A 10-year-old girl is brought to the emergency department because of a 2-day history of bloody diarrhea and abdominal pain. Four days ago, she visited a petting zoo with her family. Her temperature is 39.4°C (102.9°F). Abdominal examination shows tenderness to palpation of the right lower quadrant. Stool cultures at 42°C grow colonies that turn black after adding phenylenediamine. Which of the following best describes the most likely causal organism?
Q2
A 14-year-old boy presents with abdominal pain and diarrhea after returning from an East Asian vacation. Stool sample reveals the presence of red and white blood cells. Stool culture shows growth of immobile, non-lactose fermenting gram-negative rods. The attending physician explains to the medical students that the bacteria function by invading intestinal M-cells. The bacterium responsible for this patient's infection is:
Q3
A 46-year-old woman presents to the emergency department complaining of bloody diarrhea, fatigue, and confusion. A few days earlier she went to a fast-food restaurant for a college reunion party. Her friends are experiencing similar symptoms. Laboratory tests show anemia, thrombocytopenia, and uremia. Lactate dehydrogenase (LDH) is raised while haptoglobin is decreased. Peripheral blood smears show fragmented red blood cells (RBCs). Coombs tests are negative. Which of the following is the responsible organism?
Q4
A 62-year-old man is brought to the emergency department with fatigue, dry cough, and shortness of breath for 3 days. He reports a slight fever and has also had 3 episodes of watery diarrhea earlier that morning. Last week, he attended a business meeting at a hotel and notes some of his coworkers have also become sick. He has a history of hypertension and hyperlipidemia. He takes atorvastatin, hydrochlorothiazide, and lisinopril. He appears in mild distress. His temperature is 102.1°F (38.9°C), pulse is 56/min, respirations are 16/min, and blood pressure is 150/85 mm Hg. Diffuse crackles are heard in the thorax. Examination shows a soft and nontender abdomen. Laboratory studies show:
Hemoglobin 13.5 g/dL
Leukocyte count 15,000/mm3
Platelet count 130,000/mm3
Serum
Na+ 129 mEq/L
Cl- 100 mEq/L
K+ 4.6 mEq/L
HCO3- 22 mEq/L
Urea nitrogen 14 mg/dL
Creatinine 1.3 mg/dL
An x-ray of the chest shows infiltrates in both lungs. Which of the following is the most appropriate next step in diagnosis?
Q5
A 21-year-old woman presents with the complaints of nausea, vomiting, and diarrhea for 5 days. She adds that she has fever and abdominal cramping as well. She had recently attended a large family picnic and describes eating many varieties of cold noodle salads. Her past medical history is insignificant. Her temperature is 37.5°C (99.6°F), respiratory rate is 15/min, pulse is 67/min, and blood pressure is 92/68 mm Hg. Physical examination is non-contributory. Given the clinical information provided and most likely diagnosis, which of the following would be the next best step in the management of this patient?
Q6
A 38-year-old man complains of a persistent high fever with chills, malaise, and diffuse abdominal pain for over a week. He recently returned from a trip to India. The fever began slowly and climbed its way up to 40.0°C (104.0°F) over the last 4 days. A physical exam reveals a white-coated tongue, enlarged spleen, and rose spots on the abdomen. A bone marrow aspirate was sent for culture which revealed motile gram-negative rods. Which of the following is true about the organism and the pathophysiology of this condition?
Q7
A previously healthy 29-year-old man comes to the emergency department for a 2-day history of abdominal pain, vomiting, and watery diarrhea. Bowel movements occur every 3 hours and are non-bloody. He recently returned from a backpacking trip in Central America. He does not take any medications. Stool culture shows gram-negative, rod-shaped bacteria that ferment lactose. Which of the following toxins is most likely to be involved in the pathogenesis of this patient's symptoms?
Q8
A group of scientists studied the effects of cytokines on effector cells, including leukocytes. They observed that interleukin-12 (IL-12) is secreted by antigen-presenting cells (APCs) in response to bacterial lipopolysaccharide. When a CD4+ T cell is exposed to this interleukin, which of the following responses will it have?
Q9
A 32-year-old woman comes to the emergency department with a 2-day history of abdominal pain and diarrhea. She has had about 8 voluminous stools per day, some of which were bloody. She visited an international food festival three days ago. She takes no medications. Her temperature is 39.5°C (103.1°F), pulse is 90/min, and blood pressure is 110/65 mm Hg. Examination shows a tender abdomen, increased bowel sounds, and dry mucous membranes. Microscopic examination of the stool shows polymorphonuclear leukocytes. Stool culture results are pending. Which of the following most likely caused the patient's symptoms?
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?
Waterborne bacterial pathogens US Medical PG Practice Questions and MCQs
Question 1: A 10-year-old girl is brought to the emergency department because of a 2-day history of bloody diarrhea and abdominal pain. Four days ago, she visited a petting zoo with her family. Her temperature is 39.4°C (102.9°F). Abdominal examination shows tenderness to palpation of the right lower quadrant. Stool cultures at 42°C grow colonies that turn black after adding phenylenediamine. Which of the following best describes the most likely causal organism?
A. Gram-positive, anaerobic, rod-shaped bacteria that form spores
B. Gram-positive, aerobic, rod-shaped bacteria that produce catalase
C. Gram-negative, non-flagellated bacteria that do not ferment lactose
D. Gram-negative, flagellated bacteria that do not ferment lactose (Correct Answer)
E. Gram-negative, non-flagellated bacteria that ferment lactose
Explanation: ***Gram-negative, flagellated bacteria that do not ferment lactose***
- The clinical presentation of **bloody diarrhea**, **abdominal pain**, and fever, along with a history of **petting zoo exposure**, strongly suggests a *Campylobacter* infection, which is a **gram-negative, flagellated, curved rod** that does not ferment lactose.
- The growth at **42°C (thermophilic)** and a **positive oxidase test** (indicated by colonies turning black after adding phenylenediamine, an oxidase reagent) are characteristic features of *Campylobacter spp*.
*Gram-positive, anaerobic, rod-shaped bacteria that form spores*
- This description typically refers to organisms like *Clostridium difficile* or *Clostridium perfringens*, which can cause diarrhea.
- However, they are **anaerobic** and would not grow well in typical stool culture conditions without specific anaerobic techniques, nor would they produce a positive oxidase test.
*Gram-positive, aerobic, rod-shaped bacteria that produce catalase*
- This describes organisms like *Listeria monocytogenes* or *Bacillus cereus*.
- While *Listeria* can cause gastrointestinal symptoms, it's less commonly associated with the acute, bloody diarrhea and petting zoo exposure seen here, and *Bacillus cereus* typically causes food poisoning with vomiting.
*Gram-negative, non-flagellated bacteria that do not ferment lactose*
- This description commonly applies to *Shigella spp.*
- While *Shigella* causes **bloody diarrhea** and **abdominal pain**, it is typically **non-motile** (non-flagellated), whereas *Campylobacter* is motile due to its flagella.
*Gram-negative, non-flagellated bacteria that ferment lactose*
- This description would fit organisms like enteropathogenic *E. coli* (EPEC) or enterotoxigenic *E. coli* (ETEC).
- However, the specific growth conditions (thermophilic) and positive oxidase test pointed to by phenylenediamine reactivity are not characteristic of these organisms.
Question 2: A 14-year-old boy presents with abdominal pain and diarrhea after returning from an East Asian vacation. Stool sample reveals the presence of red and white blood cells. Stool culture shows growth of immobile, non-lactose fermenting gram-negative rods. The attending physician explains to the medical students that the bacteria function by invading intestinal M-cells. The bacterium responsible for this patient's infection is:
A. Shigella dysenteriae (Correct Answer)
B. Salmonella enteritidis
C. Helicobacter pylori
D. Escherichia coli
E. Vibrio cholerae
Explanation: ***Shigella dysenteriae***
- The combination of **abdominal pain**, **bloody diarrhea** (red and white blood cells in stool), **immobile, non-lactose fermenting gram-negative rods**, and **invasion of M-cells** is classic for *Shigella* infection.
- *Shigella* species, particularly *S. dysenteriae*, cause **dysentery** by directly invading and destroying the intestinal epithelium, often in M-cells, leading to inflammation and ulceration.
*Salmonella enteritidis*
- While *Salmonella enteritidis* is also a **non-lactose fermenting gram-negative rod** and can cause diarrhea, it is typically **motile** (unlike the immobile bacteria described) and invades enterocytes, not specifically M-cells for its primary pathogenic mechanism.
- While it can cause bloody diarrhea, the **immotility** and primary M-cell invasion point away from *Salmonella*.
*Helicobacter pylori*
- *Helicobacter pylori* is a **spiral-shaped, gram-negative bacterium** primarily associated with gastritis and peptic ulcers, not acute bloody diarrhea.
- It colonizes the stomach lining and is not characteristically an immobile, non-lactose fermenting rod found in diarrheal stool.
*Vibrio cholerae*
- *Vibrio cholerae* causes **profuse watery diarrhea** (cholera) and is characterized by a **comma-shaped gram-negative rod** that is highly motile.
- It does not cause bloody diarrhea or invade M-cells; its pathogenicity is due to the production of an enterotoxin.
*Escherichia coli*
- While *E. coli* is a **gram-negative rod** and some strains can cause diarrhea (e.g., EHEC, ETEC), most strains are **lactose fermenting**.
- Pathogenic *E. coli* strains have various mechanisms, but the specific combination of **immobile, non-lactose fermenting rods with M-cell invasion** leading to dysentery is not characteristic of common diarrheagenic *E. coli*.
Question 3: A 46-year-old woman presents to the emergency department complaining of bloody diarrhea, fatigue, and confusion. A few days earlier she went to a fast-food restaurant for a college reunion party. Her friends are experiencing similar symptoms. Laboratory tests show anemia, thrombocytopenia, and uremia. Lactate dehydrogenase (LDH) is raised while haptoglobin is decreased. Peripheral blood smears show fragmented red blood cells (RBCs). Coombs tests are negative. Which of the following is the responsible organism?
A. Entamoeba histolytica
B. Salmonella
C. Shigella
D. E. coli (Correct Answer)
E. Campylobacter jejuni
Explanation: ***E. coli***
- The combination of **bloody diarrhea**, acute renal failure (**uremia**), **thrombocytopenia**, and **microangiopathic hemolytic anemia** (fragmented RBCs, elevated LDH, decreased haptoglobin) after consuming fast food is characteristic of **Hemolytic-Uremic Syndrome (HUS)**.
- **Shiga toxin-producing E. coli (STEC)**, particularly **E. coli O157:H7**, is the most common cause of HUS acquired from contaminated food, especially undercooked ground beef.
*Entamoeba histolytica*
- Causes **amebic dysentery** with bloody stools but typically does not lead to **HUS** with microangiopathic hemolytic anemia and renal failure.
- More common in areas with poor sanitation and transmitted via the **fecal-oral route**, often presenting with liver abscesses.
*Salmonella*
- Can cause **bloody diarrhea** (typhoid fever, non-typhoidal salmonellosis) and sometimes bacteremia but is not typically associated with **HUS**.
- While it can be acquired from contaminated food, the constellation of symptoms points away from Salmonella as the primary cause.
*Shigella*
- Causes **shigellosis**, a dysentery characterized by **bloody diarrhea**, and can produce **Shiga toxin**.
- While it can occasionally cause **HUS**, especially in children, E. coli O157:H7 is a more frequent cause of foodborne HUS cases.
*Campylobacter jejuni*
- A common cause of **bacterial gastroenteritis** with **bloody diarrhea**, which can be acquired from contaminated food (e.g., undercooked poultry).
- While it is associated with **Guillain-Barré syndrome**, it is rarely a cause of **HUS**.
Question 4: A 62-year-old man is brought to the emergency department with fatigue, dry cough, and shortness of breath for 3 days. He reports a slight fever and has also had 3 episodes of watery diarrhea earlier that morning. Last week, he attended a business meeting at a hotel and notes some of his coworkers have also become sick. He has a history of hypertension and hyperlipidemia. He takes atorvastatin, hydrochlorothiazide, and lisinopril. He appears in mild distress. His temperature is 102.1°F (38.9°C), pulse is 56/min, respirations are 16/min, and blood pressure is 150/85 mm Hg. Diffuse crackles are heard in the thorax. Examination shows a soft and nontender abdomen. Laboratory studies show:
Hemoglobin 13.5 g/dL
Leukocyte count 15,000/mm3
Platelet count 130,000/mm3
Serum
Na+ 129 mEq/L
Cl- 100 mEq/L
K+ 4.6 mEq/L
HCO3- 22 mEq/L
Urea nitrogen 14 mg/dL
Creatinine 1.3 mg/dL
An x-ray of the chest shows infiltrates in both lungs. Which of the following is the most appropriate next step in diagnosis?
A. Urine antigen assay (Correct Answer)
B. CT Chest
C. Direct immunofluorescent antibody test
D. Stool culture
E. Polymerase chain reaction
Explanation: ***Urine antigen assay***
- This patient presents with **pneumonia symptoms** (low-grade fever, dry cough, dyspnea, bilateral infiltrates) along with **gastrointestinal symptoms** (watery diarrhea) and **hyponatremia**, after attending a hotel meeting with other sick attendees. These are classic features of **Legionnaires' disease**.
- A **urine antigen assay** is a rapid and highly specific test for **Legionella pneumophila serogroup 1**, which causes the majority of Legionnaires' disease cases.
*CT Chest*
- A CT scan of the chest would provide more detailed imaging of the lung infiltrates but is typically used to characterize findings once pneumonia is diagnosed or to rule out other lung pathologies, not as an initial diagnostic test for the specific pathogen.
- While it can reveal characteristic patterns, it doesn't identify the causative organism and is not the most appropriate *next step in diagnosis* for a presumed Legionella infection.
*Direct immunofluorescent antibody test*
- A **direct immunofluorescent antibody (DFA) test** is used to identify legionella in respiratory secretions. However, collecting a sufficiently good sputum sample can be difficult, especially with a **dry cough**.
- Its sensitivity is lower than urine antigen testing for serogroup 1 and requires a respiratory sample, making it less convenient for initial diagnosis.
*Stool culture*
- While the patient has diarrhea, a **stool culture** would primarily detect typical bacterial enteric pathogens (e.g., Salmonella, Shigella, Campylobacter) and would not identify **Legionella**.
- The diarrhea, in this context, is likely an extrapulmonary manifestation of Legionnaires' disease caused by Legionella, not a separate primary enteric infection.
*Polymerase chain reaction*
- **PCR testing** can detect Legionella DNA in respiratory samples, offering high sensitivity and specificity.
- However, it is generally less rapid and widely available than the urine antigen test for initial diagnosis of Legionella pneumophila serogroup 1, which is the most common cause of Legionnaires' disease.
Question 5: A 21-year-old woman presents with the complaints of nausea, vomiting, and diarrhea for 5 days. She adds that she has fever and abdominal cramping as well. She had recently attended a large family picnic and describes eating many varieties of cold noodle salads. Her past medical history is insignificant. Her temperature is 37.5°C (99.6°F), respiratory rate is 15/min, pulse is 67/min, and blood pressure is 92/68 mm Hg. Physical examination is non-contributory. Given the clinical information provided and most likely diagnosis, which of the following would be the next best step in the management of this patient?
A. IV antibiotic therapy to prevent disseminated disease
B. Empiric therapy assuming multi-drug resistance
C. Prolonged oral antibiotics
D. Replacement of fluids and electrolytes (Correct Answer)
E. Short course of oral antibiotics to prevent asymptomatic carrier state
Explanation: ***Replacement of fluids and electrolytes***
- The patient presents with **nausea, vomiting, and diarrhea for 5 days**, along with **low blood pressure (92/68 mm Hg)**, indicating **dehydration** as the primary concern.
- **Fluid and electrolyte replacement** is crucial to correct dehydration and maintain vital organ function, especially in the setting of persistent gastrointestinal losses.
*IV antibiotic therapy to prevent disseminated disease*
- While foodborne illnesses can sometimes disseminate, the current presentation does not strongly suggest severe invasive disease requiring immediate IV antibiotics without further workup.
- Many common foodborne pathogens causing gastroenteritis are self-limiting, and antibiotics may not be beneficial or could even worsen outcomes (e.g., in E. coli O157:H7).
*Empiric therapy assuming multi-drug resistance*
- Initiating empiric multi-drug resistant therapy without identifying the causative agent or evidence of antibiotic failure is generally not recommended due to concerns about promoting resistance.
- The patient's symptoms are consistent with a common foodborne gastroenteritis, where supportive care is usually the first-line management.
*Prolonged oral antibiotics*
- **Prolonged oral antibiotics** are typically reserved for specific bacterial infections with identified pathogens requiring extended treatment or in immunocompromised patients.
- The given clinical picture primarily points to acute gastroenteritis requiring symptom management rather than a chronic or severe infection needing prolonged antibiotic courses.
*Short course of oral antibiotics to prevent asymptomatic carrier state*
- A short course of oral antibiotics to prevent an asymptomatic carrier state is typically considered for specific infections like **Typhoid fever** or in certain high-risk individuals, which is not the immediate concern here.
- In most cases of acute gastroenteritis, antibiotics are not given to prevent carrier states and may even prolong bacterial shedding in some Salmonella infections.
Question 6: A 38-year-old man complains of a persistent high fever with chills, malaise, and diffuse abdominal pain for over a week. He recently returned from a trip to India. The fever began slowly and climbed its way up to 40.0°C (104.0°F) over the last 4 days. A physical exam reveals a white-coated tongue, enlarged spleen, and rose spots on the abdomen. A bone marrow aspirate was sent for culture which revealed motile gram-negative rods. Which of the following is true about the organism and the pathophysiology of this condition?
A. Incidence increases after cholecystectomy.
B. Splenectomy may be necessary for carriers.
C. It survives intracellularly within phagocytes of Peyer's patches. (Correct Answer)
D. It forms blue-green colonies with fruity odor.
E. It releases a toxin which inactivates 60S ribosomes.
Explanation: ***It survives intracellularly within phagocytes of Peyer's patches.***
- *Salmonella Typhi*, the causative agent of **typhoid fever**, is a **facultative intracellular bacterium** that invades and replicates within macrophages, particularly in the **Peyer's patches** of the small intestine.
- This intracellular survival mechanism allows it to evade the host immune system and disseminate throughout the body, leading to systemic symptoms like persistent fever, hepatosplenomegaly, and rose spots.
*Incidence increases after cholecystectomy.*
- The **gallbladder** is a common site for chronic carriage of *Salmonella Typhi*, as the bacteria can establish a biofilm within the organ.
- While cholecystectomy may be considered in chronic carriers to eliminate the reservoir, it does not increase the incidence of typhoid fever; rather, it aims to reduce transmission.
*Splenectomy may be necessary for carriers.*
- **Splenectomy** is not a standard treatment for chronic carriers of *Salmonella Typhi*; the primary site of chronic carriage is the gallbladder.
- Treatment for carriers typically involves prolonged courses of antibiotics to eradicate the bacteria from the gallbladder and biliary tree.
*It forms blue-green colonies with fruity odor.*
- **Blue-green colonies with a fruity odor** are characteristic of *Pseudomonas aeruginosa* on specific culture media, not *Salmonella Typhi*.
- *Salmonella Typhi* typically forms non-lactose fermenting colonies on selective media like MacConkey agar.
*It releases a toxin which inactivates 60S ribosomes.*
- The toxin that inactivates 60S ribosomes is **Shiga toxin**, produced by *Shigella dysenteriae* and Shiga toxin-producing *E. coli* (STEC), leading to hemorrhagic colitis and hemolytic-uremic syndrome.
- *Salmonella Typhi* does not produce Shiga toxin; its pathogenesis primarily involves bacterial invasion and systemic dissemination.
Question 7: A previously healthy 29-year-old man comes to the emergency department for a 2-day history of abdominal pain, vomiting, and watery diarrhea. Bowel movements occur every 3 hours and are non-bloody. He recently returned from a backpacking trip in Central America. He does not take any medications. Stool culture shows gram-negative, rod-shaped bacteria that ferment lactose. Which of the following toxins is most likely to be involved in the pathogenesis of this patient's symptoms?
A. Enterotoxin B
B. Cereulide
C. Toxin A
D. Heat-labile toxin (Correct Answer)
E. Shiga toxin
Explanation: ***Heat-labile toxin***
- The patient's symptoms (non-bloody watery diarrhea, vomiting) following travel to Central America are consistent with **traveler's diarrhea** caused by **enterotoxigenic Escherichia coli (ETEC)**.
- ETEC produces **heat-labile toxin (LT)**, which acts similarly to cholera toxin by activating **adenylate cyclase**, increasing **cAMP**, and leading to electrolyte and water secretion into the bowel lumen.
*Enterotoxin B*
- **Enterotoxin B** is a superantigen produced by **Staphylococcus aureus** and is primarily associated with **staphylococcal food poisoning**, characterized by rapid-onset nausea, vomiting, and non-bloody diarrhea.
- While it causes gastrointestinal symptoms, the stool culture showing a gram-negative, lactose-fermenting rod points away from **S. aureus** (a gram-positive coccus).
*Cereulide*
- **Cereulide** is a toxin produced by **Bacillus cereus**, typically associated with rapid-onset vomiting after consuming contaminated rice.
- The symptoms are more acute and the causative organism (gram-positive rod) does not match the stool culture findings.
*Toxin A*
- **Toxin A** (and Toxin B) are produced by **Clostridioides difficile** and are responsible for **pseudomembranous colitis**, characterized by severe watery diarrhea, abdominal pain, and sometimes fever, often following antibiotic use.
- The patient's presentation and the stool culture for a gram-negative, lactose-fermenting rod do not fit **C. difficile** infection.
*Shiga toxin*
- **Shiga toxin** is produced by **Shiga toxin-producing E. coli (STEC)**, including E. coli O157:H7, and **Shigella dysenteriae**.
- It typically causes **bloody diarrhea** (dysentery) and is associated with complications like **hemolytic uremic syndrome (HUS)**, which is not described in this patient's non-bloody diarrhea.
Question 8: A group of scientists studied the effects of cytokines on effector cells, including leukocytes. They observed that interleukin-12 (IL-12) is secreted by antigen-presenting cells (APCs) in response to bacterial lipopolysaccharide. When a CD4+ T cell is exposed to this interleukin, which of the following responses will it have?
A. Responds to extracellular pathogens
B. Cell-mediated immune responses (Correct Answer)
C. Releases granzymes
D. Activate B cells
E. Secrete IL-4
Explanation: ***Cell-mediated immune responses***
- **IL-12** from antigen-presenting cells promotes the differentiation of **naïve CD4+ T cells** into **Th1 cells**.
- **Th1 cells** are the primary drivers of **cell-mediated immunity**, producing cytokines like **IFN-γ** that activate macrophages and cytotoxic T cells to combat intracellular pathogens.
*Responds to extracellular pathogens*
- Responses to extracellular pathogens are primarily mediated by **Th2 cells** and **humoral immunity**.
- **Th2 cells** are induced by cytokines like **IL-4** and are involved in allergic reactions and antiparasitic responses.
*Releases granzymes*
- **Granzymes** are released by **cytotoxic T lymphocytes (CTLs)** and **natural killer (NK) cells** to induce apoptosis in infected or cancerous cells.
- While Th1 cells help activate CTLs, they do not directly release granzymes themselves.
*Activate B cells*
- **B cell activation** and antibody production are primarily driven by **Th2 cells** and **follicular helper T (Tfh) cells**.
- Th1 cells are more involved in responses against intracellular pathogens, which typically do not involve direct B cell activation.
*Secrete IL-4*
- **IL-4** is the signature cytokine of **Th2 cells**, which are primarily involved in humoral immunity and allergic responses.
- **IL-12** inhibits Th2 differentiation and promotes Th1 differentiation, so a CD4+ T cell exposed to IL-12 would not secrete IL-4.
Question 9: A 32-year-old woman comes to the emergency department with a 2-day history of abdominal pain and diarrhea. She has had about 8 voluminous stools per day, some of which were bloody. She visited an international food festival three days ago. She takes no medications. Her temperature is 39.5°C (103.1°F), pulse is 90/min, and blood pressure is 110/65 mm Hg. Examination shows a tender abdomen, increased bowel sounds, and dry mucous membranes. Microscopic examination of the stool shows polymorphonuclear leukocytes. Stool culture results are pending. Which of the following most likely caused the patient's symptoms?
A. Home-canned vegetables
B. Yogurt dip
C. Reheated rice
D. Toxic mushrooms
E. Omelette (Correct Answer)
Explanation: **Omelette**
- The symptoms, including **bloody diarrhea**, fever, and exposure to an international food festival suggest a **bacterial infection**, likely from contaminated eggs (e.g., **Salmonella**).
- The presence of **polymorphonuclear leukocytes** in the stool indicates an **invasive bacterial infection**, consistent with salmonellosis.
*Home-canned vegetables*
- Poorly preserved home-canned vegetables are a classic cause of **botulism**, which presents with **neurological symptoms** (e.g., flaccid paralysis) and is not characterized by bloody diarrhea or fever.
- While it can cause gastrointestinal upset, bloody stools are not typical, and the primary concern is neurotoxicity due to **Clostridium botulinum toxin**.
*Yogurt dip*
- Yogurt is a dairy product, and contamination typically leads to **non-bloody diarrhea** and vomiting, often caused by bacteria like *Staphylococcus aureus* or *Bacillus cereus* producing enterotoxins.
- The symptoms would likely be less severe and lack the invasive features (bloody stools, fever, PMNs) seen in this patient.
*Reheated rice*
- Reheated rice is commonly associated with **Bacillus cereus** food poisoning, which typically causes either an emetic (vomiting) or diarrheal syndrome.
- The diarrhea caused by *Bacillus cereus* is usually **watery and non-bloody**, and it rarely presents with significant fever or invasive features like polymorphonuclear leukocytes in stool.
*Toxic mushrooms*
- Mushroom poisoning can present with a wide range of symptoms, including gastrointestinal distress (vomiting, diarrhea), but the presentation varies greatly depending on the mushroom species.
- **Bloody diarrhea** with fever and polymorphonuclear leukocytes in stool is not a typical hallmark of common toxic mushroom ingestions, which often involve hepatotoxicity or neurotoxicity.
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.
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