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: 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 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 4

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