A 26-year-old female presents to her primary care physician concerned that she has contracted a sexually transmitted disease. She states that she is having severe pain whenever she urinates and seems to be urinating more frequently than normal. She reports that her symptoms started after she began having unprotected sexual intercourse with 1 partner earlier this week. The physician obtains a urinalysis which demonstrates the following, SG: 1.010, Leukocyte esterase: Positive, Nitrites: Positive, Protein: Trace, pH: 5.0, RBC: Negative. A urease test is performed which is negative. This patient has most likely been infected with which of the following organisms?
Q2
A 32-year-old man with hypertension and gout comes to the physician with left flank pain and bloody urine for two days. He does not smoke cigarettes but drinks two beers daily. Home medications include hydrochlorothiazide and ibuprofen as needed for pain. Physical examination shows left costovertebral angle tenderness. Urine dipstick is strongly positive for blood. Microscopic analysis of a stone found in the urine reveals a composition of magnesium ammonium phosphate. Which of the following is the strongest predisposing factor for this patient's condition?
Q3
A 26-year-old woman presents to the emergency department with fever, chills, lower quadrant abdominal pain, and urinary frequency for the past week. Her vital signs include temperature 38.9°C (102.0°F), pulse 110/min, respirations 16/min, and blood pressure 122/78 mm Hg. Physical examination is unremarkable. Urinalysis reveals polymorphonuclear leukocytes (PMNs) > 10 cells/HPF and the presence of bacteria (> 105 CFU/mL). Which of the following is correct concerning the most likely microorganism responsible for this patient’s condition?
Q4
A previously healthy 26-year-old woman comes to the physician because of a 2-day history of pain with urination. She has been sexually active with two partners over the past year. She uses condoms for contraception. Vital signs are within normal limits. Physical examination shows suprapubic tenderness. Urinalysis shows neutrophils and a positive nitrite test. Urine culture grows gram-negative, oxidase-negative rods that form greenish colonies on eosin-methylene blue agar. Which of the following virulence factors of the causal organism increases the risk of infection in this patient?
Q5
A previously healthy 24-year-old woman comes to the physician because of a 1-day history of nausea and weakness. She is sexually active with 2 male partners and uses an oral contraceptive; she uses condoms inconsistently. Her last menstrual period was 4 days ago. Her temperature is 38.4°C (101°F). Physical examination shows right costovertebral angle tenderness. Pelvic examination is normal. Which of the following is the most likely cause of this patient's condition?
Q6
A 27-year-old woman comes to the physician for a 1-week-history of painful urination and urinary frequency. She has no history of serious illness and takes no medications. She is sexually active with her boyfriend. Her temperature is 36.7°C (98.1°F). There is no costovertebral angle tenderness. Urine dipstick shows leukocyte esterase. A Gram stain does not show any organisms. Which of the following is the most likely causal pathogen?
Q7
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?
Q8
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?
Q9
A 10-year-old boy is brought in to the emergency room by his parents after he complained of being very weak during a soccer match the same day. The parents noticed that yesterday, the patient seemed somewhat clumsy during soccer practice and was tripping over himself. Today, the patient fell early in his game and complained that he could not get back up. The patient is up-to-date on his vaccinations and has no previous history of illness. The parents do report that the patient had abdominal pain and bloody diarrhea the previous week, but the illness resolved without antibiotics or medical attention. The patient’s temperature is 100.9°F (38.3°C), blood pressure is 110/68 mmHg, pulse is 84/min, and respirations are 14/min. On exam, the patient complains of tingling sensations that seem reduced in his feet. He has no changes in vibration or proprioception. Achilles and patellar reflexes are 1+ bilaterally. On strength testing, foot dorsiflexion and plantar flexion are 3/5 and knee extension and knee flexion are 4-/5. Hip flexion, hip extension, and upper extremity strength are intact. Based on this clinical history and physical exam, what pathogenic agent could have been responsible for the patient’s illness?
Q10
A 4-year-old boy is brought to the physician because of a 1-day history of passing small quantities of dark urine. Two weeks ago, he had fever, abdominal pain, and bloody diarrhea for several days that were treated with oral antibiotics. Physical examination shows pale conjunctivae and scleral icterus. His hemoglobin concentration is 7.5 g/dL, platelet count is 95,000/mm3, and serum creatinine concentration is 1.9 mg/dL. A peripheral blood smear shows irregular red blood cell fragments. Avoiding consumption of which of the following foods would have most likely prevented this patient's condition?
Proteus species US Medical PG Practice Questions and MCQs
Question 1: A 26-year-old female presents to her primary care physician concerned that she has contracted a sexually transmitted disease. She states that she is having severe pain whenever she urinates and seems to be urinating more frequently than normal. She reports that her symptoms started after she began having unprotected sexual intercourse with 1 partner earlier this week. The physician obtains a urinalysis which demonstrates the following, SG: 1.010, Leukocyte esterase: Positive, Nitrites: Positive, Protein: Trace, pH: 5.0, RBC: Negative. A urease test is performed which is negative. This patient has most likely been infected with which of the following organisms?
A. Enterobacter cloacae
B. Staphylococcus saprophyticus
C. Proteus mirabilis
D. Klebsiella pneumoniae
E. Escherichia coli (Correct Answer)
Explanation: ***Escherichia coli***
- The urinalysis findings of **positive leukocyte esterase**, **nitrites**, and **trace protein** with a slightly acidic pH (5.0) are highly suggestive of a **urinary tract infection (UTI)**.
- *E. coli* is the most common cause of UTIs, especially in young, sexually active women, and is typically **urease-negative**, consistent with the information provided.
- *E. coli* accounts for **80-90% of uncomplicated UTIs** and produces nitrites from dietary nitrates, making it the most likely pathogen in this clinical scenario.
*Enterobacter cloacae*
- While *Enterobacter cloacae* can cause UTIs, it is less common than *E. coli* in uncomplicated cases and is often associated with nosocomial infections or those in immunocompromised individuals.
- Its urease activity can vary, so a negative urease test doesn't rule it out completely but makes *E. coli* a more likely primary choice in this context.
*Staphylococcus saprophyticus*
- *S. saprophyticus* is a common cause of UTIs in young, sexually active women (second most common cause after *E. coli*) and is typically **urease-negative**, which is consistent with the negative test.
- However, the presence of **positive nitrites** points more strongly towards **Gram-negative bacteria** like *E. coli*, as *S. saprophyticus* is a **Gram-positive coccus** that does not produce nitrite reductase and therefore does not convert nitrates to nitrites.
*Proteus mirabilis*
- *Proteus mirabilis* is known for causing UTIs and is characteristically **urease-positive**, leading to alkaline urine (higher pH) and sometimes **struvite stones**.
- The **negative urease test** and acidic urine pH (5.0) in this case effectively rule out *Proteus mirabilis*.
*Klebsiella pneumoniae*
- *Klebsiella pneumoniae* can cause UTIs and is generally **urease-negative**, but it is less frequently the cause of uncomplicated UTIs compared to *E. coli*.
- Although it can produce nitrites, *E. coli* remains the most common etiology in this clinical scenario.
Question 2: A 32-year-old man with hypertension and gout comes to the physician with left flank pain and bloody urine for two days. He does not smoke cigarettes but drinks two beers daily. Home medications include hydrochlorothiazide and ibuprofen as needed for pain. Physical examination shows left costovertebral angle tenderness. Urine dipstick is strongly positive for blood. Microscopic analysis of a stone found in the urine reveals a composition of magnesium ammonium phosphate. Which of the following is the strongest predisposing factor for this patient's condition?
A. Uric acid precipitation
B. Hereditary deficiency in amino acid reabsorption
C. Use of vitamin C supplements
D. Urinary tract infection (Correct Answer)
E. Ethylene glycol ingestion
Explanation: ***Urinary tract infection***
- The presence of a **magnesium ammonium phosphate stone**, also known as a **struvite stone**, is highly indicative of a urinary tract infection (UTI). These stones are formed in the presence of **urease-producing bacteria** (e.g., *Proteus mirabilis, Klebsiella pneumoniae*) that metabolize urea into ammonia, increasing localized pH and promoting crystal formation.
- While the patient has multiple predisposing factors for other types of kidney stones (e.g., gout and hydrochlorothiazide for calcium and uric acid stones), the specific composition of the stone points directly to an underlying infection as the primary predisposing factor.
*Uric acid precipitation*
- This typically leads to **uric acid stones**, which are common in patients with **gout** and **hyperuricemia**. The stone described is magnesium ammonium phosphate, not uric acid.
- Uric acid stones are usually radiolucent and are not directly associated with infection, unlike struvite stones.
*Hereditary deficiency in amino acid reabsorption*
- This condition, such as **cystinuria**, leads to the formation of **cystine stones**. These stones are hexagonal in shape and are caused by impaired tubular reabsorption of certain amino acids.
- The described stone composition is magnesium ammonium phosphate, not cystine.
*Use of vitamin C supplements*
- Excessive vitamin C (ascorbic acid) intake can be metabolized to **oxalate**, potentially contributing to **calcium oxalate stone** formation, especially in susceptible individuals.
- This patient's stone is a struvite stone, not a calcium oxalate stone.
*Ethylene glycol ingestion*
- Ethylene glycol poisoning is associated with the formation of **calcium oxalate monohydrate crystals** in the urine, which can lead to acute kidney injury and flank pain.
- The stone composition here is magnesium ammonium phosphate, indicating a different etiology.
Question 3: A 26-year-old woman presents to the emergency department with fever, chills, lower quadrant abdominal pain, and urinary frequency for the past week. Her vital signs include temperature 38.9°C (102.0°F), pulse 110/min, respirations 16/min, and blood pressure 122/78 mm Hg. Physical examination is unremarkable. Urinalysis reveals polymorphonuclear leukocytes (PMNs) > 10 cells/HPF and the presence of bacteria (> 105 CFU/mL). Which of the following is correct concerning the most likely microorganism responsible for this patient’s condition?
A. Gram-positive cocci that grow in clusters
B. Pear-shaped motile protozoa
C. Gram-positive cocci that grow in chains
D. Gram-negative rod-shaped bacilli (Correct Answer)
E. Nonmotile, pleomorphic rod-shaped, gram-negative bacilli
Explanation: ***Gram-negative rod-shaped bacilli***
- The symptoms of **fever, chills, abdominal pain, and urinary frequency**, along with urinalysis showing **pyuria (>10 PMNs/HPF) and bacteriuria (>10^5 CFU/mL)**, are highly suggestive of a **urinary tract infection (UTI)**.
- **_Escherichia coli_**, a **gram-negative rod-shaped bacillus**, is the most common cause of community-acquired UTIs, accounting for over 80% of cases.
*Gram-positive cocci that grow in clusters*
- This morphology describes **Staphylococcus species**, which can cause UTIs but are **less common** than *E. coli* in uncomplicated cases.
- **_Staphylococcus saprophyticus_** is a notable cause of UTIs in young, sexually active women, but it is not the most likely overall.
*Pear-shaped motile protozoa*
- This description typically refers to **_Giardia lamblia_**, which causes **gastrointestinal infections** (giardiasis) and is not associated with UTIs.
- UTIs are bacterial infections, not protozoal.
*Gram-positive cocci that grow in chains*
- This morphology describes **Streptococcus species**, such as **_Streptococcus agalactiae_** (Group B Streptococcus), which can cause UTIs, especially during pregnancy.
- However, they are **less frequent causes** of uncomplicated UTIs compared to *E. coli*.
*Nonmotile, pleomorphic rod-shaped, gram-negative bacilli*
- This description might fit certain bacteria like **_Haemophilus influenzae_**, which typically causes **respiratory tract infections or meningitis**, not UTIs.
- While *E. coli* is a gram-negative rod, it is **motile**, distinguishing it from this option.
Question 4: A previously healthy 26-year-old woman comes to the physician because of a 2-day history of pain with urination. She has been sexually active with two partners over the past year. She uses condoms for contraception. Vital signs are within normal limits. Physical examination shows suprapubic tenderness. Urinalysis shows neutrophils and a positive nitrite test. Urine culture grows gram-negative, oxidase-negative rods that form greenish colonies on eosin-methylene blue agar. Which of the following virulence factors of the causal organism increases the risk of infection in this patient?
A. Fimbriae (Correct Answer)
B. Lecithinase
C. IgA protease
D. Biofilm production
E. Lipoteichoic acid
Explanation: ***Fimbriae***
- The patient's symptoms (dysuria, suprapubic tenderness), urinalysis findings (neutrophils, positive nitrite), and culture results (gram-negative, oxidase-negative rods, greenish colonies on EMB agar) are highly suggestive of a **urinary tract infection (UTI)** caused by **Escherichia coli**.
- **P-fimbriae (pili)** are crucial virulence factors for *E. coli* in UTIs, enabling the bacteria to **adhere to uroepithelial cells** and colonize the urinary tract.
*Lecithinase*
- **Lecithinase (alpha-toxin)** is a virulence factor primarily associated with bacteria like *Clostridium perfringens*, causing gas gangrene, and some *Bacillus cereus* strains.
- It is not a significant virulence factor for *E. coli* in the context of UTIs.
*IgA protease*
- **IgA protease** is an enzyme produced by bacteria such as *Neisseria gonorrhoeae*, *Neisseria meningitidis*, and *Haemophilus influenzae*.
- It cleaves IgA antibodies, preventing their protective effects at mucosal surfaces, but it is not a primary virulence factor for *E. coli* in UTIs.
*Biofilm production*
- While *E. coli* can form biofilms, particularly in chronic infections or on catheters, **biofilm production** is not the primary mechanism that increases the **initial risk** of acquiring an acute uncomplicated UTI in a healthy individual.
- The *initial* adherence to uroepithelium, facilitated by fimbriae, is key for colonization and infection establishment.
*Lipoteichoic acid*
- **Lipoteichoic acid** is a major component of the cell wall in **Gram-positive bacteria** and contributes to their immune stimulation and adherence properties.
- The causative organism in this case is a **Gram-negative rod**, making lipoteichoic acid an irrelevant virulence factor.
Question 5: A previously healthy 24-year-old woman comes to the physician because of a 1-day history of nausea and weakness. She is sexually active with 2 male partners and uses an oral contraceptive; she uses condoms inconsistently. Her last menstrual period was 4 days ago. Her temperature is 38.4°C (101°F). Physical examination shows right costovertebral angle tenderness. Pelvic examination is normal. Which of the following is the most likely cause of this patient's condition?
A. Noninfectious inflammation of the bladder
B. Ascending bacteria from the endocervix
C. Decreased renal calcium reabsorption
D. Decreased urinary pH
E. Ascending bacteria from the bladder (Correct Answer)
Explanation: ***Ascending bacteria from the bladder***
- The patient presents with **fever**, **nausea**, **weakness**, and **right costovertebral angle (CVA) tenderness**, which are classic symptoms of **acute pyelonephritis**.
- **Pyelonephritis** most commonly results from an **ascending urinary tract infection**, where bacteria (typically *E. coli*) from the bladder travel up the ureters to infect the kidneys.
- This accounts for approximately **95% of pyelonephritis cases** in young women.
*Noninfectious inflammation of the bladder*
- **Noninfectious cystitis** (interstitial cystitis) would not typically present with systemic symptoms like **fever** and **nausea**, or with **CVA tenderness**, which indicates kidney involvement.
- Bladder inflammation typically causes dysuria and frequency without systemic signs of infection.
*Ascending bacteria from the endocervix*
- **Ascending bacteria from the endocervix** can cause **pelvic inflammatory disease (PID)**, which presents with lower abdominal pain, cervical motion tenderness, and vaginal discharge.
- While PID can cause fever, the **normal pelvic examination** in this patient rules out this diagnosis, and PID **does not typically cause CVA tenderness**.
*Decreased renal calcium reabsorption*
- **Decreased renal calcium reabsorption** is associated with **hypercalciuria** and **nephrolithiasis** (kidney stones), which can present with acute flank pain if obstruction occurs.
- However, this condition does not explain the **fever** and systemic symptoms characteristic of an acute infectious process.
*Decreased urinary pH*
- **Decreased urinary pH** (acidic urine) can predispose to certain types of kidney stone formation but is not a direct cause of **pyelonephritis**.
- It does not explain the presence of **fever**, **CVA tenderness**, and systemic symptoms indicative of a bacterial kidney infection.
Question 6: A 27-year-old woman comes to the physician for a 1-week-history of painful urination and urinary frequency. She has no history of serious illness and takes no medications. She is sexually active with her boyfriend. Her temperature is 36.7°C (98.1°F). There is no costovertebral angle tenderness. Urine dipstick shows leukocyte esterase. A Gram stain does not show any organisms. Which of the following is the most likely causal pathogen?
A. Escherichia coli
B. Chlamydia trachomatis (Correct Answer)
C. Gardnerella vaginalis
D. Neisseria gonorrhoeae
E. Trichomonas vaginalis
Explanation: ***Chlamydia trachomatis***
- This patient presents with symptoms of **dysuria** and **urinary frequency**, consistent with a **urethritis**. The absence of bacteria on Gram stain points towards an **atypical pathogen**.
- **Chlamydia trachomatis** is a common cause of **non-gonococcal urethritis** and is a sexually transmitted infection, which fits with the sexually active history.
*Escherichia coli*
- **E. coli** is the most common cause of **bacterial urinary tract infections (UTIs)**, but a Gram stain in this case would typically reveal Gram-negative rods.
- While it causes dysuria and frequency, the **negative Gram stain** makes it less likely than an atypical pathogen.
*Gardnerella vaginalis*
- **Gardnerella vaginalis** is associated with **bacterial vaginosis**, causing a characteristic **fishy odor** and **vaginal discharge**, which are not reported here.
- It does not typically cause urethritis leading to painful urination and urinary frequency.
*Neisseria gonorrhoeae*
- **Neisseria gonorrhoeae** can cause **urethritis** with symptoms similar to those presented, and it is a sexually transmitted infection.
- However, Gram stain would typically show **Gram-negative diplococci** (intracellularly), which were not observed in this case.
*Trichomonas vaginalis*
- **Trichomonas vaginalis** is a **protozoan parasite** causing **trichomoniasis**, which commonly presents with **vaginitis** (frothy, green-yellow discharge, itching) or sometimes urethritis.
- While it is a **sexually transmitted infection**, this organism is not detected by Gram stain (which only stains bacteria); it would require **wet mount microscopy** for visualization. The primary presentation is usually vaginal, and it's less likely to be the sole cause of these urinary symptoms without other signs of vaginitis.
Question 7: 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 8: 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.
Question 9: A 10-year-old boy is brought in to the emergency room by his parents after he complained of being very weak during a soccer match the same day. The parents noticed that yesterday, the patient seemed somewhat clumsy during soccer practice and was tripping over himself. Today, the patient fell early in his game and complained that he could not get back up. The patient is up-to-date on his vaccinations and has no previous history of illness. The parents do report that the patient had abdominal pain and bloody diarrhea the previous week, but the illness resolved without antibiotics or medical attention. The patient’s temperature is 100.9°F (38.3°C), blood pressure is 110/68 mmHg, pulse is 84/min, and respirations are 14/min. On exam, the patient complains of tingling sensations that seem reduced in his feet. He has no changes in vibration or proprioception. Achilles and patellar reflexes are 1+ bilaterally. On strength testing, foot dorsiflexion and plantar flexion are 3/5 and knee extension and knee flexion are 4-/5. Hip flexion, hip extension, and upper extremity strength are intact. Based on this clinical history and physical exam, what pathogenic agent could have been responsible for the patient’s illness?
A. Gram-negative, oxidase-negative, bacillus without hydrogen sulfide gas production
B. Gram-negative, oxidase-positive bacillus
C. Gram-negative, oxidase-positive, comma-shaped bacteria (Correct Answer)
D. Gram-negative, oxidase-negative, bacillus with hydrogen sulfide gas production
E. Gram-positive bacillus
Explanation: ***Gram-negative, oxidase-positive, comma-shaped bacteria***
- The patient's presentation of **ascending weakness**, **tingling sensations (paresthesias)**, and **diminished reflexes** following a diarrheal illness is highly suggestive of **Guillain-Barré Syndrome (GBS)**.
- **_Campylobacter jejuni_**, a **Gram-negative, oxidase-positive, comma-shaped bacteria**, is the most common antecedent infection leading to GBS through molecular mimicry with myelin gangliosides.
*Gram-negative, oxidase-negative, bacillus without hydrogen sulfide gas production*
- This description commonly refers to organisms like **_Shigella_** or **_Escherichia coli_ (EHEC)**.
- While these can cause bloody diarrhea, they are less frequently associated with post-infectious GBS compared to _Campylobacter jejuni_.
*Gram-negative, oxidase-positive bacillus*
- This general description could fit bacteria such as _Pseudomonas aeruginosa_ or _Vibrio cholerae_ (although _Vibrio_ is more specifically comma-shaped).
- While _Vibrio_ can cause diarrheal illness, _Campylobacter_ is a more classic and frequent trigger for GBS.
*Gram-negative, oxidase-negative, bacillus with hydrogen sulfide gas production*
- This characterizes bacteria like **_Salmonella_ species**.
- While **_Salmonella_ enteritis can cause diarrheal illness, it is a less common antecedent infection for GBS compared to _Campylobacter jejuni_**.
*Gram-positive bacillus*
- **Gram-positive bacilli** include organisms like _Clostridium difficile_ (which causes pseudomembranous colitis) or _Listeria monocytogenes_.
- These are not typically associated with bloody diarrhea followed by acute ascending paralysis and GBS.
Question 10: A 4-year-old boy is brought to the physician because of a 1-day history of passing small quantities of dark urine. Two weeks ago, he had fever, abdominal pain, and bloody diarrhea for several days that were treated with oral antibiotics. Physical examination shows pale conjunctivae and scleral icterus. His hemoglobin concentration is 7.5 g/dL, platelet count is 95,000/mm3, and serum creatinine concentration is 1.9 mg/dL. A peripheral blood smear shows irregular red blood cell fragments. Avoiding consumption of which of the following foods would have most likely prevented this patient's condition?
A. Undercooked beef (Correct Answer)
B. Mushrooms
C. Shellfish
D. Canned carrots
E. Raw pork
Explanation: ***Undercooked beef***
- The patient's symptoms (hemolytic anemia, thrombocytopenia, acute kidney injury) following a diarrheal illness are characteristic of **hemolytic uremic syndrome (HUS)**, most commonly caused by **Shiga toxin-producing E. coli (STEC)**, particularly serotype O157:H7.
- STEC infections are frequently acquired through consumption of **undercooked ground beef** or contaminated produce.
- **Note**: Antibiotic treatment of STEC gastroenteritis (as in this case) is associated with **increased risk of HUS** due to enhanced Shiga toxin release, making prevention through proper food handling even more critical.
*Mushrooms*
- While some mushrooms can be poisonous, they typically cause **gastrointestinal upset**, hepatotoxicity, or neurotoxicity, not the specific triad of HUS (hemolytic anemia, thrombocytopenia, and renal failure).
- Mushroom poisoning does not typically lead to the characteristic **microangiopathic hemolytic anemia** with schistocytes.
*Shellfish*
- Contaminated shellfish can cause various illnesses, including **bacterial infections** (e.g., Vibrio) or **paralytic shellfish poisoning** (neurotoxins).
- These conditions do not typically lead to the development of HUS with its specific hematologic and renal manifestations.
*Canned carrots*
- **Botulism** is associated with improperly canned foods, but it presents with **flaccid paralysis** and other neurologic symptoms, not HUS.
- Canned carrots are not a common source of pathogens leading to HUS.
*Raw pork*
- Raw pork is associated with infections like **trichinellosis** or **Taenia solium** (cysticercosis).
- These infections do not cause the constellation of symptoms defining HUS, particularly the **microangiopathic hemolytic anemia** and acute kidney injury.
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