NEET-PG 2015 - Microbiology Practice Questions

Q: Bartonella quintana causes:

Trench fever. ***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.

Q: Salmonella and Shigella can be differentiated from other Enterobacteriaceae members by isolation on:

XLD agar. ***XLD agar*** - **Xylose Lysine Deoxycholate (XLD) agar** is a selective and differential medium used to isolate and identify *Salmonella* and *Shigella* species from other Enterobacteriaceae. - It differentiates *Salmonella* and *Shigella* based on their ability to ferment **xylose**, decarboxylate **lysine**, and produce **hydrogen sulfide (H2S)**. *MacConkey agar* - **MacConkey agar** is a selective and differential medium used to isolate Gram-negative bacteria and differentiate them based on **lactose fermentation**. - While it can grow *Salmonella* and *Shigella* (which are non-lactose fermenters), it does not specifically differentiate them from other non-lactose fermenting Enterobacteriaceae. *Mannitol salt agar* - **Mannitol salt agar (MSA)** is a selective and differential medium primarily used for the isolation of **staphylococci**. - It is highly selective due to its high salt concentration and differentiates staphylococci based on their ability to ferment **mannitol**. *BCYE medium* - **Buffered Charcoal Yeast Extract (BCYE) medium** is a specialized enrichment medium used for the isolation of **Legionella species**. - It provides specific nutrients required for the growth of *Legionella* and is not suitable for differentiating *Salmonella* and *Shigella* from other Enterobacteriaceae.

Q: Which type of DNase produced by Streptococcus is known to be the most antigenic in humans?

DNase B. ***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**.

Q: Proteus isolated from a patient of UTI will show which biochemical reaction.

Production of phenylpyruvic acid from phenylalanine. ***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.

Q: Which bacteria can be isolated using crystal violet blood agar?

β-hemolytic streptococci. ***β-hemolytic streptococci*** - **Crystal violet blood agar** is a selective medium that inhibits the growth of most Gram-positive bacteria, except for **beta-hemolytic streptococci**. - The crystal violet dye suppresses the growth of competing flora, allowing for better isolation and identification of these bacteria, which exhibit **complete hemolysis (beta-hemolysis)** on blood agar. *Corynebacterium diphtheriae* - This bacterium requires more specialized media, such as **Tinsdale agar** or **Loeffler's serum agar**, for optimal growth and identification due to specific nutritional requirements and colony morphology. - Crystal violet blood agar is not the primary medium used for its isolation. *Staph aureus* - **Staphylococcus aureus** is a common contaminant that is typically inhibited by the crystal violet in the medium. - It grows well on routine blood agar but is not selectively grown or isolated using crystal violet blood agar. *Meningococcus* - **Neisseria meningitidis** (Meningococcus) requires enriched media like **chocolate agar** or **Thayer-Martin agar** for successful isolation, as it is a fastidious organism. - Crystal violet blood agar is not suitable for its growth due to its inhibitory properties and lack of necessary nutrients.

Q: Most common site for Staphylococcus carriage?

Nose. ***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.

Q: All are true about anaerobic infections except:

Exudates and swabs are ideal for culture. ***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.

Q: Which of the following statements about Legionella is most accurate?

Aerosol inhalation is a common mode of transmission.. ***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

Q: Which of the following statements about the Widal test is true?

The O antigen used in the Widal test is from S. typhi.. ***Correct: The O antigen used in the Widal test is from S. typhi.*** - The Widal test uses **O (somatic) antigens from S. Typhi** to detect anti-O antibodies - It also uses **H (flagellar) antigens from S. Typhi** to detect anti-H antibodies - Additionally, antigens from **S. Paratyphi A and B** are included for comprehensive detection of enteric fever - The statement is correct that O antigen from S. typhi is used (along with antigens from other organisms) *Incorrect: The H-antigen is the most immunogenic.* - The **O antigen** is generally considered more immunogenic than the H antigen in enteric fever - Anti-O antibodies appear earlier and are more specific for acute infection - However, O antibodies disappear faster after recovery *Incorrect: Felix tubes are not used in the Widal test.* - **Dreyer's tubes** (also known as Felix tubes) are traditionally used in the Widal test - These special tubes allow for quantitative antibody titration - They enable observation of agglutination patterns at different serum dilutions *Incorrect: Anti-O antibody persists longer than anti-H antibody.* - This is **backwards** - Anti-H antibodies actually persist longer (can last for years) - **Anti-O antibodies** appear later and disappear relatively quickly after infection resolves - Anti-O antibodies are more indicative of acute/recent infection - Anti-H antibodies are less specific due to their prolonged persistence and possible cross-reactions

Q: What is the clinical significance of the Vi antigen in Salmonella typhi?

Indicates carrier status in individuals. ***Indicates carrier status in individuals*** - The **Vi (Virulence) antigen** is a **capsular polysaccharide** found on *Salmonella typhi* that helps the bacterium evade immune responses - The presence of persistent **anti-Vi antibodies** is the **hallmark of chronic typhoid carriers**, particularly those harboring bacteria in the **gallbladder** - Vi antibody testing is specifically used for **carrier screening** and identification, as carriers maintain high anti-Vi titers even without active symptoms - This is the **primary clinical significance** of the Vi antigen in diagnostic microbiology *Used for diagnosing typhoid fever* - This is **incorrect** - the Vi antigen is NOT used for diagnosing acute typhoid fever - The standard **Widal test** detects antibodies against **O (somatic)** and **H (flagellar)** antigens, NOT Vi antigen - Acute diagnosis relies on **blood culture** and detection of O and H antibodies, not Vi antibodies - Vi antibodies appear later in infection and persist longer, making them markers of **chronic carriage** rather than acute disease *Stimulates an immune response* - While true that Vi antigen stimulates antibody production, this is not its **clinical significance** - All bacterial antigens stimulate immune responses - this doesn't distinguish Vi antigen's specific clinical utility - The key clinical value lies in its use for **carrier detection**, not merely immunogenicity *Not primarily used in Widal test* - This is a **true statement** but not the answer to what the clinical significance IS - The Widal test uses O and H antigens for acute diagnosis - While accurate, this option describes what Vi antigen is NOT used for, rather than its actual clinical significance as a **carrier marker**

Question 1

Bartonella quintana causes:

Accepted Answer

Trench fever

Answer

Scrub typhus

Answer

Epidemic typhus

Answer

Endemic typhus

Question 2

Salmonella and Shigella can be differentiated from other Enterobacteriaceae members by isolation on:

Accepted Answer

XLD agar

Answer

MacConkey agar

Answer

Mannitol salt agar

Answer

BCYE medium

Question 3

Which type of DNase produced by Streptococcus is known to be the most antigenic in humans?

Accepted Answer

DNase B

Answer

DNase C

Answer

DNase D

Answer

DNase A

Question 4

Proteus isolated from a patient of UTI will show which biochemical reaction.

Accepted Answer

Production of phenylpyruvic acid from phenylalanine

Answer

Hydrolysis of esculin in bile

Answer

Sensitivity to colchicine

Answer

Sensitivity to bacitracin

Question 5

Which bacteria can be isolated using crystal violet blood agar?

Accepted Answer

β-hemolytic streptococci

Answer

Corynebacterium diphtheriae

Answer

Staph aureus

Answer

Meningococcus

Question 6

Most common site for Staphylococcus carriage?

Accepted Answer

Nose

Answer

Skin

Answer

Oropharynx

Answer

Perineum

Question 7

All are true about anaerobic infections except:

Accepted Answer

Exudates and swabs are ideal for culture

Answer

Specimen for UTI is suprapubic aspiration

Answer

They are found normally on skin and GIT

Answer

Most infections are endogenous

Question 8

Which of the following statements about Legionella is most accurate?

Accepted Answer

Aerosol inhalation is a common mode of transmission.

Answer

Prolonged carriers are common.

Answer

There is no human-to-human transmission.

Answer

All of the options are true

Question 9

Which of the following statements about the Widal test is true?

Accepted Answer

The O antigen used in the Widal test is from S. typhi.

Answer

The H-antigen is the most immunogenic.

Answer

Felix tubes are not used in the Widal test.

Answer

Anti-O antibody persists longer than anti-H antibody.

Question 10

What is the clinical significance of the Vi antigen in Salmonella typhi?

Accepted Answer

Indicates carrier status in individuals

Answer

Stimulates an immune response

Answer

Not primarily used in Widal test

Answer

Used for diagnosing typhoid fever

NEET-PG 2015 — Microbiology