What is the primary use of the freezing method in microbiology?
Viral DNA is integrated into Bacterial DNA in:
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:
What is the causative agent of Izumi fever?
Primary complex of M bovis involves:
Brill-Zinsser disease is a recrudescent form of which infection?
Listeria escapes from phagosomes (phagolysosomes) due to:
NEET-PG 2015 - Microbiology NEET-PG Practice Questions and MCQs
Question 21: 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 22: 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 23: 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 24: 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 25: 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 26: 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 27: 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.
Question 28: 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
Question 29: Brill-Zinsser disease is a recrudescent form of which infection?
- A. Recrudescence of R prowazekii infection (Correct Answer)
- B. Recrudescence of R typhi infection
- C. None of the options
- D. Recrudescence of Coxiella burnetii infection
Explanation: **Recrudescence of R prowazekii infection** - Brill-Zinsser disease is a **late-onset complication** of **epidemic typhus**, caused by *Rickettsia prowazekii*. - It occurs years after the initial infection, due to **reactivation of dormant bacteria** in the body. *Recrudescence of R typhi infection* - *Rickettsia typhi* causes **murine typhus**, but its recrudescent form is not referred to as Brill-Zinsser disease. - Murine typhus is typically a **milder disease** compared to epidemic typhus. *Recrudescence of Coxiella burnetii infection* - *Coxiella burnetii* causes **Q fever**, which can have a chronic form but is not a recrudescence of a typhus infection. - Q fever presents with different clinical manifestations, such as **endocarditis** or **hepatitis**, not typically a rash or neurological symptoms seen in typhus. *None of the options* - This option is incorrect because the specific recrudescent form described in the question clearly points to *Rickettsia prowazekii*.
Question 30: Listeria escapes from phagosomes (phagolysosomes) due to:
- A. Opacity associated protein (OAP)
- B. Caspases
- C. Cell membrane adhesion molecules
- D. beta-hemolysin (Correct Answer)
Explanation: ***beta-hemolysin*** - *Listeria monocytogenes* produces **listeriolysin O (LLO)**, a **beta-hemolysin**, which is a pore-forming toxin that lyses the phagosomal membrane. - This allows the bacteria to escape into the host cell cytoplasm, thus **avoiding destruction** by lysosomal enzymes and neutralizing the microbicidal environment. *Caspases* - **Caspases** are a family of proteases that play essential roles in programmed cell death (apoptosis) and inflammation. - While bacteria can manipulate host cell apoptosis, caspases themselves are **host enzymes** and do not directly confer resistance to phagosome destruction. *Cell membrane adhesion molecules* - **Adhesion molecules** facilitate bacterial attachment to host cells and internalisation, but they do not directly provide a mechanism for **escaping the phagosome** once internalised. - Examples include internalins, which are involved in bacterial entry into cells. *Opacity associated protein (OAP)* - **Opacity associated proteins (OAPs)** are primarily associated with *Neisseria gonorrhoeae* and are involved in adherence to host cells and evasion of the immune response. - They are not a mechanism for **phagosomal escape** or directly related to *Listeria's* intracellular survival.