Foodborne bacterial pathogens US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Foodborne bacterial pathogens. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Foodborne bacterial pathogens US Medical PG Question 1: 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)
Foodborne bacterial pathogens 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.
Foodborne bacterial pathogens US Medical PG Question 2: A 34-year-old, previously healthy woman is admitted to the hospital with abdominal pain and bloody diarrhea. She reports consuming undercooked beef a day before the onset of her symptoms. Her medical history is unremarkable. Vital signs include: blood pressure 100/70 mm Hg, pulse rate 70/min, respiratory rate 16/min, and temperature 36.6℃ (97.9℉). Physical examination shows paleness, face and leg edema, and abdominal tenderness in the lower right quadrant. Laboratory investigation shows the following findings:
Erythrocytes 3 x 106/mm3
Hemoglobin 9.4 g/dL
Hematocrit 0.45 (45%)
Corrected reticulocyte count 5.5%
Platelet count 18,000/mm3
Leukocytes 11,750/mm3
Total bilirubin 2.33 mg/dL (39.8 µmol/L)
Direct bilirubin 0.2 mg/dL (3.4 µmol/L)
Serum creatinine 4.5 mg/dL (397.8 µmol/L)
Blood urea nitrogen 35.4 mg/dL (12.6 mmol/L)
E. coli O157: H7 was identified in the patient’s stool. Which toxin is likely responsible for her symptoms?
- A. Erythrogenic toxin
- B. Shiga toxin (Correct Answer)
- C. Enterotoxin type B
- D. α-hemolysin
- E. Exotoxin A
Foodborne bacterial pathogens Explanation: ***Shiga toxin***
- The clinical presentation of **abdominal pain, bloody diarrhea, thrombocytopenia, microangiopathic hemolytic anemia** (indicated by low hemoglobin, elevated reticulocyte count, and elevated indirect bilirubin), and **acute kidney injury** (elevated creatinine and BUN with edema) strongly suggests **hemolytic uremic syndrome (HUS)**.
- ***E. coli* O157:H7** is a common cause of HUS, and it produces **Shiga toxins** (Stx1 and Stx2, also known as verotoxins), which cause endothelial damage leading to the characteristic features of HUS.
- Shiga toxins inhibit protein synthesis by cleaving ribosomal RNA, resulting in **endothelial cell damage, thrombotic microangiopathy**, and the classic triad of HUS.
*Erythrogenic toxin*
- This toxin is produced by **_Streptococcus pyogenes_** and is responsible for the rash seen in **scarlet fever**.
- It is not associated with **_E. coli_ O157:H7 infection** or the development of HUS.
*Enterotoxin type B*
- **Enterotoxin type B** is typically associated with **_Staphylococcus aureus_** and acts as a **superantigen** causing food poisoning with symptoms like vomiting and diarrhea.
- It does not cause HUS or the specific hematological and renal manifestations described in the patient.
*α-hemolysin*
- **Alpha-hemolysin** is a pore-forming cytolytic toxin produced by various bacteria, including **_Staphylococcus aureus_** and **_E. coli_**.
- While some *E. coli* strains produce alpha-hemolysin, it is not the primary toxin responsible for HUS caused by **_E. coli_ O157:H7**.
*Exotoxin A*
- **Exotoxin A** is produced by **_Pseudomonas aeruginosa_** and inhibits protein synthesis by ADP-ribosylation of elongation factor-2 (EF-2).
- It is not produced by *E. coli* O157:H7 and is not associated with HUS or the clinical presentation in this patient.
Foodborne bacterial pathogens US Medical PG Question 3: A 2-year-old male presents to the emergency department with fatigue and lethargy. Upon presentation, the patient is found to be severely dehydrated. The patient's mother says that he has been having non-bloody diarrhea for a day. She also says that the patient has not received any vaccinations after 6 months and currently attends a daycare center. Which of the following organisms is most likely responsible for the symptoms seen in this child?
- A. Campylobacter jejuni
- B. Norovirus
- C. Shigella
- D. Salmonella
- E. Rotavirus (Correct Answer)
Foodborne bacterial pathogens Explanation: ***Rotavirus***
- The presentation of severe **dehydration** due to **non-bloody diarrhea** in an **unvaccinated** 2-year-old attending daycare is highly characteristic of **rotavirus gastro-enteritis**.
- Rotavirus is a common cause of severe infantile diarrhea and is notable for causing **epidemics in daycare settings** due to its easy transmission and high infectivity.
*Campylobacter jejuni*
- This typically causes **bloody diarrhea**, which is not seen in the patient's presentation.
- While it can occur in children, the sudden onset of severe dehydration with non-bloody diarrhea is less typical for *Campylobacter*.
*Norovirus*
- Norovirus is a common cause of **gastroenteritis** with vomiting and diarrhea in children and adults.
- However, rotavirus more commonly leads to **severe dehydration** requiring hospitalization in very young children, especially in unvaccinated populations.
*Shigella*
- *Shigella* infections commonly cause **dysentery**, characterized by **bloody stools**, fever, and cramps, which is not present in this case.
- While *Shigella* can cause severe illness, the history of non-bloody diarrhea makes it less likely.
*Salmonella*
- *Salmonella* gastroenteritis often presents with **fever**, **abdominal cramps**, and **bloody or non-bloody diarrhea**.
- However, it is less commonly associated with the rapid onset of severe dehydration in this age group compared to rotavirus, particularly with no mention of fever or other systemic symptoms.
Foodborne bacterial pathogens US Medical PG Question 4: A 24-year-old college student consumed a container of canned vegetables for dinner. Fourteen hours later, he presents to the E.R. complaining of difficulty swallowing and double-vision. The bacterium leading to these symptoms is:
- A. Rod-shaped (Correct Answer)
- B. An obligate aerobe
- C. Gram-negative
- D. Non-spore forming
- E. Cocci-shaped
Foodborne bacterial pathogens Explanation: ***Rod-shaped***
- The symptoms of **difficulty swallowing (dysphagia)** and **double vision (diplopia)**, following consumption of canned food, are highly indicative of **botulism**, caused by *Clostridium botulinum*.
- *Clostridium botulinum* is a **rod-shaped (bacillus)** bacterium, which is a key morphological characteristic.
*An obligate aerobe*
- *Clostridium botulinum* is actually an **obligate anaerobe**, meaning it thrives in environments without oxygen, such as sealed cans.
- An obligate aerobe requires oxygen for growth; therefore, this statement is incorrect.
*Gram-negative*
- *Clostridium botulinum* is a **Gram-positive bacterium**, specifically a Gram-positive rod.
- Gram-negative bacteria have a different cell wall structure and stain pink/red, unlike the purple of Gram-positive bacteria.
*Non-spore forming*
- *Clostridium botulinum* is a **spore-forming bacterium**, and its spores are famously heat-resistant, allowing them to survive inadequate canning processes.
- The formation of spores is crucial for its survival and persistence in various environments.
*Cocci-shaped*
- **Cocci-shaped** bacteria are spherical, but *Clostridium botulinum* is explicitly **rod-shaped (bacillus)**.
- This morphological description does not match the causative agent of botulism.
Foodborne bacterial pathogens US Medical PG Question 5: A 3-year-old girl is brought to the emergency department for 2 days of abdominal pain and watery diarrhea. This morning her stool had a red tint. She and her parents visited a circus 1 week ago. The patient attends daycare. Her immunizations are up-to-date. Her temperature is 38°C (100.4°F), pulse is 140/min, and blood pressure is 80/45 mm Hg. Abdominal examination shows soft abdomen that is tender to palpation in the right lower quadrant with rebound. Stool culture grows Yersinia enterocolitica. Exposure to which of the following was the likely cause of this patient's condition?
- A. Undercooked poultry
- B. Home-canned food
- C. Deli meats
- D. Unwashed vegetables
- E. Undercooked pork (Correct Answer)
Foodborne bacterial pathogens Explanation: ***Undercooked pork***
- **Yersinia enterocolitica** is commonly transmitted through contaminated food, especially **undercooked pork** and **chitterlings**.
- The patient's symptoms (abdominal pain, watery diarrhea with a red tint, fever) and the growth of *Yersinia enterocolitica* in stool culture are consistent with yersiniosis acquired from this source.
*Undercooked poultry*
- **Undercooked poultry** is a common source of **Salmonella** and **Campylobacter**, which also cause gastroenteritis symptoms.
- However, the stool culture specifically identified *Yersinia enterocolitica*, making poultry less likely as the primary source in this case.
*Home-canned food*
- **Home-canned foods** are primarily associated with **Clostridium botulinum** and **botulism**, which presents with neurological symptoms (e.g., paralysis) rather than gastroenteritis.
- *Yersinia enterocolitica* is not typically linked to home-canned food contamination.
*Deli meats*
- **Deli meats** are often implicated in **Listeria monocytogenes** infections or **Staphylococcus aureus** food poisoning.
- While they can cause gastrointestinal symptoms, the specific pathogen *Yersinia enterocolitica* is not primarily associated with deli meats.
*Unwashed vegetables*
- **Unwashed vegetables** can be a source of various pathogens, including **E. coli**, **Salmonella**, and **norovirus**.
- While possible, *Yersinia enterocolitica* has a stronger epidemiological link to undercooked pork products.
Foodborne bacterial pathogens US Medical PG Question 6: A 33-year-old woman presents to the urgent care center with 4 days of abdominal pain and increasingly frequent bloody diarrhea. She states that she is currently having 6 episodes of moderate volume diarrhea per day with streaks of blood mixed in. Her vital signs include: blood pressure 121/81 mm Hg, heart rate 77/min, and respiratory rate 15/min. Physical examination is largely negative. Given the following options, which is the most likely pathogen responsible for her presentation?
- A. Campylobacter
- B. Shigella (Correct Answer)
- C. Salmonella
- D. Clostridium difficile
- E. E. coli O157:H7
Foodborne bacterial pathogens Explanation: ***Shigella***
- **Shigella** infection commonly presents with sudden onset of high fever, **abdominal cramps**, and **bloody, watery diarrhea**, often with a small volume.
- The patient's presentation of 4 days of abdominal pain and increasingly frequent **bloody diarrhea** with **6 episodes per day** is highly characteristic of shigellosis.
*Campylobacter*
- **Campylobacter** infection often manifests with **bloody diarrhea**, but it typically presents with preceding **fever** and **malaise**, followed by diarrhea that can be bloody.
- While it can cause bloody diarrhea, the progression described in the patient (increasingly frequent and bloody) might be more indicative of other bacterial dysenteries.
*E. coli 0157:H7*
- **E. coli O157:H7** is a common cause of **hemorrhagic colitis**, characterized by **severe abdominal cramps** and **bloody diarrhea** without significant fever.
- However, its association with **hemolytic uremic syndrome (HUS)**, especially in children, makes it a concern, and while it *can* cause this presentation, other options are more likely given the pure dysenteric picture.
*Salmonella*
- **Salmonella** gastroenteritis typically causes **non-bloody diarrhea**, fever, and abdominal cramps.
- While some serotypes can cause invasive disease and bloody stool, the classic presentation is usually **watery diarrhea**.
*Clostridium difficile*
- **Clostridium difficile** infection is usually associated with **recent antibiotic use** or hospitalization, and commonly causes **foul-smelling, watery diarrhea**, which can occasionally be bloody in severe cases.
- The patient's history does not mention recent antibiotic use, and the presentation of increasingly frequent and bloody diarrhea makes other pathogens more likely.
Foodborne bacterial pathogens US Medical PG Question 7: A previously healthy 9-year-old, Caucasian girl presents to your office with severe abdominal pain. Her mother also mentions that she has been urinating significantly less lately. History from the mother reveals that the girl suffers from acne vulgaris, mild scoliosis, and had a bout of diarrhea 3 days ago after a family barbecue. Lab work is done and is notable for a platelet count of 97,000 with a normal PT and PTT. The young girl appears dehydrated, yet her serum electrolyte levels are normal. What is the most likely etiology of this girl's urinary symptoms?
- A. Hypothalamic dysfunction
- B. Shiga-like toxin production from EHEC (Correct Answer)
- C. Shiga toxin production from Shigella
- D. Surreptitious laxative use
- E. Toxic shock syndrome
Foodborne bacterial pathogens Explanation: ***Shiga-like toxin production from EHEC***
- The combination of recent **diarrhea** (suggesting a gastrointestinal infection), severe **abdominal pain**, decreased urination (pointing to **renal impairment**), and **thrombocytopenia** (platelet count of 97,000) in a previously healthy child strongly indicates **Hemolytic Uremic Syndrome (HUS)**.
- HUS is characterized by the classic triad: **microangiopathic hemolytic anemia** (which would show schistocytes on blood smear), **thrombocytopenia**, and **acute kidney injury**.
- **Enterohemorrhagic E. coli (EHEC)**, particularly serotype O157:H7, is the most common cause of HUS through its production of **Shiga-like toxins**.
- The history of a family barbecue strongly suggests contaminated food (typically undercooked ground beef) as the source.
*Hypothalamic dysfunction*
- Hypothalamic dysfunction might cause symptoms like **polyuria** (due to diabetes insipidus) or hormonal imbalances, but it does not explain the **diarrhea**, **abdominal pain**, and significant **thrombocytopenia**.
- It would not lead to an acute presentation of **renal failure** and platelet abnormalities as seen in this case.
*Shiga toxin production from Shigella*
- While *Shigella dysenteriae* also produces a **Shiga toxin** and can cause HUS, the question mentions a family barbecue, which is a classic setting for **EHEC** transmission from contaminated food (e.g., undercooked meat).
- *Shigella* infections typically present with more severe, **bloody diarrhea** and are less commonly associated with foodborne outbreaks from barbecues compared to EHEC.
*Surreptitious laxative use*
- This might cause diarrhea and dehydration, however, it would not explain the severe **abdominal pain**, significant **thrombocytopenia**, or the acute **renal injury** manifested by decreased urination.
- Electrolyte abnormalities are also more commonly associated with chronic laxative abuse, whereas this patient has normal electrolytes.
*Toxic shock syndrome*
- Toxic shock syndrome (TSS) presents with **fever**, **rash**, **hypotension**, and multi-organ involvement, but it is typically associated with *Staphylococcus aureus* or *Streptococcus pyogenes* infections.
- While it can cause renal failure and thrombocytopenia, the preceding **diarrhea** is less characteristic of TSS, and it usually lacks the specific triad of HUS (microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury).
Foodborne bacterial pathogens US Medical PG Question 8: 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
Foodborne bacterial pathogens 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*.
Foodborne bacterial pathogens US Medical PG Question 9: 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
Foodborne bacterial pathogens 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.
Foodborne bacterial pathogens US Medical PG Question 10: A 44-year-old man presents to urgent care with severe vomiting. He states that he was at a camping ground for a party several hours ago and then suddenly began vomiting profusely. He denies experiencing any diarrhea and otherwise states he feels well. The patient only has a past medical history of lactose intolerance and hypertension managed with exercise and a low salt diet. His temperature is 99.3°F (37.4°C), blood pressure is 123/65 mmHg, pulse is 110/min, respirations are 14/min, and oxygen saturation is 98% on room air. Physical exam is notable only for tachycardia and diffuse abdominal discomfort. Which of the following foods is associated with the most likely cause of this patient's presentation?
- A. Egg salad
- B. Home-made ice cream
- C. Fish
- D. Unfiltered stream water
- E. Refried rice (Correct Answer)
Foodborne bacterial pathogens Explanation: ***Refried rice***
- The rapid onset of symptoms after eating foods like refried rice, especially following
social gatherings where food may have been left out, is highly suggestive of
**_Bacillus cereus_ food poisoning**.
- **_Bacillus cereus_** produces toxins (emetic toxin) that cause **vomiting** within 1-6 hours of
ingestion, often without diarrhea.
*Egg salad*
- Egg salad, particularly if improperly refrigerated, is a common source of **_Salmonella_**
infection.
- However, **_Salmonella_** typically causes **diarrhea, fever, and abdominal cramps**, often with a
longer incubation period of 6-72 hours, which is not consistent with this patient's
presentation of rapid onset **vomiting** and no diarrhea.
*Home-made ice cream*
- Home-made ice cream made with raw eggs can be a source of **_Salmonella_ infection**.
- Similar to commercially prepared egg salad, **_Salmonella_** presents with symptoms of
**diarrhea, fever**, and a longer incubation period, distinguishing it from this case.
*Fish*
- Poorly preserved fish can lead to **scombroid poisoning** (histamine toxicity), which can
cause rapid onset symptoms including flushing, headache, and gastrointestinal
disturbances.
- While it can cause rapid symptoms, **scombroid poisoning** typically causes a wider range
of symptoms including **rash, flushing, and headaches**, which are absent here.
*Unfiltered stream water*
- Ingestion of unfiltered stream water increases the risk of parasitic infections such as
**_Giardia lamblia_** or bacterial infections like **_E. coli_ (traveler's diarrhea)**.
- These infections typically cause **diarrhea, abdominal cramps**, and sometimes nausea
and vomiting, but their onset is usually delayed (days to weeks), and diarrhea is a
prominent symptom, unlike this patient's presentation.
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