Antimicrobial Agents — MCQs

Antimicrobial Agents Indian Medical PG Practice Questions and MCQs

Question 1441: Drug of choice for Enterococcus infection in a patient allergic to penicillin?

A. Streptomycin
B. Cephalosporin
C. Vancomycin (Correct Answer)
D. Rifampicin

Explanation: ***Vancomycin*** - **Vancomycin** is a glycopeptide antibiotic that is effective against **Gram-positive bacteria**, including *Enterococcus*, especially in patients with a **penicillin allergy**. - It inhibits **cell wall synthesis** by binding to the D-Ala-D-Ala terminus of peptidoglycan precursors, a different mechanism from penicillins. *Streptomycin* - **Streptomycin** is an aminoglycoside that inhibits **protein synthesis** and is primarily used in **combination therapy** for serious *Enterococcal* infections, but typically alongside a cell-wall active agent (like penicillin or vancomycin) for synergistic killing in endocarditis or other severe infections. - It is not usually recommended as a **monotherapy** for *Enterococcus*, especially in the context of penicillin allergy, as it doesn't provide bactericidal activity on its own against all enterococcal strains. *Cephalosporin* - **Cephalosporins** are **not active** against *Enterococcus spp.* as these bacteria intrinsically lack the **penicillin-binding proteins (PBPs)** that cephalosporins target effectively. - This **intrinsic resistance** makes cephalosporins an inappropriate choice for treating *Enterococcal* infections, regardless of penicillin allergy status. *Rifampicin* - **Rifampicin** is an antibiotic primarily used for **Mycobacterial infections** (e.g., tuberculosis) and some **Staphylococcal infections**, often in combination to prevent resistance. - It has **poor activity** against *Enterococcus* and is not a recommended treatment for *Enterococcal* infections.

Question 1442: Drug resistance is most seen with which STI?

A. Gonorrhoea (Correct Answer)
B. Chancroid
C. Syphilis
D. Donovanosis

Explanation: ***D. Gonorrhoea*** - *Neisseria gonorrhoeae* has a remarkable capacity to develop **antimicrobial resistance** through genetic mutations and horizontal gene transfer, leading to resistance to multiple classes of antibiotics, including cephalosporins. - The Centers for Disease Control and Prevention (CDC) monitors increasing resistance patterns and regularly updates treatment guidelines to combat this growing public health threat. *A. Chancroid* - Chancroid, caused by *Haemophilus ducreyi*, has shown some isolated instances of resistance to certain antibiotics like ciprofloxacin and erythromycin, but it is **not as widespread or severe** as observed with gonorrhoea. - Treatment typically involves single-dose azithromycin or ceftriaxone, which remain largely effective. *C. Syphilis* - Syphilis, caused by *Treponema pallidum*, has largely remained **susceptible to penicillin**, which has been the cornerstone of treatment for decades. - While there are rare reports of macrolide resistance, penicillin resistance has not emerged as a significant clinical problem. *B. Donovanosis* - Donovanosis (granuloma inguinale), caused by *Klebsiella granulomatis*, typically responds well to antibiotics like azithromycin, doxycycline, or trimethoprim-sulfamethoxazole. - **Antibiotic resistance is generally not a major concern** or a widespread issue in the treatment of donovanosis.

Question 1443: Which of the following vaccines is not a live attenuated vaccine?

A. Hepatitis B (Correct Answer)
B. Oral polio vaccine
C. Measles
D. BCG

Explanation: ***Hepatitis B*** - The **Hepatitis B vaccine** is a **recombinant vaccine**, meaning it contains only a purified component (the outer surface protein) of the virus, not the whole live attenuated virus. - As it's not a live vaccine, it's generally safe for immunocompromised individuals and pregnant women. *Oral polio vaccine* - The **oral polio vaccine (OPV)** is a **live attenuated vaccine** that contains weakened forms of the poliovirus strains. - It induces strong mucosal immunity in the gut, which is crucial for preventing transmission. *Measles* - The **measles vaccine** (part of the MMR vaccine) is a **live attenuated vaccine** containing a weakened form of the measles virus. - It stimulates a robust immune response that closely mimics natural infection without causing the disease. *BCG* - The **BCG vaccine** is a **live attenuated vaccine** derived from a weakened strain of *Mycobacterium bovis*. - It is primarily used to prevent severe forms of tuberculosis, especially in children.

Question 1444: Which of the following is NOT a mechanism of antibiotic resistance?

A. Efflux pump activity
B. Inactivation by enzymes such as beta-lactamase
C. Modification of drug target sites
D. Increased drug absorption (Correct Answer)

Explanation: ***Increased drug absorption*** - **Increased drug absorption** would lead to a higher intracellular concentration of the antibiotic, making it *more potent* against the bacteria rather than contributing to resistance. - Antibiotic resistance mechanisms aim to *reduce the effective concentration* of the drug at its target site or *alter the target itself*. *Efflux pump activity* - **Efflux pumps** are bacterial membrane proteins that actively pump antibiotics out of the bacterial cell [3]. - This mechanism *reduces the intracellular concentration* of the antibiotic, preventing it from reaching its therapeutic target [3]. *Inactivation by enzymes such as beta-lactamase* - Bacteria can produce enzymes like **beta-lactamase** that *chemically modify or degrade* the antibiotic molecule, rendering it inactive [2]. - This is a common mechanism of resistance against **beta-lactam antibiotics** (e.g., penicillin, cephalosporins) [2]. *Modification of drug target sites* - Bacteria can develop mutations that *alter the structure of the antibiotic's target site*, such as a bacterial ribosome or cell wall component [1]. - This change in the target means the antibiotic can no longer bind effectively or interfere with cellular processes, thus *losing its efficacy* [1].

Question 1445: All of the following regarding rotavirus vaccine are correct except?

A. Inactivated vaccine (Correct Answer)
B. Available as monovalent and pentavalent
C. Last dose should be completed by 8 months of age
D. Administered orally

Explanation: ***Inactivated vaccine*** - The rotavirus vaccines (Rotarix and RotaTeq) are **live-attenuated vaccines**, meaning they contain weakened forms of the virus, not inactivated forms. - Live-attenuated vaccines replicate in the host to induce a robust immune response similar to natural infection. - This is the **incorrect statement**, making it the correct answer to this "except" question. *Available as monovalent and pentavalent* - This statement is correct. There are two main types: **Rotarix**, which is a **monovalent** vaccine targeting G1P strains, and **RotaTeq**, which is a **pentavalent** vaccine targeting G1, G2, G3, G4, and P strains. - Both forms provide broad protection against common rotavirus strains. *Last dose should be completed by 8 months of age* - This statement is correct. The first dose should be given between **6-14 weeks**, and the final dose should be administered by **8 months (32 weeks) of age**. - For **Rotarix** (2-dose series): complete by 24 weeks; for **RotaTeq** (3-dose series): complete by 32 weeks. - This age limit is primarily due to a theoretical increased risk of **intussusception** when administered later in infancy. *Administered orally* - This statement is correct. Rotavirus vaccines are given **orally** and are not injectable. - This method of administration makes the vaccine easy to administer and simulates the natural route of rotavirus infection, promoting mucosal immunity.

Question 1446: Which of the following is not a polysaccharide vaccine?

A. Pneumococcal vaccine
B. Meningococcal vaccine
C. H. Influenzae B vaccine
D. Hepatitis B vaccine (Correct Answer)

Explanation: ***Hepatitis B vaccine (recombinant protein vaccine)*** - This is a **recombinant protein vaccine** which contains **HBsAg** (Hepatitis B surface antigen) produced in yeast. - As it uses a protein antigen, it is not a polysaccharide vaccine. *Pneumococcal vaccine (includes polysaccharide forms)* - There are two types: **Pneumococcal Polysaccharide Vaccine (PPSV23)** which is a pure polysaccharide vaccine, and **Pneumococcal Conjugate Vaccine (PCV13, PCV15, PCV20)** which contains polysaccharides conjugated to a protein carrier. - Both types utilize **polysaccharide antigens** from *Streptococcus pneumoniae* to elicit an immune response. *Meningococcal vaccine (includes polysaccharide forms)* - Similar to pneumococcal vaccines, there are **meningococcal polysaccharide vaccines (MPSV4)** and **meningococcal conjugate vaccines (MCV4)**. - These vaccines use **polysaccharides** from the capsule of *Neisseria meningitidis* as their immunogenic component, either alone or conjugated. *H. Influenza B vaccine (conjugate vaccine derived from polysaccharides)* - This is a **conjugate vaccine** that uses a **polysaccharide capsule antigen** from *Haemophilus influenzae type B* (Hib) chemically linked to a protein carrier. - Conjugation improves immunogenicity, especially in infants, by converting the T-independent polysaccharide antigen into a T-dependent one.

Question 1447: Which antimicrobial inhibits cell wall synthesis?

A. Metronidazole
B. Azithromycin
C. Vancomycin (Correct Answer)
D. Ciprofloxacin

Explanation: ***Vancomycin*** - **Vancomycin** is a glycopeptide antibiotic that inhibits cell wall synthesis by binding to the **D-Ala-D-Ala** terminal of peptidoglycan precursors. - This binding prevents the **transpeptidation** and **transglycosylation** steps necessary for peptidoglycan chain elongation and cross-linking, ultimately weakening the bacterial cell wall and leading to bacterial lysis. *Metronidazole* - **Metronidazole** is an antimicrobial that works by forming **toxic free-radical metabolites** that damage bacterial **DNA**. - Its mechanism of action does not involve direct inhibition of cell wall synthesis. *Azithromycin* - **Azithromycin** is a macrolide antibiotic that inhibits bacterial protein synthesis by binding to the **50S ribosomal subunit**. - This binding prevents **peptide chain elongation**, thereby halting protein production, rather than affecting the cell wall. *Ciprofloxacin* - **Ciprofloxacin** is a fluoroquinolone antibiotic that inhibits bacterial **DNA replication** and repair. - It achieves this by targeting **DNA gyrase** (topoisomerase II) and **topoisomerase IV**, enzymes crucial for bacterial DNA handling, and thus does not act on the cell wall.

Question 1448: Which antiretroviral drug causes hyperpigmentation?

A. Nevirapine
B. Efavirenz
C. Zidovudine
D. Emtricitabine (Correct Answer)

Explanation: ***Emtricitabine*** - **Emtricitabine** is a nucleoside reverse transcriptase inhibitor (NRTI) most commonly known to cause mucocutaneous hyperpigmentation, particularly on the **palms and soles**. - This side effect is more commonly seen in individuals with darker skin tones and can manifest as **darkening of nails** or skin. - Among NRTIs, emtricitabine has the **highest incidence** of hyperpigmentation. *Nevirapine* - **Nevirapine** is a non-nucleoside reverse transcriptase inhibitor (NNRTI) primarily associated with **rash**, including severe cases like Stevens-Johnson syndrome. - It does not typically cause **hyperpigmentation** as a prominent side effect. *Efavirenz* - **Efavirenz** is another NNRTI commonly associated with **central nervous system side effects** such as dizziness, vivid dreams, and psychiatric symptoms. - While skin rash can occur, **hyperpigmentation** is not a characteristic adverse effect of efavirenz. *Zidovudine* - **Zidovudine** (AZT) is an NRTI known for causing **bone marrow suppression** (anemia, neutropenia) and **myopathy**. - While zidovudine can cause **nail and skin hyperpigmentation**, this side effect occurs **less frequently** compared to emtricitabine, making emtricitabine the more characteristic answer for hyperpigmentation among antiretroviral drugs.

Question 1449: Which TB drug causes optic neuritis as a side effect?

A. Isoniazid
B. Pyrazinamide
C. Rifampicin
D. Ethambutol (Correct Answer)

Explanation: ***Ethambutol*** - **Ethambutol** is known to cause **optic neuritis**, leading to **decreased visual acuity** and impaired **red-green color discrimination**. - This side effect is **dose-dependent** and usually **reversible** upon discontinuing the drug, though permanent damage can occur with prolonged use. *Isoniazid* - **Isoniazid** is primarily associated with **peripheral neuropathy** and **hepatotoxicity**, which can be mitigated with **pyridoxine (vitamin B6)** supplementation. - While visual disturbances can occur, **optic neuritis** is not its most characteristic or frequent ocular side effect. *Pyrazinamide* - The main side effects of **pyrazinamide** include **hepatotoxicity** and **hyperuricemia**, which can lead to **gouty arthritis**. - It does not typically cause **optic neuritis** or other significant ocular complications. *Rifampicin* - **Rifampicin** is well-known for causing **hepatotoxicity**, **red-orange discoloration of body fluids** (urine, tears, sweat), and various **drug interactions** due to enzyme induction. - Ocular side effects like **optic neuritis** are not a common or characteristic adverse effect of rifampicin.

Question 1450: Which of the following drugs can cause ototoxicity?

A. Metronidazole
B. Amoxicillin
C. Ciprofloxacin
D. Amikacin (Correct Answer)

Explanation: ***Amikacin*** - **Amikacin** is an **aminoglycoside antibiotic** and is **the most well-known** drug among the options for causing **ototoxicity** (damage to the ear, leading to hearing loss, tinnitus, or vestibular dysfunction) [1], [2]. - This adverse effect is **dose-dependent** and related to the **cumulative dose** and **peak plasma levels** of the drug [2]. - Aminoglycosides cause both **cochlear toxicity** (hearing loss) and **vestibular toxicity** (balance problems) [1], [2]. *Metronidazole* - **Metronidazole** is an antibiotic and antiprotozoal drug that primarily causes **gastrointestinal upset** and a **metallic taste** in the mouth. - While it can cause neurological side effects like **peripheral neuropathy**, **ototoxicity is not a typical adverse effect** associated with metronidazole. *Amoxicillin* - **Amoxicillin** is a common **penicillin-class antibiotic** generally considered safe with a good side effect profile. - Its most common side effects are **gastrointestinal disturbances** like nausea, vomiting, and diarrhea, as well as **allergic reactions** and skin rashes. - **Ototoxicity is not a recognized side effect** of beta-lactam antibiotics. *Ciprofloxacin* - **Ciprofloxacin** is a **fluoroquinolone antibiotic** primarily associated with side effects like **tendinopathy**, **arthropathy**, and **QT prolongation**. - While fluoroquinolones **can cause ototoxicity** (tinnitus, hearing disturbances), this is **much less common and less severe** compared to aminoglycosides. - Ciprofloxacin is not the primary drug associated with ototoxicity in this context.

Practice by Chapter

Beta-Lactam Antibiotics

Practice Questions

Aminoglycosides

Practice Questions

Macrolides and Ketolides

Practice Questions

Tetracyclines

Practice Questions

Quinolones

Practice Questions

Sulfonamides and Trimethoprim

Practice Questions

Antimycobacterial Drugs

Practice Questions

Antifungal Agents

Practice Questions

Antiviral Drugs

Practice Questions

Antiparasitic Agents

Practice Questions

Principles of Antimicrobial Selection

Practice Questions

Antimicrobial Resistance

Practice Questions

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