33 Year 2: Microbiology exam questions on MBPL3822 Chemotherapy CAT 1 for medical students. Includes MCQs, answers, explanations and written questions. Sample:
This MCQ set contains 33 questions on MBPL3822 Chemotherapy CAT 1 in the Year 2: Microbiology unit. Each question includes the correct answer and a detailed explanation for active recall and exam preparation.
Correct answer: C – Gentamicin
Gentamicin, when used in combination with penicillin G, shows synergistic activity against enterococci. The penicillin disrupts the cell wall, allowing better penetration of the aminoglycoside (gentamicin) into the bacterial cell, resulting in enhanced bactericidal activity. ---
Correct answer: C – Gentamicin continues to exert antibacterial effects even after plasma levels decrease below detectable levels
Gentamicin exhibits a post-antibiotic effect (PAE) , meaning it continues to suppress bacterial growth even after drug concentrations fall below the minimum inhibitory concentration (MI C). This is characteristic of concentration-dependent antibiotics like aminoglycosides. ---
Correct answer: D – Valacyclovir
Valacyclovir, famciclovir, penciclovir, and acyclovir are all indicated for herpes simplex virus infection. Cidofovir and ganciclovir are used for CMV retinitis. Zanamivir is indicated for influenza. ---
Correct answer: A – Vancomycin + cefepime + ciprofloxacin
Vancomycin provides adequate coverage against MRSA, and cefepime and ciprofloxacin provide adequate empiric coverage of Pseudomonas. Option B is incorrect because cefazolin does not have activity against Pseudomonas. Option C is incorrect because telavancin should be avoided if possible with drugs that prolong the QTc interval (ciprofloxacin). Daptomycin is inactivated by pulmonary surfactant and
Correct answer: A – Tigecycline
Tigecycline is the first glycylcycline to be launched and is one of the very few new antimicrobials with activity against Gram-negative bacteria. It evades acquired efflux and target-mediated resistance to classical tetracyclines, but not chromosomal efflux in Proteeae and Pseudomonas. It has shown equivalence to imipenem/cilastatin in intra-abdominal infections and is useful for treating multires
Correct answer: D – Use of antibiotic combinations covering both gram positive and gram negative bacteria
Broad-spectrum antibiotics or antibiotic combinations that cover both gram-positive and gram-negative bacteria disrupt the normal flora more extensively, allowing opportunistic organisms (like C. difficile or Candida) to overgrow, leading to superinfections. ---
Correct answer: C – Amikacin
Amikacin is an aminoglycoside that is often effective against MDR-TB strains, including those resistant to streptomycin. It is one of the second-line agents used in the treatment of drug-resistant tuberculosis due to its different resistance profile compared to streptomycin. ---
Correct answer: B – Tobramycin
Aminoglycosides such as tobramycin accumulate in the proximal tubular cells of the kidney and disrupt calcium-mediated transport processes. This results in kidney damage ranging from mild, reversible renal impairment to severe, potentially irreversible acute tubular necrosis. Nephrotoxicity is not commonly associated with tetracyclines, macrolides, or oxazolidinones. ---
Correct answer: D – The post antibiotic effect
The post-antibiotic effect (PAE) is the continued suppression of bacterial growth after brief exposure to an antimicrobial agent, even after drug concentrations have fallen below the MIC. This is particularly notable with aminoglycosides and fluoroquinolones. ---
Correct answer: D – Tobramycin
Tobramycin (an aminoglycoside) is primarily eliminated by the kidneys through glomerular filtration. In patients with renal insufficiency, the drug can accumulate to toxic levels, so dose adjustment is necessary to prevent nephrotoxicity and ototoxicity. ---
Correct answer: C – Requires pyridoxine supplementation
Isoniazid can cause peripheral neuropathy by interfering with pyridoxine (vitamin B6) metabolism. Pyridoxine supplementation is given to prevent this adverse effect, especially in high-risk patients (diabetics, alcoholics, malnourished individuals, pregnant women). ---
Correct answer: D – Pneumonia caused by drug-resistant Streptococcus pneumoniae
Linezolid has excellent coverage against resistant gram-positive organisms including drug-resistant S. pneumoniae. It is not an optimal choice for treatment of bacteremia (static, not cidal). Linezolid also does not have gram-negative coverage against E. coli and P. aeruginosa. ---
Correct answer: D – Nafcillin
Nafcillin is a penicillinase-resistant penicillin that provides excellent coverage against methicillin-sensitive Staphylococcus aureus (MSSA). It is often used in combination with aminoglycosides for empiric treatment of severe infections where staphylococcal involvement is suspected. ---
Correct answer: B – Azithromycin has better activity against respiratory pathogens such as Haemophilus influenzae and Moraxella catarrhalis but less potent activity again
Azithromycin has improved activity against gram-negative respiratory pathogens like H. influenzae and M. catarrhalis compared to erythromycin, but erythromycin has better activity against gram-positive organisms (staphylococci and streptococci). ---
Correct answer: D – They may decrease nephrotoxicity of amphotericin B
Lipid formulations of amphotericin B (liposomal, lipid complex) have the same spectrum of activity but significantly reduced nephrotoxicity compared to conventional amphotericin B. The lipid carrier preferentially delivers the drug to tissues rather than kidneys, reducing renal toxicity while maintaining antifungal efficacy. ---
Correct answer: C – Blockade of binding of aminoacyl-tRNA to bacterial ribosomes
Tetracyclines bind to the 30S ribosomal subunit and prevent the binding of aminoacyl-tRNA to the acceptor site on the ribosome, thereby inhibiting protein synthesis. This is a bacteriostatic mechanism. ---
Correct answer: D – Penicillin G, imipenem, amphotericin B, metronidazole
All four drugs in this group (Penicillin G, imipenem, amphotericin B, and metronidazole) can lower the seizure threshold and cause seizures, especially in high-risk patients (those with renal impairment, CNS disorders, or receiving high doses). These drugs require careful monitoring for neurological adverse effects. ---
Correct answer: B – Inhibiting transpeptidases and carboxypeptidases which cross link the peptidoglycan residues
Penicillins are β-lactam antibiotics that inhibit bacterial transpeptidases (also called penicillin-binding proteins or PBPs), which are essential for cross-linking peptidoglycan chains in the bacterial cell wall. This weakens the cell wall and leads to bacterial cell lysis. ---
Correct answer: B – It is not susceptible to penicillinase
Vancomycin is a glycopeptide antibiotic that is not affected by β-lactamases (penicillinases) because it has a completely different structure and mechanism of action from β-lactam antibiotics. It inhibits cell wall synthesis by binding to D-alanyl-D-alanine terminals, not to PBPs. ---
Correct answer: C – Aztreonam
The patient has a documented severe penicillin allergy (anaphylaxis). Aztreonam is a monobactam that has no cross-reactivity with penicillins and can be safely used in penicillin-allergic patients. It provides good gram-negative coverage. Cephalosporins and carbapenems have potential cross-reactivity with penicillins and should be avoided in severe allergic reactions. ---
Correct answer: B – Is more active against Mycobacterium avium complex
Clarithromycin has greater intracellular activity than erythromycin against Mycobacterium avium complex (MAC), making it a preferred agent for MAC infections, particularly in HIV-infected individuals. Both drugs have similar spectrums against typical bacteria, but clarithromycin's enhanced activity against MAC is a key distinguishing feature. ---
Correct answer: A – Methylation of binding sites on the 50S ribosomal subunit
The most common mechanism of macrolide resistance in gram-positive bacteria is methylation of the 23S rRNA component of the 50S ribosomal subunit (mediated by erm genes). This modification prevents macrolide binding to the ribosome, conferring resistance. ---
Correct answer: D – Moxifloxacin
Moxifloxacin is a 4th generation fluoroquinolone with improved gram-positive coverage (including S. pneumoniae), maintains gram-negative coverage, and gains anaerobic coverage. This broader spectrum distinguishes it from earlier fluoroquinolones like ciprofloxacin. ---
Correct answer: C – Cefotaxime
Cefotaxime is a 3rd generation cephalosporin with excellent CSF penetration and broad coverage against common meningitis pathogens (S. pneumoniae, N. meningitidis, H. influenzae). Cefdinir and cefuroxime axetil are only available orally and not appropriate for serious CNS infections. Cefazolin has inadequate CSF penetration and spectrum. ---
Correct answer: A – Aztreonam
Aztreonam is a monobactam with no cross-reactivity with penicillins and can be safely given to penicillin-allergic patients, even those with anaphylaxis. Although cross-reactivity between cephalosporins/carbapenems and penicillins is low (<1-10%), the risk rarely outweighs the benefit in cases of documented anaphylaxis. Aztreonam provides good gram-negative coverage for UTI. ---