DNB CET 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. Match the Clostridium species to its disease and mechanism.

   C. tetani: tetanus (tetanospasmin blocks GABA/glycine release -> spastic paralysis). C. botulinum: botulism (toxin blocks acetylcholine -> flaccid paralysis). C. perfringens: gas gangrene/food poisoning (alpha toxin, lecithinase). C. difficile: pseudomembranous colitis (toxins A and B).

2. Which spirochete causes syphilis and what serological tests are used?

   Treponema pallidum; non-treponemal tests (VDRL, RPR - screening, become negative after treatment) and treponemal tests (TPHA, FTA-ABS - confirmatory, remain positive for life). Seen by dark-ground microscopy.

3. Name the spirochetes causing leptospirosis and Lyme disease and a diagnostic clue.

   Leptospira interrogans -> leptospirosis (Weil's disease; MAT is reference test; exposure to rodent urine/water). Borrelia burgdorferi -> Lyme disease (erythema migrans rash, tick-borne).

4. How are viruses classified by nucleic acid and an example of each major group?

   DNA viruses: mostly double-stranded (Herpesviruses, Adenovirus, Poxvirus, Hepadnavirus); Parvovirus is ssDNA. RNA viruses: mostly single-stranded (Picornavirus, Orthomyxovirus, Retrovirus); Reovirus/Rotavirus is dsRNA.

5. Name the eight human herpesviruses and one disease each.

   HSV-1 (oral herpes), HSV-2 (genital herpes), VZV/HHV-3 (chickenpox/shingles), EBV/HHV-4 (infectious mononucleosis), CMV/HHV-5 (congenital infection), HHV-6/7 (roseola), HHV-8 (Kaposi sarcoma).

6. Which RNA virus causes antigenic shift/drift and what do these terms mean?

   Influenza virus (Orthomyxovirus). Antigenic drift: minor point mutations in HA/NA -> epidemics. Antigenic shift: major reassortment of genome segments -> pandemics.

7. List the five hepatitis viruses with their genome type and route of transmission.

   HAV (RNA, feco-oral), HBV (DNA, parenteral/sexual/vertical), HCV (RNA, parenteral), HDV (RNA defective, needs HBV), HEV (RNA, feco-oral - severe in pregnancy).

8. What does each Hepatitis B serological marker indicate?

   HBsAg: active infection (acute/chronic). Anti-HBs: immunity/recovery or vaccination. HBeAg: high infectivity/replication. Anti-HBc IgM: acute infection. HBV DNA: viral load.

9. What is the marker of the 'window period' in acute Hepatitis B?

   Anti-HBc IgM is the only positive marker during the window period (HBsAg has disappeared and anti-HBs has not yet appeared).

10. What type of virus is HIV, which cells does it infect, and what enzymes does it carry?

    HIV is an enveloped ssRNA retrovirus (Lentivirus); infects CD4+ T cells (via gp120 binding CD4 + CCR5/CXCR4 coreceptors); carries reverse transcriptase, integrase, and protease.

11. Which dermatophyte genera cause superficial mycoses and what are dermatophytes called collectively?

    Trichophyton, Microsporum, and Epidermophyton; collectively called dermatophytes causing tinea (ringworm); they invade keratinized tissue (skin, hair, nails).

12. Match each systemic dimorphic fungus to its endemic clue.

    Histoplasma capsulatum (bird/bat droppings, intracellular in macrophages), Blastomyces dermatitidis, Coccidioides immitis (spherules, desert/SW USA), Paracoccidioides. All are thermally dimorphic (mold at 25 C, yeast at 37 C).

13. Which opportunistic fungus causes infection in neutropenic patients and shows septate acute-angle branching hyphae?

    Aspergillus (especially A. fumigatus); septate hyphae with acute-angle (45 degree, dichotomous) branching. Mucor/Rhizopus show broad aseptate ribbon-like hyphae with wide-angle (90 degree) branching.

14. What is the diagnostic clue for Cryptococcus neoformans and Pneumocystis jirovecii in immunocompromised patients?

    Cryptococcus: India ink shows capsulated yeast in CSF; cryptococcal antigen (CrAg) positive; causes meningitis. Pneumocystis jirovecii: causes PCP pneumonia; cysts seen on silver (GMS) stain, treated with cotrimoxazole.

15. Name the malarial Plasmodium species and which two cause relapses.

    P. falciparum (most severe, cerebral malaria), P. vivax, P. ovale, P. malariae, P. knowlesi. P. vivax and P. ovale cause relapses due to dormant hypnozoites in the liver.

16. Differentiate the cyst and trophozoite features of Entamoeba histolytica from commensal amoebae.

    E. histolytica: mature cyst has 4 nuclei; trophozoite contains ingested RBCs (erythrophagocytosis - pathognomonic), causes amoebic dysentery and liver abscess (anchovy-sauce pus).

17. How is Leishmania transmitted, what form is seen in tissue, and what disease does L. donovani cause?

    Transmitted by sandfly (Phlebotomus) bite; amastigote (LD bodies) form seen intracellularly in macrophages; L. donovani causes kala-azar (visceral leishmaniasis) with fever, splenomegaly, pancytopenia.

18. Classify helminths into the three major groups with an example of each.

    Cestodes (tapeworms - Taenia, Echinococcus), Trematodes (flukes - Schistosoma, Fasciola), Nematodes (roundworms - Ascaris, hookworm, Enterobius, Wuchereria).

19. Differentiate Taenia solium from Taenia saginata and which causes cysticercosis.

    T. solium (pork tapeworm): scolex with rostellum and hooklets, gravid segment has <13 uterine branches; causes neurocysticercosis if eggs ingested. T. saginata (beef tapeworm): no hooklets, >13 branches; no cysticercosis in humans.

20. Which nematode causes lymphatic filariasis, how is it diagnosed, and when is the parasite found in blood?

    Wuchereria bancrofti (and Brugia malayi); diagnosed by demonstrating microfilariae in a nocturnal (night) peripheral blood smear (nocturnal periodicity); causes elephantiasis.

21. What is the difference between exotoxins and endotoxins?

    Exotoxins: secreted proteins, highly toxic, specific action, heat-labile, antigenic (form toxoids), from Gram +/-. Endotoxins: LPS/Lipid A in Gram-negative cell wall, released on lysis, heat-stable, poorly antigenic, non-specific (fever/shock).

22. Define hospital-acquired (nosocomial) infection and name the most common type.

    An infection acquired in a healthcare setting, not present or incubating at admission (typically appearing >48 hours after admission). Catheter-associated urinary tract infection (CAUTI) is the most common nosocomial infection.

23. What does the acronym ESKAPE stand for in hospital-acquired multidrug-resistant pathogens?

    Enterococcus faecium, Staphylococcus aureus (MRSA), Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Enterobacter species - leading MDR nosocomial pathogens.

24. What are the core objectives of an antimicrobial stewardship program?

    Optimize antimicrobial use to improve patient outcomes, reduce resistance, minimize toxicity/adverse effects, and decrease costs - via the 'right drug, right dose, right duration, right route', de-escalation, and audit/feedback.

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