NEET MDS Microbiology Flashcards

24 sample cards from the Microbiology deck

Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.

1. List the five major mechanisms of action of antibacterial antibiotics with a drug class for each.

   1) Inhibit cell wall synthesis (beta-lactams, vancomycin); 2) inhibit protein synthesis (aminoglycosides, tetracyclines, macrolides); 3) inhibit nucleic acid synthesis (fluoroquinolones, rifampin); 4) inhibit folate/metabolic pathways (sulfonamides, trimethoprim); 5) disrupt cell membrane (polymyxins).

2. What are the main mechanisms by which bacteria develop antibiotic resistance?

   Enzymatic inactivation of the drug (e.g., beta-lactamases), alteration/modification of the drug target, decreased uptake/increased efflux of the drug, and bypass of the inhibited metabolic pathway.

3. How is antibiotic resistance commonly spread between bacteria?

   By horizontal gene transfer—mainly plasmid-mediated conjugation, as well as transduction (via phages) and transformation (uptake of free DNA)—and by vertical transfer of mutations.

4. Name two mechanisms of antiviral drugs with a drug example.

   Inhibition of viral DNA polymerase by nucleoside analogues (acyclovir for herpes); inhibition of reverse transcriptase (zidovudine for HIV); neuraminidase inhibition (oseltanivir for influenza) also blocks viral release.

5. Why are antiviral drugs generally harder to develop than antibacterials?

   Viruses replicate using the host cell's own machinery, so there are few virus-specific targets, making selective toxicity (harming the virus without harming the host cell) difficult to achieve.

6. State the targets of the three main antifungal classes: polyenes, azoles, and echinocandins.

   Polyenes (amphotericin B, nystatin) bind ergosterol in the membrane; azoles (fluconazole, ketoconazole) inhibit ergosterol synthesis (lanosterol 14-alpha-demethylase); echinocandins (caspofungin) inhibit beta-(1,3)-glucan synthesis in the cell wall.

7. Name the first-line antimalarial drugs and one drug for amoebiasis/giardiasis.

   Antimalarials include chloroquine and artemisinin-based combination therapy (ACT); metronidazole is used for amoebiasis and giardiasis.

8. What is DNA composed of, and how do its bases pair (Chargaff's rule)?

   DNA is a polymer of nucleotides (deoxyribose sugar, phosphate, and a nitrogenous base). Adenine pairs with thymine (A-T, two H-bonds) and guanine pairs with cytosine (G-C, three H-bonds); the two strands are antiparallel.

9. State the central dogma of molecular biology.

   Genetic information flows DNA → RNA → protein: DNA is transcribed into RNA (transcription), and RNA is translated into protein (translation); reverse transcription (RNA→DNA) is an exception.

10. What is a codon, and what are start and stop codons?

    A codon is a sequence of three nucleotides (mRNA) coding for one amino acid; AUG is the start codon (methionine), and UAA, UAG, and UGA are stop codons that terminate translation.

11. Distinguish the three mechanisms of horizontal gene transfer in bacteria.

    Transformation: uptake of free naked DNA from the environment. Transduction: transfer of DNA via a bacteriophage. Conjugation: direct transfer of DNA (often a plasmid) through a sex pilus between cells.

12. What is a plasmid and why is it medically significant?

    A plasmid is a small, circular, extrachromosomal DNA molecule that replicates independently; it often carries antibiotic-resistance and virulence genes that can spread between bacteria by conjugation.

13. Define mutation and name the major types of point mutations.

    A mutation is a permanent change in the nucleotide sequence of DNA. Point mutation types: silent (no amino acid change), missense (different amino acid), nonsense (creates a stop codon), and frameshift (insertion/deletion shifting the reading frame).

14. What is PCR (polymerase chain reaction) and what are its three temperature steps?

    PCR is a technique to amplify specific DNA sequences in vitro. Its cycle has three steps: denaturation (~94–95°C, strands separate), annealing (~50–65°C, primers bind), and extension (~72°C, Taq polymerase synthesizes new DNA).

15. What are restriction endonucleases and their role in genetic engineering?

    Enzymes that cut DNA at specific recognition sequences, often producing 'sticky ends'; they are used to cut DNA fragments and vectors for recombinant DNA cloning.

16. What general principles govern proper specimen collection for microbiology?

    Collect from the actual site of infection before antimicrobial therapy, using aseptic technique to avoid contamination, in adequate quantity, in an appropriate sterile container, and transport promptly with proper labeling.

17. Why is rapid transport or use of transport media important for specimens, and name a common bacterial transport medium.

    To preserve organism viability, prevent overgrowth of commensals, and avoid drying; Stuart's or Amies transport medium is commonly used for swabs.

18. Differentiate selective, differential, and enriched culture media with an example.

    Selective media inhibit unwanted organisms while allowing target growth (e.g., MacConkey for Gram-negatives); differential media distinguish organisms by appearance (e.g., MacConkey shows lactose fermenters as pink); enriched media add nutrients for fastidious organisms (e.g., blood/chocolate agar).

19. What does ELISA detect and what is its basic principle?

    ELISA (enzyme-linked immunosorbent assay) detects and quantifies antigens or antibodies using an enzyme-linked antibody that produces a measurable color change upon binding; widely used in serology (e.g., HIV screening).

20. How does the Kirby-Bauer disk diffusion test determine antimicrobial susceptibility?

    Antibiotic-impregnated disks are placed on a lawn of bacteria on Mueller-Hinton agar; after incubation, the diameter of the zone of inhibition around each disk is measured and compared to standards to classify the organism as susceptible, intermediate, or resistant.

21. Define MIC and MBC in antimicrobial testing.

    MIC (Minimum Inhibitory Concentration) is the lowest concentration of an antimicrobial that visibly inhibits bacterial growth; MBC (Minimum Bactericidal Concentration) is the lowest concentration that kills 99.9% of the bacteria.

22. Define sterilization, disinfection, and antisepsis.

    Sterilization: complete destruction/removal of all microorganisms including spores. Disinfection: killing of most pathogens on inanimate surfaces (usually not all spores). Antisepsis: destruction/inhibition of microbes on living tissue (skin).

23. What is the standard autoclave condition for sterilization, and what method does it use?

    121°C at 15 psi (pounds per square inch) for 15–20 minutes; it uses moist heat (saturated steam under pressure), which kills organisms including spores by protein coagulation.

24. What are standard precautions in infection control, and which single measure is the most effective for preventing healthcare-associated infections?

    Standard precautions treat all blood/body fluids as potentially infectious (hand hygiene, gloves/PPE, safe sharps disposal, proper waste handling); hand hygiene (hand washing) is the single most effective measure to prevent cross-infection.

What this deck covers

Microbiology flashcards FAQ