Medical Bacteriology and Parasitology Exam 2024/2025

34 clinical MCQs in Microbiology. Fish are second intermediate hosts of?

Questions, Answers & Explanations

1. Q1. Fish are second intermediate hosts of?

   • Echinostoma ilocaanum
   • Hepatic fascia
   • Fasciolopsis buski
   • Hymenolepis nana
   • Clonorchis sinensis **ANSWER: (e) Clonorchis sinensis**

   Answer: Echinostoma ilocaanum

   Explanation: Fish serve as the second intermediate host for Clonorchis sinensis (Chinese liver fluke). Humans get infected by eating raw or undercooked fish containing the parasite's metacercariae.

2. Q2. Which of the following secretes defensive secretions to cause irritation on human skin?

   • Millipedes
   • Centipedes
   • American killer
   • Enterobius vermicularis
   • All of the above **ANSWER: (a) Millipedes**

   Answer: Millipedes

   Explanation: Millipedes have defensive glands that secrete irritating chemicals (benzoquinones, hydrogen cyanide) causing skin burns and discoloration.

3. Q3. Holometabolous insects have?

   • 2 life stages
   • 3 life stages
   • 4 life stages
   • 5 life stages
   • 1 life stage **ANSWER: (c) 4 life stages**

   Answer: 2 life stages

   Explanation: Holometabolous insects undergo complete metamorphosis with four stages: egg → larva → pupa → adult.

4. Q4. Which of the following transmits parasites for river blindness?

   • Culex species
   • Chrysops species
   • Simulium species
   • Toxorhynchitinae species
   • All of the above **ANSWER: (c) Simulium species**

   Answer: Culex species

   Explanation: Simulium species (blackflies) are the vectors of Onchocerca volvulus, causing river blindness (onchocerciasis).

5. Q5. Which insecticide targets GABA in its action?

   • DDT
   • DEET
   • Permethrin
   • Bendiocarb
   • Malathion **ANSWER: (d) Bendiocarb**

   Answer: DDT

   Explanation: Bendiocarb is a carbamate insecticide that inhibits acetylcholinesterase, affecting GABA neurotransmission.

6. Q6. Presence of triatomine bugs could predispose the population to?

   • Sleeping sickness
   • Leishmaniasis
   • Malaria
   • Chagas disease
   • River blindness **ANSWER: (d) Chagas disease**

   Answer: Sleeping sickness

   Explanation: Triatomine bugs (kissing bugs) transmit Trypanosoma cruzi, which causes Chagas disease.

7. Q7. People living in forested areas are at a risk of?

   • Sleeping sickness
   • Leishmaniasis
   • Malaria
   • Encephalitis
   • River blindness **ANSWER: (b) Leishmaniasis**

   Answer: Sleeping sickness

   Explanation: Forested areas harbor sandflies (Phlebotomus/Lutzomyia species) that transmit Leishmania parasites.

8. Q8. Which of the following insects are commonly found in Latin America?

   • Glossina species
   • Triatomine bugs
   • Cimex species
   • Chrysops species
   • Steam bugs **ANSWER: (b) Triatomine bugs**

   Answer: Glossina species

   Explanation: Triatomine bugs are endemic to Latin America where they transmit Chagas disease. Glossina species (tsetse flies) are found in sub-Saharan Africa.

9. Q9. Pruritus can be best diagnosed for?

   • Sarcoptes scabiei
   • Leptothrombidium species
   • Blattella species
   • Pediculus species
   • Pthirus species **ANSWER: (a) Sarcoptes scabiei**

   Answer: Sarcoptes scabiei

   Explanation: Sarcoptes scabiei (scabies mite) burrows into skin causing intense pruritus (itching), especially at night.

10. Q10. If you found lice eggs (nits) in someone's clothing, what species would they most likely be from?

    • Crab lice
    • Pediculus humanus
    • Pediculus capitis
    • Pthirus species
    • All of the above **ANSWER: (b) Pediculus humanus**

    Answer: Crab lice

    Explanation: Pediculus humanus (body lice) live and lay eggs in clothing seams, unlike head lice which attach to hair.

11. Q11. Which of the following is odd one out in terms of transmission?

    • Vibrio cholerae
    • Entamoeba histolytica
    • Rotavirus
    • Thelazia species
    • None of the above **ANSWER: (d) Thelazia species**

    Answer: Vibrio cholerae

    Explanation: Thelazia species (eye worm) is transmitted by flies (mechanical vectors), while the others are fecal-oral.

12. Q12. Which one of the following is larviparous?

    • Phlebotomus species
    • Lutzomyia species
    • Triatomine bugs
    • Glossina gambiense
    • Dermacentor species **ANSWER: (d) Glossina gambiense**

    Answer: Phlebotomus species

    Explanation: Glossina species (tsetse flies) are larviparous—they give birth to live larvae rather than laying eggs.

13. Q13. Argasid ticks have?

    • One host
    • Two hosts
    • Three hosts
    • Multiple hosts
    • Four hosts **ANSWER: (d) Multiple hosts**

    Answer: One host

    Explanation: Argasid (soft) ticks are multi-host ticks that feed quickly on different hosts throughout their life stages.

14. Q14. Ixodid ticks have nymphal stages.

    • One
    • Two
    • Three
    • Four
    • Multiple **ANSWER: (a) One**

    Answer: One

    Explanation: Ixodid (hard) ticks have a single nymphal stage: egg → larva → nymph → adult.

15. Q15. Traps for Aedes mosquitoes are composed of?

    • Black and white colors
    • Black and blue colors
    • White and blue colors
    • White only
    • Black only **ANSWER: (a) Black and white colors**

    Answer: Black and white colors

    Explanation: Aedes mosquitoes are attracted to contrasting black and white patterns.

16. Q16. Traps for Glossina species are composed of?

    • Black and white colors
    • Black and blue colors
    • White and blue colors
    • White only
    • Black only **ANSWER: (b) Black and blue colors**

    Answer: Black and white colors

    Explanation: Tsetse flies (Glossina species) are attracted to black and blue colors.

17. Q17. Black water disease is due to presence of in the environment.

    • Simulium species
    • Anopheles species
    • Culicoides species
    • Lutzomyia species
    • Musca species **ANSWER: (b) Anopheles species**

    Answer: Simulium species

    Explanation: Blackwater fever is a complication of falciparum malaria, transmitted by Anopheles mosquitoes.

18. Q18. Hepatitis B virus has been associated with?

    • Cimex species
    • Xenopsylla species
    • Pthirus species
    • Tabanids species
    • Steam bugs **ANSWER: (a) Cimex species**

    Answer: Cimex species

    Explanation: Cimex species (bed bugs) have been studied for potential mechanical transmission of Hepatitis B.

19. Q19. Which of the following statements regarding vaccination for Bacillus anthracis is correct?

    • It is routinely available for all citizens
    • Recombinant vaccine trials have shown good safety and efficacy
    • The current vaccine is well tolerated
    • A single dose is adequate after exposure to spores
    • Vaccination of animals is not useful **ANSWER: (b) Recombinant vaccine trials have shown good safety and efficacy**

    Answer: It is routinely available for all citizens

20. Q20. Lowenstein Jensen media is used to isolate?

    • Streptococcus species
    • Proteus species
    • coli
    • Mycobacterium tuberculosis
    • None of the above **ANSWER: (d) Mycobacterium tuberculosis**

    Answer: Streptococcus species

    Explanation: LJ medium is an egg-based selective medium for culturing mycobacteria.

21. Q21. All of the following statements regarding Clostridium perfringens are correct EXCEPT:

    • It produces an enterotoxin
    • It produces a double zone of β-hemolysis when grown on blood agar
    • Some strains are aerotolerant
    • It is the most common cause of antibiotic-associated diarrhea
    • It can cause intravascular hemolysis **ANSWER: (d) It is the most common cause of antibiotic-associated diarrhea**

    Answer: It produces an enterotoxin

    Explanation: Clostridioides difficile is the primary cause of antibiotic-associated diarrhea.

22. Q22. Motility of the bacteria can be observed by:

    • Hanging drop method
    • Soft agar method
    • Both "A" and "B"
    • Pour plate method
    • All the above **ANSWER: (c) Both "A" and "B"**

    Answer: Hanging drop method

23. Q23. A 53-year-old woman with breast cancer develops a cough and progressive weakness. Gram stain of sputum shows branching gram-positive rods that were partially acid fast. Which organism is the cause?

    • Actinomyces israelii
    • Corynebacterium pseudodiphtheriticum
    • Aspergillus fumigatus
    • Nocardia farcinica
    • Erysipelothrix rhusiopathiae **ANSWER: (d) Nocardia farcinica**

    Answer: Actinomyces israelii

    Explanation: Branching gram-positive, partially acid-fast rods in an immunocompromised patient with pulmonary and CNS symptoms are characteristic of Nocardia.

24. Q24. The drug of choice to treat Nocardia infection is:

    • Penicillin G
    • Trimethoprim-sulfamethoxazole
    • Gentamicin
    • Amphotericin B
    • A third-generation cephalosporin **ANSWER: (b) Trimethoprim-sulfamethoxazole**

    Answer: Penicillin G

25. Q25. Which can cause food INTOXICATION?

    • Staphylococcus aureus
    • Streptococcus pyogenes
    • coli
    • Salmonella
    • None above **ANSWER: (a) Staphylococcus aureus**

    Answer: Staphylococcus aureus

    Explanation: S. aureus produces preformed enterotoxins in food.

26. Q26. Helicobacter pylori possesses that helps to neutralize stomach acid (HCl).

    • Coagulase
    • Urease
    • Hyaluronidase
    • Catalase
    • Lipase **ANSWER: (b) Urease**

    Answer: Coagulase

27. Q27. An 8-year-old boy with a grayish pseudomembrane over the tonsils. The cause is most likely:

    • A gram-negative bacillus
    • A single-stranded positive-sense RNA virus
    • A catalase-positive gram-positive coccus
    • A club-shaped gram-positive bacillus
    • A double stranded RNA virus **ANSWER: (d) A club-shaped gram-positive bacillus**

    Answer: A gram-negative bacillus

    Explanation: This describes Corynebacterium diphtheriae.

28. Q28. The primary mechanism in the pathogenesis of diphtheria is:

    • Increase in cAMP
    • Action of superantigen
    • Inactivation of acetylcholine esterase
    • Action of enterotoxin A
    • Inactivation of elongation factor 2 **ANSWER: (e) Inactivation of elongation factor 2**

    Answer: Increase in cAMP

29. Q29. Which of the following aerobic gram-positive bacilli is modified acid-fast positive?

    • Nocardia brasiliensis
    • Lactobacillus acidophilus
    • Erysipelothrix rhusiopathiae
    • Listeria monocytogenes **ANSWER: (a) Nocardia brasiliensis**

    Answer: Nocardia brasiliensis

30. Q30. A fisherman with a violaceous nodule on his finger. Culture shows gram-positive bacilli causing greenish discoloration and long filaments in broth. The cause is:

    • Lactobacillus acidophilus
    • Erysipelothrix rhusiopathiae
    • Listeria monocytogenes
    • Rhodococcus equi
    • Nocardia brasiliensis **ANSWER: (b) Erysipelothrix rhusiopathiae**

    Answer: Lactobacillus acidophilus

31. Q31. A biochemical reaction useful in the identification of Erysipelothrix rhusiopathiae is:

    • Catalase positivity
    • Acid fastness
    • Esculin hydrolysis
    • Tumbling motility
    • Production of H2S **ANSWER: (e) Production of H2S**

    Answer: Catalase positivity

32. Q32. A catheterized patient develops bladder stones. Urine culture grows a short, irregular gram-positive rod. The organism is:

    • Corynebacterium urealyticum
    • Nocardia brasiliensis
    • Actinomadura
    • Erysipelothrix **ANSWER: (a) Corynebacterium urealyticum**

    Answer: Corynebacterium urealyticum

33. Q33. Drug of choice for treatment of mycoplasma infection are:

    • Tetracycline
    • Erythromycin
    • A and B
    • Penicillin **ANSWER: (c) A and B**

    Answer: Tetracycline

34. Q34. The mode of spread of tetanus neurotoxin from blood to brain is via:

    • Lymphatics
    • Arterial blood
    • Cranial nerve
    • None of the above **ANSWER: (d) None of the above**

    Answer: Lymphatics

    Explanation: Tetanus toxin spreads via retrograde axonal transport.