BDS 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. Define bacteremia, septicemia, and toxemia.

   Bacteremia: presence of bacteria in the blood. Septicemia (sepsis): active multiplication of bacteria in blood causing systemic illness. Toxemia: presence of bacterial toxins in the blood.

2. What is the general mechanism of action of penicillin against bacteria?

   Penicillin (a beta-lactam) inhibits the transpeptidase enzymes (penicillin-binding proteins) that cross-link peptidoglycan, blocking cell-wall synthesis and causing lysis of growing bacteria.

3. Describe the basic structural components of a virus (virion).

   A nucleic acid genome (DNA or RNA) surrounded by a protein coat (capsid, made of capsomeres); together the nucleocapsid. Some viruses have an outer lipid envelope with glycoprotein spikes.

4. What are the three main types of viral capsid symmetry?

   Icosahedral (cubic) symmetry, helical symmetry, and complex symmetry (e.g. bacteriophages with head-and-tail structure).

5. According to the Baltimore classification, how are viruses grouped?

   By genome type and replication strategy: dsDNA, ssDNA, dsRNA, (+)ssRNA, (−)ssRNA, ssRNA reverse-transcribing (retroviruses), and dsDNA reverse-transcribing viruses (seven classes).

6. Compare an enveloped virus with a naked (non-enveloped) virus in terms of environmental resistance.

   Naked viruses lack a lipid envelope, are more resistant to drying, acids, detergents and disinfectants. Enveloped viruses have a lipid membrane, are more susceptible to these agents (envelope is essential for infectivity).

7. List the main stages of the viral replication cycle in order.

   1) Attachment (adsorption), 2) Penetration/entry, 3) Uncoating, 4) Biosynthesis (genome replication and protein synthesis), 5) Assembly (maturation), 6) Release (lysis or budding).

8. What enzyme do retroviruses (e.g. HIV) use, and what reaction does it catalyze?

   Reverse transcriptase (RNA-dependent DNA polymerase); it synthesizes complementary DNA from the viral RNA genome, which is then integrated into host DNA by integrase.

9. Distinguish the lytic cycle from the lysogenic cycle of a bacteriophage.

   Lytic cycle: the phage replicates immediately and lyses the host cell to release progeny. Lysogenic cycle: the phage DNA integrates into the host genome as a prophage and replicates passively until induced into the lytic cycle.

10. Which virus causes AIDS, what cells does it target, and via which receptor?

    HIV (Human Immunodeficiency Virus, a retrovirus) targets CD4+ T-helper lymphocytes (and macrophages) by binding the CD4 receptor plus a co-receptor (CCR5 or CXCR4).

11. Name the herpesviruses responsible for cold sores, genital herpes, chickenpox/shingles, and infectious mononucleosis.

    HSV-1 (oral/cold sores), HSV-2 (genital herpes), Varicella-zoster virus (chickenpox and shingles), and Epstein-Barr virus (infectious mononucleosis).

12. Which hepatitis viruses are transmitted by the faecal-oral route versus by blood/body fluids?

    Faecal-oral: Hepatitis A and E. Blood/body fluids (parenteral/sexual): Hepatitis B, C, and D.

13. What is antigenic drift versus antigenic shift in influenza virus?

    Antigenic drift: minor, gradual point mutations in H and N genes causing seasonal epidemics. Antigenic shift: major abrupt reassortment of genome segments producing a new subtype, potentially causing pandemics.

14. Distinguish a latent viral infection from a persistent (chronic) infection.

    Latent infection: the virus remains dormant with no production of infectious particles until reactivation (e.g. herpesviruses). Persistent/chronic infection: continuous low-level production of virus over a long period (e.g. hepatitis B/C).

15. Describe the two main morphological forms of fungi and define a dimorphic fungus.

    Yeasts (single, round/oval cells reproducing by budding) and molds (filamentous hyphae forming a mycelium). Dimorphic fungi grow as mold at ~25°C (environment) and as yeast at ~37°C (in the body), e.g. Histoplasma.

16. What is the main structural component of the fungal cell wall, distinguishing it from bacteria?

    Chitin (a polymer of N-acetylglucosamine), along with glucans and mannoproteins. Fungi lack peptidoglycan, and their cell membrane contains ergosterol instead of cholesterol.

17. Differentiate septate from coenocytic (aseptate) hyphae.

    Septate hyphae have cross-walls (septa) dividing the filament into cells; coenocytic (aseptate) hyphae lack septa and contain multinucleate cytoplasm in a continuous tube.

18. Why does the antifungal drug amphotericin B selectively target fungi, and what fungal molecule does it bind?

    It binds ergosterol, the sterol in fungal cell membranes (absent in human cells, which use cholesterol), forming pores that cause leakage of ions and cell death; azoles instead block ergosterol synthesis.

19. Name the fungal genus that causes oral/vaginal thrush and the most common species.

    Candida, most commonly Candida albicans, an opportunistic dimorphic yeast causing thrush (oral candidiasis), vaginitis and systemic candidiasis in immunocompromised hosts.

20. Which fungus causes cryptococcal meningitis, and what special stain highlights its capsule?

    Cryptococcus neoformans; its thick polysaccharide capsule is highlighted by India ink preparation (negative stain) of cerebrospinal fluid.

21. What are dermatophytes and give the three main genera causing ringworm (tinea).

    Dermatophytes are keratinophilic fungi that infect skin, hair and nails. The three genera are Trichophyton, Microsporum, and Epidermophyton.

22. Which protozoan causes malaria, what genus is it, and what is the vector?

    Plasmodium (species include P. falciparum, P. vivax, P. ovale, P. malariae); it is transmitted by the bite of the female Anopheles mosquito.

23. Classify the causative agents and distinguishing features of amoebic versus bacillary dysentery.

    Amoebic dysentery: caused by the protozoan Entamoeba histolytica (flask-shaped ulcers, blood/mucus, gradual onset). Bacillary dysentery: caused by the bacterium Shigella (acute, more inflammatory).

24. Give one example each of the major helminth groups: nematode, cestode, and trematode.

    Nematode (roundworm): Ascaris lumbricoides. Cestode (tapeworm): Taenia solium. Trematode (fluke): Schistosoma species. Also compare Ectoparasites such as Sarcoptes scabiei (mite causing scabies) and lice (Pediculus), which live on the host surface and can act as disease vectors.

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