NEET-PG 2018 - Microbiology PYQs Practice Questions

Q: What is the Australian antigen for hepatitis B?

HBsAg. ***HBsAg*** - **HBsAg** stands for **Hepatitis B surface antigen**, which was originally discovered by Baruch Blumberg in 1965 and was initially called the **Australia antigen** due to its discovery in the serum of an Australian aboriginal. - Its presence indicates an **active hepatitis B infection**, either acute or chronic. *HBeAg* - **HBeAg** (Hepatitis B e-antigen) is a marker of **viral replication** and **infectivity**. - It is distinct from HBsAg and indicates a high level of **transmissibility** of the virus. *HBDAg* - **HBDAg** is not a standard or recognized antigen for hepatitis B. - The correct antigen for hepatitis D is **HDAg** (Hepatitis D antigen), which is only found in individuals co-infected with hepatitis D virus and hepatitis B virus. *HBV DNA* - **HBV DNA** refers to the viral genetic material of the hepatitis B virus. - While its presence indicates active viral replication and is used to monitor **viral load**, it is not an antigen but rather the **viral genome** itself. [Practice more Microbiology PYQs on OnCourse]

Q: Mycoplasma is inherently resistant to which of the following antibiotic classes due to its lack of a peptidoglycan cell wall?

Ceftriaxone (a cephalosporin). ***Ceftriaxone (a cephalosporin)*** - Cephalosporins are **beta-lactam antibiotics** that inhibit **peptidoglycan cell wall synthesis** by binding to penicillin-binding proteins (PBPs) - *Mycoplasma* species **completely lack a peptidoglycan cell wall**, which is the primary target of all beta-lactam antibiotics - Therefore, cephalosporins (and all beta-lactams) are **inherently ineffective** against *Mycoplasma* infections - This is a classic example of **intrinsic resistance** due to absence of the drug target *Penicillins (e.g., Amoxicillin)* - While penicillins are also beta-lactam antibiotics that target cell wall synthesis, the question specifically asks about ceftriaxone - Penicillins are similarly ineffective against *Mycoplasma* for the same reason (lack of cell wall) - However, when given a specific drug example (ceftriaxone), it is the most precise answer *Aminoglycosides (e.g., Gentamicin)* - Aminoglycosides target the **30S ribosomal subunit** to inhibit **protein synthesis** - While they have **poor penetration** into *Mycoplasma* cells and limited clinical efficacy, the resistance is not due to lack of cell wall - The mechanism of reduced susceptibility is different from the intrinsic resistance seen with beta-lactams *Fluoroquinolones (e.g., Ciprofloxacin)* - Fluoroquinolones inhibit **DNA gyrase** and **topoisomerase IV**, enzymes essential for DNA replication - These antibiotics are **effective** against *Mycoplasma* species and are commonly used to treat *Mycoplasma* infections - They represent appropriate treatment options along with macrolides and tetracyclines [Practice more Microbiology PYQs on OnCourse]

Q: Which fungus is most commonly associated with orbital cellulitis in patients with diabetic ketoacidosis?

Rhizopus. ***Rhizopus*** - *Rhizopus* is the most common cause of **mucormycosis** (also called zygomycosis), an aggressive fungal infection that frequently affects immunocompromised patients, especially those with **diabetic ketoacidosis (DKA)**. - *Rhizopus arrhizus* (formerly *R. oryzae*) accounts for approximately **70% of all mucormycosis cases**, making it the single most common causative organism. - In DKA, the acidic environment and high glucose levels favor the growth of **Mucorales fungi**, leading to rapid progression from the sinuses to the orbit and brain (rhinoorbital-cerebral mucormycosis). *Candida* - While *Candida* is a common cause of fungal infections, it typically manifests as **candidemia**, **esophagitis**, or **vulvovaginitis**, and is rarely associated with orbital cellulitis in DKA. - *Candida* infections are more likely in patients with indwelling catheters or those on broad-spectrum antibiotics, rather than specifically linked to DKA-induced orbital cellulitis. *Mucor* - The genus *Mucor* is part of the **Mucorales order** and can cause **mucormycosis** with identical clinical presentations to *Rhizopus*. - However, *Mucor* species account for only **10-20% of mucormycosis cases**, making *Rhizopus* the **most commonly** associated genus as asked in the question. - While both are clinically grouped under "mucormycosis," *Rhizopus* is the more specific and statistically correct answer when identifying the most common causative fungus. *Aspergillus* - *Aspergillus* species are common environmental fungi that can cause invasive infections, particularly in immunocompromised patients, leading to conditions like **aspergilloma** or **invasive aspergillosis**. - While *Aspergillus* can cause sinus and orbital infections, it is less commonly associated with the rapid, aggressive form of orbital cellulitis seen in DKA compared to mucormycosis caused by *Rhizopus*. [Practice more Microbiology PYQs on OnCourse]

Q: Cutaneous larva migrans is caused by which organism?

Ancylostoma braziliense. ***Ancylostoma braziliense*** - This **hookworm** species commonly found in dogs and cats is the most frequent cause of **cutaneous larva migrans** in humans. - The larvae penetrate the skin but cannot complete their life cycle in humans, instead migrating aimlessly creating **serpiginous tracks**. *Strongyloides* - **_Strongyloides stercoralis_** causes **strongyloidiasis**, which presents with a rapidly advancing (up to 10 cm/hr) migratory rash known as **larva currens**, and not the slower cutaneous larva migrans. - It differs from cutaneous larva migrans in its ability to complete its life cycle in humans, leading to **autoinfection**. *Toxocara canis* - **_Toxocara canis_** is the causative agent of **visceral larva migrans** and **ocular larva migrans**, not cutaneous larva migrans. - In visceral larva migrans, larvae migrate through internal organs, causing symptoms like **hepatomegaly** and **eosinophilia**. *Necator americanus* - This is a human hookworm that can cause **iron deficiency anemia** due to chronic blood loss in the intestines. - While its larvae can penetrate the skin, causing a transient itchy rash known as **ground itch**, they do not cause the prolonged, migratory cutaneous larva migrans. [Practice more Microbiology PYQs on OnCourse]

Question 1

What is the Australian antigen for hepatitis B?

Accepted Answer

HBsAg

Answer

HBeAg

Answer

HBDAg

Answer

HBV DNA

Question 2

Mycoplasma is inherently resistant to which of the following antibiotic classes due to its lack of a peptidoglycan cell wall?

Accepted Answer

Ceftriaxone (a cephalosporin)

Answer

Penicillins (e.g., Amoxicillin)

Answer

Aminoglycosides (e.g., Gentamicin)

Answer

Fluoroquinolones (e.g., Ciprofloxacin)

Question 3

Identify the organism related to the blood smear image.

Accepted Answer

Plasmodium falciparum

Answer

Salmonella Typhi

Answer

Toxoplasma gondii

Answer

Treponema pallidum

Question 4

Which fungus is most commonly associated with orbital cellulitis in patients with diabetic ketoacidosis?

Accepted Answer

Rhizopus

Answer

Candida

Answer

Mucor

Answer

Aspergillus

Question 5

Cutaneous larva migrans is caused by which organism?

Accepted Answer

Ancylostoma braziliense

Answer

Strongyloides

Answer

Toxocara canis

Answer

Necator americanus

Question 6

A boy presented with multiple non suppurative osteomyelitis with sickle cell anaemia. What will be the causative organism?

Accepted Answer

Salmonella

Answer

H. influenzae

Answer

Enterobacter species

Answer

Staphylococcus aureus

Question 7

Acute Hemorrhagic Conjunctivitis is primarily caused by which type of Enterovirus?

Accepted Answer

Enterovirus type 70

Answer

Enterovirus type 68

Answer

Enterovirus type 69

Answer

Enterovirus type 71

Question 8

Which of the following organisms is MOST associated with histamine production in scombroid fish poisoning?

Accepted Answer

Morganella morganii

Answer

P. aeruginosa

Answer

Staphylococcus

Answer

Salmonella

Question 9

Which organism is the most common cause of acute bacterial prostatitis?

Accepted Answer

E.coli

Answer

Enterococcus

Answer

Streptococcus viridans

Answer

Peptostreptococcus

Question 10

Burkholderia cepacia is resistant to which of the following antibiotics?

Accepted Answer

Cefotetan

Answer

Trimethoprim-sulfamethoxazole

Answer

Ceftazidime

Answer

Temocillin

NEET-PG 2018 — Microbiology