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Gas gangrene is most commonly caused by Clostridium perfringens, an anaerobic, spore-forming bacterium that produces potent exotoxins leading to rapid muscle tissue necrosis and gas production. The infection typically follows trauma or surgical wounds with deep tissue contamination. Prompt surgical debridement of necrotic tissue and administration of high-dose antibiotics are critical to control the spread. The characteristic presence of gas in tissue on imaging helps confirm diagnosis. Early recognition and aggressive fasciotomy or amputation may be life-saving to prevent systemic toxicity and mortality.

Reference: Robbins Basic Pathology, Kumar et al., 10th Edition.
The bacterium responsible for causing plague is Yersinia pestis. It is a Gram-negative rod that primarily infects rodents and is transmitted to humans through flea bites. Yersinia pestis causes different clinical forms of plague, including bubonic, septicemic, and pneumonic plague, characterized by swollen lymph nodes (buboes), septicemia, and severe pneumonia respectively. The high virulence and rapid progression of infection make early identification and treatment critical. Other options listed cause different diseases and are not associated with plague.

Reference: Mandell, Douglas and Bennett's Principles and Practice of Infectious Diseases, Mandell GL et al., 9th Edition.
Candida albicans is the most common cause of candidiasis because it is a normal commensal organism of the human mucosa that can become pathogenic under conditions of immunosuppression, antibiotic use, or disruption of normal flora. It exhibits the ability to switch between yeast and hyphal forms, facilitating tissue invasion and evasion of the host immune response. This polymorphism is key to its virulence, making it the predominant species responsible for both superficial and systemic candidiasis. Other fungi listed do not commonly cause candidiasis.

Reference: Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases, J.E. Bennett et al., 9th Edition.
Hypersensitivity is an exaggerated or inappropriate immune response to an antigen that causes tissue damage and clinical harm. Unlike a normal immune response, hypersensitivity leads to pathological inflammation and contributes to conditions such as allergies, autoimmune diseases, and transplant rejection. It is distinct from immunodeficiency, where the immune response is inadequate, and from autoimmune tolerance, where harmful self-reactive responses are suppressed. Understanding hypersensitivity is crucial for identifying and managing immune-mediated tissue injury effectively.

Reference: Robbins Basic Pathology, Kumar et al., 10th Edition.
Escherichia coli appears as rod-shaped bacteria under the microscope, which classifies it as Bacillus. This shape is significant because it influences bacterial growth patterns and motility. Understanding the morphology helps in identifying the organism during Gram staining and guides appropriate antimicrobial treatment. Unlike cocci, which are spherical, or spirilla and vibrios, which have spiral or curved shapes, E. coli’s rod shape aids in clinical diagnosis of infections caused by Enterobacteriaceae family members.

Reference: Medical Microbiology, Jawetz, Melnick & Adelberg, 28th Edition.
The unit used to measure absorbed radiation dose is the Gray (Gy). It quantifies the amount of energy deposited by ionizing radiation per unit mass of tissue, where 1 Gray equals 1 joule per kilogram. This measurement is crucial in clinical settings to assess the direct biological impact of radiation exposure on tissues. Unlike Sievert, which accounts for radiation type and biological effect (effective dose), Gray strictly measures the physical dose absorbed, making it key in radiation therapy and radiology.

Reference: Radiobiology for the Radiologist, Eric J. Hall, 7th Edition.
A tumor arising from connective tissue is called a sarcoma because sarcomas originate from mesenchymal cells which form connective tissues such as bone, muscle, fat, and cartilage. Unlike carcinomas, which arise from epithelial cells, sarcomas are distinct in their tissue origin and biological behavior. Recognizing this differentiation is crucial for diagnosis, surgical planning, and treatment, as sarcomas may require wide local excision with clear margins to prevent recurrence. Understanding tumor origin guides the surgeon in selecting appropriate resection techniques and anticipating potential complications related to connective tissue involvement.

Reference: Robbins Basic Pathology, Kumar V. et al., 10th Edition.
The most suitable method for sterilizing heat-sensitive liquids like culture media is filtration because it physically removes microorganisms without the need for heat. Autoclaving and dry heat involve high temperatures that can denature essential nutrients and growth factors in the media. Filtration using membrane filters (0.22 µm pore size) effectively excludes bacteria and fungi while preserving the liquid’s integrity. Radiation
Reference: Medical Microbiology, Murray et al., 9th Edition.
Prostaglandins are lipid compounds that play a crucial role in the inflammatory response by sensitizing nerve endings, leading to the sensation of pain. They also act on the hypothalamus to raise body temperature, causing fever during inflammation. These actions contribute to the classic signs of inflammation, aiding in the body's defense mechanism. Therefore, prostaglandins are key mediators that promote pain and fever, making Option 2 the correct choice.

Reference: Robbins Basic Pathology, Kumar, Abbas, Aster, 10th Edition.

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 main function of ribosomes is protein synthesis. Ribosomes read messenger RNA (mRNA) sequences and translate them into polypeptide chains by linking amino acids in the correct order. Proteins produced by ribosomes are essential for cell structure, function, and regulation of tissues and organs. Unlike other organelles, ribosomes do not synthesize lipids, replicate DNA, or produce energy, making their role in protein production critical for cell viability and function. Disruption in ribosomal activity can lead to severe cellular dysfunction and disease.

Reference: Molecular Biology of the Cell, Alberts et al., 6th Edition.
The OPV (Oral Polio Vaccine) is specifically designed to prevent Poliomyelitis, a highly infectious viral disease that primarily affects children and can cause permanent paralysis. OPV contains a weakened form of the poliovirus, which stimulates the immune system to produce antibodies without causing the disease. It is administered orally, making it easy to deliver during mass vaccination campaigns. OPV is preferred in many regions due to its ability to provide both individual immunity and community-wide protection through herd immunity. This vaccine is not used for diseases like measles, hepatitis B, or tetanus, which require different vaccines.

Reference: Harrison's Principles of Internal Medicine, Longo et al., 20th Edition.
Air pollution is a common environmental health hazard because it contains harmful substances like particulate matter, nitrogen dioxide, and sulfur dioxide that adversely affect respiratory and cardiovascular health. Exposure to air pollution increases the risk of diseases such as asthma, chronic obstructive pulmonary disease (COPD), lung cancer, and heart disease. It also contributes to premature mortality and exacerbates existing health conditions. Unlike balanced diet, physical exercise, and vaccination, which promote health, air pollution directly threatens human health by contaminating the air we breathe. Recognizing and minimizing exposure to air pollution is critical in environmental health management.

Reference: Environmental Health: From Global to Local, Frumkin H., 3rd Edition.
The main purpose of a health campaign is to raise awareness and change behaviors to improve public health outcomes. By educating the target population, these campaigns encourage the adoption of healthier habits and preventive measures, ultimately reducing the incidence of disease and promoting wellness. Increasing knowledge and motivation are essential steps in modifying risk factors and enhancing individual and community health. This is critical as behavior change is a cornerstone in preventing many surgical and medical conditions. Effective health campaigns do not aim to increase hospital admissions or promote commercial interests but focus on empowering individuals with information for better health decisions.

Reference: Public Health Education and Promotion, Green & Tones, 3rd Edition.
A health behavior is defined as an action taken by an individual that influences their health status either positively or negatively. These behaviors include activities like diet, exercise, smoking, and medication adherence, which directly affect health outcomes. Unlike genetic traits, laboratory findings, or disease symptoms, health behaviors are modifiable factors that individuals can control to prevent illness or promote wellness. Understanding and promoting healthy behaviors is a cornerstone of public health and clinical practice aimed at reducing disease risk and improving quality of life.

Reference: Health Behavior: Theory, Research, and Practice, Glanz K., Edition 5.
The major challenge in achieving Millennium Development Goal 5 (maternal health) was the limited availability of skilled birth attendants. Skilled birth attendants are crucial for managing complications during labor and delivery, thereby reducing maternal mortality. Their presence ensures timely interventions, appropriate use of surgical procedures like cesarean sections, and effective neonatal resuscitation. Without adequately trained personnel, preventable maternal deaths due to hemorrhage, sepsis, and obstructed labor remain high. Thus, increasing the number and accessibility of trained healthcare providers directly impacts maternal survival rates.

Reference: Obstetrics by Ten Teachers, Keith Edmonds, 20th Edition.
A core principle of primary health care (PHC) is community participation because it empowers individuals and communities to take an active role in their own health management. This involvement ensures that health services are tailored to the specific needs and values of the population, improving accessibility, acceptability, and sustainability of care. PHC emphasizes integrated, culturally appropriate, and preventive services rather than relying solely on specialist or tertiary care. Engaging communities helps in resource mobilization, health education, and fostering local ownership, which are essential for effective health outcomes.

Reference: Primary Health Care: Theory and Practice, Margaret M. Barry, 2nd Edition.
Serological testing in clinical microbiology is primarily used to detect antibodies or antigens in patient samples. This allows identification of current or past infections by assessing the immune response or presence of specific microbial components. It is essential for diagnosing infectious diseases, guiding treatment, and epidemiological surveillance. Unlike biochemical tests, serology does not measure metabolic substances like glucose or electrolytes. The detection of antibodies indicates exposure to a pathogen, while antigen detection can confirm active infection.

Reference: Medical Microbiology, Murray et al., 9th Edition.
The main purpose of a throat swab culture is to identify the presence of Streptococcus pyogenes, the bacterium responsible for group A streptococcal pharyngitis (strep throat). This test is crucial for confirming bacterial infection, guiding appropriate antibiotic treatment, and preventing complications such as rheumatic fever. Throat swab cultures are highly sensitive and specific for detecting this pathogen, making them the gold standard in diagnosis. Other pathogens like viruses or fungi are not reliably diagnosed with this method. Hence, its primary clinical utility is to detect Streptococcus pyogenes.

Reference: Principles and Practice of Infectious Diseases, Mandell, Douglas, and Bennett, 9th Edition.
Methicillin-resistant Staphylococcus aureus (MRSA) is a leading cause of hospital-acquired infections due to its resistance to multiple antibiotics, making it difficult to treat. MRSA commonly colonizes the skin and nasal passages, facilitating transmission in healthcare settings. Its ability to survive on surfaces and invasive devices increases infection risk, especially in surgical wounds, catheters, and ventilators. Prompt identification and strict infection control measures are essential to prevent MRSA spread in hospitals, where vulnerable patients are at high risk. Other options are less commonly associated with nosocomial infections.

Reference: Medical Microbiology, Murray et al., 9th Edition.

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
Shigellosis is caused by Shigella dysenteriae, a gram-negative, non-motile bacterium responsible for bacillary dysentery. It invades the colonic mucosa, leading to inflammation, ulceration, and bloody diarrhea. The organism produces the Shiga toxin, which contributes to mucosal damage and systemic complications. This pathogen's ability to penetrate epithelial cells distinguishes it from other enteric bacteria such as Salmonella, E. coli, and Vibrio cholerae. Therefore, Shigella dysenteriae is the definitive causative agent of shigellosis.

Reference: Medical Microbiology, Murray et al., 9th Edition.
Actinomycosis is a chronic granulomatous infection caused primarily by Actinomyces israelii, a gram-positive, anaerobic bacterium that normally resides in the oral cavity. The infection typically arises after mucosal disruption, leading to the formation of characteristic abscesses, sinus tracts, and sulfur granules in infected tissues. It often presents as a slowly progressive mass, commonly in the cervicofacial region. Unlike Nocardia or Bacillus anthracis, Actinomyces does not cause acute systemic illness but rather a localized indolent infection. Effective treatment requires prolonged high-dose penicillin therapy, often combined with surgical drainage of abscesses to remove fibrotic tissue and sinus tracts. Early recognition and management prevent extensive tissue destruction and complications.

Reference: Jawetz, Melnick & Adelberg’s Medical Microbiology, Murray et al, 28th Edition.
The main distinction between Streptococcus pyogenes and Streptococcus pneumoniae lies in their hemolytic patterns on blood agar. S. pyogenes is beta-hemolytic, causing complete lysis of red blood cells, resulting in a clear zone around colonies. In contrast, S. pneumoniae is alpha-hemolytic, partially lysing red blood cells and producing a greenish discoloration on the agar. This difference is crucial for laboratory identification and subsequent clinical management. Both are Gram-positive cocci, but their hemolysis type distinguishes their pathogenic mechanisms and treatment protocols.

Reference: Medical Microbiology, Murray et al., 9th Edition.
Tuberculosis is caused by the bacterium Mycobacterium tuberculosis, a slow-growing, acid-fast bacillus. It primarily affects the lungs but can involve other organs. The unique cell wall of Mycobacterium tuberculosis contains mycolic acid, which provides resistance to standard stains and antibiotics, requiring special staining techniques like the Ziehl-Neelsen stain for diagnosis. Its ability to survive within macrophages leads to chronic granulomatous inflammation, a hallmark of tuberculosis. Effective treatment targets this bacterium specifically, highlighting its critical role in the disease.

Reference: Robbins Basic Pathology, Kumar et al., 10th Edition.
Herpes labialis, commonly known as cold sores, is primarily caused by Herpes simplex virus type 1 (HSV-1). This virus establishes latency in the trigeminal ganglion and reactivates to cause recurrent vesicular lesions on the lips and perioral area. Unlike Varicella-zoster virus, which causes shingles, or Cytomegalovirus and Epstein-Barr virus, HSV-1 specifically targets the oral mucosa and adjacent skin. The clinical presentation of grouped vesicles on an erythematous base is characteristic of HSV-1 infection. Effective diagnosis and management focus on this viral etiology.

Reference: Clinical Microbiology Made Ridiculously Simple, Mark Gladwin, Edition 7.
Viral latency is a state in which a virus remains dormant within host cells without active replication. This allows the virus to persist in the host over long periods without causing symptoms or triggering an immediate immune response. During latency, viral genomes are maintained but not expressed, enabling the virus to evade detection and clearance by the immune system. This characteristic is critical for viruses like herpes simplex and varicella-zoster, which can reactivate later, causing disease recurrence. Thus, the significance of viral latency lies in its role in long-term viral persistence without active disease manifestation.

Reference: Medical Microbiology, Murray et al., 9th Edition.
Rotavirus diarrhea is caused by infection with Rotavirus, a double-stranded RNA virus belonging to the Reoviridae family. It primarily affects children under five years old, causing severe watery diarrhea, vomiting, and dehydration. The virus infects the mature enterocytes of the small intestine, leading to malabsorption and osmotic diarrhea. Rotavirus is the leading cause of severe gastroenteritis in infants and young children worldwide. Diagnosis is confirmed by detecting viral antigens in stool. Vaccination has significantly reduced the incidence and severity of rotavirus infections.

Reference: Nelson Textbook of Pediatrics, Kliegman et al., 21st Edition.
The primary mode of transmission of the influenza virus is through respiratory droplets expelled when an infected person coughs, sneezes, or talks. These droplets can directly enter the respiratory tract of a nearby person or contaminate surfaces that others touch, leading to infection when they touch their face. This mode facilitates rapid spread in crowded or close-contact settings. Unlike fecal-oral, vector-borne, or sexual contact routes, respiratory droplet transmission aligns with the virus’s tropism for respiratory epithelial cells. Effective prevention includes wearing masks, maintaining physical distance, and vaccination.

Reference: Harrison’s Principles of Internal Medicine, J. Larry Jameson, 20th Edition.
Virology is the branch of science that specifically studies viruses, which are microscopic infectious agents that can only replicate inside living host cells. Unlike bacteria, fungi, or parasites, viruses lack cellular structure and require a host for reproduction. Understanding viruses is crucial for diagnosing, preventing, and treating viral infections. This specialization focuses on viral structure, genetics, pathogenesis, and the immune response to viral infections, making it distinct from microbiology branches that study other microorganisms.

Reference: Medical Microbiology, Murray et al., 9th Edition.
Paracoccidioidomycosis is a systemic fungal infection caused specifically by Paracoccidioides brasiliensis, a dimorphic fungus endemic to Latin America. This pathogen primarily affects the lungs but can disseminate to mucous membranes, skin, and lymph nodes. The diagnosis is confirmed by identifying the characteristic multiple budding yeast cells resembling a "pilot's wheel" in clinical specimens. Other fungi listed do not cause this disease. Effective treatment requires antifungal therapy targeted at this organism, emphasizing the importance of correct identification.

Reference: Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases, Mandell et al., 9th Edition.

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
Chromoblastomycosis is a chronic fungal infection of the skin and subcutaneous tissue caused primarily by dematiaceous (pigmented) fungi. Fonsecaea pedrosoi is the most common etiologic agent, typically introduced through traumatic implantation of contaminated soil or vegetation. The infection presents as verrucous, crusted, or nodular lesions mainly on the lower extremities. Diagnosis is confirmed by identifying characteristic brown, thick-walled, sclerotic bodies ("Medlar bodies") in tissue. Other fungi listed are not associated with chromoblastomycosis but cause different systemic mycoses.

Key clinical point: Fonsecaea pedrosoi is the primary pathogen in chromoblastomycosis, a localized cutaneous mycosis best diagnosed by microscopic examination of skin lesions.

Reference: Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases, 9th Edition.
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