Antimicrobial Agents — MCQs

Antimicrobial Agents Indian Medical PG Practice Questions and MCQs

Question 1591: All of the following organisms are susceptible to amikacin except:

A. Serratia
B. Proteus
C. Enterococci (Correct Answer)
D. Pseudomonas

Explanation: ***Enterococci*** - Amikacin, like other **aminoglycosides**, generally has poor activity against **Enterococci** when used as a single agent. - While enterococci are intrinsically resistant to many aminoglycosides, synergy with **beta-lactams** or **vancomycin** is often required for effective treatment of serious infections. *Pseudomonas* - **Amikacin** is highly effective against **Pseudomonas aeruginosa**, a common target for aminoglycoside therapy, especially in multi-drug resistant strains. - It works by inhibiting bacterial protein synthesis, making it a crucial agent for severe **gram-negative infections**. *Serratia* - **Serratia marcescens** is often susceptible to **amikacin**, particularly in nosocomial infections where resistance to other antibiotics is common. - Amikacin is a viable option for treating serious Serratia infections, often in combination with other antibiotics. *Proteus* - **Proteus species** are generally susceptible to **amikacin**, which is commonly used for complicated urinary tract infections and other severe infections caused by these bacteria. - Amikacin's broad spectrum of activity against many **gram-negative bacilli** includes Proteus.

Question 1592: Which one of the following penicillin group drugs is penicillinase resistant?

A. Amoxicillin
B. Cloxacillin (Correct Answer)
C. Penicillin G
D. Piperacillin

Explanation: ***Cloxacillin*** - **Cloxacillin** is a narrow-spectrum beta-lactam antibiotic of the penicillin class that is **penicillinase-resistant**. - It is often used to treat infections caused by penicillinase-producing **staphylococci**. *Amoxicillin* - **Amoxicillin** is an **aminopenicillin** that is **not penicillinase-resistant** and is often combined with a **beta-lactamase inhibitor** like **clavulanic acid** to enhance its spectrum of activity. - It is a **broad-spectrum antibiotic** effective against a wide range of gram-positive and gram-negative bacteria. *Penicillin G* - **Penicillin G** is a **natural penicillin** and is **susceptible to penicillinase (beta-lactamase)** enzymes, which break down its beta-lactam ring. - It has a narrow spectrum of activity, primarily against **gram-positive cocci** and **some gram-negative cocci**. *Piperacillin* - **Piperacillin** is a **ureidopenicillin**, a **broad-spectrum** penicillin that is **not penicillinase-resistant** when used alone. - It is usually combined with a **beta-lactamase inhibitor** like **tazobactam** to protect it from degradation and expand its coverage, especially against **Pseudomonas aeruginosa.**

Question 1593: Which of the following statements is false regarding drug resistance?

A. High degree of resistance is seen in transferable drug resistance.
B. Virulence is decreased in transferable resistance. (Correct Answer)
C. In mutational drug resistance, one drug resistance at a time is seen.
D. Drug combinations can prevent mutational drug resistance.

Explanation: ***Virulence is decreased in transferable resistance.*** - This statement is **FALSE** and is the correct answer. - Transferable drug resistance (mediated through **plasmids, transposons, or integrons**) typically does **not decrease bacterial virulence**. - In fact, bacteria can acquire multiple resistance genes via horizontal gene transfer while maintaining or even enhancing their pathogenicity. - The fitness cost of carrying resistance plasmids is often minimal, allowing resistant bacteria to remain highly virulent. *High degree of resistance is seen in transferable drug resistance.* - This statement is **TRUE**. - **Transferable resistance** often confers **high-level, multi-drug resistance** because plasmids can carry multiple resistance genes simultaneously. - Mobile genetic elements encode mechanisms like beta-lactamases, efflux pumps, and target modifications that provide significant resistance. *In mutational drug resistance, one drug resistance at a time is seen.* - This statement is **TRUE**. - **Mutational resistance** typically involves **chromosomal mutations** that confer resistance to **one drug at a time** (single-step mutation). - This is in contrast to transferable resistance, where multiple resistance genes can be acquired simultaneously. - While cross-resistance to structurally similar drugs may occur, each mutation generally affects a specific drug-target interaction. *Drug combinations can prevent mutational drug resistance.* - This statement is **TRUE**. - **Combination therapy** is a key strategy to **prevent or delay mutational resistance**. - The probability of simultaneous spontaneous mutations conferring resistance to multiple unrelated drugs is extremely low (product of individual mutation rates). - By using drugs with different mechanisms of action, combination therapy ensures that if resistance develops to one agent, the other(s) remain effective.

Question 1594: Which of the following is not indicated for the treatment of anaerobic infections?

A. Gentamicin (Correct Answer)
B. Piperacillin-tazobactam
C. Metronidazole
D. Clindamycin

Explanation: ***Gentamicin*** - **Gentamicin** is an **aminoglycoside**, which primarily targets **aerobic gram-negative bacteria** by inhibiting protein synthesis. - Aminoglycosides are **ineffective against anaerobes** because their transport into bacterial cells is an oxygen-dependent process. *Metronidazole* - **Metronidazole** is a highly effective antimicrobial treatment for a wide range of **anaerobic bacterial infections**, disrupting their DNA synthesis. - It is a drug of choice for infections caused by organisms like *Bacteroides fragilis* and *Clostridium difficile*. *Piperacillin-tazobactam* - **Piperacillin-tazobactam** is a broad-spectrum penicillin combined with a beta-lactamase inhibitor, offering excellent coverage against both **aerobic** and **anaerobic bacteria**. - It is commonly used for severe mixed infections, including intra-abdominal, skin, and soft tissue infections where anaerobes are implicated. *Clindamycin* - **Clindamycin** is a lincosamide antibiotic that is very effective against most **anaerobic bacteria**, preventing protein synthesis by binding to the 50S ribosomal subunit. - It is frequently used for anaerobic infections above the diaphragm, such as **aspiration pneumonia** and certain skin/soft tissue infections.

Question 1595: All of the following are features of streptomycin, except which of the following?

A. It is an antitubercular drug
B. Effective against g-ve organisms
C. It can be given orally (Correct Answer)
D. None of the options

Explanation: ***It can be given orally*** - Streptomycin is an **aminoglycoside** antibiotic that is **poorly absorbed** from the gastrointestinal tract due to its highly polar nature. - For systemic effects, it must be administered parenterally, typically **intramuscularly** or **intravenously**, making oral administration ineffective. - This is the **exception** among the listed features—streptomycin cannot be given orally. *It is an antitubercular drug* - Streptomycin was the **first effective antibiotic against Mycobacterium tuberculosis** and is still used in combination regimens for susceptible strains, particularly in drug-resistant cases. - It works by **inhibiting bacterial protein synthesis** by binding to the 30S ribosomal subunit. *Effective against g-ve organisms* - Streptomycin, like other aminoglycosides, is highly effective against many aerobic **Gram-negative bacteria**. - It is used for severe infections caused by organisms such as **Pseudomonas aeruginosa**, Francisella tularensis (tularemia), and Yersinia pestis (plague). *None of the options* - This option is incorrect because option "It can be given orally" is clearly **not** a feature of streptomycin. - "None of the options" would imply that all listed statements are true features, which is not the case.

Question 1596: Which of the following drugs is most commonly associated with ototoxicity?

A. Chloramphenicol
B. Dapsone
C. Isoniazid
D. Gentamicin (Correct Answer)

Explanation: ***Gentamicin*** - **Gentamicin** is an **aminoglycoside antibiotic** well-known for its potential to cause **ototoxicity**, leading to hearing loss and/or vestibular dysfunction. - This adverse effect is often irreversible and can be dose-dependent or due to prolonged exposure. *Dapsone* - **Dapsone** is primarily used for **leprosy** and various dermatological conditions and is not commonly associated with ototoxicity. - Its main side effects include **hemolytic anemia**, methemoglobinemia, and peripheral neuropathy. *Isoniazid* - **Isoniazid** is a first-line drug for **tuberculosis**, and its most common adverse effects include **hepatotoxicity** and **peripheral neuropathy**. - While it can cause neurological side effects, ototoxicity is not a prominent or common association. *Chloramphenicol* - **Chloramphenicol** is an antibiotic known for serious side effects such as **bone marrow suppression** (aplastic anemia) and **gray baby syndrome** in neonates. - Ototoxicity is not a commonly recognized adverse effect of chloramphenicol.

Question 1597: According to WHO, what is the recommended treatment for uncomplicated Plasmodium falciparum malaria?

A. Mefloquine
B. Chloroquine
C. Artemether + lumefantrine (Correct Answer)
D. Artemisinin only

Explanation: ***Artemether + lumefantrine*** - The **World Health Organization (WHO)** strongly recommends **Artemisinin-based combination therapies (ACTs)** as the first-line treatment for uncomplicated **Plasmodium falciparum malaria** due to their high efficacy and ability to overcome drug resistance. - **Artemether + lumefantrine** is one of the most widely used and effective ACTs, combining a fast-acting artemisinin derivative with a longer-acting partner drug. *Mefloquine* - While effective against some malaria strains and used for prophylaxis, **mefloquine** is not the primary recommended first-line treatment for uncomplicated *P. falciparum* malaria due to potential neuro-psychiatric side effects and existing resistance in some regions. - It is typically reserved for situations where other ACTs are unavailable or contraindicated. *Chloroquine* - **Chloroquine** resistance is widespread globally for *P. falciparum* malaria, making it largely ineffective as a first-line treatment for this species. - It remains effective for uncomplicated *P. vivax, P. ovale*, and *P. malariae* infections in non-resistant areas. *Artemisinin only* - Treating **uncomplicated malaria** with **artemisinin monotherapy** is **strongly discouraged** by the WHO because it promotes the rapid development of drug resistance. - Artemisinin derivatives should always be used in combination with a partner drug to protect their efficacy and prevent resistance.

Question 1598: According to current WHO guidelines, the first-line treatment for uncomplicated chloroquine-resistant falciparum malaria is:

A. Quinine
B. Pyrimethamine
C. Primaquine
D. Artemisinin-based combination therapy (ACT) (Correct Answer)

Explanation: ***Artemisinin-based combination therapy (ACT)*** - The World Health Organization (WHO) currently recommends **artemisinin-based combination therapies (ACTs)** as the first-line treatment for uncomplicated *Plasmodium falciparum* malaria, even in areas with chloroquine resistance. - ACTs are highly effective due to the **synergistic action** of artemisinin derivatives, which rapidly reduce parasite biomass, and a longer-acting partner drug that eliminates residual parasites, preventing recrudescence and resistance development. *Quinine* - While historically used for malaria, **quinine** is no longer the first-line treatment for uncomplicated *falciparum* malaria due to a **higher rate of treatment failure** and more side effects compared to ACTs. - It is often reserved for severe malaria or in cases where ACTs are contraindicated or unavailable. *Pyrimethamine* - **Pyrimethamine** is an antifolate drug that inhibits dihydrofolate reductase and is typically used in combination with sulfadoxine (as **Fansidar**). - Widespread **resistance** to pyrimethamine, particularly in *P. falciparum*, has made it largely ineffective as a standalone or first-line treatment for uncomplicated malaria. *Primaquine* - **Primaquine** is an 8-aminoquinoline derivative used to eliminate **hypnozoites** of *P. vivax* and *P. ovale* to prevent relapse, and as a gametocytocide for *P. falciparum* to reduce transmission. - It is **not effective** as a primary treatment for the asexual blood stages of *P. falciparum* that cause acute illness and therefore is not a first-line treatment for uncomplicated *falciparum* malaria.

Question 1599: Third-generation cephalosporins include all of the following except:

A. Cefoperazone
B. Cefixime
C. Ceftizoxime
D. Cefoxitin (Correct Answer)

Explanation: ***Cefoxitin*** - **Cefoxitin** is a **second-generation cephalosporin**, primarily known for its activity against **anaerobic bacteria** (like *Bacteroides fragilis*) and certain **Gram-negative bacteria**. - Its spectrum of activity and chemical structure classify it distinctly from third-generation cephalosporins, which offer broader Gram-negative coverage and better penetration into the CNS. *Ceftizoxime* - **Ceftizoxime** is a **third-generation cephalosporin** with a broad spectrum of activity against many **Gram-negative bacilli** and some **Gram-positive cocci**. - It is often used for serious infections, including intra-abdominal and lower respiratory tract infections. *Cefoperazone* - **Cefoperazone** is another **third-generation cephalosporin** known for its activity against ***Pseudomonas aeruginosa***, a common feature of many third-generation agents. - It also provides good activity against other Gram-negative organisms, making it suitable for a range of severe infections. *Cefixime* - **Cefixime** is an **oral third-generation cephalosporin** commonly used for outpatient treatment of infections such as **otitis media**, **streptococcal pharyngitis**, and **uncomplicated urinary tract infections**. - Its oral bioavailability distinguishes it from many injectable third-generation cephalosporins but it shares the typical third-generation spectrum of activity.

Question 1600: Nitazoxanide is specifically indicated for the treatment of which opportunistic infection in AIDS patients?

A. Cryptococcosis
B. Cryptosporidiosis (Correct Answer)
C. Histoplasmosis
D. Candidiasis

Explanation: ***Cryptosporidiosis*** - **Nitazoxanide** is an **antiprotozoal agent** specifically indicated for treating **cryptosporidiosis**, particularly in immunocompromised patients like those with AIDS. - It works by inhibiting the **pyruvate ferredoxin oxidoreductase enzyme pathway** in *Cryptosporidium parvum*, disrupting their energy metabolism. *Cryptococcosis* - **Cryptococcosis** is a fungal infection usually treated with **amphotericin B** and **flucytosine**, followed by fluconazole. - Nitazoxanide has **no significant activity** against *Cryptococcus neoformans*. *Histoplasmosis* - **Histoplasmosis** is a fungal infection primarily treated with **amphotericin B** for severe disease or **itraconazole** for milder forms. - Nitazoxanide is an **antiprotozoal** medication and is not effective against *Histoplasma capsulatum*. *Candidiasis* - **Candidiasis** is a fungal infection commonly treated with **fluconazole**, topical azoles, or other antifungal agents depending on the site and severity. - Nitazoxanide is **not indicated** for the treatment of **Candida infections**.

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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