What is a common characteristic of the H5N1 and H7N7 strains of influenza?
Capsular polysaccharide derived vaccine is available for all meningococci except?
A woman traveling from Bihar to Delhi is suspected to have Kala-azar. Suitable investigation is?
Draughtsman colonies are seen with:
Which of the following statements about Chromobacterium violaceum is false?
Oil paint appearance on nutrient agar is seen in -
What is the most common age group affected by Streptococcus pyogenes?
Naegler's reaction is due to:
Disruption of which of the following oropharyngeal commensals predisposes to candidiasis?
Primary complex of M bovis involves:
NEET-PG 2015 - Microbiology NEET-PG Practice Questions and MCQs
Question 21: What is a common characteristic of the H5N1 and H7N7 strains of influenza?
- A. Frequent endemic infection in man
- B. Have same frequency of antigenic variation
- C. Strains of avian influenza (Correct Answer)
- D. None of the options
Explanation: ***Strains of avian influenza*** - Both **H5N1** and **H7N7** are well-known subtypes of the **influenza A virus** that primarily infect birds. - While they can infect humans, their natural reservoir and main hosts are **avian species**. *Frequent endemic infection in man* - These strains are not endemic in humans; human infections are typically **sporadic** and associated with close contact with infected birds. - They lack efficient **human-to-human transmission**, which prevents them from becoming endemic in the human population. *Have same frequency of antigenic variation* - Although both undergo **antigenic variation**, the specific frequency and patterns can differ between strains and are influenced by various factors, including their host range and circulation dynamics. - It is inaccurate to assume identical frequencies of **antigenic drift** and **shift** for different viral subtypes. *None of the options* - This option is incorrect because "Strains of avian influenza" is a correct and common characteristic shared by both H5N1 and H7N7.
Question 22: Capsular polysaccharide derived vaccine is available for all meningococci except?
- A. Group C
- B. Group B (Correct Answer)
- C. Group Y
- D. Group A
Explanation: ***Group B*** - The capsular polysaccharide of **Group B meningococci** is composed of **polysialic acid**, which is poorly immunogenic in humans because it structurally mimics human neural cell adhesion molecules. - Due to its **poor immunogenicity** and risk of autoantibody production, traditional polysaccharide vaccines are ineffective against Group B. *Group A* - Polysaccharide vaccines for **Group A meningococci** (e.g., in Menactra, Menveo) are effective in inducing a protective immune response. - Group A is a major cause of meningococcal disease, particularly in the **"meningitis belt"** of sub-Saharan Africa. *Group C* - **Capsular polysaccharide vaccines** are available and effective against Group C meningococcal disease, often included in quadrivalent formulations. - These vaccines elicit a robust **antibody response** against the Group C polysaccharide. *Group Y* - Vaccines containing the **capsular polysaccharide** of Group Y meningococci are effective and commonly included in quadrivalent vaccines. - Group Y is a significant cause of meningococcal disease, particularly in **North America and Europe**.
Question 23: A woman traveling from Bihar to Delhi is suspected to have Kala-azar. Suitable investigation is?
- A. P24 antigen
- B. Rk-39 test (Correct Answer)
- C. Combo RDT
- D. HRP-2 antigen
Explanation: ***Rk-39 test*** - The **Rk-39 test** is a rapid diagnostic test highly sensitive and specific for detecting antibodies against the **kinesin-related protein K39** of *Leishmania donovani*, the causative agent of **Kala-azar (visceral leishmaniasis)**. - It is particularly useful in **endemic regions** like Bihar for quick and accurate diagnosis, especially in patients with suspected Kala-azar presenting with fever, splenomegaly, and pancytopenia. *P24 antigen* - **P24 antigen** testing is primarily used for the diagnosis of **HIV infection**. - It detects the **core protein p24** of the HIV virus, which is not relevant for the diagnosis of Kala-azar. *Combo RDT* - A **Combo RDT** (Rapid Diagnostic Test), without further specification, typically refers to tests for **malaria**, which detect antigens like **HRP-2** and **aldolase**. - While RDTs are used for parasitic diseases, this general term does not specifically refer to a test for **Kala-azar**. *HRP-2 antigen* - **HRP-2 (Histidine-rich protein 2) antigen** is a specific marker for **Plasmodium falciparum**, used in the diagnosis of **malaria**. - It is not associated with the diagnosis of **Kala-azar**, which is caused by *Leishmania donovani*.
Question 24: Draughtsman colonies are seen with:
- A. Anthrax
- B. Pertussis
- C. Pneumococci (Correct Answer)
- D. Yersinia
Explanation: ***Pneumococci*** - **Draughtsman colonies** (or **draughtsman-like colonies**) are a characteristic morphological feature observed when *Streptococcus pneumoniae* (pneumococci) grows on certain agar media, such as blood agar. - This appearance is due to the **central umbilication or depression** of the colony caused by autolytic enzymes that break down the bacterial cells in the center as the colony matures. *Anthrax* - Colonies of *Bacillus anthracis* are typically described as **"Medusa head" colonies**, characterized by swirling projections at the periphery. - They are generally **non-hemolytic** on blood agar, distinguishing them from other *Bacillus* species. *Pertussis* - *Bordetella pertussis* colonies are characteristic on **Bordet-Gengou agar**, appearing as small, glistening, pearl-like, or "mercury droplet" colonies. - This distinct morphology is crucial for its identification in laboratory cultures. *Yersinia* - *Yersinia pestis* (which causes plague) colonies on blood agar at 28°C often show a **"fried egg" appearance** over several days, with a dark center and lighter periphery. - Other *Yersinia* species like *Y. enterocolitica* can show a **bull's-eye pattern** on CIN (Cefsulodin-Irgasan-Novobiocin) agar.
Question 25: Which of the following statements about Chromobacterium violaceum is false?
- A. Normal flora in human (Correct Answer)
- B. Gram negative
- C. Causes cellulitis
- D. Produces violet-colored pigment
Explanation: **This question asks for the FALSE statement about *Chromobacterium violaceum*.** ***Normal flora in human*** ✓ (FALSE STATEMENT - This is the correct answer) - *Chromobacterium violaceum* is **not considered normal flora** in humans. It is an environmental bacterium typically found in **soil and water** in tropical and subtropical regions. - Its presence in humans usually signifies a serious **opportunistic infection**, often resulting from exposure to contaminated environments. - Since this statement is FALSE, this is the correct answer. *Gram negative* (TRUE statement) - *Chromobacterium violaceum* is indeed a **Gram-negative bacterium**. This characteristic is crucial for its identification and determining appropriate antibiotic treatment. - Like other Gram-negative bacteria, it possesses an **outer membrane** containing lipopolysaccharide (LPS). *Causes cellulitis* (TRUE statement) - *Chromobacterium violaceum* can cause severe infections in humans, including **cellulitis**, often following skin breaches like cuts or abrasions. - The infections are frequently aggressive and can lead to systemic disease such as **sepsis and abscess formation**. *Produces violet-colored pigment* (TRUE statement) - *Chromobacterium violaceum* is notable for producing **violacein**, a distinctive **violet-colored pigment**. - This pigment production is a key identifying feature on culture media and is associated with some of its pathogenic properties.
Question 26: Oil paint appearance on nutrient agar is seen in -
- A. Staphylococcus aureus (Correct Answer)
- B. Streptococcus pyogenes
- C. Bordetella pertussis
- D. H. influenzae
Explanation: ***Staphylococcus aureus*** - *Staphylococcus aureus* forms characteristic **golden-yellow, smooth, opaque colonies** on nutrient agar with a **buttery or creamy consistency** - Some texts describe this appearance as **"oil paint-like"** due to the pigmented, smooth, and glistening surface that can resemble brushed paint - Colonies are typically **2-4 mm in diameter**, round, and show **golden pigmentation** (due to carotenoid pigments) - On **blood agar**, *S. aureus* shows **beta-hemolysis** with golden colonies *Streptococcus pyogenes* - *Streptococcus pyogenes* grows poorly on plain nutrient agar and requires **enriched media** like blood agar - On blood agar, it forms **small, translucent, grey-white colonies** surrounded by a wide zone of **beta-hemolysis** - Colonies are typically **pinpoint** in size and do not show pigmentation *Bordetella pertussis* - *Bordetella pertussis* is a **fastidious organism** that does **not grow on plain nutrient agar** - Requires specialized enriched media like **Bordet-Gengou agar** (with potato-glycerol-blood) or **Regan-Lowe agar** - On Bordet-Gengou agar, colonies appear as **small, smooth, pearl-like** or **"mercury droplet"** colonies after 3-7 days *H. influenzae* - *Haemophilus influenzae* is also fastidious and requires **X factor (hemin)** and **V factor (NAD)** for growth - Does **not grow on plain nutrient agar** - On **chocolate agar**, forms **small, smooth, translucent, greyish colonies** with a characteristic musty odor - Colonies are typically **1-2 mm** in diameter
Question 27: What is the most common age group affected by Streptococcus pyogenes?
- A. 30-40 years
- B. <5 years
- C. 5-15 years (Correct Answer)
- D. 20-25 years
Explanation: ***5-15 years*** - **Streptococcus pyogenes** (Group A Strep) commonly causes **pharyngitis** (strep throat), which primarily affects school-aged children. - This age group is more susceptible due to increased exposure in school and daycare settings. *<5 years* - While younger children can get strep infections, it is less common in those under **3 years of age**, as viral etiologies are more prevalent for pharyngitis in this group. - They are more prone to **non-streptococcal bacterial infections** and certain viral infections. *20-25 years* - Although adults can get **Streptococcus pyogenes** infections, the incidence significantly decreases after childhood. - Pharyngitis in this age group is more often **viral** in origin. *30-40 years* - The prevalence of **Streptococcus pyogenes** infections, particularly pharyngitis, is typically low in this age group compared to children. - Infections, if they occur, may stem from exposure to infected children or close contact environments.
Question 28: Naegler's reaction is due to:
- A. Lecithinase (Correct Answer)
- B. Coagulase
- C. Hyaluronidase
- D. None of the options
Explanation: ***Lecithinase*** - The **Naegler reaction** is a bacterial identification test used to detect the production of **lecithinase** (also known as alpha-toxin) by certain bacteria, particularly *Clostridium perfringens*. - This enzyme hydrolyzes **lecithin** (a lipid found in egg yolk), resulting in a visible opaque precipitate around the bacterial colonies on egg yolk agar. *Coagulase* - **Coagulase** is an enzyme produced by some bacteria (e.g., *Staphylococcus aureus*) that causes the coagulation of blood plasma. - While it is an important virulence factor, it is not involved in the **Naegler reaction**. *Hyaluronidase* - **Hyaluronidase** is an enzyme that breaks down **hyaluronic acid**, a component of connective tissue, facilitating the spread of bacteria. - It is often referred to as a **spreading factor** but is not detected by the **Naegler reaction**. *None of the options* - This option is incorrect because **Lecithinase** is directly responsible for the **Naegler reaction**.
Question 29: Disruption of which of the following oropharyngeal commensals predisposes to candidiasis?
- A. Staphylococcus
- B. Streptococcus (Correct Answer)
- C. Lactobacillus
- D. Haemophilus influenzae
Explanation: ***Streptococcus*** - **Streptococcus** species, particularly *S. sanguinis* and *S. mitis*, are major commensals in the oral cavity that **inhibit the growth of *Candida albicans*** through competition for nutrients and production of antimicrobial substances. - Disruption of this normal **streptococcal flora**, often by broad-spectrum antibiotics, creates an environment where *Candida albicans* can proliferate, leading to candidiasis. *Staphylococcus* - **Staphylococcus** species are primarily skin and nasal commensals; while *S. aureus* can be found in the oral cavity, it is not a primary competitor against *Candida* in the same way as streptococci. - Their presence or absence is not typically a direct predisposing factor for oral candidiasis compared to the dominant streptococcal flora. *Lactobacillus* - **Lactobacillus** species are common in the gastrointestinal tract and vagina, where they maintain an acidic environment that inhibits pathogen growth; however, they are less dominant in the oropharynx as a defense against *Candida*. - While beneficial for overall host health, their disruption in the oral cavity does not typically precipitate candidiasis as directly as that of the **streptococcal flora**. *Hemophilus influenzae* - *Haemophilus influenzae* is a common inhabitant of the **upper respiratory tract** and can be an opportunistic pathogen, but it is not known to have a significant role in directly inhibiting *Candida* growth in the oropharynx. - Its presence or absence in the commensal flora in the oral cavity does not typically influence the development of candidiasis.
Question 30: Primary complex of M bovis involves:
- A. Tonsil and skin
- B. Tonsil and intestine (Correct Answer)
- C. Tonsil and lung
- D. Skin and Intestine
Explanation: ***Tonsil and intestine*** - *Mycobacterium bovis* is primarily transmitted through **consumption of contaminated milk and dairy products**, making the **alimentary tract** the main route of infection - The primary complex (Ghon complex) involves the **initial site of infection plus regional lymph nodes** - In alimentary tuberculosis, the organisms enter through the **intestinal mucosa** (Peyer's patches) or **tonsillar tissue**, creating foci with associated mesenteric or cervical lymphadenopathy - Both tonsils and intestines are part of the **alimentary system**, representing the typical primary complex for M. bovis in humans *Tonsil and lung* - This incorrectly combines **two different routes of entry** (alimentary and respiratory) - A primary complex involves a **single portal of entry**, not multiple unrelated organ systems - While M. bovis can rarely cause pulmonary TB through inhalation, this would create a separate lung + hilar node complex, not a combined tonsil-lung complex *Tonsil and skin* - **Skin involvement** requires direct inoculation through cuts or abrasions and does not form a primary complex with tonsillar infection - These represent different portals of entry and would not occur together as a primary complex *Skin and Intestine* - **Skin infection** by M. bovis is rare and requires occupational exposure with direct inoculation (e.g., veterinarians, butchers) - This incorrectly pairs two different routes of infection that would not form a single primary complex