An 18-year-old male in his first year of college presents to the emergency room with a fever and a severe headache. He reports having unprotected sex with several partners over the past few weeks. Upon examination, the male demonstrates nuchal rigidity and photophobia. His past medical history is notable for a lack of vaccinations beginning from infancy due to his parents' belief that vaccinations may cause autism. The bacteria causing these symptoms would most likely demonstrate which of the following?
Q2
A previously healthy 17-year-old boy is brought to the emergency department because of fever, nausea, and myalgia for the past day. His temperature is 39.5°C (103.1°F), pulse is 112/min, and blood pressure is 77/55 mm Hg. Physical examination shows scattered petechiae over the anterior chest and abdomen. Blood culture grows an organism on Thayer-Martin agar. Which of the following virulence factors of the causal organism is most likely responsible for the high mortality rate associated with it?
Q3
A 25-day-old male infant presents to the emergency department because his mother states that he has been acting irritable for the past 2 days and has now developed a fever. On exam, the infant appears uncomfortable and has a temperature of 39.1 C. IV access is immediately obtained and a complete blood count and blood cultures are drawn. Lumbar puncture demonstrates an elevated opening pressure, elevated polymorphonuclear neutrophil, elevated protein, and decreased glucose. Ampicillin and cefotaxime are immediately initiated and CSF culture eventually demonstrates infection with a Gram-negative rod. Which of the following properties of this organism was necessary for the infection of this infant?
Q4
A 39-year-old man presents with a 4-week history of painless, non-discharging lesions on his penis and scrotum. He was diagnosed with chronic myeloid leukemia two years ago and treated with imatinib. He currently takes no medications. He has a 20-pack-year smoking history and drinks 1-2 beers on weekends. He reports unprotected intercourse with a woman while traveling abroad 4 months ago. His temperature is 37°C, pulse is 85/min, and blood pressure is 128/82 mm Hg. Examination reveals three non-tender lesions, each approximately 1 cm in size, on his genitalia. There is no inguinal lymphadenopathy. Which of the following is the most likely causative organism?
Q5
A 34-year-old woman presents with confusion, drowsiness, and headache. The patient’s husband says her symptoms began 2 days ago and have progressively worsened with an acute deterioration of her mental status 2 hours ago. The patient describes the headaches as severe, localized to the frontal and periorbital regions, and worse in the morning. Review of symptoms is significant for a mild, low-grade fever, fatigue, and nausea for the past week. Past medical history is significant for HIV infection for which she is not currently receiving therapy. Her CD4+ T cell count last month was 250/mm3. The blood pressure is 140/85 mm Hg, the pulse rate is 90/min, and the temperature is 37.7°C (100.0°F). On physical examination, the patient is conscious but drowsy. Papilledema is present. No pain is elicited with extension of the leg at the knee joint. The remainder of the physical examination is negative. Laboratory findings, including panculture, are ordered. A noncontrast CT scan of the head is negative and is followed by a lumbar puncture. CSF analysis is significant for:
Opening pressure 250 mm H2O (70-180 mm H2O)
Glucose 30 mg/dL (40-70 mg/dL)
Protein 100 mg/dL (<40 mg/dL)
Cell count 20/mm3 (0-5/mm3)
Which of the following additional findings would most likely be found in this patient?
Q6
While testing various strains of Streptococcus pneumoniae, a researcher discovers that a certain strain of this bacteria is unable to cause disease in mice when deposited in their lungs. What physiological test would most likely deviate from normal in this strain of bacteria as opposed to a typical strain?
Q7
A 24-year-old man presents with a painless genital ulcer for the past 2 weeks. He reports that he recently has been having unprotected sex with multiple partners. Past medical history is unremarkable. On physical examination, a single ulcer is present on the dorsal shaft of the penis which is circumscribed, indurated, and partially healed. There is moderate inguinal lymphadenopathy but no buboes. Which of the following tests would confirm the most likely diagnosis in this patient?
Q8
A 32-year-old man comes to the physician because of low-grade fever and progressive painful lumps in his right groin for 6 days. The lumps have been discharging purulent fluid since the evening of the previous day. He had a shallow, painless lesion on his penis 3 weeks ago, but was too embarrassed to seek medical attention; it has resolved in the meantime. There is no personal or family history of serious illness. He has smoked one pack of cigarettes daily for 12 years. He is sexually active with multiple male partners and uses condoms inconsistently. His temperature is 38.0°C (100.4°F). Examination of his groin shows multiple masses discharging pus. The remainder of the examination shows no abnormalities. Which of the following is the most likely causal organism?
Q9
A 50-year-old HIV-positive male presents to the ER with a two-day history of fever and hemoptysis. Chest radiograph shows a fibrocavitary lesion in the right middle lobe. Biopsy of the afflicted area demonstrates septate hyphae that branch at acute angles. Which of the following is the most likely causal organism?
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?
Klebsiella species US Medical PG Practice Questions and MCQs
Question 1: An 18-year-old male in his first year of college presents to the emergency room with a fever and a severe headache. He reports having unprotected sex with several partners over the past few weeks. Upon examination, the male demonstrates nuchal rigidity and photophobia. His past medical history is notable for a lack of vaccinations beginning from infancy due to his parents' belief that vaccinations may cause autism. The bacteria causing these symptoms would most likely demonstrate which of the following?
A. Negative catalase test
B. Gram-negative bacteria (Correct Answer)
C. Urease positive
D. Positive quellung reaction
E. Lactose fermentation
Explanation: ***Gram-negative bacteria***
- The clinical picture of fever, severe headache, **nuchal rigidity**, and photophobia in an unvaccinated 18-year-old college student strongly suggests **bacterial meningitis** caused by *Neisseria meningitidis*.
- *Neisseria meningitidis* is a **Gram-negative diplococcus**, which is the most definitive laboratory characteristic for identifying this organism.
- College dormitory settings and unvaccinated status are major risk factors for **meningococcal meningitis**, and Gram stain is typically the first diagnostic step showing Gram-negative diplococci in CSF.
*Positive quellung reaction*
- The Quellung reaction (capsular swelling) is classically associated with **Streptococcus pneumoniae**, not *Neisseria meningitidis*.
- While *N. meningitidis* does have a polysaccharide capsule, the Quellung test is not the standard identification method for this organism.
- *S. pneumoniae* would be more common in older adults or those with specific risk factors like asplenia.
*Negative catalase test*
- *Neisseria meningitidis* is **catalase-positive**, so a negative catalase test would rule out this organism.
- Catalase-negative organisms include Streptococcus and Enterococcus species, which have different clinical presentations.
*Lactose fermentation*
- *Neisseria meningitidis* is a **non-lactose fermenter** and does not utilize lactose fermentation for energy.
- Lactose fermentation is characteristic of enteric Gram-negative bacteria like *E. coli* and *Klebsiella*, not Neisseria species.
- *N. meningitidis* ferments **maltose and glucose**, which distinguishes it from *N. gonorrhoeae* (glucose only).
*Urease positive*
- *Neisseria meningitidis* is **urease-negative**, so urease positivity would rule out this organism.
- Urease-positive bacteria include *Helicobacter pylori*, *Proteus* species, and *Klebsiella*, none of which typically cause meningitis in this clinical setting.
Question 2: A previously healthy 17-year-old boy is brought to the emergency department because of fever, nausea, and myalgia for the past day. His temperature is 39.5°C (103.1°F), pulse is 112/min, and blood pressure is 77/55 mm Hg. Physical examination shows scattered petechiae over the anterior chest and abdomen. Blood culture grows an organism on Thayer-Martin agar. Which of the following virulence factors of the causal organism is most likely responsible for the high mortality rate associated with it?
A. Immunoglobulin A protease
B. Lipooligosaccharide (Correct Answer)
C. Toxic shock syndrome toxin-1
D. Lipoteichoic acid
E. Erythrogenic exotoxin A
Explanation: ***Lipooligosaccharide***
- The patient's presentation with **fever**, **hypotension**, and **petechiae**, along with a positive blood culture on Thayer-Martin agar, points to **meningococcemia** caused by *Neisseria meningitidis*.
- **Lipooligosaccharide (LOS)** acts as an **endotoxin**, triggering an excessive inflammatory response that leads to widespread vascular damage, **capillary leakage**, and **septic shock**, accounting for the high mortality.
*Immunoglobulin A protease*
- While *N. meningitidis* produces **IgA protease** to cleave secretory IgA and evade host defenses on mucosal surfaces, this factor is primarily involved in colonization and initial invasion rather than the systemic severity and mortality of septic shock.
- Its role is to help the bacteria **adhere and penetrate** host mucous membranes, but it does not directly cause the shock and petechiae seen in this severe presentation.
*Toxic shock syndrome toxin-1*
- **Toxic shock syndrome toxin-1 (TSST-1)** is a **superantigen** produced by *Staphylococcus aureus* that causes **toxic shock syndrome**, which can present with fever, rash, and hypotension.
- However, the organism grown on **Thayer-Martin agar** is characteristic of *Neisseria meningitidis*, not *Staphylococcus aureus*.
*Lipoteichoic acid*
- **Lipoteichoic acid** is a major component of the cell wall of **Gram-positive bacteria**, acting as a potent proinflammatory molecule and contributing to septic shock in those infections.
- *Neisseria meningitidis* is a **Gram-negative bacterium**, and therefore does not possess lipoteichoic acid.
*Erythrogenic exotoxin A*
- **Erythrogenic exotoxin A** is primarily produced by ***Streptococcus pyogenes*** and is responsible for the characteristic rash of **scarlet fever**.
- While *S. pyogenes* can cause invasive infections, the clinical picture and the specific growth on **Thayer-Martin agar** are not consistent with streptococcal infection.
Question 3: A 25-day-old male infant presents to the emergency department because his mother states that he has been acting irritable for the past 2 days and has now developed a fever. On exam, the infant appears uncomfortable and has a temperature of 39.1 C. IV access is immediately obtained and a complete blood count and blood cultures are drawn. Lumbar puncture demonstrates an elevated opening pressure, elevated polymorphonuclear neutrophil, elevated protein, and decreased glucose. Ampicillin and cefotaxime are immediately initiated and CSF culture eventually demonstrates infection with a Gram-negative rod. Which of the following properties of this organism was necessary for the infection of this infant?
A. K capsule (Correct Answer)
B. M protein
C. Fimbriae
D. IgA protease
E. LPS endotoxin
Explanation: ***K capsule***
- The K capsule (specifically **K1 antigen**) is a specific virulence factor found in **E. coli** strains, which are a common cause of neonatal meningitis.
- This capsule is **antiphagocytic** and helps the bacteria evade the immune system, allowing it to cross the **blood-brain barrier** and cause meningitis in neonates.
*M protein*
- **M protein** is a major virulence factor associated with **Streptococcus pyogenes** (Group A Strep), playing a role in attachment and immune evasion.
- While *S. pyogenes* can cause infections, it is not typically the Gram-negative rod responsible for **neonatal meningitis** and its M protein is not relevant here.
*Fimbriae*
- **Fimbriae** (pili) are important for bacterial **adhesion** to host cells, often in the initial stages of infection, particularly in urinary tract infections (UTIs).
- While gram-negative rods possess fimbriae, the specific virulence factor critical for **meningitis** caused by *E. coli* in neonates is the K1 capsule, not fimbriae which are more for initial colonization.
*IgA protease*
- **IgA protease** is an enzyme produced by some bacteria (e.g., *N. meningitidis, H. influenzae, S. pneumoniae*) that cleaves **IgA antibodies**, helping them colonize mucous membranes.
- This enzyme is not a primary virulence factor for the **Gram-negative rod** causing neonatal meningitis, where capsule formation is more critical for invasion.
*LPS endotoxin*
- **Lipopolysaccharide (LPS) endotoxin** is a component of the outer membrane of Gram-negative bacteria and is responsible for many symptoms of sepsis and **systemic inflammation**.
- While LPS contributes to the overall disease severity, it primarily mediates **inflammation and fever**, and is not the specific factor necessary for **invasion and survival within the central nervous system**, which is facilitated by the K capsule.
Question 4: A 39-year-old man presents with a 4-week history of painless, non-discharging lesions on his penis and scrotum. He was diagnosed with chronic myeloid leukemia two years ago and treated with imatinib. He currently takes no medications. He has a 20-pack-year smoking history and drinks 1-2 beers on weekends. He reports unprotected intercourse with a woman while traveling abroad 4 months ago. His temperature is 37°C, pulse is 85/min, and blood pressure is 128/82 mm Hg. Examination reveals three non-tender lesions, each approximately 1 cm in size, on his genitalia. There is no inguinal lymphadenopathy. Which of the following is the most likely causative organism?
A. Haemophilus ducreyi
B. Chlamydia trachomatis
C. Treponema pallidum (Correct Answer)
D. Herpes simplex virus
E. Klebsiella granulomatis
Explanation: ***Treponema pallidum***
- The presentation of **painless, non-discharging genital lesions** (chancre) after unprotected intercourse 4 months prior is highly characteristic of **primary syphilis**, caused by *Treponema pallidum*.
- The absence of **inguinal lymphadenopathy** is not uncommon in early primary syphilis, and the patient's history of travel and unprotected sex increases the risk.
*Haemophilus ducreyi*
- This bacterium causes **chancroid**, which typically presents as **painful genital ulcers** with irregular borders and often significant **inguinal lymphadenopathy** (buboes).
- The patient's lesions are described as painless, ruling out chancroid.
*Chlamydia trachomatis*
- While certain serovars of *Chlamydia trachomatis* cause **lymphogranuloma venereum (LGV)**, initial lesions are usually small, transient, and often go unnoticed, followed by prominent and often painful **inguinal lymphadenopathy**.
- Other serovars cause nongonococcal urethritis or cervicitis, which do not typically present with the described painless ulcers.
*Herpes simplex virus*
- **Herpes simplex virus (HSV)** infection usually causes **painful, vesicular lesions** that can ulcerate and crust, often accompanied by prodromal symptoms like itching or tingling.
- The lesions in this case are described as painless and non-vesicular.
*Klebsiella granulomatis*
- This organism causes **granuloma inguinale (donovanosis)**, which is characterized by **painless, beefy-red, friable ulcers** that can be extensive and bleed easily.
- While painless, the description of "non-discharging lesions" and the typical appearance of syphilis differ from the classic "beefy red" appearance of donovanosis.
Question 5: A 34-year-old woman presents with confusion, drowsiness, and headache. The patient’s husband says her symptoms began 2 days ago and have progressively worsened with an acute deterioration of her mental status 2 hours ago. The patient describes the headaches as severe, localized to the frontal and periorbital regions, and worse in the morning. Review of symptoms is significant for a mild, low-grade fever, fatigue, and nausea for the past week. Past medical history is significant for HIV infection for which she is not currently receiving therapy. Her CD4+ T cell count last month was 250/mm3. The blood pressure is 140/85 mm Hg, the pulse rate is 90/min, and the temperature is 37.7°C (100.0°F). On physical examination, the patient is conscious but drowsy. Papilledema is present. No pain is elicited with extension of the leg at the knee joint. The remainder of the physical examination is negative. Laboratory findings, including panculture, are ordered. A noncontrast CT scan of the head is negative and is followed by a lumbar puncture. CSF analysis is significant for:
Opening pressure 250 mm H2O (70-180 mm H2O)
Glucose 30 mg/dL (40-70 mg/dL)
Protein 100 mg/dL (<40 mg/dL)
Cell count 20/mm3 (0-5/mm3)
Which of the following additional findings would most likely be found in this patient?
A. Gram-positive diplococci are present on microscopy
B. CSF shows a positive acid-fast bacillus stain
C. Multiple ring-enhancing lesions are seen on a CT scan
D. CSF shows gram negative diplococci
E. CSF India ink stain shows encapsulated yeast cells (Correct Answer)
Explanation: ***CSF India ink stain shows encapsulated yeast cells***
- The patient's presentation with **subacute meningitis symptoms** (headache, confusion, low-grade fever) in the setting of **untreated HIV infection** with a low CD4+ count (250/mm3) strongly suggests an opportunistic infection.
- The CSF findings of **elevated opening pressure**, **low glucose**, **high protein**, and **moderate pleocytosis** are classic for **cryptococcal meningitis**, for which the India ink stain is diagnostic for encapsulated yeast cells.
*Gram-positive diplococci are present on microscopy*
- This finding suggests **bacterial meningitis**, specifically caused by organisms like *Streptococcus pneumoniae*.
- While bacterial meningitis presents acutely with severe symptoms, the **subacute course** and moderate pleocytosis are less typical, and the patient's immune status points towards an opportunistic infection.
*CSF shows a positive acid-fast bacillus stain*
- A positive **acid-fast bacillus (AFB) stain** in CSF would indicate **tuberculous meningitis**.
- While tuberculous meningitis can present subacutely with similar CSF findings in HIV patients, it typically involves a more significant lymphocytic pleocytosis and a more pronounced chronic course than suggested by the acute worsening.
*Multiple ring-enhancing lesions are seen on a CT scan*
- **Multiple ring-enhancing lesions** on CT or MRI are characteristic of **Toxoplasma encephalopathy** or **CNS lymphoma** in HIV-positive patients.
- While these are common HIV-related CNS complications, the patient's primary presentation points to **meningitis** (inflammation of meninges with CSF abnormalities) rather than focal brain lesions without meningeal involvement.
*CSF shows gram negative diplococci*
- **Gram-negative diplococci** in CSF suggest **meningococcal meningitis** (*Neisseria meningitidis*).
- This typically presents as an **acute, severe bacterial meningitis** with rapid deterioration, usually in immunocompetent individuals or specific outbreaks, which doesn't align with the subacute onset and specific CSF profile for cryptococcus.
Question 6: While testing various strains of Streptococcus pneumoniae, a researcher discovers that a certain strain of this bacteria is unable to cause disease in mice when deposited in their lungs. What physiological test would most likely deviate from normal in this strain of bacteria as opposed to a typical strain?
A. Quellung reaction (Correct Answer)
B. Hemolytic reaction when grown on sheep blood agar
C. Bile solubility
D. Optochin sensitivity
E. Motility
Explanation: ***Quellung reaction***
- The **Quellung reaction** tests for the presence of the **polysaccharide capsule**, which is the primary virulence factor of *S. pneumoniae*.
- An **avirulent strain** that cannot cause disease would most likely lack the capsule and show a **negative Quellung reaction** (no capsular swelling), deviating from the **positive reaction** seen in typical encapsulated pathogenic strains.
- The capsule enables *S. pneumoniae* to evade phagocytosis and complement-mediated killing, which is essential for establishing infection in the lungs.
*Hemolytic reaction when grown on sheep blood agar*
- Both virulent and avirulent strains of *S. pneumoniae* typically exhibit **alpha-hemolysis** (partial hemolysis, producing a greenish discoloration) on sheep blood agar due to the production of pneumolysin.
- This characteristic does not differentiate between pathogenic and non-pathogenic strains in terms of disease-causing ability.
*Bile solubility*
- *S. pneumoniae* is characteristically **bile-soluble** due to the presence of autolysin enzymes that are activated by bile salts, leading to cellular lysis.
- This property is a **species characteristic** present in both virulent and avirulent strains, thus it would not explain the inability to cause disease.
*Optochin sensitivity*
- *S. pneumoniae* is universally **sensitive to optochin**, a chemical agent that inhibits its growth and is used for laboratory identification.
- This characteristic is used for **species identification** but does not correlate with strain virulence or disease-causing ability.
*Motility*
- *Streptococcus pneumoniae* is a **non-motile** bacterium; it lacks flagella.
- This characteristic is consistent across all strains and is not a virulence factor for this species.
Question 7: A 24-year-old man presents with a painless genital ulcer for the past 2 weeks. He reports that he recently has been having unprotected sex with multiple partners. Past medical history is unremarkable. On physical examination, a single ulcer is present on the dorsal shaft of the penis which is circumscribed, indurated, and partially healed. There is moderate inguinal lymphadenopathy but no buboes. Which of the following tests would confirm the most likely diagnosis in this patient?
A. Perform a darkfield microscopic examination of a swab from the chancre (Correct Answer)
B. Swab the chancre and perform a saline wet mount
C. Fluorescent treponemal antibody absorption (FTA-ABS) test
D. Frei test
E. Venereal Disease Research Laboratory (VDRL) test
Explanation: ***Perform a darkfield microscopic examination of a swab from the chancre***
- This patient's presentation with a **painless, indurated genital ulcer** (chancre) and regional lymphadenopathy is highly suggestive of **primary syphilis**.
- **Darkfield microscopy** directly visualizes the spirochetes (**_Treponema pallidum_**) from the chancre, providing a definitive and rapid diagnosis.
*Swab the chancre and perform a saline wet mount*
- A **saline wet mount** is used to identify mobile organisms like **_Trichomonas vaginalis_** or clue cells suggestive of **bacterial vaginosis**, neither of which are associated with this type of ulcer.
- This test would not reveal the spirochetes responsible for syphilis and is not appropriate for diagnosing a genital ulcer.
*Fluorescent treponemal antibody absorption (FTA-ABS) test*
- The **FTA-ABS test** is a **treponemal-specific serological test** used to confirm a syphilis diagnosis, particularly in later stages or when non-treponemal tests are reactive.
- While sensitive for syphilis, it's typically reactive later in the disease course and cannot directly visualize the bacteria from the ulcer, making darkfield microscopy a more immediate and direct diagnostic tool for primary syphilis.
*Frei test*
- The **Frei test** is an obsolete intradermal skin test used to diagnose **lymphogranuloma venereum (LGV)**, which typically presents with a transient, unnoticed lesion followed by severe lymphadenopathy and buboes.
- It is not used for the diagnosis of syphilis and would not be helpful for this patient's presentation.
*Viral and rickettsial disease research laboratory (VDRL) test*
- The **VDRL test** is a **non-treponemal serological test** for syphilis that detects antibodies against cardiolipin, a lipid released from damaged host cells.
- While used for screening and monitoring treatment response, it can be **negative in early primary syphilis** (before seroconversion) and may not be positive at the time of presentation with a fresh chancre.
Question 8: A 32-year-old man comes to the physician because of low-grade fever and progressive painful lumps in his right groin for 6 days. The lumps have been discharging purulent fluid since the evening of the previous day. He had a shallow, painless lesion on his penis 3 weeks ago, but was too embarrassed to seek medical attention; it has resolved in the meantime. There is no personal or family history of serious illness. He has smoked one pack of cigarettes daily for 12 years. He is sexually active with multiple male partners and uses condoms inconsistently. His temperature is 38.0°C (100.4°F). Examination of his groin shows multiple masses discharging pus. The remainder of the examination shows no abnormalities. Which of the following is the most likely causal organism?
A. Herpes simplex virus 2
B. Klebsiella granulomatis
C. Chlamydia trachomatis (Correct Answer)
D. Yersinia pestis
E. Haemophilus ducreyi
Explanation: ***Chlamydia trachomatis***
- The presentation of **painless genital ulcers** followed by painful inguinal lymphadenopathy that progresses to **suppurative buboes** (lumps discharging purulent fluid) is classic for **lymphogranuloma venereum (LGV)**, which is caused by specific serovars of *Chlamydia trachomatis* (L1, L2, L3).
- The patient's history of multiple male partners and inconsistent condom use puts him at high risk for acquiring sexually transmitted infections like LGV.
*Herpes simplex virus 2*
- HSV-2 typically causes **painful, vesicular lesions** that can lead to recurrent outbreaks, which is inconsistent with the initial painless penile lesion described.
- While HSV can cause lymphadenopathy, it usually presents as **tender, non-suppurative lymph nodes** rather than large, discharging buboes.
*Klebsiella granulomatis*
- This organism causes **donovanosis (granuloma inguinale)**, characterized by progressive, painless, beefy red **ulcerative lesions** that bleed easily.
- It typically does not involve regional lymphadenopathy or bubo formation, but rather **pseudobuboes** formed by subcutaneous granulomas.
*Yersinia pestis*
- *Yersinia pestis* is the causative agent of **plague**, a severe systemic illness spread by fleas or respiratory droplets.
- While plague can cause **buboes** (swollen, painful lymph nodes), it is associated with a much more acute and severe systemic illness, including high fever, prostration, and often hemorrhagic manifestations, which are not described here.
*Haemophilus ducreyi*
- This bacterium causes **chancroid**, which presents with **painful, friable genital ulcers** with ragged borders and often associated with tender inguinal lymphadenopathy that can suppurate.
- The initial lesion described in the patient was **painless**, which rules out chancroid.
Question 9: A 50-year-old HIV-positive male presents to the ER with a two-day history of fever and hemoptysis. Chest radiograph shows a fibrocavitary lesion in the right middle lobe. Biopsy of the afflicted area demonstrates septate hyphae that branch at acute angles. Which of the following is the most likely causal organism?
A. Mycobacterium tuberculosis
B. Pneumocystis jirovecii
C. Aspergillus fumigatus (Correct Answer)
D. Candida albicans
E. Mucor species
Explanation: ***Aspergillus fumigatus***
- The combination of **fever**, **hemoptysis**, a **fibrocavitary lesion** in an **HIV-positive** patient, and the presence of **septate hyphae branching at acute angles** on biopsy are classic findings for invasive **aspergillosis**.
- **Aspergillus** specifically targets individuals with compromised immune systems, and the pathological description of the hyphae is highly characteristic of this fungus.
*Mycobacterium tuberculosis*
- While **Mycobacterium tuberculosis** can cause **fever**, **hemoptysis**, and **cavitary lesions** in HIV-positive patients, the microscopic description of **septate hyphae branching at acute angles** is not consistent with bacterial infection.
- Tuberculosis is characterized by **acid-fast bacilli** and granulomatous inflammation, not fungal hyphae.
*Mucor species*
- **Mucor** (along with Rhizopus) causes **mucormycosis**, an invasive fungal infection that can affect immunocompromised patients and present with pulmonary involvement and cavitary lesions.
- However, mucormycosis is characterized by **non-septate (aseptate) hyphae branching at right (90-degree) angles**, not septate hyphae at acute angles, making it distinguishable from Aspergillus.
*Pneumocystis jirovecii*
- **Pneumocystis jirovecii** is a common cause of pneumonia in HIV-positive patients, typically presenting as **diffuse interstitial infiltrates** rather than cavitary lesions.
- Microscopic examination would reveal **cysts** and **trophozoites**, not septate hyphae, making it inconsistent with the biopsy findings.
*Candida albicans*
- While **Candida albicans** can cause infections in immunocompromised individuals, it typically presents as **oral thrush**, esophagitis, or disseminated candidiasis.
- Pulmonary involvement is less common and usually manifests as **pneumonitis** rather than cavitary lesions, and its hyphae are typically **pseudohyphae** or budding yeasts, not septate hyphae branching at acute angles.
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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