Microbiology - Problem Drill 16: Antibiotics. Question No. 1 of 10. Question. Feedback. Question

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1 Microbiology - Problem Drill 16: Antibiotics No. 1 of An effective chemotherapeutic drug should have. (A) Low therapeutic index (B) More toxicity (C) Selective toxicity (D) Mutation inducing properties It should have high therapeutic index. B. Incorrect! If it is more toxic, it may cause side effects. C. Correct! It should selectively inhibit the pathogen and do no harm to the host. If it induces mutations, it may harm the host. An effective chemotherapeutic agent must have selective toxicity. A drug with great selective toxicity has a high therapeutic index and usually disrupts a structure or process unique to the pathogen. It typically has fewer side effects.

2 No. 2 of Methylation of 23S ribosomal RNA in bacteria confers resistance to which antibiotic? (A) Rifampicin (B) Streptomycin (C) Tetracycline (D) Chloramphenicol It can change the drug by chemical modification. B. Incorrect! Here the receptor protein changes. Resistance is plasmid mediated. D. Correct! A change in the 23s ribosomal RNA, leads to resistance. Many bacterial pathogens resist attack by inactivating drugs through chemical modifications. Because each chemotherapeutic agent acts on a specific target, resistance arises when the target, enzyme or organelle is modified so that it is no longer susceptible to the antibiotic. The affinity of ribosomes for erythromycin and chloramphenicol can be decreased by a change in the 23 ribosomal RNA to which these antibiotics bind.

3 No. 3 of Amino glycosides act on bacteria by binding to the? (A) 80S bacterial ribosome (B) 30S bacterial ribosome (C) 70S bacterial ribosome (D) 16S bacterial ribosome Bacteria do not have 80S ribosomes. B. Correct! They bind to the 30S ribosome and interfere with transcription. They do not bind to the 70S ribosomes. Bacteria do not have 16S ribosomes. The amino glycosides bind to the 30S subunit of the bacterial ribosome and interfere with the formation of the initiation complex causing misreading of the mrna.

4 No. 4 of Which of the following is a beta lactam antibiotic? (A) Polymyxin (B) Trimethoprim (C) Kanamycin (D) Cephalosporin There is no beta lactam ring in polymyxin. B. Incorrect! There is no beta lactam ring in trimethoprim. There is no beta lactam ring in kanamycin. D. Correct! Beta lactam antibiotics have a heteroatomic ring structure consisting of three carbon atoms and one Nitrogen atom.cephalosporins have a 6 ringed structure. Cephalosporins are beta lactam antibiotics. They differ from penicillin by having the beta-lactam ring a 6 member ring. The other difference, which is more significant from a medicinal chemistry stand point, is the existence of a functional group (R) at position 3 of the fused ring system. This now allows for molecular variations to effect changes in properties by varying the groups at position 3.

5 No. 5 of Which of the following antibiotics prevents the transfer of amino acids to ribosomes such that protein synthesis is prevented leading to cell death? (A) Polymyxin (B) Tetracycline (C) Penicillin (D) Rifampicin Polymyxin increases the permeability of bacterial membranes causing the contents of the bacterial cell to leak out. B. Correct! It inhibits transfer of amino acids by t-rna. Penicillin inhibits cell wall synthesis. Rifampicin binds to the bacterial RNA polymerase and prevents transcription. Tetracyclines inhibit bacterial protein synthesis by blocking the attachment of the transfer RNA-amino acid to the ribosome. More precisely they are inhibitors of the codon-anticodon interaction. Tetracycline can also inhibit protein synthesis in the host, but are less likely to reach the concentration required because eukaryotic cells do not have a tetracycline uptake mechanism.

6 No. 6 of Which antibiotic mimics parabenzoic acid and inhibits folic acid synthesis in bacteria? (A) Penicillin (B) Sulphonamide (C) Tetracycline (D) Kanamycin Penicillin inhibits cell wall synthesis. B. Correct! Sulphonamide is an analog of parabenzoic acid and thus inhibits folic acid synthesis. They prevent the transfer of activated amino acids to the ribosome. Kanamycin binds to the 30S subunit of the bacterial ribosome and interferes with the formation of the initiation complex causing misreading of the mrna. When sulfonamide enters a bacterial cell, it competes with para amino benzoic acid for the active site of one of the enzymes involved in folic acid synthesis and the folate concentration decreases. The decline in folic acid is detrimental because folic acid is essential for synthesis of DNA, RNA etc.

7 No. 7 of Beta lactam antibiotics are produced by. (A) Bacteria (B) Fungi (C) Viruses (D) Algae Some bacteria do make antibiotics but not this type. B. Correct! Most of the fungi produce antibiotics. Viruses do not produce any antibiotics. Algae do not produce any antibiotic. The most commonly used beta lactam antibiotics are produced by filamentous fungi.cephaosporins are produced by Cephalosporin acremonium/streptomyces clavuligerus. Similarly penicillin is produced by Penicilium chrysogenum /Pencillium notatum.

8 No. 8 of An example of amino glycoside antibiotic is. (A) Erythromycin (B) Streptomycin (C) Chloramphenicol (D) Cephalosporin A. Incorrect Erythromycin is a macrolide antibiotic. B. Correct Streptomycin is an amino glycoside antibiotic. C. Incorrect Chloramphenicol is not an amino glycoside. D. Incorrect Cephalosporins are beta lactam antibiotics. There are several important amino glycoside antibiotics. Streptomycin, kanamycin, neomycin and tobramycin are synthesized by streptomyces.the amino glycosides are bactericidal and tend to be most active against gram negative pathogens.aminoglycosides are quite toxic and can cause deafness, renal damage, loss of balance, nausea and allergic responses.

9 No. 9 of Antifungal drugs produce more side effects because. (A) It is hard to kill fungi. (B) Fungal and human cells are similar. (C) A higher dosage is required to be effective. (D) They cause systemic infections. Just because it is hard to kill fungi doesn t mean antifungal drugs have more side effects. B. Correct! Since fungi and human cells are both eukaryotic they share a lot of common features. So what affects the fungi would also affect us. The dosage of antifungal drugs are not the cause of the side effects. Consider the similarities between human and fungi cells. Antifungal drugs do not cause systemic infections, they are used to treat infections. Eukaryotic fungal cells are more similar to human cells then to bacteria. The similarity between human cells and that of fungi means that many of the drugs that inhibit or kill fungi are toxic to humans. Effective antifungal agents work by extracting membrane sterols or preventing their synthesis. Similarly because animal cells do not have cell walls; the enzyme chitin synthase is the target for some anti fungal medications. The antibiotic polyoxin D inhibits chitin synthetase and consequently cell wall formation as does nikkomycin.

10 No. 10 of Which of the following is correctly matched? (A) Antifungal-streptomycin (B) Antifungal-penicillin (C) Antifungal-imidazole (D) Antifungal-kanamycin Streptomycin is antibacterial. B. Incorrect! Penicillin is antibacterial. C. Correct! Imidazole is an antifungal drug. Kanamycin is antibacterial. Several drugs are used to treat superficial mycoses. Three drugs containing imidazole-micanozole, ketoconazole and clotrimazole are broad spectrum agents available for treatment of dermatophyte infections.