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Type I hypersensitivity is primarily mediated by IgE antibodies, which bind to allergens and trigger mast cell degranulation and release of histamine, leading to immediate allergic reactions. This mechanism is distinct from other hypersensitivity types that involve different antibodies or immune cells. IgE's role in rapid onset reactions such as anaphylaxis and allergic asthma defines Type I hypersensitivity as immediate and antibody-dependent.

Reference: Abbas AK, Lichtman AH, Pillai S. Cellular and Molecular Immunology, 9th Edition, Chapter 11: Hypersensitivity Reactions, p. 406-410.
The correct answer is Flagella. Flagella are long, whip-like structures that extend from the bacterial cell surface and enable active movement by rotation. This motility allows bacteria to navigate toward favorable environments or away from harmful stimuli, a process known as chemotaxis. Unlike pili, capsule, or cell wall, flagella are specifically designed for locomotion.

Reference: Jawetz, Melnick & Adelberg's Medical Microbiology, 27th Edition, Chapter 3, p. 45
Hepatitis B virus (HBV) is a DNA virus that integrates into the host genome, causing chronic liver inflammation and cellular damage. This persistent injury leads to fibrosis, cirrhosis, and ultimately hepatocellular carcinoma (HCC). HBV's direct oncogenic effect through viral proteins like HBx also promotes hepatic carcinogenesis. Other viruses listed do not primarily infect hepatocytes or cause this cancer type.

Reference: *Robbins & Cotran Pathologic Basis of Disease*, 10th Edition, Volume 2, Chapter 18, pp. 1104-1106.
The correct answer is Mucormycosis because it most commonly affects patients with diabetic ketoacidosis (DKA). The high blood sugar and acidic environment in DKA patients facilitate the growth of Mucorales fungi. These fungi exhibit angioinvasion, leading to rapid tissue necrosis, especially in the rhino-orbital-cerebral region. This unique susceptibility is not typically seen with Aspergillosis, Cryptococcosis, or Candidiasis in DKA patients.

Reference:
Feigin and Cherry's Textbook of Pediatric Infectious Diseases, Vol 1, Chapter 22, Page 805
The Latex agglutination test is commonly used to detect rheumatoid factor (RF) because it is a simple, rapid, and sensitive method where patient serum antibodies cause visible clumping of latex particles coated with human IgG. This test directly identifies RF, an important marker for rheumatoid arthritis diagnosis. Although other methods like ELISA detect specific antibodies (e.g., anti-CCP), the latex agglutination test remains widely used for initial RF screening in clinical practice.

Reference: Harrison's Principles of Internal Medicine, 20th Edition, Volume 2, Chapter 272, Page 2141
The Ziehl-Neelsen stain is specifically designed to detect acid-fast bacilli like Mycobacterium tuberculosis because their cell walls contain mycolic acid, which retains the red dye even after acid-alcohol decolorization. This property is unique to mycobacteria, making Ziehl-Neelsen the gold standard for identifying tuberculosis in sputum samples. Other stains, such as Gram stain, do not reliably highlight these organisms due to their waxy cell envelope.

Reference:
Jawetz, Melnick & Adelberg's Medical Microbiology, 27th Edition, Chapter on Mycobacteria/Tuberculosis, Page 250.
The primary vector for Leishmania donovani, which causes visceral leishmaniasis, is the sandfly of the Phlebotomus species. This insect transmits the parasite through its bite, introducing the promastigote form into the human host. Unlike Anopheles mosquitoes (malaria vectors), tsetse flies (sleeping sickness vectors), or blackflies (onchocerciasis vectors), only Phlebotomus sandflies carry and transmit Leishmania donovani. Their role is critical for the parasite’s life cycle and disease transmission.

Reference:
Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases, 9th Edition, Volume 2, Chapter 114, p. 3179.
Measles (Rubeola) is classically identified by the presence of Koplik spots, which are small, irregular, bluish-white lesions on the buccal mucosa opposite the molars. These spots appear 1-2 days before the characteristic measles rash and serve as a pathognomonic sign. Rubella, Varicella-Zoster, and Herpes Simplex viruses do not produce Koplik spots. This makes Koplik spots a key early diagnostic feature specific to measles infection.

Reference: Harrison's Principles of Internal Medicine, 20th Edition, Volume 2, Infectious Diseases, Chapter 157, p. 1139
In patients with sickle cell disease, Salmonella species are the most frequent cause of osteomyelitis due to their ability to invade the damaged bone tissue. Sickle cell-related bone infarctions create a nidus for infection, and Salmonella, a facultative intracellular pathogen, thrives in this environment. While Staphylococcus aureus is the most common cause of osteomyelitis in the general population, in sickle cell patients, the risk for Salmonella is significantly higher. This reflects the specific vulnerability caused by spleen dysfunction and ischemic bone damage in these patients.

Reference:
Harrison’s Principles of Internal Medicine, 20th Edition, Volume 2, Chapter 228 (Sickle Cell Disease)

ফ্রিতে ২ লাখ প্রশ্নের টপিক, সাব-টপিক ভিত্তিক ও ১০০০+ জব শুলুশন্স বিস্তারিতে ব্যাখ্যাসহ পড়তে ও আপনার পড়ার ট্র্যাকিং রাখতে সাইটে লগইন করুন।

লগইন করুন
Clostridioides difficile infection is the most frequent cause of diarrhea acquired during hospitalization because it commonly occurs after antibiotic use, which disrupts normal gut flora. This leads to overgrowth of C. difficile and toxin production, causing colitis and diarrhea. It is a major healthcare-associated infection with significant morbidity. Other causes like norovirus or Giardia are less common in hospital settings, and antibiotic-associated diarrhea without infection lacks the severity and frequency seen with C. difficile.

Reference: Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases, 9th Edition, Volume 2, Chapter 152, p. 3274.
The correct answer is Interferon-gamma (IFN-γ) because it is the primary cytokine responsible for classical (M1) activation of macrophages. IFN-γ, produced mainly by Th1 cells and NK cells, enhances macrophage microbicidal functions by stimulating increased production of reactive oxygen species and nitric oxide. This activation leads to enhanced antigen presentation and pro-inflammatory cytokine secretion, crucial for effective immunity against intracellular pathogens. Other cytokines like IL-4 and IL-10 promote alternative (M2) macrophage activation, which is anti-inflammatory.

Reference: Janeway’s Immunobiology, 9th Edition, Chapter 7 - The Innate Immune System
During a primary immune response, B cells initially produce IgM antibodies because IgM is the first immunoglobulin expressed before class switching occurs. IgM has a pentameric structure that allows effective agglutination and complement activation, providing early defense against pathogens. Other isotypes like IgG, IgA, and IgE appear later after class switching guided by cytokines and antigen stimulation.

Reference: Janeway's Immunobiology, 9th Edition, Chapter 5: The Humoral Immune Response, Page 190
Gamma rays have the greatest tissue penetration ability because they are electromagnetic waves with no mass or charge, allowing them to pass through most materials, including body tissues, with minimal interaction. In contrast, alpha and beta particles are charged and have mass, causing them to lose energy quickly and be stopped by a few centimeters of tissue or even skin. Ultraviolet rays are non-ionizing and absorbed mostly by the skin's surface, limiting their penetration. Therefore, the high penetration power of gamma rays makes them the most deeply penetrating ionizing radiation.

Reference: Robbins Basic Pathology, 10th Edition, Chapter 3, p. 108
The correct answer is Fibroma, as it is the most frequently diagnosed benign tumor of the oral cavity. It commonly arises due to chronic irritation or trauma, leading to a reactive hyperplasia of fibrous connective tissue. Unlike true neoplasms, fibromas represent a localized fibrous tissue overgrowth. They are typically firm, painless, and slow-growing. Other options like papilloma, lipoma, and neurofibroma are less common in the oral cavity.

Reference:
Shafer's Textbook of Oral Pathology, 7th Edition, Volume 1, Chapter 3, Page 58
Ethylene oxide gas sterilization is ideal for medical instruments that cannot withstand high temperatures because it is a low-temperature, chemical sterilization method. Unlike autoclaving or dry heat, it effectively sterilizes delicate, heat-sensitive instruments without causing damage. It penetrates packaging and kills all microorganisms by alkylating DNA and proteins. This makes it the best choice for items with plastics or electronics that would be damaged by steam or heat.

Reference: Medical Microbiology, 8th Edition, Murray et al., Volume 1, Chapter 5, p. 102
Cerebral infarction (ischemic stroke) is the most frequent cause of liquefactive necrosis because the brain contains abundant lipid-rich myelin and high enzymatic activity. Ischemic injury leads to rapid enzymatic digestion of dead cells, resulting in a liquid viscous mass. In contrast, myocardial infarction typically causes coagulative necrosis, and tuberculous lymphadenitis causes caseous necrosis. Fat necrosis is a distinct form involving enzymatic fat digestion, not liquefactive. Thus, the brain's unique structure and metabolism explain why cerebral infarction predominantly leads to liquefactive necrosis.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th Edition, Volume 1, Chapter 5: Cell Injury, Cell Death, and Adaptations / Pages 53-55
Bradykinin is the primary mediator responsible for causing pain during inflammation because it directly stimulates nociceptors (pain receptors) and increases their sensitivity. It also promotes vasodilation and increases vascular permeability, amplifying inflammatory signals. Unlike prostaglandins that sensitize pain receptors, bradykinin actively triggers the sensation of pain. This makes bradykinin the key inflammatory mediator in pain induction during the inflammatory response.

Reference: Robbins Basic Pathology, 10th Edition, Volume 1, Chapter 2, Page 58
Tight junctions form a continuous seal around epithelial cells, creating a barrier that prevents the passage of fluids and solutes between adjacent cells. This function is crucial for maintaining distinct compartments and controlling paracellular transport. Unlike gap junctions (which allow communication), desmosomes and adherens junctions (which provide mechanical strength), tight junctions specifically regulate permeability and maintain cell polarity.

Reference:
Ross & Wilson, *Anatomy and Physiology in Health and Illness*, 13th Edition, Chapter 3, Page 54
Lysosomes are membrane-bound organelles containing hydrolytic enzymes responsible for breaking down macromolecules such as proteins, lipids, carbohydrates, and nucleic acids. Their primary role is to digest material taken up by endocytosis or from damaged organelles, facilitating cellular recycling and waste removal. This intracellular digestion helps maintain cellular homeostasis and prevents accumulation of debris. Unlike the synthesis of proteins, energy production, or genetic material storage, lysosomes specialize in degradation and recycling processes.

Reference: *Molecular Biology of the Cell*, 6th Edition, Chapter 4, Section “Lysosomes and Endocytosis”

ফ্রিতে ২ লাখ প্রশ্নের টপিক, সাব-টপিক ভিত্তিক ও ১০০০+ জব শুলুশন্স বিস্তারিতে ব্যাখ্যাসহ পড়তে ও আপনার পড়ার ট্র্যাকিং রাখতে সাইটে লগইন করুন।

লগইন করুন
The Golgi apparatus is the cellular organelle responsible for the modification, sorting, and packaging of proteins that are synthesized in the endoplasmic reticulum and destined for secretion or delivery to other organelles. It processes proteins by adding carbohydrate groups and tags them for their specific destinations. Unlike the lysosome or mitochondrion, the Golgi functions as the cell’s central protein trafficking hub. The endoplasmic reticulum primarily synthesizes proteins but does not sort or package them for secretion.

Reference:
Molecular Biology of the Cell, 6th Edition, Bruce Alberts, Chapter 15: The Golgi Apparatus and Intracellular Transport
- The Quellung reaction is primarily used to identify Streptococcus pneumoniae by detecting its polysaccharide capsule.
- When specific anti-capsular antibodies bind to the capsule, it causes the capsule to appear swollen and more refractile under a microscope.
- This reaction is a rapid and specific method to differentiate S. pneumoniae from other bacteria, as the capsule is a major virulence factor and unique to pneumococci in this context.
- Other organisms listed do not typically exhibit a visible capsular swelling in the Quellung test.
- The correct answer is Bordetella pertussis because it is the primary causative agent of whooping cough, a highly contagious respiratory disease.
- This gram-negative bacterium produces toxins that damage the respiratory epithelium, leading to the characteristic severe paroxysmal coughing spells with a “whooping” sound.
- Neither Haemophilus influenzae, Mycobacterium tuberculosis, nor Streptococcus pneumoniae cause this specific clinical syndrome.
- Therefore, Bordetella pertussis is uniquely associated with whooping cough.
- The Weil-Felix test is used to detect antibodies against Rickettsia species.
- It is based on the principle of cross-reactivity between certain Proteus bacterial antigens (OX strains) and rickettsial organisms.
- When a patient is infected with Rickettsia, their serum contains antibodies that agglutinate these Proteus antigens, producing a positive test.
- This serological test helps in the diagnosis of rickettsial infections, such as typhus and spotted fever.
- It is not used for Brucella, Leptospira, or Mycoplasma detection, as these organisms do not cross-react with Proteus antigens.
- Helicobacter pylori is a microaerophilic bacterium that colonizes the acidic environment of the stomach.
- It produces urease enzyme, which neutralizes stomach acid by converting urea to ammonia, allowing it to survive and damage the gastric mucosa.
- This damage leads to inflammation and ulcer formation, making H. pylori the primary cause of peptic ulcers.
- Other bacteria listed do not colonize or affect the stomach lining in this way.
- Bartonella quintana is the primary causative agent of trench fever, an illness historically associated with poor hygiene and body louse infestation during World War I. It is transmitted specifically by the human body louse (Pediculus humanus corporis).
- Unlike the other options, Bartonella quintana uniquely causes the recurrent fever, headache, and shin pain characteristic of trench fever.
- Other bacteria listed cause different diseases: Coxiella burnetii causes Q fever, Rickettsia prowazekii causes epidemic typhus, and Borrelia recurrentis causes louse-borne relapsing fever.

Reference: Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases, 9th Edition, Volume 2, Chapter 179
- The correct answer is Mycobacterium leprae because it is the acid-fast bacillus specifically responsible for causing Hansen's disease (leprosy).

- It primarily affects the skin and peripheral nerves, leading to characteristic symptoms.
- Unlike Mycobacterium tuberculosis, which causes tuberculosis, M. leprae has a unique predilection for nerve tissue.
- Other options like Nocardia asteroides and Corynebacterium diphtheriae cause different diseases and are not responsible for Hansen's disease.

Reference: Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases, Volume 2, Chapter 123
- The primary virulence factor of Vibrio cholerae is the cholera toxin, which is an A-B toxin that increases intracellular cAMP in intestinal epithelial cells.
- This leads to massive chloride and water secretion into the intestinal lumen, causing the characteristic profuse watery diarrhea (rice-water stools) of cholera.
- None of the other options are associated with Vibrio cholerae; they are virulence factors of other bacteria.
- Neisseria gonorrhoeae is a Gram-negative diplococcus that primarily infects the urogenital tract, making it the classic etiologic agent of urethritis.
- It adheres to and invades mucosal epithelial cells, causing inflammation and purulent discharge.
- In contrast, other options like Streptococcus pneumoniae are Gram-positive, and Haemophilus influenzae or Moraxella catarrhalis have different morphology and clinical presentations.
- The identification as a Gram-negative diplococcus combined with urethritis confirms Neisseria gonorrhoeae as the correct organism.
- Streptococcus pyogenes is the causative agent of scarlet fever, characterized by the classic "strawberry tongue" due to inflammation and desquamation of the tongue's papillae.
- Additionally, it can trigger rheumatic fever, an autoimmune complication resulting from molecular mimicry between streptococcal M proteins and host tissues.
- Neither Staphylococcus aureus, Corynebacterium diphtheriae, nor Haemophilus influenzae cause this specific clinical syndrome or rheumatic fever.
- This makes Streptococcus pyogenes the correct and sole responsible microorganism for these presentations.

Reference: Harrison’s Principles of Internal Medicine, 20th Edition, Infectious Diseases Chapter, p. 1113

ফ্রিতে ২ লাখ প্রশ্নের টপিক, সাব-টপিক ভিত্তিক ও ১০০০+ জব শুলুশন্স বিস্তারিতে ব্যাখ্যাসহ পড়তে ও আপনার পড়ার ট্র্যাকিং রাখতে সাইটে লগইন করুন।

লগইন করুন
- Prions are unique infectious agents because they consist solely of misfolded proteins without any nucleic acids (DNA or RNA).
- Unlike viruses, bacteria, or fungi, prions replicate by inducing the normal host proteins to adopt the abnormal prion conformation, leading to disease.
- This protein-only replication mechanism is the defining characteristic that distinguishes prions from all other infectious agents.
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