Haemophilus and HACEK Group — MCQs

10 questions

An otherwise healthy patient who has just received a prosthetic aortic valve develops postoperative fever. Blood cultures are done and she is placed on broad-spectrum antibiotics. Two days later she is still febrile and clinically deteriorating. Which of the following organisms is the most probable etiologic agent?

What is the Hib conjugate vaccine made of?

A 6-year-old boy presents with fever and chills, cough, rapid breathing, difficulty breathing, and chest pain. A culture from a respiratory sample shows Gram-positive bacteria. What is the most likely organism causing this infection?

Which microorganism causes chancroid?

Genital ulcers are seen in all except:

What are the essential major blood culture criteria for diagnosing infective endocarditis?

A patient with large, penetrating vegetations on his mitral and aortic valves develops severe headaches. Funduscopic examination reveals papilledema. CT scan of the brain demonstrates a ring-enhancing lesion. Which of the following organisms is the most likely cause of the patient's disorder?

A 9-year-old child presented to OPD with complaints of high-grade fever, vomiting, and one episode of seizure. CSF examination was done and Gram staining of the culture showed lanceolate-shaped gram-positive diplococci. What is the probable causative agent?

HACEK group of organisms includes all, except:

Q10

HACEK group of organisms includes all except:

Haemophilus and HACEK Group Indian Medical PG Practice Questions and MCQs

Question 1: An otherwise healthy patient who has just received a prosthetic aortic valve develops postoperative fever. Blood cultures are done and she is placed on broad-spectrum antibiotics. Two days later she is still febrile and clinically deteriorating. Which of the following organisms is the most probable etiologic agent?

A. Nocardia asteroides
B. Actinomyces israelii
C. Histoplasma capsulatum
D. Candida albicans (Correct Answer)

Explanation: ***Candida albicans*** - *Candida albicans* is a common cause of **early prosthetic valve endocarditis**, especially in patients with prolonged hospitalization, broad-spectrum antibiotic use, or central venous catheters [1]. - The patient's clinical deterioration despite broad-spectrum antibacterial antibiotics suggests a **fungal etiology**, as bacteria are typically covered by such therapy [2]. *Nocardia asteroides* - *Nocardia asteroides* typically causes **pulmonary or cutaneous infections** in immunocompromised individuals, less commonly endocarditis. - It would usually respond to specific antibiotics like **trimethoprim-sulfamethoxazole**, and its presentation as prosthetic valve endocarditis is rare. *Actinomyces israelii* - *Actinomyces israelii* causes **actinomycosis**, characterized by chronic, slowly progressive infections with abscesses and draining sinuses, often following oral or abdominal trauma. - While it can cause endocarditis, it is less common in the context of acute prosthetic valve infection and would likely present with a more indolent course. *Histoplasma capsulatum* - *Histoplasma capsulatum* is a **dimorphic fungus** endemic to the Ohio and Mississippi River valleys, primarily causing pulmonary infections. - Disseminated histoplasmosis with endocarditis is rare and typically occurs in immunocompromised patients, not usually in an otherwise healthy individual post-surgery.

Question 2: What is the Hib conjugate vaccine made of?

A. Capsular polysaccharide
B. Purified protein with carrier
C. Cell wall polysaccharide
D. Capsular polysaccharide with carrier (Correct Answer)

Explanation: ***Capsular polysaccharide with carrier*** - The Hib conjugate vaccine uses a **polysaccharide capsule** from *Haemophilus influenzae* type b (Hib) covalently linked to a **protein carrier** [1]. - This conjugation allows activated B cells to present the polysaccharide to T helper cells, inducing a strong **T-cell dependent immune response** and **immunological memory**, especially in infants [1]. *Capsular polysaccharide* - A vaccine made only of **capsular polysaccharide** would be a **polysaccharide vaccine**, which induces a **T-cell independent immune response**. - This type of vaccine is **poorly immunogenic in infants** and does not generate long-lasting memory. *Purified protein with carrier* - This describes components of some **protein subunit vaccines**, but not specifically the Hib vaccine, which targets the polysaccharide capsule. - While it employs a carrier protein, the primary antigen is the **polysaccharide**, not a purified bacterial protein. *Cell wall polysaccharide* - The Hib vaccine specifically targets the **capsular polysaccharide**, which is distinct from the general cell wall polysaccharides found in the bacterial outer membrane. - The **capsule** is the primary virulence factor and target for protective immunity in Hib.

Question 3: A 6-year-old boy presents with fever and chills, cough, rapid breathing, difficulty breathing, and chest pain. A culture from a respiratory sample shows Gram-positive bacteria. What is the most likely organism causing this infection?

A. Streptococcus pyogenes
B. Streptococcus pneumoniae (Correct Answer)
C. Staphylococcus aureus
D. Propionibacterium acnes

Explanation: ***Streptococcus pneumoniae*** - This clinical picture describes typical symptoms of **pneumonia** in a child, including fever, cough, rapid and difficult breathing, and chest pain. - **_Streptococcus pneumoniae_** is the most common bacterial cause of community-acquired pneumonia in children. The respiratory sample showing gram-positive bacteria further supports this. *Staphylococcus aureus* - While **_Staphylococcus aureus_** can cause pneumonia, it is less common than _Streptococcus pneumoniae_ in community-acquired cases in healthy children and often associated with more severe, necrotizing forms or post-viral infections. - While it is a **Gram-positive bacterium**, its clinical presentation would not be the most likely first choice for typical pneumonia symptoms in this age group. *Propionibacterium acnes* - **_Propionibacterium acnes_** (now *Cutibacterium acnes*) is primarily associated with **acne vulgaris** and, less commonly, opportunistic infections related to implanted devices or some rare soft tissue infections. - It is not a typical cause of primary respiratory infections like pneumonia. *Streptococcus pyogenes* - **_Streptococcus pyogenes_** (Group A Streptococcus) is known for causing **pharyngitis** (strep throat), skin infections (impetigo, cellulitis), and scarlet fever. - While it can rarely cause pneumonia, it is not a common cause, and the constellation of symptoms points more strongly to _Streptococcus pneumoniae_.

Question 4: Which microorganism causes chancroid?

A. Chlamydia trachomatis
B. Haemophilus ducreyi (Correct Answer)
C. Klebsiella granulomatis
D. Treponema pallidum

Explanation: ***Haemophilus ducreyi*** - This bacterium is the definitive causative agent of **chancroid**, a sexually transmitted infection. - Chancroid is characterized by **painful genital ulcers** with ragged edges and often associated with **buboes** (swollen, tender lymph nodes). - Diagnosis: Clinical presentation plus identification of gram-negative coccobacilli in "school of fish" pattern. *Chlamydia trachomatis* - This bacterium causes **chlamydia**, a common STI leading to urethritis, cervicitis, and lymphogranuloma venereum (LGV). - It does not cause the painful, ragged ulcers characteristic of chancroid. *Klebsiella granulomatis* - Previously known as **Calymmatobacterium granulomatis**, this is the causative agent of **donovanosis** (granuloma inguinale). - Donovanosis causes gradually enlarging, **painless**, beefy-red ulcers with rolled edges, distinct from chancroid's painful ulcers. *Treponema pallidum* - This spirochete causes **syphilis**, another sexually transmitted infection. - Primary syphilis presents with a **painless chancre** (indurated ulcer), which differs from the painful ulcers of chancroid.

Question 5: Genital ulcers are seen in all except:

A. H. ducreyi
B. HSV
C. Chlamydia
D. H. aegyptius (Correct Answer)

Explanation: ***H. aegyptius*** - *Haemophilus aegyptius* is primarily known to cause **conjunctivitis (pinkeye)**, especially in children, and **Brazilian purpuric fever**, which is a severe systemic illness. - It does **not typically cause genital ulcers**, differentiating it from other listed pathogens. *H. ducreyi* - *Haemophilus ducreyi* is the causative agent of **chancroid**, which typically presents as painful **genital ulcers** with soft, friable bases. - These ulcers are often accompanied by **inguinal lymphadenopathy (buboes)**. *HSV* - **Herpes Simplex Virus (HSV)**, particularly HSV-2, is a common cause of **genital herpes**, characterized by painful, vesicular eruptions that progress to **ulcers** on the genitals. - These lesions often recur and are associated with **neuropathic pain and tenderness**. *Chlamydia* - While *Chlamydia trachomatis* is known for causing **genital infections** like urethritis and cervicitis, specific serovars (L1, L2, L3) are responsible for **lymphogranuloma venereum (LGV)**. - LGV typically begins with a **transient, often unnoticed, small genital ulcer** or papule, followed by marked **inguinal lymphadenopathy** and systemic symptoms.

Question 6: What are the essential major blood culture criteria for diagnosing infective endocarditis?

A. Single positive culture of Coxiella burnetii (Correct Answer)
B. Single positive culture of Corynebacterium species
C. Both HACEK and Coxiella cultures
D. Single positive culture of HACEK group

Explanation: ***Single positive culture of Coxiella burnetii*** - A single positive blood culture for **Coxiella burnetii** or **anti-phase I IgG antibody titer > 1:800** is considered a major criterion for infective endocarditis due to its highly pathogenic nature in this context [1], [2]. - This organism is a known cause of **culture-negative endocarditis**, and specific serology or molecular tests are often required for diagnosis [1]. *Single positive culture of Corynebacterium species* - **Corynebacterium species** are often considered **contaminants** in blood cultures, especially *Corynebacterium jeikeium*, and typically require multiple positive cultures, often from different sites, to be considered significant pathogens for infective endocarditis [2]. - A single positive culture of these organisms alone is generally insufficient to meet major diagnostic criteria for endocarditis [2]. *Both HACEK and Coxiella cultures* - While both **HACEK organisms** and **Coxiella burnetii** can cause endocarditis, the combination of both is not a specific major criterion in itself. - The diagnostic criteria address each organism individually [2]. *Single positive culture of HACEK group* - **HACEK organisms** (**H**aemophilus, **A**ggregatibacter, **C**ardiobacterium, **E**ikenella, **K**ingella) are well-known causes of endocarditis, but usually require **two separate positive blood cultures** for infective endocarditis major criteria [2]. - A single positive culture of a HACEK organism is typically classified as a minor criterion unless other supporting evidence is present.

Question 7: A patient with large, penetrating vegetations on his mitral and aortic valves develops severe headaches. Funduscopic examination reveals papilledema. CT scan of the brain demonstrates a ring-enhancing lesion. Which of the following organisms is the most likely cause of the patient's disorder?

A. Herpesvirus
B. Streptococcus pneumoniae
C. Mycobacterium tuberculosis
D. Staphylococcus aureus (Correct Answer)

Explanation: ***Staphylococcus aureus*** - This organism is a common cause of **infective endocarditis**, particularly in patients with intravenous drug use, and is known for producing **large, destructive vegetations** that can readily embolize [2]. - The development of **severe headaches**, **papilledema**, and a **ring-enhancing brain lesion** strongly suggests a **septic embolism** leading to a **brain abscess**, a known complication of infective endocarditis caused by virulent organisms like *S. aureus* [1], [2]. *Herpesvirus* - Herpesvirus infections, such as **HSV-1**, can cause **encephalitis**, which might present with headaches and neurological signs, but they are not typically associated with **infective endocarditis** or the formation of **septic emboli** from heart valves. - While herpes encephalitis can cause ring-enhancing lesions in specific brain regions (e.g., temporal or frontal lobes), the primary presentation here points to a systemic embolic source from the heart. *Streptococcus pneumoniae* - *Streptococcus pneumoniae* can cause endocarditis, though it is less common than *Staphylococcus aureus* and often occurs in patients with pre-existing valvular disease. - While septic emboli can occur, *S. pneumoniae* endocarditis is not as frequently associated with **large, destructive vegetations** and subsequent brain abscess formation as *S. aureus* [2]. *Mycobacterium tuberculosis* - **Tuberculous meningitis** can cause severe headaches, papilledema, and ring-enhancing lesions (tuberculomas) in the brain. - However, **tuberculous_endocarditis** is extremely rare and typically does not manifest with large, destructive vegetations or, more importantly, with a primary infectious source from the heart valves as indicated by the "large, penetrating vegetations."

Question 8: A 9-year-old child presented to OPD with complaints of high-grade fever, vomiting, and one episode of seizure. CSF examination was done and Gram staining of the culture showed lanceolate-shaped gram-positive diplococci. What is the probable causative agent?

A. Haemophilus influenzae
B. Streptococcus agalactiae
C. Neisseria meningitidis
D. Streptococcus pneumoniae (Correct Answer)

Explanation: ***Streptococcus pneumoniae*** - The description of **lanceolate-shaped gram-positive diplococci** in CSF is characteristic of *S. pneumoniae*. - This bacterium is a common cause of **bacterial meningitis** in children and can present with high fever, vomiting, and seizures. *Haemophilus influenzae* - This is a **gram-negative coccobacillus**, which would appear as small, pleomorphic rods rather than lanceolate-shaped diplococci on Gram stain. - While it causes meningitis, its Gram stain morphology is distinct from *S. pneumoniae*. *Streptococcus agalactiae* - *S. agalactiae* (Group B Streptococcus) is a **gram-positive coccus**, but it typically appears in **chains** and is a major cause of neonatal meningitis, not usually in a 9-year-old child. - Its morphology on Gram stain would not be described as lanceolate diplococci. *Neisseria meningitidis* - *N. meningitidis* is a **gram-negative diplococcus** and would appear as kidney-bean shaped or flattened paired cocci, not gram-positive. - Though a common cause of meningitis, the Gram stain morphology described rules it out.

Question 9: HACEK group of organisms includes all, except:

A. Cardiobacterium hominis
B. Eikenella corrodens
C. Haemophilus parainfluenzae
D. Haemophilus ducreyi (Correct Answer)

Explanation: ***Haemophilus ducreyi*** - *Haemophilus ducreyi* is the causative agent of **chancroid**, a sexually transmitted infection, and is not considered part of the HACEK group. - The **HACEK group** consists of fastidious, gram-negative bacteria known for causing **endocarditis**. *Haemophilus parainfluenzae* - *Haemophilus parainfluenzae* is one of the five genera included in the **HACEK group** acronym, specifically the 'H'. - This organism is a known cause of **infective endocarditis**, particularly in patients with pre-existing valvular disease. *Cardiobacterium hominis* - *Cardiobacterium hominis* is represented by the 'C' in the **HACEK group** acronym. - It is a significant cause of **culture-negative endocarditis** due to its fastidious nature and slow growth. *Eikenella corrodens* - *Eikenella corrodens* is the 'E' in the **HACEK group** acronym. - It is often associated with **oral cavity infections**, human bite wounds, and can cause **endocarditis** in susceptible individuals.

Question 10: HACEK group of organisms includes all except:

A. Cardiobacterium hominis
B. Eikenella corrodens
C. Haemophilus aphrophilus
D. Acinetobacter baumannii (Correct Answer)

Explanation: ***Acinetobacter baumannii*** ✓ Correct Answer - *Acinetobacter baumannii* is a **Gram-negative coccobacillus** but is **NOT part of the HACEK group**. - This is the correct answer as the question asks "all EXCEPT." - It is an important opportunistic pathogen known for causing **healthcare-associated infections** and often exhibits multidrug resistance. *Haemophilus aphrophilus* (now **Aggregatibacter aphrophilus**) - This organism **IS part of the HACEK group**, with the 'H' (or 'A') standing for **Haemophilus/Aggregatibacter**. - It is a common cause of **culture-negative endocarditis**. - Incorrect choice as it belongs to HACEK. *Cardiobacterium hominis* - This organism **IS a member of the HACEK group**, with the 'C' representing **Cardiobacterium**. - It is a known cause of **infective endocarditis**, particularly on damaged heart valves. - Incorrect choice as it belongs to HACEK. *Eikenella corrodens* - This bacterium **belongs to the HACEK group**, with the 'E' standing for **Eikenella**. - It is frequently associated with infections following **human bites** or dental procedures due to its presence in oral flora. - Incorrect choice as it belongs to HACEK.

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