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Antibiotics (GATE)

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Which of the following statements regarding bacitracin is correct?

  1. Bacitracin is used for the treatment of MRSA (methicillin resistant Staphylococcus aureus).

  2. Ribosomes are involved in the synthesis of bacitracin.

  3. Bacitracin can be used to distinguish Streptococcus pyogenes from other 'strep' bacteria.

  4. Bacitracin alters bacterial outer-membrane permeability.


Correct Option: C
Explanation:

This is the correct statement. Bacitracin can be used to distinguish Streptococcus pyogenes from other 'strep' bacteria because Streptococcus pyogenes is sensitive to bacitracin while others are resistant.

Which of the following statements about teixobactin is true?

  1. It is widely used against Gram-positive bacteria.

  2. Mycobacteria soon develops resistance to this antibiotic.

  3. It inhibits cell wall synthesis by binding to lipid II molecule.

  4. It inhibits isoprenyl pyrophosphate, a molecule that carries the building blocks of the peptidoglycan bacterial cell wall.


Correct Option: C
Explanation:

This is the correct answer. Teixobactin is an inhibitor of cell wall synthesis that acts primarily by binding to lipid II, a fatty molecule which is a precursor to peptidoglycan. Binding of teixobactin to lipid precursors inhibits production of the peptidoglycan layer, leading to lysis of vulnerable bacteria.

Which of the following organisms is not affected by chloramphenicol?

  1. Tetracycline-resistant vibrio cholerae

  2. Salmonella typhi

  3. Enterococcus faecium

  4. Pseudomonas aeruginosa


Correct Option: D
Explanation:

Chloramphenicol is not effective against Pseudomonas aeruginosa. Chloramphenicol resistance may be carried on a plasmid that also codes for resistance to other drugs or it is effectively pumped out by efflux pumps.

Which of the following statements about mupirocin (a protein synthesis inhibitor) is true?

  1. Mupirocin is a bactericidal drug at low concentrations.

  2. Mupirocin binds to t-RNA synthetase.

  3. Mupirocin is very effective on Propionibacterium acne.

  4. Mupirocin binds to 50S sub-unit of ribosomes.


Correct Option: B
Explanation:

This is the correct answer. Mupirocin reversibly binds to the isoleucyl t-RNA synthetase in Staphylococcus aureus and Streptococcus, resulting in inhibition of protein synthesis.

Which of the following drugs belonging to ansamycin family has received orphan drug status?

  1. Gelandamycin

  2. Rifaximin

  3. Rifampin

  4. Herbimycin


Correct Option: B
Explanation:

Rifaximin is used to treat traveler's diarrhoea, irritable bowel syndrome and hepatic encephalopathy, for which it received orphan drug status from the U.S. Food and Drug Administration in 1998. An orphan drug is a pharmaceutical agent that has been developed specifically to treat a rare medical condition. Rifaximin has orphan drug status for the treatment of hepatic encephalopathy, which is a rare disease.

Which of the following come(s) under the cover of fourth generation cephalosporins?

  1. MRSA (methicillin Resistant Staphylococcus aureus)

  2. Mycobacteria

  3. Pseudomonas

  4. VRE (vancomycin resistant enterococci)


Correct Option: C
Explanation:

Fourth generation cephalosporins covers Pseudomonas infection.

Which of the following drugs is most likely to treat whooping cough, if the person is not administered DPT vaccine?

  1. Metranidazole

  2. Erythromycin

  3. Penicillin G

  4. Cefalexin


Correct Option: B
Explanation:

Whooping cough is caused by a Gram-negative, aerobic, pathogenic and encapsulated coccobacillus of the genus Bordetella called Bordetella pertussis. It affects the respiratory tract. Erythromycin is likely to treat whooping cough as it is effective on aerobic respiratory pathogens.

Which of the following is false regarding mode of action of quinupristin/dalfopristin antibiotic?

  1. The combination is used to treat infections by Staphylococci and by vancomycin-resistant Enterococcus faecium.

  2. Quinupristin/dalfopristin combination produces bacteriostatic activity.

  3. Quinupristin binds to 50S ribosomal subunit.

  4. Dalfopristin binds to 23S ribosomal subunit.


Correct Option: B
Explanation:

This statement is false. Both drugs are bacteriostatic, when used alone, but the combination shows bactericidal activity.

Trimethoprim is an effective inhibitor of bacterial growth due to which of the following reasons?

  1. It is a competitive inhibitor of dihydropteroate synthase.

  2. It has an affinity for bacterial dihydrofolate reductase (DHFR).

  3. It blocks the synthesis of dihydrofolic acid.

  4. It is a non-competitive inhibitor of dihydrofolic acid and reduces its activity.


Correct Option: B
Explanation:

Trimethoprim has a very high affinity for bacterial dihydrofolate reductase. It competitively inhibits the activity of DHFR and inhibits the reduction of dihydrofolic acid (DHF) to tetrahydrofolic acid (THF). THF is an essential precursor in the thymidine synthesis pathway and interference with this pathway inhibits bacterial DNA synthesis.

Which of the following antibiotics is most likely to treat VRE (vancomycin resistant enterococci) infections?

  1. Piperacillin

  2. Clindamycin

  3. Pristinamycin

  4. Cefepime


Correct Option: C
Explanation:

Pristinamycin belongs to the streptogramin family. It is used to treat VRE (vancomycin resistant enterococci) infections. It is effective against VRE because it inhibits protein synthesis and vancomycin acts on the cell wall. Thus, its mechanism of action is altogether different than vancomycin. It also enters the bacterial cell easily, whereas other protein inhibitors fail to do so.

Daptomycin (lipopeptide antibiotic) is effective against which of the following?

  1. Gram-negative organisms + GRE (glycopeptide resistant enterococcus) + MRSA (methicillin resistant Staphylococcus aureus)

  2. Gram-positive organisms + GRE (glycopeptide resistant enterococcus) + MRSA (methicillin resistant Staphylococcus aureus)

  3. Mycobacteria + GRE (glycopeptide eesistant enterococcus) + MRSA (methicillin resistant Staphylococcus aureus)

  4. Resistant Gram-negative organisms


Correct Option: B
Explanation:

Daptomycin is active against all Gram-positive organisms. They include glycopeptide resistant enterococci (GRE), Staphylococci (including methicillin resistant Staphylococcus aureus), Streptococci, corynebacteria and stationary-phase Borrelia burgdorferi persisters.

Initiation of protein synthesis (translation) is inhibited by which of the following?

  1. Doxycycline

  2. Radezolid

  3. Rifampicin

  4. Mupirocin


Correct Option: B
Explanation:

Radezolid inhibits the initiation step of protein synthesis. It targets an early step involving the binding of N-formylmethionyl-tRNA to the ribosome.

Which of the following is true about lantibiotics?

  1. Lantibiotics are produced by Gram-negative bacteria and act against other Gram-negative bacteria.

  2. Lantibiotics are broad spectrum glycopeptides.

  3. Lantibiotics are similar to bacteriocins.

  4. Nisin and epidermin are members of class lantibiotics that bind phosphoethanolamine in the membranes of their target cells.


Correct Option: C
Explanation:

Lantibiotics are similar to bacteriocins. In fact, the lantibiotics are a class of more extensively modified bacteriocins, also called Class I bacteriocins (toxins produced by bacteria).

Which of the following is the most recently marketed antibiotic and what is its spectrum of activity?

  1. Telavancin/Resistant to Gram-negative organisms and Pseudomonas

  2. Ceftolozane and tazobactam combination/MRSA (methicillin resistant Staphylococcus aureus) and VRE (vancomycin resistant enterococci)

  3. Ceftolozane and tazobactam combination/Resistant to Gram-negative organisms and Pseudomonas

  4. Telavancin/MRSA (methicillin resistant Staphylococcus aureus) and Gram-positive organisms


Correct Option: C
Explanation:

Ceftolozane/tazobactam combination was marketed in 2015. The combination has activity against many Gram-positive and is resistant to Gram-negative pathogens and Pseudomonas aeruginosa. Thus, ceftolozane and tazobactam combination antibiotic is the latest antibiotic in the market.

Match the antibiotics with their mechanism of action.

 
Antibiotic MOA
1. Polymyxin B a. Cross linking of DNA
2. Enoxacin b. Disrupts cell membrane function
3. Furazolidone c. Alters bacterial outer membrane permeability
4. Daptomycin d. Inhibits bacterial gyrase
  1.  
    1. Polymyxin B b. Disrupts cell membrane function
    2. Enoxacin a. Cross linking of DNA
    3. Furazolidone c. Alters bacterial outer membrane permeability
    4. Daptomycin d. Inhibits bacterial gyrase
  2.  
    1. Polymyxin B c. Alters bacterial outer membrane permeability
    2. Enoxacin d. Inhibits bacterial gyrase
    3. Furazolidone a. Cross linking of DNA
    4. Daptomycin b. Disrupts cell membrane function
  3.  
    1. Polymyxin B d. Inhibits bacterial gyrase
    2. Enoxacin b. Disrupts cell membrane function
    3. Furazolidone c. Alters bacterial outer membrane permeability
    4. Daptomycin a. Cross linking of DNA
  4.  
    1. Polymyxin B d. Inhibits bacterial gyrase
    2. Enoxacin a. Cross linking of DNA
    3. Furazolidone b. Disrupts cell membrane function
    4. Daptomycin c. Alters bacterial outer membrane permeability

Correct Option: B
Explanation:

This is the correct match. Polymyxin B alters bacterial outer membrane permeability by binding to a negatively charged site in the lipopolysaccharide layer and destabilises the outer membrane. Enoxacin functions by inhibiting bacterial DNA gyrase and topoisomerase IV and prevents bacterial DNA replication, transcription, repair and recombination. Furazolidone works by crosslinking of DNA. Daptomycin disrupts multiple aspects of bacterial cell membrane function which results in bacterial cell death.

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