JKSSB Junior Microbiologist 2025 Solved Question Paper

Question 1

Which medium is selectively used for isolating Gram-negative bacteria from a mixed culture?

Accepted Answer

Option B: MacConkey agar. MacConkey agar is a selective and differential culture medium designed to isolate and differentiate Gram-negative enteric bacilli. It contains bile salts and crystal violet dye, which selectively inhibit the growth of Gram-positive organisms, while neutral red serves as a pH indicator to differentiate lactose fermenters (pink colonies) from non-fermenters (colorless colonies).

Question 2

The hanging drop technique is primarily utilized to examine bacterial:

Accepted Answer

Option C: Motility behaviour. The hanging drop technique is a classic microscopic wet mount preparation used to observe the motility behavior of living, unstained microorganisms in a suspended fluid droplet within a concave cavity slide, allowing true directional flagellar movement to be distinguished from passive Brownian motion.

Question 3

During Gram staining, iodine functions as a:

Accepted Answer

Option C: Mordant. In the Gram stain procedure, Gram's iodine functions as a mordant. It chemically interacts with the primary dye (crystal violet) inside the bacterial cell wall to form large, water-insoluble crystal violet-iodine (CV-I) complexes, which become trapped within the thick, multi-layered peptidoglycan mesh of Gram-positive bacteria.

Question 4

Ziehl-Neelsen staining is specifically designed to visualize:

Accepted Answer

Option C: Acid-fast organisms. The Ziehl-Neelsen (acid-fast) staining technique is specifically designed to visualize acid-fast organisms, predominantly Mycobacterium tuberculosis and Mycobacterium leprae. Their cell walls contain high concentrations of waxy mycolic acids that resist decolorization by mineral acid-alcohol solutions.

Question 5

The Methyl Red (MR) biochemical test is employed to detect:

Accepted Answer

Option C: Mixed acid fermentation pathway. The Methyl Red (MR) test (part of the IMViC battery) determines whether a bacterium ferments glucose via the mixed acid fermentation pathway. Organisms like E. coli produce stable, large quantities of mixed organic acids (lactic, acetic, succinic, formic), driving broth pH below 4.4, which turns the methyl red indicator bright red.

Question 6

The pelvic bone is a composite of which three fused structures?

Accepted Answer

Option A: Ilium, ischium, and pubis. Each hip bone (os coxae / pelvic bone) is formed embryologically by the fusion of three separate bones at the acetabular triradiate cartilage: the superior, fan-shaped Ilium, the posteroinferior Ischium, and the anteroinferior Pubis.

Question 7

Which hormone is secreted by the parafollicular (C) cells of the thyroid gland?

Accepted Answer

Option C: Calcitonin. The parafollicular cells (also known as C cells) scattered in the connective tissue between thyroid follicles secrete Calcitonin. Calcitonin is a 32-amino acid polypeptide hormone that decreases plasma calcium concentrations by inhibiting osteoclast bone resorption.

Question 8

The limbic system plays a central role in:

Accepted Answer

Option C: Regulating emotions and forming memories. The limbic system (comprising the hippocampus, amygdala, cingulate gyrus, and hypothalamus) is the emotional and motivational control center of the brain. It is critically responsible for emotional regulation, fear conditioning, autonomic drives, and the consolidation of short-term into long-term memories.

Question 9

Which structure listed below is anatomically considered part of the Peripheral Nervous System (PNS), not the Central Nervous System (CNS)?

Accepted Answer

Option C: Optic nerve. The Central Nervous System (CNS) consists strictly of the Brain, Cerebellum, Brainstem, and Spinal Cord. All cranial and spinal nerves connecting peripheral organs to the central neuraxis are anatomically classified under the Peripheral Nervous System (PNS). The Optic Nerve (Cranial Nerve II) is thus listed under PNS cranial nerves in standard anatomical classifications.

Question 10

Which ligament is recognized as the strongest in the human body due to its role in stabilizing the hip joint?

Accepted Answer

Option B: Iliofemoral ligament. The Iliofemoral ligament (also known as the ligament of Bigelow or Y-ligament of the hip) is the strongest ligament in the human body, boasting a tensile strength of over 350 kg. Located on the anterior aspect of the hip joint capsule, it prevents excessive hyperextension of the hip while maintaining erect posture.

Question 11

The right lung is anatomically divided into:

Accepted Answer

Option B: Three lobes and two fissures. The right lung is anatomically larger than the left lung and is divided into three lobes (Superior, Middle, and Inferior lobes) separated by two distinct fissures: the Oblique fissure and the Horizontal fissure. (The left lung has two lobes and one fissure).

Question 12

Which muscle group is located anteriorly on the thigh?

Accepted Answer

Option C: Quadriceps femoris. The Quadriceps femoris (comprising rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius) is the massive extensor muscle group situated in the anterior compartment of the thigh, innervated by the femoral nerve.

Question 13

Which ISO standard specifically governs laboratory quality management systems?

Accepted Answer

Option B: ISO 15189. ISO 15189 ('Medical laboratories - Requirements for quality and competence') is the international gold standard that specifically governs quality management systems in clinical, medical, and diagnostic laboratories. (ISO 17025 applies to general testing and calibration laboratories, while ISO 9001 is a generic corporate QMS).

Question 14

Which law ensures biosafety compliance in Indian biomedical laboratories?

Accepted Answer

Option B: Environmental Protection Act, 1986. In India, biosafety compliance for genetically modified organisms and hazardous microorganisms is legally grounded under the Environment (Protection) Act, 1986 (EPA 1986) through the 'Rules for the Manufacture, Use, Import, Export and Storage of Hazardous Microorganisms/Genetically Engineered Organisms or Cells, 1989', implemented via IBSC, RCGM, and GEAC.

Question 15

An example of a biosafety level 3 (BSL-3) pathogen is:

Accepted Answer

Option C: Mycobacterium tuberculosis. Mycobacterium tuberculosis is a classified Risk Group 3 (BSL-3) pathogen. Because it causes severe and potentially lethal pulmonary disease primarily via aerosol transmission, it must be handled in BSL-3 facilities with negative pressure airflow and HEPA filtration.

Question 16

Which biosafety cabinet class provides protection for both personnel and laboratory materials?

Accepted Answer

Option B: Class II. Class II Biosafety Cabinets (BSCs) provide three-way protection: personnel protection (via inward face velocity air curtain), product/material protection (via HEPA-filtered vertical laminar downflow over the work area), and environmental protection (via HEPA-filtered exhaust). Class I protects only personnel and environment; horizontal laminar flow clean benches protect only the product.

Question 17

Which of the following systems is designed to perpetually maintain microbial populations at steady-state growth by continuous nutrient supply and waste removal?

Accepted Answer

Option B: Chemostatic reactor. A chemostat (chemostatic reactor) is an open continuous culture bioreactor system designed to maintain microbial populations at a permanent exponential steady-state. Sterile fresh nutrient medium is introduced at a fixed dilution rate ($D$) while spent culture containing cells and metabolites is removed at the exact same rate.

Question 18

Which environmental condition most commonly initiates the stringent response in prokaryotic cells, leading to altered gene expression?

Accepted Answer

Option B: Deprivation of nutritional substrates. The stringent response in bacteria is an adaptive stress response triggered primarily by the deprivation of amino acids (nutritional substrate starvation). Uncharged tRNAs binding to the ribosomal A-site activate RelA to synthesize the alarmone (p)ppGpp, which shuts down rRNA/tRNA transcription and redirects resources to amino acid biosynthesis.

Question 19

Among the following, which method is categorized as indirect for assessing microbial proliferation by quantifying biomass-related optical properties?

Accepted Answer

Option B: Spectrophotometric turbidity analysis. Spectrophotometric turbidity analysis (optical density, OD600) is an indirect method of measuring microbial biomass. It measures the degree of light scattering by cell suspensions rather than physically counting individual viable or total cells.

Question 20

A culture exhibits an increase in optical density from 0.2 to 1.6 over 6 hours. If the doubling time is 1.5 hours, how many generations have occurred?

Accepted Answer

Option C: Four. The number of generations ($n$) is calculated from total incubation time ($t$) and the generation/doubling time ($g$): $n = \frac{t}{g} = \frac{6	ext{ hours}}{1.5	ext{ hours}} = 4	ext{ generations}$. (Note that in exponential growth, 4 generations yields $2^4 = 16	imes$ growth; from $0.2 	imes 2^3 = 1.6$ represents three doublings in OD reading, but based strictly on time and doubling time parameter $6 / 1.5 = 4$).

Question 21

Which among the following fungi exhibits thermal dimorphism-existing in mold form at lower temperatures and yeast form at body temperature?

Accepted Answer

Option C: Histoplasma capsulatum. Histoplasma capsulatum is a classic thermally dimorphic endemic systemic fungal pathogen. In nature or in vitro at ambient temperatures (25°C), it grows as a saprophytic mold with tuberculate macroconidia; at mammalian body temperature (37°C), it converts into a small parasitic yeast inside reticuloendothelial macrophages.

Question 22

Which staining technique is preferred for demonstrating polysaccharide-rich fungal cell walls in histopathological tissue sections?

Accepted Answer

Option B: Periodic Acid-Schiff (PAS) stain. The Periodic Acid-Schiff (PAS) reaction is the standard histopathological stain for fungi. Periodic acid selectively oxidizes the vicinal diols of cell-wall structural polysaccharides (glucan, mannan, chitin) into aldehydes, which react with Schiff's leucofuchsin reagent to produce an intense, diagnostic bright magenta/pink staining.

Question 23

A filamentous fungus that forms septate hyphae and produces large, multicelled macroconidia most likely belongs to:

Accepted Answer

Option B: Trichophyton rubrum. Trichophyton rubrum is an anthropophilic dermatophyte featuring septate hyphae that produces characteristic pencil- or cigar-shaped, thin-walled, multi-celled macroconidia (along with teardrop microconidia). Candida and Cryptococcus are unicellular yeasts, while Malassezia forms unbranched short hyphae with yeast cells.

Question 24

Fungal invasion of the corneal tissue resulting in ocular infection is referred to as:

Accepted Answer

Option B: Keratomycosis. Fungal infection of the cornea is clinically known as 'Keratomycosis' (or fungal keratitis), frequently caused by Fusarium, Aspergillus, or Candida following vegetative ocular trauma. (Otomycosis affects the external ear canal; Mycetoma affects subcutaneous tissue).

Question 25

Identify the non-pathogenic yeast frequently employed in industrial fermentation processes like baking and brewing:

Accepted Answer

Option A: Saccharomyces cerevisiae. Saccharomyces cerevisiae (baker's and brewer's yeast) is the non-pathogenic model budding yeast used universally in commercial bread baking, ethanol brewing, winemaking, and recombinant biotechnology.

Question 26

Which encapsulated yeast is urease-positive and associated with meningoencephalitis in immunocompromised individuals, particularly those with AIDS?

Accepted Answer

Option B: Cryptococcus neoformans. Cryptococcus neoformans is an encapsulated, urease-positive basidiomycetous yeast. In severely immunocompromised individuals (such as patients with advanced HIV/AIDS, CD4 < 100/uL), it disseminates to the central nervous system to cause life-threatening subacute cryptococcal meningoencephalitis.

Question 27

Which culture medium is specifically formulated to enhance the growth of fungi while inhibiting bacterial contaminants in clinical samples?

Accepted Answer

Option A: Sabouraud Dextrose Agar (SDA). Sabouraud Dextrose Agar (SDA), developed by Raymond Sabouraud, has an acidic pH (~5.6) and high dextrose content (4%) that selectively supports fungal proliferation while suppressing bacterial overgrowth. Antibacterial agents like chloramphenicol and gentamicin are frequently added.

Question 28

A researcher performing native PAGE zymography for gelatinase detection observes no enzymatic bands after gel incubation. What is the most probable cause of this observation?

Accepted Answer

Option B: Omission of gelatin substrate from the polyacrylamide gel formulation. In substrate zymography, the target substrate (e.g., gelatin for MMP-2/MMP-9 gelatinases) must be copolymerized directly into the resolving polyacrylamide gel during casting. If gelatin substrate is omitted during gel preparation, no substrate is present for the migrated protease to digest, resulting in complete failure to produce clear lytic bands against the Coomassie background.

Question 29

According to Beer-Lambert law, absorbance in UV-Vis spectrophotometry is proportionally related to:

Accepted Answer

Option B: Both solute concentration and optical path length. The Beer-Lambert law states that absorbance ($A$) is directly proportional to both the molar concentration of the absorbing solute ($c$) and the optical path length of the cuvette ($l$): $A = \varepsilon \cdot c \cdot l$, where $\varepsilon$ is the molar extinction coefficient.

Question 30

Which chromogenic compound is utilized in the Bradford method for quantitative determination of proteins?

Accepted Answer

Option D: Coomassie Brilliant Blue G-250 dye. The Bradford protein assay is a rapid colorimetric method utilizing Coomassie Brilliant Blue G-250 dye. In acidic solution, binding of the dye to basic and aromatic amino acid residues converts the red/brown cationic form (465 nm) into the unprotonated blue anionic form, shifting the absorption maximum to 595 nm.

Question 31

In a zymographic enzyme assay, what is the critical step performed post-electrophoresis to reveal enzymatic activity within the gel?

Accepted Answer

Option B: Incubation in a suitable buffer to allow substrate hydrolysis. Following electrophoresis and Triton X-100 washing (which removes SDS to allow enzyme renaturation), the crucial step in zymography is incubating the gel in an optimal reaction buffer (typically with $Ca^{2+}$ and $Zn^{2+}$ at 37°C) to allow the active immobilized enzymes to hydrolyze the copolymerized substrate.

Question 32

Which aromatic amino acid residues predominantly absorb at 280 nm during UV-based protein quantification?

Accepted Answer

Option C: Tryptophan and Tyrosine. Proteins exhibit a characteristic ultraviolet absorbance peak at 280 nm primarily due to the aromatic resonance rings of Tryptophan (indole ring, $\lambda_{max} \approx 280	ext{ nm}$) and Tyrosine (phenolic ring, $\lambda_{max} \approx 274	ext{ nm}$), with minor contribution from cystine disulfides.

Question 33

Ammonium sulfate is employed in protein purification protocols primarily to:

Accepted Answer

Option C: Reduce protein solubility and induce selective precipitation. Ammonium sulfate fractionation operates on the 'salting out' principle. High kosmotropic salt concentrations strip the hydration shell from exposed hydrophobic patches on protein surfaces, promoting hydrophobic aggregation and reversible precipitation without denaturing the native protein.

Question 34

To resolve high molecular weight proteins more effectively during PAGE, which of the following should be adjusted?

Accepted Answer

Option B: Reduction in acrylamide concentration. The pore size of a polyacrylamide gel is inversely proportional to total acrylamide monomer concentration (%T). To resolve high molecular weight proteins (>100-200 kDa), the acrylamide concentration must be reduced (e.g. to 6% or 7.5%) to enlarge the gel pore matrix, allowing large macromolecular complexes to migrate without getting excluded at the top.

Question 35

Which anticoagulant-preservative combination is routinely employed for accurate blood glucose determination in clinical samples?

Accepted Answer

Option B: Sodium fluoride with potassium oxalate. Gray-top vacutainer tubes containing Sodium fluoride and Potassium oxalate are standard for glucose estimation. Sodium fluoride acts as an antiglycolytic agent by irreversibly inhibiting the glycolytic enzyme enolase, preventing in vitro RBC glucose breakdown, while potassium oxalate prevents coagulation by chelating calcium.

Question 36

Which analytical instrument is primarily used in clinical biochemistry laboratories for lipid profile assessment (e.g., cholesterol, HDL, LDL)?

Accepted Answer

Option C: Spectrophotometric autoanalyzer. Clinical biochemistry laboratories utilize automated, high-throughput Spectrophotometric Autoanalyzers (clinical chemistry analyzers) to perform enzymatic, photometric absorbance assays measuring total cholesterol, triglycerides, HDL, and calculating LDL.

Question 37

Which classical biochemical method is employed for quantifying total serum proteins by forming a violet-colored complex with peptide bonds?

Accepted Answer

Option C: Biuret method using copper ions.. The Biuret reaction is the classical clinical method for total protein quantification. Cupric ions ($Cu^{2+}$) in an alkaline medium react with the nitrogens of four or more peptide bonds to form a characteristic purple/violet coordination complex absorbing at 540 nm.

Question 38

For evaluating exocrine pancreatic function, which of the following enzymes is most commonly measured in serum?

Accepted Answer

Option C: Alpha-amylase. Serum Alpha-amylase (along with lipase) is the primary clinical biomarker assessed to evaluate exocrine pancreatic function and diagnose acute pancreatitis. During inflammation, acinar cells release amylase into the bloodstream, peaking within 12–24 hours.

Question 39

In cases of nephrotic syndrome, which serum protein typically exhibits a marked decrease due to urinary loss?

Accepted Answer

Option B: Albumin. In nephrotic syndrome, disruption of the glomerular filtration barrier (podocyte effacement and loss of negative charge) leads to massive proteinuria (>3.5 g/day). Because of its small molecular weight (66.5 kDa), Albumin is selectively filtered and lost in urine, causing profound hypoalbuminemia.

Question 40

Which of the following factors exerts the least influence on blood urea concentration?

Accepted Answer

Option C: Hyperthyroid metabolic state. Blood urea nitrogen (BUN) is profoundly impacted by renal excretion efficiency (chronic renal failure), renal perfusion (prerenal azotemia from dehydration), and substrate load (high protein catabolism). A hyperthyroid state marginally increases turnover but exerts the least direct influence on circulating urea levels among the choices.

Question 41

Which AST:ALT ratio is most suggestive of chronic alcoholic liver disease?

Accepted Answer

Option B: AST: ALT greater than 2. In alcoholic liver disease, the serum AST (aspartate aminotransferase) to ALT (alanine aminotransferase) ratio (De Ritis ratio) is characteristically greater than 2 (often exceeding 2:1 or even 3:1). Alcohol causes direct mitochondrial damage that preferentially releases mitochondrial AST into circulation, while alcoholics commonly suffer from pyridoxal 5'-phosphate (vitamin B6) deficiency, which impairs ALT synthesis more severely than AST synthesis.

Question 42

Which of the following viruses is frequently utilized as a vector in gene therapy due to its ability to infect a wide range of human cells?

Accepted Answer

Option C: Adenovirus. Adenoviruses are widely employed as vectors in gene therapy and recombinant vaccine platforms because of their exceptional transduction efficiency across a broad spectrum of dividing and quiescent human cell types, high nuclear entry efficiency without chromosomal integration (reducing insertional mutagenesis risks), and substantial cloning capacity for therapeutic transgene inserts.

Question 43

Which bacteriophage replication pathway involves integration of viral DNA into the bacterial host genome?

Accepted Answer

Option B: Lysogenic cycle. In the lysogenic cycle of temperate bacteriophages (such as phage lambda), viral DNA is integrated into the host bacterial chromosome where it persists as a dormant prophage. The viral genome is replicated faithfully along with host DNA during binary fission without causing immediate lysis of the bacterial cell.

Question 44

Which diagnostic technique offers the highest sensitivity for detecting HIV infection during its early phase?

Accepted Answer

Option C: Reverse transcription-polymerase chain reaction (RT-PCR). Reverse transcription-polymerase chain reaction (RT-PCR) offers the highest analytical sensitivity for detecting acute HIV infection during the initial 'window period' (first 10–14 days). RT-PCR directly amplifies and quantifies circulating viral genomic RNA in plasma days to weeks before host anti-HIV IgM/IgG antibodies or p24 antigen become detectable by serological or Western blot assays.

Question 45

Retroviruses employ which enzyme for replication, enabling the conversion of viral RNA into DNA?

Accepted Answer

Option C: RNA-dependent DNA polymerase (reverse transcriptase). Retroviruses encode the unique multifunctional enzyme RNA-dependent DNA polymerase (reverse transcriptase). This enzyme utilizes the single-stranded positive-sense viral RNA genome as a template to synthesize complementary single-stranded DNA (cDNA), degrades the RNA template via RNase H activity, and synthesizes a double-stranded proviral DNA that integrates into the host genome.

Question 46

The measles vaccine administered in immunization programs is classified as a:

Accepted Answer

Option B: Live attenuated vaccine. The measles vaccine (such as the Edmonston-Enders strain, administered alone or combined as MMR/MR) is a live attenuated viral vaccine. It contains live virus particles that have been weakened through repeated passage in chick embryo cell culture, allowing them to replicate and stimulate lifelong humoral and cellular immunity without provoking clinical disease.

Question 47

Which form of Entamoeba histolytica is infectious to humans?

Accepted Answer

Option B: Cyst. The mature, quadrinucleate cyst of Entamoeba histolytica is the infective form that transmits amoebiasis to humans through fecal-oral ingestion of contaminated water or raw food. Its thick chitinous cyst wall allows it to survive in the external environment and resist the acidic gastric barrier, whereas fragile motile trophozoites are rapidly degraded by gastric acid.

Question 48

Plasmodium falciparum primarily targets which cells in the body?

Accepted Answer

Option B: Red blood cells. Plasmodium falciparum primarily targets and destroys red blood cells (erythrocytes) during its asexual erythrocytic schizogonic cycle. Unlike Plasmodium vivax (which selectively infects immature reticulocytes), P. falciparum is capable of invading erythrocytes of all ages, leading to massive parasitemia, severe hemolytic anemia, microvascular clogging, and cerebral malaria.

Question 49

Which P. falciparum stage is transmitted to mosquitoes?

Accepted Answer

Option C: Gametocyte. The sexual erythrocytic stages known as gametocytes (crescent- or banana-shaped microgametocytes and macrogametocytes in P. falciparum) are ingested by female Anopheles mosquitoes during a blood meal. Inside the mosquito gut, gametocytes exflagellate, fertilize, and initiate the sporogonic cycle that produces infectious sporozoites.

Question 50

'Winterbottom's sign' is typically associated with which parasitic infection?

Accepted Answer

Option B: Trypanosoma brucei gambiense. Winterbottom's sign refers to marked enlargement and non-tender swelling of the posterior cervical lymph nodes along the posterior triangle of the neck. It is a classic clinical indicator of the early hemolymphatic phase of West African human sleeping sickness (African trypanosomiasis) caused by Trypanosoma brucei gambiense transmitted by the tsetse fly (Glossina).

Question 51

What sample is typically used for diagnosing kala-azar (visceral leishmaniasis)?

Accepted Answer

Option B: Bone marrow biopsy. Bone marrow aspirate or biopsy (along with splenic puncture) is the standard and safest routine clinical specimen collected to diagnose visceral leishmaniasis (kala-azar caused by Leishmania donovani). Microscopic examination of Giemsa-stained smears reveals intracellular amastigotes (Leishman-Donovan bodies) inside mononuclear phagocytic cells.

Question 52

In a Giardia lamblia infection, which part of the gastrointestinal tract is most affected?

Accepted Answer

Option B: Duodenum. Giardia lamblia (Giardia duodenalis) trophozoites preferentially colonize the duodenum and upper jejunum of the human small intestine. They adhere firmly to the microvillus brush border of intestinal enterocytes using their specialized ventral sucking disc, causing mechanical irritation, brush border enzyme suppression, and malabsorption.

Question 53

Which condition is marked by the presence of fatty stools (steatorrhea)?

Accepted Answer

Option C: Giardia lamblia infection. Giardia lamblia infection classically manifests with steatorrhea (pale, greasy, foul-smelling, non-bloody stools that float). Attachment of vast numbers of trophozoites causes extensive mechanical coverage of the duodenal mucosa, blunting of microvilli, and impaired micellar fat breakdown, resulting in fat malabsorption.

Question 54

What is the most suitable technique to detect microfilariae in peripheral blood?

Accepted Answer

Option D: Thick blood smear. A thick blood smear (dehemoglobinized and stained with Giemsa or Leishman stain) collected during nocturnal hours (10:00 PM to 2:00 AM) is the gold standard diagnostic method to detect circulating microfilariae of Wuchereria bancrofti or Brugia malayi, as it concentrates a larger volume of blood on a small slide area to identify low parasitemia.

Question 55

Which parasite is known to cause chyluria as a result of lymphatic obstruction?

Accepted Answer

Option A: Wuchereria bancrofti. Wuchereria bancrofti is the lymphatic filarial parasite that resides in human lymph nodes and major vessels. Chronic infection causes inflammatory damage, fibrosis, and severe obstruction of retroperitoneal lymph vessels, raising lymphatic pressure until dilated lymphatics rupture into the renal pelvic tract, producing chyluria (milky urine containing lymph and emulsified fat).

Question 56

Which of the following viruses has a double-stranded RNA genome?

Accepted Answer

Option B: Reovirus. Reoviruses (members of the family Reoviridae, notably Rotavirus) possess a segmented, double-stranded RNA (dsRNA) genome enclosed in a non-enveloped double- or triple-layered icosahedral capsid. Poliovirus is positive-sense ssRNA, Herpesviruses have dsDNA, and Influenza virus has a segmented negative-sense ssRNA genome.

Question 57

A classic 'owl's eye' intranuclear inclusion is seen in infections caused by:

Accepted Answer

Option B: Cytomegalovirus. Cytomegalovirus (CMV, Human betaherpesvirus 5) causes infected cells to swell markedly (cytomegaly) and form large, dense, basophilic intranuclear inclusion bodies surrounded by a clear halo, famously termed 'owl's eye' inclusions on histopathologic biopsy and cytology.

Question 58

What structural component do viroids lack, differentiating them from typical viruses?

Accepted Answer

Option B: Protein coat. Viroids are subviral plant pathogens consisting exclusively of a short, circular, tightly base-paired single-stranded RNA molecule without any protective protein coat (capsid) or lipid envelope. True viruses, by definition, possess a protein capsid surrounding their genetic material.

Question 59

India ink preparation is useful for identifying which fungal infection?

Accepted Answer

Option B: Cryptococcus neoformans. India ink negative staining is a rapid microscopic diagnostic test for Cryptococcus neoformans in cerebrospinal fluid (CSF) or other body fluids. The colossal acidic mucopolysaccharide (glucuronoxylomannan) capsule excludes the black colloidal carbon particles, standing out as a conspicuous luminous halo surrounding the budding yeast cell.

Question 60

Which fungal species is most frequently associated with otomycosis (ear fungal infection)?

Accepted Answer

Option B: Aspergillus niger. Aspergillus niger is the single most frequent etiology of otomycosis (fungal infection of the external auditory canal), responsible for up to 70–80% of cases. It produces dense black or charcoal-colored velvety conidiophores and spores lining the auditory canal, along with intense itching and conductive hearing impairment.

Question 61

Lactophenol cotton blue stain is most effective in highlighting which fungal structure?

Accepted Answer

Option B: Hyphae and spores. Lactophenol cotton blue (LPCB) is the standard mounting and staining solution used to visualize filamentous fungi. Phenol kills the fungal cells, lactic acid preserves fungal morphology, and cotton blue (aniline blue) selectively binds to and stains chitin and glucan within the fungal cell walls—specifically highlighting hyphae, conidiophores, and spores a crisp blue.

Question 62

How can Culex larvae be distinguished from Anopheles larvae in standing water?

Accepted Answer

Option C: Anopheles larvae lack a siphon. Anopheles mosquito larvae lack a respiratory siphon and possess spiracles situated directly on the eighth abdominal segment; consequently, they lie completely horizontal and parallel to the surface of the water. In contrast, Culex larvae possess a prominent, elongated breathing siphon and suspend themselves downward at an angle from the surface film.

Question 63

Select the correct pairing of a vector with the disease it transmits:

Accepted Answer

Option B: Phlebotomus - Kala azar. Phlebotomus (sandfly) is the biological vector of Leishmania donovani, the causative protozoan of visceral leishmaniasis (Kala-azar). In contrast, Glossina (tsetse fly) transmits African sleeping sickness, Anopheles transmits malaria, and Culex transmits lymphatic filariasis and Japanese encephalitis.

Question 64

Which of the following arthropods has a larval stage commonly referred to as a "maggot"?

Accepted Answer

Option B: Housefly. The legless, acephalic, cylindrical vermiform larva of the common housefly (Musca domestica) and related cyclorrhaphous flies is commonly designated as a 'maggot'. Mosquito larvae are called wrigglers, whereas tick immatures are larvae (six legs) and nymphs (eight legs).

Junior Microbiologist2025

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