Bartonella quintana causes:
Which immunoglobulin does Protein A of Staphylococcus aureus bind to?
Which type of DNase produced by Streptococcus is known to be the most antigenic in humans?
Proteus isolated from a patient of UTI will show which biochemical reaction.
What is the most sensitive test for diagnosing syphilis?
Most common site for Staphylococcus carriage?
All are true about anaerobic infections except:
Which of the following statements about Legionella is most accurate?
Granuloma inguinale is caused by:
What is the causative agent of Izumi fever?
NEET-PG 2015 - Microbiology NEET-PG Practice Questions and MCQs
Question 41: Bartonella quintana causes:
- A. Trench fever (Correct Answer)
- B. Scrub typhus
- C. Epidemic typhus
- D. Endemic typhus
Explanation: ***Trench fever*** - **Bartonella quintana** is the causative agent of **trench fever**, a louse-borne disease historically common during wartime. - Symptoms include **recurrent fevers**, headache, bone pain (especially in the shins), and rash. *Scrub typhus* - Scrub typhus is caused by **Orientia tsutsugamushi**, a rickettsial bacterium, not Bartonella. - It is transmitted by **chiggers** and characterized by a rash, fever, and eschar at the bite site. *Epidemic typhus* - Epidemic typhus is caused by **Rickettsia prowazekii** and is also louse-borne. - It presents with sudden high fever, severe headache, and a maculopapular rash that spares the face, palms, and soles. *Endemic typhus* - Endemic typhus (murine typhus) is caused by **Rickettsia typhi** and is transmitted by **rat fleas**. - Its symptoms are generally milder than epidemic typhus, including fever, headache, and a truncal rash.
Question 42: Which immunoglobulin does Protein A of Staphylococcus aureus bind to?
- A. IgA
- B. IgG (Correct Answer)
- C. IgD
- D. IgE
Explanation: ***IgG*** - **Protein A** of *Staphylococcus aureus* binds to the **Fc region** of IgG antibodies. - This binding mechanism helps *S. aureus* in **evading opsonization** and phagocytosis by interfering with the host immune response. *IgA* - IgA is primarily found in **mucosal secretions** and its primary role is in mucosal immunity. - Protein A does not preferentially bind to IgA; instead, some bacteria produce specific **IgA proteases** to cleave and inactivate IgA. *IgD* - IgD is found mostly on the surface of **B lymphocytes** and its main role is in B cell activation. - Protein A does not have a significant binding affinity for IgD. *IgE* - IgE is involved in **allergic reactions** and defense against parasites. - Protein A does not bind to IgE; binding to IgE is typically mediated by specific IgE receptors on mast cells and basophils.
Question 43: Which type of DNase produced by Streptococcus is known to be the most antigenic in humans?
- A. DNase C
- B. DNase D
- C. DNase A
- D. DNase B (Correct Answer)
Explanation: ***DNase B*** - **DNase B** is the most **antigenic** of the four DNases (A, B, C, D) produced by *Streptococcus pyogenes*. - Antibodies against DNase B are commonly measured as anti-DNase B titers in the diagnosis of **streptococcal infections** and their sequelae, like **acute rheumatic fever** and **post-streptococcal glomerulonephritis**, especially when ASO titers are negative. *DNase A* - While *Streptococcus pyogenes* produces **DNase A**, it is not considered the most antigenically potent or clinically relevant for antibody testing in humans. - Its antigenicity is generally **lower** than that of DNase B in response to streptococcal infection. *DNase C* - **DNase C** is another deoxyribonuclease produced by *Streptococcus pyogenes*. - Similar to DNase A, it does not elicit as strong or as consistent an **antibody response** in human infections compared to DNase B. *DNase D* - **DNase D** is the fourth type of deoxyribonuclease produced by *Streptococcus pyogenes*. - Its **antigenicity** in humans is less pronounced and less diagnostically significant than that of **DNase B**.
Question 44: Proteus isolated from a patient of UTI will show which biochemical reaction.
- A. Production of phenylpyruvic acid from phenylalanine (Correct Answer)
- B. Hydrolysis of esculin in bile
- C. Sensitivity to colchicine
- D. Sensitivity to bacitracin
Explanation: ***Production of phenylpyruvic acid from phenylalanine*** - *Proteus* species possess the enzyme **phenylalanine deaminase**, which deaminates phenylalanine to **phenylpyruvic acid**. - This reaction is a **key biochemical test** used to identify *Proteus*, *Providencia*, and *Morganella* species. *Hydrolysis of esculin in bile* - This reaction is characteristic of **Group D streptococci** and **enterococci**, not *Proteus* species. - The organism hydrolyzes **esculin** in the presence of bile, turning the agar black. *Sensitivity to colchicine* - **Colchicine** is an anti-inflammatory drug, not part of standard **biochemical identification tests** for bacteria. - This is not a recognized biochemical reaction used to identify *Proteus* or any bacterial species. *Sensitivity to bacitracin* - **Bacitracin sensitivity** is primarily used to differentiate **Group A streptococci** (e.g., *Streptococcus pyogenes*) from other beta-hemolytic streptococci. - It is an **antibiotic susceptibility test**, not a biochemical reaction characteristic of *Proteus* species.
Question 45: What is the most sensitive test for diagnosing syphilis?
- A. VDRL
- B. RPR
- C. TP-PA
- D. FTA-ABS (Correct Answer)
Explanation: ***FTA-ABS*** - The **fluorescent treponemal antibody absorption (FTA-ABS)** test is a treponemal test that is highly sensitive (>95%) and specific for detecting antibodies to *Treponema pallidum*. - It was traditionally considered the gold standard confirmatory test and is often used to confirm positive screening results. - It detects antibodies early in infection and remains positive for life, even after successful treatment. - **Note:** Modern treponemal tests like TP-PA have comparable sensitivity, but FTA-ABS remains widely recognized in clinical practice. *VDRL* - The **Venereal Disease Research Laboratory (VDRL)** test is a non-treponemal test that measures antibodies to cardiolipin, a lipid released from damaged host cells and *T. pallidum*. - While useful for screening and monitoring treatment response (titers decrease with successful treatment), it is less sensitive than treponemal tests, especially in early primary and late/tertiary syphilis. - Can yield false positives in various conditions (pregnancy, autoimmune diseases, infections). *TP-PA* - The **Treponema pallidum particle agglutination (TP-PA)** test is a highly sensitive and specific treponemal test that detects antibodies to *T. pallidum*. - It has sensitivity comparable to FTA-ABS (>95%) and is increasingly preferred in modern laboratories due to easier performance and objective reading. - Like other treponemal tests, it remains positive for life. *RPR* - The **rapid plasma reagin (RPR)** test is a non-treponemal test similar to VDRL, detecting antibodies to cardiolipin. - It is commonly used for screening due to ease of use and ability to monitor treatment response through quantitative titers. - Like VDRL, it has lower sensitivity compared to treponemal tests and can produce false positives.
Question 46: Most common site for Staphylococcus carriage?
- A. Skin
- B. Nose (Correct Answer)
- C. Oropharynx
- D. Perineum
Explanation: ***Nose*** - The **anterior nares** are the most common site for **Staphylococcus aureus** colonization in healthy individuals. - Nasal carriage is a significant risk factor for subsequent **Staphylococcus aureus infections**, both self-acquired and transmitted to others. *Skin* - While Staphylococcus aureus can colonize the skin, especially in areas like the axillae and groin, it is **less common** as a primary carrier site compared to the nose. - Skin colonization often occurs due to spread from **nasal carriage**. *Oropharynx* - The oropharynx can be colonized by various bacteria, but it is **not the primary or most common site** for Staphylococcus aureus carriage. - Other bacteria like **Streptococcus species** are more prevalent colonizers of the oropharynx. *Perineum* - The perineum can harbor Staphylococcus aureus, particularly in specific populations or in individuals with certain skin conditions, but it is **not the most common or primary site** of colonization. - Colonization here is often **secondary** to nasal carriage or contact with contaminated surfaces.
Question 47: All are true about anaerobic infections except:
- A. Specimen for UTI is suprapubic aspiration
- B. They are found normally on skin and GIT
- C. Exudates and swabs are ideal for culture (Correct Answer)
- D. Most infections are endogenous
Explanation: ***Exudates and swabs are ideal for culture.*** - **Swabs exposed to air** are generally **not ideal** for anaerobic culture because oxygen exposure can kill obligate anaerobes, leading to false-negative results. - Optimal anaerobic specimen collection requires techniques that **minimize oxygen exposure**, such as aspirates or tissue biopsies placed in anaerobic transport media. *Most infections are endogenous* - Anaerobic infections commonly arise from **one's own commensal flora**, which becomes pathogenic under specific conditions like tissue damage or impaired blood supply. - These bacteria are part of the normal microbiota of various body sites, including the gastrointestinal tract, oral cavity, and skin. *Specimen for UTI is suprapubic aspiration* - For **suspected anaerobic urinary tract infections (UTIs)**, suprapubic aspiration is considered the gold standard for specimen collection. - This method bypasses potential contamination from urethral flora and ensures a sterile, oxygen-free sample for accurate anaerobic culture. *They are found normally on skin and GIT* - **Anaerobic bacteria** are a significant component of the normal flora of the **skin and gastrointestinal tract (GIT)**, as well as the oral cavity and genitourinary tract. - Their presence in these sites is crucial for maintaining normal physiological functions and preventing the overgrowth of pathogens.
Question 48: Which of the following statements about Legionella is most accurate?
- A. Prolonged carriers are common.
- B. There is no human-to-human transmission.
- C. Aerosol inhalation is a common mode of transmission. (Correct Answer)
- D. All of the options are true
Explanation: ***Aerosol inhalation is a common mode of transmission.*** - **Legionella pneumophila** is primarily transmitted through **inhalation of aerosolized water droplets** containing the bacteria - Common sources include **cooling towers, air conditioning systems, hot tubs, showerheads**, and decorative fountains - This is the **most defining and clinically important characteristic** of Legionella transmission - Understanding aerosol transmission is crucial for **outbreak control and prevention strategies** *There is no human-to-human transmission.* - This statement is **medically accurate** - Legionella does NOT spread from person to person - However, this is a secondary characteristic compared to the primary transmission mode - The question asks for the **most accurate** statement, making aerosol transmission more definitive *Prolonged carriers are common.* - This is **INCORRECT** - Legionella does NOT cause a chronic carrier state in humans - The bacteria **colonizes environmental water systems and amoebae** (like *Acanthamoeba* and *Naegleria*), not human hosts - Humans are accidental hosts through aerosol exposure *All of the options are true* - This is **INCORRECT** because "Prolonged carriers are common" is false - Only two of the three substantive statements are true
Question 49: Granuloma inguinale is caused by:
- A. Calymmatobacterium granulomatis (Correct Answer)
- B. Haemophilus ducreyi
- C. Chlamydia trachomatis
- D. Treponema pallidum
Explanation: ***Calymmatobacterium granulomatis*** - **Granuloma inguinale**, also known as **donovanosis**, is a sexually transmitted infection caused by **_Calymmatobacterium granulomatis_**. - This bacterium is notoriously difficult to culture, so diagnosis is typically made by identifying **Donovan bodies** (macrophages filled with bacteria) in tissue samples. *Haemophilus ducreyi* - **_Haemophilus ducreyi_** is the causative agent of **chancroid**, - Chancroid is characterized by **painful genital ulcers** with a ragged, undermined border, and often accompanied by **tender inguinal lymphadenopathy**. *Chlamydia trachomatis* - **_Chlamydia trachomatis_** is responsible for several conditions, including **chlamydia** (the most common bacterial STI), **lymphogranuloma venereum (LGV)**, and **trachoma**. - LGV presents with a transient, often unnoticed genital lesion followed by painful, suppurative lymphadenopathy, which is distinct from granuloma inguinale. *Treponema pallidum* - **_Treponema pallidum_** is the spirochete that causes **syphilis**, which progresses through several stages. - Primary syphilis manifests as a **painless chancre**, while secondary syphilis can involve a widespread rash, lymphadenopathy, and mucosal lesions.
Question 50: What is the causative agent of Izumi fever?
- A. Yersinia pseudotuberculosis (Correct Answer)
- B. Yersinia enterocolitica
- C. Pseudomonas aeruginosa
- D. Pasteurella multocida
Explanation: ***Yersinia pseudotuberculosis*** - Izumi fever (also called **Far East scarlet-like fever**) is caused by Yersinia pseudotuberculosis, particularly referring to outbreaks that occurred in Japan. - This infection presents with **fever, abdominal pain, and a scarlet fever-like rash**, often mimicking appendicitis due to mesenteric lymphadenitis. - Y. pseudotuberculosis is transmitted through **contaminated food and water**, and the Izumi fever variant is characterized by systemic manifestations including erythema and desquamation. *Yersinia enterocolitica* - While this is a closely related species that also causes **gastroenteritis and mesenteric adenitis**, it is NOT the causative agent of Izumi fever. - Y. enterocolitica typically presents with diarrhea, abdominal pain, and fever, but lacks the distinctive scarlet fever-like rash seen in Izumi fever. *Pseudomonas aeruginosa* - This bacterium is an **opportunistic pathogen** often associated with nosocomial infections, especially in immunocompromised individuals. - It causes **pneumonia**, urinary tract infections, and wound infections, but not Izumi fever. *Pasteurella multocida* - This bacterium is common in the **respiratory tracts of animals**, especially cats and dogs, and is a frequent cause of wound infections from animal bites or scratches. - It typically causes localized cellulitis, abscesses, and occasionally severe infections like meningitis or osteomyelitis, not Izumi fever.