Microbiology
9 questionsViral DNA is integrated into Bacterial DNA in:
What is the primary use of the freezing method in microbiology?
Granulomatosis infantiseptica is caused by:
Salmonella and Shigella can be differentiated from other Enterobacteriaceae members by isolation on:
Which of the following statements about anthrax toxin is false?
Which of the following statements is NOT true about the El Tor biotype of Vibrio cholerae?
Draughtsman colonies are seen with:
Which of the following statements about Chromobacterium violaceum is false?
Oil paint appearance on nutrient agar is seen in -
NEET-PG 2015 - Microbiology NEET-PG Practice Questions and MCQs
Question 831: Viral DNA is integrated into Bacterial DNA in:
- A. Lysogenic cycle (Correct Answer)
- B. Bacterial transduction
- C. Bacterial transformation
- D. Bacterial conjugation
Explanation: ***Lysogenic cycle*** - In the **lysogenic cycle**, the **bacteriophage DNA integrates** into the host bacterial chromosome, becoming a **prophage**. - This integration allows the viral genome to be **replicated along with the host DNA** without immediately lysing the cell. *Bacterial transduction* - **Transduction** involves the transfer of **bacterial DNA** from one bacterium to another via a bacteriophage, not the integration of viral DNA into the host genome. - While phages are involved, the primary event is the accidental packaging and transfer of bacterial genes, not viral integration into the host for replication. *Bacterial transformation* - **Transformation** is the process where bacteria take up **naked DNA from their environment** and incorporate it into their own genome. - This DNA is typically from another bacterium or is artificially introduced, not viral DNA undergoing a natural integration process within the cell. *Bacterial conjugation* - **Conjugation** is the transfer of genetic material (usually a **plasmid**) between bacteria through direct cell-to-cell contact, mediated by a **pilus**. - This process involves the transfer of bacterial or plasmid DNA, not the integration of a viral genome into the host chromosome.
Question 832: What is the primary use of the freezing method in microbiology?
- A. Sterilization of heat-sensitive materials using freezing
- B. Killing bacteria at high temperatures
- C. Stimulating the growth of microorganisms
- D. Preservation of microorganisms through freezing (Correct Answer)
Explanation: ***Preservation of microorganisms through freezing*** - The **frozen phenomenon** or **cryopreservation** is primarily used to maintain the viability and genetic integrity of microbial cultures over long periods. - This involves rapidly freezing microorganisms, often with cryoprotectants like **glycerol** or **DMSO**, to minimize cell damage from ice crystal formation. *Sterilization of heat-sensitive materials using freezing* - Freezing is **not a reliable sterilization method** as it does not consistently kill all microbial life, especially bacterial spores. - While freezing inhibits microbial growth, it does not achieve the complete eradication required for **sterilization**. *Killing bacteria at high temperatures* - Killing bacteria at high temperatures is achieved through methods like **autoclaving** or **pasteurization**, not freezing. - High temperatures denature microbial proteins and damage cell structures, leading to cell death. *Stimulating the growth of microorganisms* - Freezing generally **inhibits microbial growth** and metabolism, putting microorganisms into a dormant state. - Growth stimulation typically involves providing optimal **nutrients, temperature, and atmospheric conditions** for replication.
Question 833: Granulomatosis infantiseptica is caused by:
- A. Pseudomonas
- B. Chlamydia trachomatis
- C. Group D streptococci
- D. Listeria (Correct Answer)
Explanation: ***Listeria*** - **Granulomatosis infantiseptica** is a severe manifestation of congenital **listeriosis**, caused by *Listeria monocytogenes*. - This condition is characterized by widespread **granulomas** and **microabscesses** in various organs of the infected newborn. *Pseudomonas* - *Pseudomonas aeruginosa* is a common cause of healthcare-associated infections but is not typically associated with **granulomatosis infantiseptica**. - It can cause severe infections in immunocompromised individuals, including **pneumonia**, **sepsis**, and wound infections. *Chlamydia trachomatis* - *Chlamydia trachomatis* is a common cause of **conjunctivitis** and **pneumonia** in neonates, acquired during passage through the birth canal. - It does not cause **granulomatosis infantiseptica**. *Group D streptococci* - While Group D streptococci (e.g., *Enterococcus faecalis*) can cause neonatal infections like **sepsis** and **meningitis**, they are not the causative agents of **granulomatosis infantiseptica**. - This condition is specifically linked to **Listeria**.
Question 834: Salmonella and Shigella can be differentiated from other Enterobacteriaceae members by isolation on:
- A. MacConkey agar
- B. Mannitol salt agar
- C. BCYE medium
- D. XLD agar (Correct Answer)
Explanation: ***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.
Question 835: Which of the following statements about anthrax toxin is false?
- A. Increase cAMP
- B. Has three components
- C. Coded by plasmid
- D. Inhibits protein synthesis (Correct Answer)
Explanation: ***Inhibits protein synthesis*** - Anthrax toxin, specifically the **lethal factor (LF)**, is a **zinc-dependent metalloprotease** that cleaves and inactivates **mitogen-activated protein kinase kinase (MAPKKs)**, leading to cell death, not directly inhibiting protein synthesis. - The **edema factor (EF)** component of the toxin is an **adenylate cyclase** that increases **intracellular cyclic AMP (cAMP)**, which also does not directly inhibit protein synthesis. *Has three components* - Anthrax toxin is indeed composed of three distinct proteins: **protective antigen (PA)**, **edema factor (EF)**, and **lethal factor (LF)**. - PA is necessary for EF and LF to enter host cells, while EF causes edema and LF is responsible for cytotoxicity. *Increase cAMP* - The **edema factor (EF)** component of anthrax toxin is a **calmodulin-dependent adenylate cyclase**. - Once inside the cell, EF converts **ATP to cyclic AMP (cAMP)**, leading to increased intracellular cAMP levels, which disrupts water homeostasis and causes edema. *Coded by plasmid* - The genes encoding the anthrax toxin components (PA, EF, and LF) are located on a large plasmid known as **pXO1**. - This plasmid, along with another plasmid (pXO2) carrying genes for the capsule, is crucial for the full virulence of *Bacillus anthracis*.
Question 836: Which of the following statements is NOT true about the El Tor biotype of Vibrio cholerae?
- A. VP (+)
- B. Lower mortality
- C. Reduced environmental persistence (Correct Answer)
- D. Hemolysis negative
Explanation: ***Reduced environmental persistence*** - The **El Tor biotype** of *Vibrio cholerae* is known for its **increased environmental persistence** compared to the classical biotype, making this statement NOT true. - El Tor survives longer in water sources due to its hardiness and ability to form biofilms, which contributes to its pandemic potential and makes outbreaks harder to control. *VP (+)* - The El Tor biotype is **Voges-Proskauer (VP) positive**, which is a key biochemical characteristic used to differentiate it from the classical biotype (VP negative). - This is a TRUE statement about El Tor. *Lower mortality* - The El Tor biotype causes **milder disease with lower mortality rates** compared to the classical biotype. - While individual cases may be less severe, the higher infectivity and asymptomatic carriage of El Tor contribute to its widespread transmission - this is a TRUE statement. *Hemolysis negative* - The El Tor biotype is **hemolysis positive** (produces beta-hemolysis on sheep blood agar), which is another key differentiating feature from the classical biotype (hemolysis negative). - This makes the statement "hemolysis negative" NOT true about El Tor.
Question 837: 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 838: 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 839: 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
Pathology
1 questionsWhich tumor is characterized by the presence of cells that resemble tennis rackets?
NEET-PG 2015 - Pathology NEET-PG Practice Questions and MCQs
Question 831: Which tumor is characterized by the presence of cells that resemble tennis rackets?
- A. Seminoma
- B. Vaginal adenocarcinoma
- C. Langerhans cell histiocytosis (Correct Answer)
- D. Sarcoma botyroides
Explanation: ***Langerhans cell histiocytosis*** - This condition is characterized by **Birbeck granules** within the Langerhans cells, which have a distinctive **tennis racket-like appearance** on electron microscopy. - The cells are also positive for **CD1a** and **S-100** immunohistochemical markers. *Sarcoma botyroides* - This is a subtype of **embryonal rhabdomyosarcoma** typically found in mucosal sites, presenting as a polypoid, grape-like mass. - Its histology shows small, undifferentiated cells with primitive skeletal muscle differentiation, but **not tennis racket-shaped cells**. *Vaginal adenocarcinoma* - This is a rare malignancy of the vagina, often associated with **diethylstilbestrol (DES) exposure** in utero, presenting as glands. - The cells show glandular differentiation and produce mucin, but **lack Birbeck granules**. *Seminoma* - This is a germ cell tumor of the testis characterized by large, uniform cells with clear cytoplasm and prominent nucleoli, divided into lobules by fibrous septa containing lymphocytes. - There are **no tennis racket-shaped cells** or Birbeck granules associated with seminoma.