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Everything you need to know about the control of microbial growth. Some of the frequently asked questions are as follows:-
Q.1. Name some antimicrobics (antibiotics) which inhibit bacterial cell-wall synthesis.
Ans. Penicillin G, ampicillin, methicillin and cephalosponns.
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Q.2. Name some antimicrobics (antibiotics) which inhibit bacterial protein synthesis.
Ans. Streptomycin, neomycin, chloramphenicol, tetracycline, bacitracin and erythromycin.
Q.3. Name an antimicrobic (antibiotic) which inhibits bacterial RNA synthesis.
Ans. Rifampicin.
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Q.4. Name the antimicrobics (antibiotics) which damage plasma membrane of fungi.
Ans. Nystatin, amphotericin B and ketoconazole.
Q.5. Name the antimicrobic (antibiotic) which inhibits mitosis.
Ans. Griseofulvin.
Q.6. Name the antimicrobics (antibiotics) which interfere with DNA synthesis in fungi.
Ans. Flucytosine and pentamidine.
Q.7. Name the antimicrobics which interfere with DNA replication of Protozoa.
Ans. Metronidazole.
Q.8. Name an antimicrobic which inhibits viral reverse transcnptase and is used against HIV infections.
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Ans. Zidovudine.
Q.9. Name antimicrobic (antibiotic) that interferes with penetration and causes un-coating of viral particles.
Ans. Amantiadine is used against influenza type infections.
Q.10. What is micro-biostatic?
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Ans. The agent or the substance that inhibits the growth of microorganisms without destroying them is called micro-biostatic.
Q.11. What is the Kirby-Bauer Test?
Ans. The Kirby-Bauer test, also known as the Baur-Kirby test is a standardized procedure to determine antibiotic susceptibility. The diameter of zone of inhibition which can be seen as a clear area around antimicrobic impregnated discs, gives the sensitivity of the microorganisms to the antibiotic.
This test was developed by Dr Kirby and Dr Alfred Baur. The agar diffusion test procedure is designed for rapidly growing bacteria. This test is not directly applicable to filamentous fungi, anaerobes or slow growing bacteria. Nonetheless modifications of the media composition and incubation conditions can be made for testing the antibiotic susceptibility of such microbes.
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Q.12. What is minimum inhibitory concentration?
Ans. It uses the dilution of antibiotics or antimicrobics to determine the lowest concentration of the antimicrobic (the MIC) which is effective for prevention of the growth of microorganisms.
Q.13. What is minimal bacterial concentration (MBC)?
Ans. The MBC, also known as minimal lethal concentration is the lowest concentration of antibiotic which destroys the defined portion of viable organisms in a bacterial suspension during a specified exposure time. A 99.9% kill rate of bacteria at an initial concentration of 105 to 106 cells per ml during an 18 to 24 hours exposure is taken to define minimal bacterial concentration.
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Q.14. Why do penicillins (obtained from fungus Penicillium) and cephalosporins (produced from fungus Cephalosporium) inhibit the formation of bacterial cell walls?
Ans. Both antibiotics contain (β-lectam rings. The (β-lectam portions of cephalosporin and penicillin bind the transpeptidase enzyme and hence prevent the binding of the enzyme to normal substrate D-alanyl-D alanine. The bacterial cell walls lacking the normal cross linking peptide chain are subject to attack by autolysins which are the antilytic enzymes produced by the bacterium and degrade the cells own cell wall structures.
Q.15. How do antimicrobics like erythromycin and tetracycline make therapeutically antibacterial agents?
Ans. They specifically target 70 S ribosomes and prevent continuation of protein synthesis by the bacterial cells.
Q.16. How does chloramphenicol inhibit protein synthesis?
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Ans. It binds to 50 S ribosomal subunits and prevents the binding of t RNA molecules to the aminoacyl and peptidyl binding sites of the ribosome. Erythromycin, another antibiotic too binds to 50 S ribosomal subunits. Likewise rifampicin a semisynthetic derivative of rifamycin B also inhibits protein synthesis.
Q.17. How do quinolones work as DNA inhibitors?
Ans. Quinolones interfere with DNA gyrase and thereby prevent the establishment of replication fork and replication of DNA. As quinolones inhibit the DNA gyrase this leads to blocking of bacterial cells reproduction.
Q.18. Name the antibiotics which have prevented premature births by treatment of women with bacterial vaginosis.
Ans. Erythromycin and metronidazole.
Q.19. How is acyclovir inhibitory to herpes simplex viruses?
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Ans. Acyclovir is an analog of guanine containing nucleoside and in vivo gets converted to acyclovir triphosphate. The enzyme uses it to form a false nucleotide that cannot be incorporated into DNA.
Q.20. Name some heavy metals which are used as germicides.
Ans. Silver, mercury, copper and zinc.
Q.21. How do heavy metals cause inhibitory action on microbes?
Ans. The heavy metals exert the antimicrobial action through oligodynamic action (oligo = a few). Heavy metal ions combine with thio (-SH) groups. As a result the proteins are denatured.
Q.22. What is the historical contribution of Ignatz Semmelweis to reduce infections in hospitals?
Ans. He introduced hand-washing with chlorinated lime by hospital personnel to reduce infections.
Q.23. What are quats?
Ans. The quats (quaternary ammonium compounds) are cationic detergents attached to NH+4, disrupting plasma membrane. It causes leakage of cytoplasmic constituents of the cell. The quats are most effective against Gram-positive bacteria.
