AIIMS/ NEET-PG 2017: Microbiology MCQs 101-110

Q-101. Reverse transcriptase enzyme present in
a) HAV
b) HBV
c) HCV
d) HEV

Answer: HBV
Explanation:
HBV is a member of the hepadnavirus family. It is a 42 nm enveloped virion with icosahedral nucleo-capsid core containing a partially double stranded circular DNA genome.
Within the core of HBV is a DNA polymerase. The DNA polymerase has both RNA dependent (Reverse transcriptase) and DNA dependent activity.

Q-102. Cholera toxin causes destruction of
a) Hemi-desmosomes
b) Gap junctions
c) Tight junction or occludens
d) Zona adherens

Answer: Tight junction or occludens
Explanation:
Cholera toxin (CTX) is one of the main virulence factors of Vibrio cholerae.
Cholera toxin (CTX) consists of an A subunit and a B subunit.
B subunit (CTXB) binds to ganglioside GM1 on the surface of the enterocytes.
The A subunit (CTXA) is inserted into the cytosol. CTXA induces water and electrolyte secretion by increasing cAMP levels via adenylate cyclase (AC).
Vibrio cholerae generates Zonula occludens toxin (ZOT) that causes tight junction disruption through protein kinase C-dependent actin polymerization.

Q-103. RNA dependent DNA polymerase used by
a) Hepatitis A
b) Hepatitis B
c) Hepatitis C
d) Hepatitis E

Answer: Hepatitis B
Explanation:
HBV is a member of the hepadnavirus family. It is a 42 nm enveloped virion with icosahedral nucleo-capsid core containing a partially double stranded circular DNA genome.
Within the core of HBV is a DNA polymerase. The DNA polymerase has both RNA dependent (Reverse transcriptase) and DNA dependent activity.

Q-104. Tropical spastic para-paresis caused by
a) HTLV
b) HIV
c) Polyoma virus
d) HBV

Answer: HTLV
Explanation:
Diseases caused by HTLV (Human retro-virus):
Adult T cell leukemia/ lymphoma
HTLV associated myelopathy or chronic progressive myelopathy or Tropical spastic para-paresis

Q-105. Filarial stage of adult worms responsible for diseases in all of the following except:
a) Onchocerca volvulus
b) Brugia
c) Wuchereria
d) Mansonella ozzardi

Answer: Onchocerca volvulus
Explanation:
The filarial nematodes which parasitize man consist of Wuchereria bancrofti, Brugia malayi, Brugia timori and Loa-loa, Onchocerca volvulus, Mansonella perstans, Mansonella streptocerca and Dipetalonema streptocerca.
Onchocerca volvulus primarily affects the skin, eyes and lymph nodes. Damage in Onchocerciasis is caused by microfilaria and not by adult parasites.

Q-106. Microscopy on Tzank smear of vesicle on skin showed giant cells. Diagnosis is
a) Vaccinia virus
b) Varicella zoster
c) Mycobacterium
d) Molluscum contagiosum

Answer: Varicella zoster
Explanation:
Tzank smear finding in bullous disorder:
Acantholytic cells- Pemphigus
Predominantly eosinophil- Bullous pemphigoid
Predominantly neutrophil- Chronic bullous disease of childhood
Multinucleated giant cells- Varicella zoster and herpes simplex
Necrotic cells- Toxic epidermal necrosis
Important point:
Giemsa stain is used to stain specimen.

Q-107. Mechanism by which students view this image
a) Cathode ray tube
b) Dark field/ Phase condenser
c) Dichroic mirror
d) Phase plate

Answer: Dichroic mirror
Explanation:
The basic function of a fluorescence microscope is to irradiate the specimen with a desired and specific band of wavelengths, and then to separate the much weaker emitted fluorescence from the excitation light.
In a properly configured microscope, only the emission light should reach the eye or detector so that the resulting fluorescent structures are superimposed with high contrast against a very dark background.
Important point:
Dichroic mirror is used to separate the much weaker emitted fluorescence from the excitation light. It reflects blue light but allow green light in specimen stained with fluorescent dye and illuminated with blue light.

Q-108. Most cost effective way to prevent infection:
a) Hand washing
b) Antibiotic
c) Chemoprophylaxis
d) Culture sensitivity

Answer: Hand washing
Explanation:
Most cost effective method for preventing infection is hand washing.
Proper hand hygiene is the single most important, simplest, and least expensive means of reducing the infections.

Q-109. Identify the organism in the given figure?
a) Histoplasmosis
b) Candida
c) Cryptococcus
d) Coccidiodomycosis

Answer: Cryptococcus
Explanation:
Cryptococcosis (Torulosis) is a sub-acute or chronic infection caused by the yeast Cryptococcus neoformans.
Diagnosis is established by demonstration of capsulated, budding yeast cells in the lesions and by culture.
Indian ink preparation of spinal fluid shows yeast cells surrounded by a large capsule.

Q-110. Stool sample from a patient shows the following. How do humans get this infection?
a) Ingestion with food
b) Work in dirty water
c) Improperly
d) Direct contact

Answer: Ingestion with food
Explanation:
Trichuris trichiura:
Trichuris trichiura causes whipworm infection or trichuriasis.
Humans are infected by the ingesting worm eggs in food or water contaminated with human feces.
Trichuris may cause diarrhoea. Trichuris may also cause rectal prolapse in children with heavy infection.
Diagnosis is based on finding the typical egg, ie, barrel shaped or lemon shaped with a plug at each end in stool.
Mebendazole is drug of choice.