NEET-PG 2013 - Microbiology PYQs Practice Questions

Q: Congenital passive immunity is INADEQUATE in -

Pertussis. ***Pertussis*** - **Congenital passive immunity** against *Bordetella pertussis* is **most inadequate** among the listed infections. - **Minimal transplacental transfer** of protective IgG antibodies occurs, and maternal antibodies decline rapidly in infants. - Newborns have **virtually no protection** from maternal antibodies, making them highly susceptible to severe whooping cough. - This is why **early vaccination at 6 weeks** is critical, unlike measles which can wait until 9-12 months. *Measles* - Maternal antibodies provide **excellent passive immunity** protecting infants for **6-9 months**. - This robust protection is why measles vaccination is delayed until 9-12 months of age. - Represents the **gold standard** of effective maternal antibody transfer. *Mumps* - Maternal antibodies provide **good passive immunity** in early infancy. - Mumps in young infants is rare due to this maternal protection. *RSV (Respiratory Syncytial Virus)* - Maternal antibodies provide **limited but present** passive immunity. - Unlike pertussis where protection is nearly absent, RSV maternal antibodies can **reduce severity** of illness. - However, RSV remains a major cause of bronchiolitis in infants despite this partial protection. - The key difference: RSV has **some** maternal protection (inadequate but present), whereas pertussis has **almost none** (most inadequate). [Practice more Microbiology PYQs on OnCourse]

Q: Which of the following organisms does not fulfill Koch's postulates?

T. pallidum. ***T. pallidum*** - **_Treponema pallidum_**, the causative agent of **syphilis**, cannot be cultured on artificial media, failing the third Koch's postulate. - Its inability to grow in pure culture makes it difficult to reproducibly cause disease in an experimental host by direct inoculation of a cultured organism. *M. tuberculosis* - **_Mycobacterium tuberculosis_** can be isolated and grown in **pure culture** on specific media like Löwenstein-Jensen medium. - It also consistently causes tuberculosis when inoculated into susceptible animals, fulfilling Koch's postulates. *E.coli* - **_Escherichia coli_** is readily cultured in various laboratory media and can be isolated from infected hosts. - Specific pathogenic strains of _E. coli_ (e.g., EHEC) fulfill Koch's postulates by reproducing disease in animal models. *All of the options* - This option is incorrect because both **_M. tuberculosis_** and **_E. coli_** largely fulfill Koch's postulates. - The primary exception among the given options is **_T. pallidum_** due to its unculturable nature. [Practice more Microbiology PYQs on OnCourse]

Q: Which immunoglobulin is most efficient at fixing C1q in the classical complement pathway?

IgM. ***IgM*** - **IgM** is the most efficient immunoglobulin at activating the **classical complement pathway** due to its pentameric structure, which provides multiple binding sites for C1q. - The **Fc portion** of IgM, when bound to an antigen, undergoes a conformational change that exposes binding sites for the **C1q component** of complement. *IgA* - **IgA** primarily functions in **mucosal immunity** and does not efficiently activate the classical complement pathway. - It can weakly activate the **alternative complement pathway** but is not known for fixing C1. *IgG* - **IgG** can activate the classical complement pathway, but it requires two or more IgG molecules to be in close proximity on the cell surface to effectively bind C1q, making it less efficient than IgM. - Its **Fc region** binds C1q only when **antigen-antibody complexes** are formed, but it's not the primary immunoglobulin for initiating C1 binding in solitary form. *IgE* - **IgE** is primarily involved in **allergic reactions** and defense against parasites, binding to Fc receptors on mast cells and basophils. - It does **not activate the complement system** via the classical pathway and therefore does not fix C1. [Practice more Microbiology PYQs on OnCourse]

Q: Thumb print appearance in a culture film smear is seen in which of the following organisms?

Bacillus anthracis. ***Bacillus anthracis*** - The "**thumb print**" or "**boxcar**" appearance refers to the characteristic microscopic morphology seen in **Gram-stained smears** of *B. anthracis*. - The bacilli appear as large, rectangular, Gram-positive rods with **square ends** (resembling boxcars), often arranged in chains. - This distinctive appearance aids in the laboratory diagnosis of **anthrax**. - On culture plates, colonies show a "**Medusa head**" appearance with irregular edges. *Bordetella pertussis* - Colonies on **Bordet-Gengou agar** exhibit a "**mercury drop**" or "**pearl-like**" appearance—smooth, glistening, dome-shaped colonies. - This is different from the "thumb print" morphology, which refers to microscopic rather than colonial appearance. - *B. pertussis* is the causative agent of **whooping cough** (pertussis). *Brucella species* - Produce small, smooth, translucent, slightly raised colonies on enriched media. - Lack any distinctive "thumb print" morphology in smears. - Causative agents of **brucellosis** (undulant fever), a zoonotic infection. *Clostridium perfringens* - Large, Gram-positive rods that may appear boxcar-shaped but are typically associated with **double zone of hemolysis** on blood agar. - Colonies are large, flat, and spreading, not exhibiting the classical "thumb print" identification feature. - Common cause of **gas gangrene** and food poisoning. [Practice more Microbiology PYQs on OnCourse]

Q: The culture medium used for Entamoeba histolytica is

TYI-S-33 medium. ***TYI-S-33 medium*** - **TYI-S-33 (Trypticase-Yeast extract-Iron-Serum) medium** is the most commonly used axenic culture medium for *Entamoeba histolytica*, meaning it supports the growth of the amoeba in the absence of other microorganisms. - This medium provides the necessary nutrients, including **trypticase**, **yeast extract**, **iron**, and **serum**, for the proliferation and maintenance of *E. histolytica* cultures in vitro. - It is the gold standard for axenic cultivation in research and diagnostic laboratories. *Robinson's medium* - **Robinson's medium** is a diphasic medium, meaning it has both solid and liquid phases, and is used for culturing *Entamoeba histolytica* but it is a **xenic** culture medium, meaning it requires the presence of other microorganisms (bacterial flora). - This medium was historically important but is less commonly used for routine culture and has been largely replaced by axenic media like TYI-S-33 for research and diagnostic purposes. *CLED medium* - The **Cystine-Lactose-Electrolyte-Deficient (CLED) medium** is a differential culture medium primarily used for the isolation and enumeration of urinary pathogens. - It is designed to prevent **swarming of Proteus species** and to differentiate lactose fermenters from non-fermenters, but it is not suitable for growing *Entamoeba histolytica*. *Blood agar* - **Blood agar** is a general-purpose enriched agar medium used for the isolation and cultivation of a wide variety of fastidious and non-fastidious bacteria. - It is particularly useful for demonstrating **hemolytic reactions** of bacteria, which are important for bacterial identification, but it does not support the growth of parasitic protozoa like *Entamoeba histolytica*. [Practice more Microbiology PYQs on OnCourse]

Question 1

Congenital passive immunity is INADEQUATE in -

Accepted Answer

Pertussis

Answer

Measles

Answer

Mumps

Answer

RSV (Respiratory Syncytial Virus)

Question 2

Which of the following organisms does not fulfill Koch's postulates?

Accepted Answer

T. pallidum

Answer

E.coli

Answer

M. tuberculosis

Answer

All of the options

Question 3

Which immunoglobulin is most efficient at fixing C1q in the classical complement pathway?

Accepted Answer

IgM

Answer

IgA

Answer

IgG

Answer

IgE

Question 4

Thumb print appearance in a culture film smear is seen in which of the following organisms?

Accepted Answer

Bacillus anthracis

Answer

Brucella species

Answer

Bordetella pertussis

Answer

Clostridium perfringens

Question 5

The culture medium used for Entamoeba histolytica is

Accepted Answer

TYI-S-33 medium

Answer

Robinson's medium

Answer

CLED medium

Answer

Blood agar

Question 6

What is the predominant bacterial genus found in the human colon?

Accepted Answer

Bacteroides

Answer

Escherichia

Answer

Clostridium

Answer

Staphylococcus

Question 7

Lysis of a bacterial colony in a culture is caused by which agent?

Accepted Answer

Bacteriophage

Answer

Pox

Answer

HSV

Answer

CMV

Question 8

Which organism is characterized by a Medusa head appearance?

Accepted Answer

Bacillus anthracis

Answer

Bacillus subtilis

Answer

Bacillus stearothermophilus

Answer

Bacillus cereus

Question 9

Persons with heterozygous sickle cell trait are protected from infection by:

Accepted Answer

P. falciparum

Answer

Pneumococcus

Answer

P. vivax

Answer

Salmonella

Question 10

Which of the following is considered the most professional antigen presenting cell (APC) in the immune system?

Accepted Answer

Dendritic cells

Answer

B cells

Answer

T cells

Answer

NK cells

NEET-PG 2013 — Microbiology