaped) do not fit *E. coli*. *Degradation of cell membranes by hydrolysis of the phospholipids* - This mechanism is associated with toxins like **phospholipases** or **lecithinases** (e.g., alpha-toxin of *Clostridium perfringens*). - These toxins cause direct cell lysis and tissue damage, which is not the primary mechanism of action for the watery diarrhea seen in cholera.

Question 5: A 57-year-old HIV-positive male with a history of intravenous drug abuse presents to the emergency room complaining of arm swelling. He reports that he developed progressively worsening swelling and tenderness over the right antecubital fossa three days prior. He recently returned from a trip to Nicaragua. His past medical history is notable for an anaphylactoid reaction to vancomycin. His temperature is 101.4°F (38.6°C), blood pressure is 140/70 mmHg, pulse is 110/min, and respirations are 20/min. Physical examination reveals an erythematous, fluctuant, and tender mass overlying the right antecubital fossa. Multiple injection marks are noted across both upper extremities. He undergoes incision and drainage and is started on an antibiotic that targets the 50S ribosome. He is discharged with plans to follow up in one week. However, five days later he presents to the same emergency room complaining of abdominal cramps and watery diarrhea. Which of the following classes of pathogens is most likely responsible for this patient’s current symptoms?

A. Gram-negative curved bacillus
B. Gram-negative bacillus
C. Anaerobic flagellated protozoan
D. Gram-positive bacillus (Correct Answer)
E. Gram-positive coccus

Explanation: ***Gram-positive bacillus*** - The patient was administered an antibiotic targeting the **50S ribosomal subunit** following incision and drainage for a suspected skin infection (likely **MRSA** given IV drug abuse). This strongly suggests **clindamycin** was used. - **Clindamycin** is a known risk factor for developing **Clostridioides (formerly Clostridium) difficile infection (CDI)**, which is caused by a **Gram-positive, spore-forming bacillus** and manifests with **abdominal cramps and watery diarrhea**. *Gram-negative curved bacillus* - This class of pathogens includes organisms like **Vibrio cholerae** or **Campylobacter jejuni**, which can cause diarrhea. - However, the patient's presentation with **colitis** after antibiotic use is more consistent with **Clostridioides difficile**, not typically a curved Gram-negative bacillus. *Gram-negative bacillus* - While some Gram-negative bacilli (e.g., E. coli, Salmonella) can cause diarrhea, their association with **antibiotic-induced colitis** following treatment for a skin abscess is less direct than that of *Clostridioides difficile*. - The initial skin infection in IV drug users is most commonly staphylococcal (Gram-positive coccus), for which a 50S targeting antibiotic would be prescribed. *Anaerobic flagellated protozoan* - This description often refers to pathogens like **Giardia lamblia** or **Trichomonas vaginalis**, which are not bacteria. - While *Giardia* can cause diarrhea, it typically causes **malabsorption** and **greasy stools**, and wouldn't be triggered by recent antibiotic use for a skin infection. *Gram-positive coccus* - **Gram-positive cocci** (e.g., Staphylococcus aureus) are the likely cause of the initial skin infection/abscess. - However, they do not typically cause **antibiotic-associated colitis** with watery diarrhea; rather, the *antibiotic treatment itself* for these organisms can predispose to *Clostridioides difficile*.

Question 6: A 17-year-old girl comes to the physician because of a 12-hour history of profuse watery diarrhea with flecks of mucus that started shortly after she returned from a trip to South America. She has not had any fever or nausea. Pulse is 104/min and blood pressure is 110/65 mm Hg. Physical examination shows dry mucous membranes and decreased skin turgor. Stool culture shows gram-negative, comma-shaped, flagellated bacilli. Therapy with oral rehydration solution is initiated. Which of the following is the most likely mechanism of this patient's diarrhea?

A. Impaired intestinal motility due to degeneration of autonomic nerves
B. Luminal chloride hypersecretion due to overactivation of adenylate cyclase (Correct Answer)
C. Excessive water excretion due to osmotically active solutes in the lumen
D. Fluid and electrolyte loss due to inflammation of luminal surface epithelium
E. Reduced ability of water absorption in the colon due to rapid intestinal transit

Explanation: ***Luminal chloride hypersecretion due to overactivation of adenylate cyclase*** - The presentation of **profuse watery diarrhea** with **no fever** or **nausea** and rapid dehydration in a traveler from South America is classic for **cholera**. - **Cholera toxin** works by activating **adenylate cyclase** in enterocytes, leading to increased intracellular **cAMP**, which stimulates continuous **secretion of chloride** and water into the intestinal lumen. *Impaired intestinal motility due to degeneration of autonomic nerves* - This mechanism is associated with **diabetic neuropathy** or other conditions causing **autonomic dysfunction**, leading to altered bowel habits, but not typically acute, profuse watery diarrhea. - The patient's acute symptoms and **gram-negative, comma-shaped bacilli** point to an infectious cause, not a neurodegenerative one. *Excessive water excretion due to osmotically active solutes in the lumen* - This describes **osmotic diarrhea**, where non-absorbable substances in the gut lumen draw water into the stool, seen in conditions like **lactose intolerance** or with certain laxatives. - While watery, the sheer volume and the specific bacterial findings rule out osmotic diarrhea as the primary mechanism here. *Fluid and electrolyte loss due to inflammation of luminal surface epithelium* - This mechanism is characteristic of **inflammatory or invasive diarrheas**, often caused by bacteria like *Shigella* or *Salmonella*, which typically present with **bloody stools**, **fever**, and abdominal pain. - The absence of fever and the *mucoid but not bloody* nature of the stool, along with the specific organism, make this less likely. *Reduced ability of water absorption in the colon due to rapid intestinal transit* - While rapid transit can contribute to diarrhea, it's generally a secondary effect or a symptom of underlying gut disturbance, not the primary mechanism of severe secretory diarrhea. - This mechanism doesn't explain the profound fluid loss seen in cholera, which is due to active secretion rather than just reduced absorption time.

Question 7: A 45-year-old woman comes to the emergency department because of abdominal cramping, vomiting, and watery diarrhea for the past 4 hours. One day ago, she went to a seafood restaurant with her family to celebrate her birthday. Three of the attendees have developed similar symptoms. The patient appears lethargic. Her temperature is 38.8°C (101.8°F). Which of the following organisms is most likely responsible for this patient's current symptoms?

A. Vibrio parahaemolyticus (Correct Answer)
B. Staphylococcus aureus
C. Salmonella enterica
D. Campylobacter jejuni
E. Listeria monocytogenes

Explanation: ***Vibrio parahaemolyticus*** - This organism is commonly associated with the consumption of **raw or undercooked seafood** and causes **acute gastroenteritis** with vomiting, watery diarrhea, and abdominal cramps. - The **24-hour incubation period** (symptoms began 4 hours ago after eating seafood 1 day ago) fits well with *V. parahaemolyticus*, which typically has an incubation of **12-24 hours** (range 4-96 hours). - The involvement of multiple individuals who ate at the same seafood restaurant strongly points to a **foodborne infection** from contaminated seafood. - The presence of fever (38.8°C) is consistent with *V. parahaemolyticus* gastroenteritis. *Staphylococcus aureus* - *S. aureus* causes food poisoning with a very **short incubation period (1-6 hours)** due to preformed enterotoxin, which does **not** match the 24-hour timeline in this case. - While it can cause rapid-onset vomiting and diarrhea, it is more commonly associated with contaminated **dairy products, mayonnaise salads, or meats**, not typically seafood. - Fever is uncommon in *S. aureus* enterotoxin-mediated food poisoning. *Salmonella enterica* - *Salmonella* infections typically have an incubation period of **6-72 hours** (often 12-36 hours) and could fit the timeline, but are more commonly associated with **poultry, eggs, or contaminated produce** rather than seafood as the primary source. - While it causes fever, vomiting, and diarrhea, the **seafood exposure** makes *Vibrio parahaemolyticus* the more likely pathogen. *Campylobacter jejuni* - *Campylobacter jejuni* usually causes **inflammatory diarrhea** (often bloody) with an incubation period of **2-5 days**, which is longer than the 24-hour period in this case. - It is commonly linked to **undercooked poultry or unpasteurized milk**, not typically seafood. - The watery (non-bloody) diarrhea presentation also makes this less likely. *Listeria monocytogenes* - *Listeria monocytogenes* is associated with **deli meats, soft cheeses, and unpasteurized dairy products**, and has a much longer and highly variable incubation period **(1-70 days, median ~3 weeks)**. - While it can cause gastroenteritis, its primary concern is severe invasive disease in immunocompromised individuals, pregnant women, and the elderly. - The rapid 24-hour onset with seafood exposure does not fit *Listeria*.

Question 8: A 24-year-old woman presents with 3 days of diarrhea. She was recently on vacation in Peru and admits that on her last day of the trip she enjoyed a dinner of the local food and drink. Upon return to the United States the next day, she developed abdominal cramps and watery diarrhea, occurring about 3-5 times per day. She has not noticed any blood or mucous in her stool. Vital signs are stable. On physical examination, she is well appearing in no acute distress. Which of the following is commonly associated with the likely underlying illness?

A. Raw oysters
B. Soft cheese
C. Unwashed fruits and vegetables (Correct Answer)
D. Fried rice
E. Ground meat

Explanation: ***Unwashed fruits and vegetables*** - The patient's symptoms (watery diarrhea, abdominal cramps, recent travel to Peru, and consuming local food/drink) are highly suggestive of **Traveler's Diarrhea (TD)**. This condition is most commonly caused by **enterotoxigenic E. coli (ETEC)**. - **Unwashed fruits and vegetables** are a common vehicle for the transmission of ETEC and other pathogens associated with TD, as they can be contaminated with fecal matter. *Raw oysters* - **Raw oysters** are typically associated with **Vibrio parahaemolyticus** or **norovirus** infections, which can cause gastroenteritis but are not the most common cause of Traveler's Diarrhea from contaminated food in a country like Peru. - While they can cause diarrhea, the clinical picture is classic for Traveler's Diarrhea, where produce is a more frequent culprit. *Soft cheese* - **Soft cheeses**, especially unpasteurized ones, are more commonly associated with bacterial infections like **Listeria monocytogenes**, which can cause severe illness, but usually presents differently than typical Traveler's Diarrhea, often with fever and systemic symptoms. - They are not a primary source for the common pathogens causing acute watery diarrhea in travelers. *Fried rice* - **Fried rice** is a common source of **Bacillus cereus** food poisoning, which typically causes a very rapid onset of vomiting within 1-6 hours (emetic form) or diarrhea within 6-15 hours (diarrheal form) after consumption. - The patient's symptoms started the day after returning, suggesting a longer incubation period than typically seen with *B. cereus* from fried rice. *Ground meat* - **Ground meat**, particularly undercooked, is a common source of **enterohemorrhagic E. coli (EHEC)**, especially O157:H7, and **Salmonella** or **Campylobacter**. - These typically cause more severe diarrhea, often with **bloody stools**, which the patient explicitly denied.

Question 9: A 23-year-old man comes to the physician because of a 2-day history of profuse watery diarrhea and abdominal cramps. Four days ago, he returned from a backpacking trip across Southeast Asia. Physical examination shows dry mucous membranes and decreased skin turgor. Stool culture shows gram-negative, oxidase-positive, curved rods that have a single polar flagellum. The pathogen responsible for this patient's condition most likely has which of the following characteristics?

A. Acts by activation of guanylate cyclase
B. Forms spores in unfavorable environment
C. Grows well in medium with pH of 9 (Correct Answer)
D. Infection commonly precedes Guillain-Barré syndrome
E. Causes necrosis of Peyer patches of distal ileum

Explanation: ***Grows well in medium with pH of 9*** - The clinical presentation with **profuse watery diarrhea** after travel to Southeast Asia, along with the finding of **gram-negative, oxidase-positive, curved rods** with a **single polar flagellum**, is highly suggestive of **_Vibrio cholerae_**. - _Vibrio cholerae_ is known for its ability to **grow well in alkaline environments**, such as a medium with a pH of 9, which distinguishes it from many other enteric pathogens. *Acts by activation of guanylate cyclase* - This mechanism of action is characteristic of **heat-stable enterotoxins (ST)** produced by **enterotoxigenic _Escherichia coli_ (ETEC)**, which cause traveler's diarrhea. - While ETEC can cause watery diarrhea, _Vibrio cholerae_ primarily acts by activating **adenylate cyclase** through its cholera toxin, not guanylate cyclase. *Forms spores in unfavorable environment* - The ability to form **spores** is a characteristic feature of certain **Gram-positive bacteria**, notably _Bacillus_ and _Clostridium_ species. - **Gram-negative rods** like _Vibrio cholerae_ do not form spores as a survival mechanism in unfavorable conditions. *Infection commonly precedes Guillain-Barré syndrome* - **_Campylobacter jejuni_** infection is a well-known precursor to **Guillain-Barré syndrome (GBS)** due to molecular mimicry between _Campylobacter_ lipo-oligosaccharides and gangliosides in peripheral nerves. - While _Campylobacter_ can cause watery diarrhea and is a curved rod, the description of **profuse watery diarrhea** and good growth in alkaline conditions points more strongly to _Vibrio cholerae_ rather than _Campylobacter_. *Causes necrosis of Peyer patches of distal ileum* - **Necrosis of Peyer patches** in the distal ileum is a characteristic pathological feature of **typhoid fever**, caused by **_Salmonella Typhi_**. - The presentation of **profuse watery diarrhea** and the microbiological description do not align with typhoid fever, which typically presents with fever, malaise, and constipation or pea-soup diarrhea.

Question 10: An 83-year-old male presents to the emergency department with altered mental status. The patient’s vitals signs are as follows: temperature is 100.7 deg F (38.2 deg C), blood pressure is 143/68 mmHg, heart rate is 102/min, and respirations are 22/min. The caretaker states that the patient is usually incontinent of urine, but she has not seen any soiled adult diapers in the past 48 hours. A foley catheter is placed with immediate return of a large volume of cloudy, pink urine. Which of the following correctly explains the expected findings from this patient’s dipstick urinalysis?

A. Detection of an enzyme produced by white blood cells
B. Detection of urinary nitrate conversion by gram-negative pathogens (Correct Answer)
C. Detection of an enzyme produced by red blood cells
D. Detection of urinary nitrate conversion by gram-positive pathogens
E. Direct detection of white blood cell surface proteins

Explanation: ***Detection of urinary nitrate conversion by gram-negative pathogens*** - The presence of **nitrites** on a urine dipstick is a highly specific indicator of a **urinary tract infection (UTI)** caused by **gram-negative bacteria**. - **Gram-negative bacteria** like *E. coli* possess an enzyme, **nitrate reductase**, which converts urinary nitrates (normally present from dietary intake) into nitrites. - This is the **most specific finding** for gram-negative UTI and directly explains the expected dipstick result in this patient with cloudy urine and clinical signs of infection. *Detection of an enzyme produced by white blood cells* - This refers to the detection of **leukocyte esterase**, an enzyme released by neutrophils (white blood cells) in response to infection or inflammation. - While **leukocyte esterase** would likely be positive in this case of UTI, it is **less specific** than nitrite detection because it can be positive in any inflammatory condition of the urinary tract, not just bacterial infections. - The **nitrite test** is more specific for identifying **gram-negative bacterial** infections, which are the most common cause of UTIs. *Detection of an enzyme produced by red blood cells* - This refers to the detection of **hemoglobin**, which can be indirectly detected by dipstick due to its peroxidase-like activity. While the patient has **pink urine** (indicating hematuria), this finding is less specific for a **bacterial UTI** than nitrites and does not explain the *cause* of the infection. - Hematuria can be caused by various factors, including irritation from infection, kidney stones, trauma, or malignancy, and doesn't directly point to the type of pathogen. *Detection of urinary nitrate conversion by gram-positive pathogens* - **Gram-positive pathogens**, such as *Staphylococcus saprophyticus* or *Enterococcus faecalis*, which can cause UTIs, typically **do not convert urinary nitrates to nitrites** because they lack nitrate reductase enzyme. - Therefore, a positive nitrite test generally rules out a gram-positive infection as the sole cause of the positive dipstick finding. *Direct detection of white blood cell surface proteins* - The dipstick test for **leukocytes** (white blood cells) detects **leukocyte esterase**, an enzyme *released by* neutrophils, not their surface proteins directly. - While **leukocyte esterase** would likely be positive in this case, a positive **nitrite** test is more specific to the type of bacterial infection (gram-negative) responsible for the majority of UTIs.

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free