UPSC-CMS 2023 - Microbiology PYQs Practice Questions

Q: The causative organism of Chancroid is

Haemophilus ducreyi. ***Haemophilus ducreyi*** - **Chancroid** is a sexually transmitted infection characterized by painful genital ulcers and regional lymphadenopathy, caused by the bacterium **Haemophilus ducreyi**. - This bacterium is a **Gram-negative coccobacillus** that requires specific culture media for isolation. *Chlamydia trachomatis* - **Chlamydia trachomatis** is responsible for **chlamydia**, a common STI, and can also cause **lymphogranuloma venereum (LGV)**, which presents with lymphadenopathy and sometimes genital ulcers but not typically the soft, painful ulcers seen in chancroid. - Infections with *Chlamydia trachomatis* are often **asymptomatic** or cause symptoms like urethritis, cervicitis, or proctitis. *Klebsiella granulomatis* - **Klebsiella granulomatis** (formerly *Calymmatobacterium granulomatis*) is the causative agent of **granuloma inguinale** (also known as donovanosis). - **Granuloma inguinale** presents with painless, beefy red, friable ulcerative lesions, which clinically differ from the painful ulcers of chancroid. *Psittacosis lymphogranuloma group* - This option incorrectly groups **psittacosis** (caused by *Chlamydia psittaci*) with **lymphogranuloma venereum (LGV)**, which is caused by specific serovars of *Chlamydia trachomatis*. - **Psittacosis** is primarily a pulmonary infection transmitted by birds, while **LGV** is a sexually transmitted infection distinct from chancroid. [Practice more Microbiology PYQs on OnCourse]

Q: Which one of the following is the correct sequence of appearance for the Hepatitis B virus serological markers?

HBsAg, HBeAg, Anti-HBc, Anti-HBe. ***HBsAg, HBeAg, Anti-HBc, Anti-HBe*** - **HBsAg** (Hepatitis B surface antigen) is the first marker to appear in acute infection, indicating active viral replication. - **HBeAg** (Hepatitis B e-antigen) appears shortly after HBsAg, correlating with high viral replication and infectivity. **Anti-HBc** (antibody to hepatitis B core antigen) is the next to appear, often during the window period. **Anti-HBe** (antibody to hepatitis B e-antigen) signals reduced viral replication and decreased infectivity, typically following the disappearance of HBeAg. *Anti-HBe, HBsAg, Anti-HBc* - This sequence is incorrect because **Anti-HBe** appears much later in the infection, typically after clearance of HBeAg, indicating reduced viral replication. - **HBsAg** is the earliest indicator of active infection, not appearing after Anti-HBe. *HBeAg, Anti-HBe, Anti-HBc, HBsAg* - This sequence is incorrect as **HBeAg** and **Anti-HBe** do not typically appear before **HBsAg**, which is the initial marker of viral presence. - The appearance of **Anti-HBe** before **HBsAg** is also not consistent with the natural history of Hepatitis B infection. *Anti-HBc, HBsAg, Anti-HBe* - This sequence is incorrect because **Anti-HBc** usually appears earlier than Anti-HBe, and while it can be detected relatively early, **HBsAg** is the first antigen to be detectable. - The appearance of **Anti-HBe** is a sign of decreasing viral activity and generally appears later than both HBsAg and Anti-HBc. [Practice more Microbiology PYQs on OnCourse]

Q: Which one of the following statements about Human Immunoglobulins is not correct?

IgG and IgM can both cross the placenta. ***IgG and IgM can both cross the placenta*** - This statement is incorrect because only **IgG** can actively cross the placenta, providing **passive immunity** to the fetus. - **IgM** is too large to cross the placental barrier, so its presence in a newborn suggests **congenital infection**. *The half life of IgM is about 10 days* - The approximate **half-life of IgM** is indeed around **5-10 days**, making this statement largely correct in general contexts. - This relatively short half-life means that IgM levels can change quickly in response to acute infections. *IgG comprises about 75-80% of the total serum immunoglobulins* - **IgG** is the most abundant immunoglobulin in serum, typically accounting for **75-80%** of the total immunoglobulins. - Its high concentration and long half-life contribute to its critical role in **secondary immune responses** and **long-term immunity**. *IgA comprises 15% of the total serum immunoglobulins and is mainly found in the body secretions* - **IgA** accounts for about **10-15%** of the total serum immunoglobulins, with a significant proportion found in secretions. - It plays a crucial role in **mucosal immunity**, protecting surfaces like the gastrointestinal, respiratory, and genitourinary tracts. [Practice more Microbiology PYQs on OnCourse]

Q: Gas Gangrene resulting in crepitus in tissues and a sweet smelling brown exudate is caused due to infection by :

Clostridium perfringens. ***Clostridium perfringens*** - **Gas gangrene** is caused by obligate anaerobic, gram-positive rods, notably **Clostridium perfringens**. - This bacterium produces **alpha-toxin (lecithinase)**, which destroys tissues and leads to gas formation (crepitus) and a characteristic **sweet-smelling brown exudate**. *Synergistic bacteria* - While synergistic infections can occur and lead to severe tissue damage, they are not the primary or specific cause of **gas gangrene** with its distinct clinical presentation. - The classic features of gas production and a specific exudate are directly tied to the metabolic activity and toxins of **Clostridial species**. *Anaerobic bacteroides spp.* - **Bacteroides** are common anaerobic bacteria, but they are typically associated with **intra-abdominal abscesses** and **wound infections**, not the specific clinical syndrome of gas gangrene. - They do not produce the potent toxins that lead to extensive gas formation and rapid tissue necrosis characteristic of **Clostridium perfringens**. *Gas-forming Klebsiella spp.* - **Klebsiella spp.** are gram-negative, facultative anaerobic bacteria that can produce gas, especially in deep-seated infections like **emphysematous pyelonephritis** or **liver abscesses**. - However, they do not cause **gas gangrene** with its rapid tissue destruction, crepitus, and sweet-smelling brown exudate, which is pathognomonic for **Clostridial infection**. [Practice more Microbiology PYQs on OnCourse]

Question 1

The causative organism of Chancroid is

Accepted Answer

Haemophilus ducreyi

Answer

Chlamydia trachomatis

Answer

Klebsiella granulomatis

Answer

Psittacosis lymphogranuloma group

Question 2

Which one of the following is the correct sequence of appearance for the Hepatitis B virus serological markers?

Accepted Answer

HBsAg, HBeAg, Anti-HBc, Anti-HBe

Answer

Anti-HBe, HBsAg, Anti-HBc

Answer

HBeAg, Anti-HBe, Anti-HBc, HBsAg

Answer

Anti-HBc, HBsAg, Anti-HBe

Question 3

Which one of the following statements about Human Immunoglobulins is not correct?

Accepted Answer

IgG and IgM can both cross the placenta

Answer

The half life of IgM is about 10 days

Answer

IgG comprises about 75-80% of the total serum immunoglobulins

Answer

IgA comprises 15% of the total serum immunoglobulins and is mainly found in the body secretions

Question 4

Which one of the following statements regarding Gas Gangrene Infection is correct?

Accepted Answer

It is caused by C. perfringens, a gram positive anaerobic spore-forming bacilli.

Answer

It is caused by C. perfringens, a gram negative aerobic non-spore-forming bacilli.

Answer

It is caused by C. tetani, a gram negative anaerobic non-spore-forming bacilli.

Answer

It is caused by C. tetani, a gram positive anaerobic spore-forming bacilli.

Question 5

Gas Gangrene resulting in crepitus in tissues and a sweet smelling brown exudate is caused due to infection by :

Accepted Answer

Clostridium perfringens

Answer

Synergistic bacteria

Answer

Anaerobic bacteroides spp.

Answer

Gas-forming Klebsiella spp.

UPSC-CMS 2023 — Microbiology