Chapter 15 with our Microbiology MCQs and explanations! Test your knowledge and understanding of key concepts with our complete set of multiple choice questions with detailed explanations for each answer. Increase your confidence and understanding of the fascinating world of microorganisms!
Microbiology MCQs 701 to 750
Drugs of choice for treatment of Mycoplasma infections?
- a) Tetracyclines
- b) Erythromycin
- c) Tetracyclines and Erythromycin
- d) Penicillins
Explanation:
Mycoplasma species lack a cell wall. Therefore, they are naturally resistant to antibiotics that target cell wall synthesis. Tetracyclines and Macrolides (like Erythromycin) are the drugs of choice because they inhibit bacterial protein synthesis by targeting the ribosomes.
Why other options are incorrect:
Why other options are incorrect:
- • Penicillins: These drugs work by inhibiting cell wall synthesis (peptidoglycan). Since Mycoplasma has no cell wall, Penicillins have no target and are completely ineffective.
- • Tetracyclines / Erythromycin (Individual): While both are used, option (c) is the more comprehensive answer as both classes represent the primary line of treatment for these infections.
A number of viruses are known to infect mycoplasmas, called?
- a) Bacteriophages
- b) Mycoplasma phages
- c) Virions
- d) Tiny strains
Explanation:
Viruses that specifically infect Mycoplasmas are known as Mycoplasma phages (or mycoplasmaviruses). They were first discovered in the 1970s and are known to infect various species of the class Mollicutes.
Why other options are incorrect:
Why other options are incorrect:
- • Bacteriophages: While mycoplasmas are bacteria, “Bacteriophage” is the broad general term for all bacterial viruses. “Mycoplasma phages” is the specific name for those infecting this unique genus.
- • Virions: A virion is simply a complete, individual virus particle outside a host cell. It is a general structural term, not a specific type of virus.
- • Tiny strains: This refers to “T-strains” (now called Ureaplasma), which are a specific type of mycoplasma bacteria known for forming very small colonies, not the viruses that infect them.
The causative agent of scrub typhus?
- a) R. quintana
- b) R. rickettsii
- c) R. orientalis
- d) R. prowazekii
Explanation:
Scrub typhus is caused by Rickettsia orientalis (now more commonly known as Orientia tsutsugamushi). It is an intracellular bacterium transmitted to humans through the bite of infected larval mites (chiggers).
Why other options are incorrect:
Why other options are incorrect:
- • R. quintana: Now known as Bartonella quintana, this organism causes Trench Fever and is transmitted by the human body louse.
- • R. rickettsii: This is the causative agent of Rocky Mountain Spotted Fever, primarily transmitted by ticks.
- • R. prowazekii: This species causes Epidemic Typhus, which is also transmitted by the human body louse.
Lymphogranuloma venereum (LGV) is a sexually transmitted disease caused by?
- a) Copthalmia
- b) C. trachomatis
- c) C. pneumoniae
- d) C. psittaci
Explanation:
Lymphogranuloma venereum (LGV) is caused by specific invasive serotypes (L1, L2, and L3) of Chlamydia trachomatis. It is a chronic infection of the lymphatic system and is characterized by genital ulcers and swollen lymph nodes in the groin.
Why other options are incorrect:
Why other options are incorrect:
- • Copthalmia: This is likely a reference to “Ophthalmia,” which is a general term for severe inflammation of the eye, not a specific pathogen.
- • C. pneumoniae: This species of Chlamydia primarily causes respiratory tract infections, such as bronchitis and pneumonia.
- • C. psittaci: This is the causative agent of psittacosis (parrot fever), a disease transmitted to humans from infected birds.
Intradermal test employed for diagnosis of LGV is?
- a) Frei test
- b) Mantoux test
- c) Schick test
- d) Dick test
Explanation:
The Frei test is a delayed hypersensitivity skin test used for the diagnosis of Lymphogranuloma Venereum (LGV). It involves the intradermal injection of an inactivated antigen (prepared from the LGV agent) into the forearm. A positive result is indicated by the appearance of an inflammatory nodule at the site.
Why other options are incorrect:
Why other options are incorrect:
- • Mantoux test: This is the standard skin test used to determine if a person is infected with Mycobacterium tuberculosis.
- • Schick test: This test is used to determine whether or not a person is susceptible to Diphtheria.
- • Dick test: This is a skin test used to determine a person’s susceptibility to Scarlet Fever (caused by Streptococcus pyogenes).
Which algae is pathogenic to human?
- a) Cephaloeuros
- b) Ulothrix
- c) Macrocystis
- d) Prototheca
Explanation:
Prototheca is a genus of achlorophyllous algae (algae that lack chlorophyll). It is the only known alga that causes infectious disease in humans and animals, a condition known as Protothecosis, which typically affects the skin, subcutaneous tissues, or joints.
Why other options are incorrect:
Why other options are incorrect:
- • Cephaloeuros: This is a genus of parasitic green algae, but it primarily affects plants (causing “red rust” in tea and coffee) rather than humans.
- • Ulothrix: This is a genus of non-branching filamentous green algae found in fresh and marine water; it is non-pathogenic.
- • Macrocystis: This is a genus of giant kelp (brown algae). It is an ecologically important seaweed and is not pathogenic to humans.
Erythromycin is obtained from?
- a) S. griseus
- b) S. rimosus
- c) S. scabies
- d) S. erythraeus
Explanation:
Erythromycin is a macrolide antibiotic produced by the actinomycete Streptomyces erythraeus (which has since been reclassified as Saccharopolyspora erythraea). It was first isolated in 1952 from metabolic products of this soil bacterium.
Why other options are incorrect:
Why other options are incorrect:
- • S. griseus: This organism is famous for being the source of Streptomycin, the first antibiotic used to treat tuberculosis.
- • S. rimosus: This species is the primary source of Oxytetracycline (Terramycin).
- • S. scabies: This is a plant pathogen that causes “common scab” disease in potatoes and other root crops; it is not a commercial source of antibiotics.
The causative agent of conjunctivitis?
- a) Adeno virus
- b) Corono virus
- c) Paramyxo virus
- d) None of these
Explanation:
Adenoviruses are the most common cause of viral conjunctivitis (often called “pink eye”). They are highly contagious and are responsible for specific clinical syndromes like epidemic keratoconjunctivitis (EKC) and pharyngoconjunctival fever.
Why other options are incorrect:
Why other options are incorrect:
- • Corono virus: While some coronaviruses (like SARS-CoV-2) can cause conjunctivitis as a secondary symptom, they are primarily respiratory viruses and not the classic causative agent for conjunctivitis.
- • Paramyxo virus: This family includes viruses like Measles and Mumps. While Measles can cause conjunctivitis as part of its systemic symptoms, it is not the primary diagnostic agent for localized conjunctivitis.
- • None of these: This is incorrect because Adenovirus is a well-established and primary cause of the condition.
Antibiotics used for treatment of cholera are?
- a) Tetracyclines
- b) Penicillins
- c) Streptomycines
- d) None of these
Explanation:
While rehydration is the primary treatment for Cholera, Tetracyclines (specifically Doxycycline) are the antibiotics of choice. They help to reduce the volume of diarrhea and shorten the duration of vibrio excretion in the stool.
Why other options are incorrect:
Why other options are incorrect:
- • Penicillins: Vibrio cholerae is generally not sensitive to Penicillins, and they are not used in the clinical management of cholera.
- • Streptomycines: While Streptomycin is an aminoglycoside, it is not a first-line treatment for cholera as it is less effective than tetracyclines or macrolides in the gut environment.
- • None of these: This is incorrect because Tetracyclines are a well-recognized medical treatment for this disease.
Salmonella typhi is the causative organism of?
- a) Undulent fever
- b) Remittent fever
- c) Dengue fever
- d) Enteric fever
Explanation:
Salmonella typhi is the bacterium responsible for Enteric fever, more commonly known as Typhoid fever. It is a systemic infection characterized by high fever, malaise, and abdominal pain, usually transmitted via the fecal-oral route.
Why other options are incorrect:
Why other options are incorrect:
- • Undulent fever: This is another name for Brucellosis, caused by bacteria of the genus Brucella. It is characterized by rising and falling (undulating) waves of fever.
- • Remittent fever: This is a clinical fever pattern (where the temperature fluctuates but never returns to normal) rather than a specific disease caused by S. typhi.
- • Dengue fever: This is a viral disease caused by the Dengue virus (DENV) and is transmitted to humans through the bite of infected Aedes mosquitoes.
Which of the following Salmonella paratyphi is the commonest in India?
- a) A
- b) B
- c) C
- d) None of these
Explanation:
In India and most of South Asia, Salmonella paratyphi A is the most common serotype causing paratyphoid fever. While Salmonella typhi remains the leading cause of enteric fever overall, the incidence of S. paratyphi A has shown a significant upward trend in recent years.
Why other options are incorrect:
Why other options are incorrect:
- • B (S. paratyphi B): This serotype is more commonly found in Europe and parts of South America, and is relatively rare in the Indian subcontinent.
- • C (S. paratyphi C): This is a very rare cause of enteric fever globally, though it is occasionally seen in parts of Africa and Southeast Asia.
- • None of these: This is incorrect because S. paratyphi A is a well-documented and prevalent pathogen in India.
True about Enteric fever is?
- a) Bacteraemia in first week
- b) Carrier in 90%
- c) All serotypes cause the disease
- d) Rosy spots on 18th day
Explanation:
In Enteric fever, bacteremia occurs during the first week of infection. This is why blood culture is the diagnostic method of choice during the first 7–10 days of the illness, yielding a positive result in about 90% of cases during this period.
Why other options are incorrect:
Why other options are incorrect:
- • Carrier in 90%: This is incorrect. Only about 1% to 5% of patients become chronic carriers; 90% is an overestimation.
- • All serotypes cause the disease: Incorrect. Enteric fever is specifically caused by Salmonella typhi and S. paratyphi (A, B, and C). Thousands of other Salmonella serotypes cause food poisoning (gastroenteritis) but not enteric fever.
- • Rosy spots on 18th day: Rose spots (faint pink macules) typically appear during the second week of the fever (usually between the 7th and 12th day), not as late as the 18th day.
The following infections caused by Esch. Coli, except?
- a) Urinary tract infections
- b) Septic infections of wounds
- c) Diarrhoea
- d) Dysentery
- e) Meningitis
Explanation:
Escherichia coli commonly causes urinary tract infections, wound infections, diarrhoea, and neonatal meningitis. Classical bacillary dysentery is primarily caused by Shigella species, not E. coli. Therefore, the correct answer is Dysentery.
Why other options are incorrect:
Why other options are incorrect:
- • Urinary tract infections: E. coli is the most common cause of UTIs.
- • Septic infections of wounds: E. coli can infect wounds, especially contaminated wounds.
- • Diarrhoea: Several strains of E. coli are important causes of diarrhoeal disease.
- • Meningitis: E. coli is a recognized cause of neonatal meningitis.
Diphtheria is caused by?
- a) Corynebacterium diphtheriae
- b) C. bovis
- c) C. jeikeium
- d) C. equi
Explanation:
Corynebacterium diphtheriae is the primary causative agent of Diphtheria. It is a Gram-positive, non-motile, club-shaped bacterium that produces a potent exotoxin, which leads to the characteristic pseudomembrane in the throat and can cause systemic damage to the heart and nerves.
Why other options are incorrect:
Why other options are incorrect:
- • C. bovis: This species is primarily associated with cattle, where it can cause bovine mastitis; it is rarely a pathogen in humans.
- • C. jeikeium: This is an opportunistic pathogen, often found as part of the normal skin flora, that can cause infections (like endocarditis) primarily in immunocompromised patients or those with indwelling catheters.
- • C. equi: Now reclassified as Rhodococcus equi, it is a well-known cause of pneumonia in foals (young horses) and can cause opportunistic lung infections in humans with weakened immune systems.
Causative organism of diphtheria was first demonstrated by?
- a) Robert Koch
- b) Louis Pasteur
- c) Klebs and Loeffler
- d) Volhard and Fahr
Explanation:
The bacterium Corynebacterium diphtheriae is often called the Klebs-Loeffler bacillus. It was first observed by Edwin Klebs in 1883 in the throat membranes of patients, and was successfully isolated and grown in pure culture by Friedrich Loeffler in 1884.
Why other options are incorrect:
Why other options are incorrect:
- • Robert Koch: While a pioneer in microbiology, he is best known for identifying the causative agents of Anthrax, Cholera, and Tuberculosis.
- • Louis Pasteur: He developed the principles of vaccination, microbial fermentation, and pasteurization, but did not discover the diphtheria bacillus.
- • Volhard and Fahr: These were German physicians famous for their classification of Bright’s disease (renal diseases), not for bacteriological discoveries.
Corynebacterium is?
- a) Gram positive
- b) Resistant to Penicillin
- c) Gram negative
- d) Resistant to Chloramphenicol
Explanation:
Corynebacterium (such as C. diphtheriae) are Gram-positive, non-spore-forming, non-motile, aerobic or facultatively anaerobic bacilli. They are characterized by their club-shaped appearance and “Chinese letter” arrangement.
Why other options are incorrect:
Why other options are incorrect:
- • Resistant to Penicillin: Most Corynebacterium species, especially C. diphtheriae, are typically sensitive to Penicillin (it is often the treatment of choice along with Erythromycin).
- • Gram negative: This is incorrect because they retain the crystal violet stain due to their thick peptidoglycan layer, making them Gram-positive.
- • Resistant to Chloramphenicol: Corynebacterium species are generally susceptible to a wide range of antibiotics, including chloramphenicol.
C. diphtheriae consists of?
- a) Starch granules
- b) Polymeta phosphate granules
- c) Lipid granules
- d) None of these
Explanation:
C. diphtheriae contains characteristic metachromatic granules, also known as Babes-Ernst granules or volutin granules. These are composed of polymetaphosphate and serve as a storage form of energy and phosphates. They appear as dark-staining spots when using specialized stains like Albert’s or Neisser’s stain.
Why other options are incorrect:
Why other options are incorrect:
- • Starch granules: These are carbohydrate storage units found in plants and some algae, but not as a diagnostic feature in Corynebacterium.
- • Lipid granules: While some bacteria (like Mycobacterium) store energy as lipids (poly-beta-hydroxybutyrate), the defining intracellular granules for Diphtheria are specifically polymetaphosphate.
- • None of these: This is incorrect as option (b) accurately describes the chemical composition of the metachromatic granules.
The incubation period of diphtheria is?
- a) Upto 2 weeks
- b) Upto 1 week
- c) 2–4 weeks
- d) None of these
Explanation:
The incubation period for Diphtheria is relatively short, typically ranging from 2 to 5 days, though it can occasionally extend up to 10 days. Therefore, “Upto 1 week” is the most accurate clinical range among the provided options.
Why other options are incorrect:
Why other options are incorrect:
- • Upto 2 weeks: While some cases might take 10 days, a 14-day incubation period is quite rare for Diphtheria.
- • 2–4 weeks: This is an excessively long incubation period for Diphtheria; such durations are more characteristic of diseases like Chickenpox or Mumps.
- • None of these: This is incorrect because option (b) correctly encompasses the standard 2–5 day window seen in most clinical infections.
Diphtheria virulence test is?
- a) Ascoli’s thermoprecipitation test
- b) Elek’s gel precipitation test
- c) C.R.P test
- d) M.R.T. test
Explanation:
The Elek’s gel precipitation test is an in vitro virulence test used to detect the toxigenicity of Corynebacterium diphtheriae. It works by observing a line of precipitation formed when the toxin produced by the bacteria reacts with a specific antitoxin-soaked filter paper strip placed on an agar plate.
Why other options are incorrect:
Why other options are incorrect:
- • Ascoli’s Test: This is a thermoprecipitin test used to detect Bacillus anthracis (Anthrax) antigens in animal tissues.
- • C.R.P Test: C-reactive protein (CRP) test is a non-specific blood test used to detect general inflammation in the body.
- • M.R.T. Test: The Milk Ring Test is used for the screening of Brucella infection (Brucellosis) in dairy cattle.
Diphtheria toxoid is prepared by using?
- a) Aldehyde
- b) Formalin
- c) Phenols
- d) None of these
Explanation:
Diphtheria toxoid is produced by the chemical detoxification of the diphtheria exotoxin. This is achieved by adding Formalin (a 40% solution of formaldehyde) to the toxin and incubating it at 37°C for several weeks. This process eliminates the toxicity of the protein while preserving its ability to stimulate an immune response (immunogenicity).
Why other options are incorrect:
Why other options are incorrect:
- • Aldehyde: While formaldehyde is technically an aldehyde, “Formalin” is the specific laboratory term for the aqueous solution used in vaccine production.
- • Phenols: Phenols are primarily used as disinfectants or as preservatives in some biological products to prevent microbial growth, but they do not convert toxins into toxoids.
- • None of these: This is incorrect as Formalin is the standard agent used for this specific biochemical conversion.
Diphtheria is an example of?
- a) Bacteraemia
- b) Pyaemia
- c) Septicemia
- d) Toxaemia
Explanation:
Diphtheria is a classic example of Toxaemia. The Corynebacterium diphtheriae bacteria remain localized at the site of infection (usually the throat) and do not typically invade the bloodstream. However, they produce a potent exotoxin that is absorbed into the blood and carried to distant organs like the heart and nerves, causing systemic damage.
Why other options are incorrect:
Why other options are incorrect:
- • Bacteraemia: This refers to the simple presence of bacteria in the blood. In Diphtheria, the bacteria themselves rarely enter the bloodstream.
- • Pyaemia: This is a type of septicemia where pyogenic (pus-forming) bacteria travel in the blood and cause multiple abscesses in various organs.
- • Septicemia: This occurs when bacteria not only enter the blood but also multiply there, causing a severe systemic inflammatory response.
Main symptom of tuberculosis is?
- a) Tubercle formation
- b) Liquid formation
- c) Both Tubercle formation and Liquid formation
- d) None of these
Explanation:
The defining pathological feature and “symptom” (sign) of the disease is Tubercle formation. A tubercle is a small, rounded nodule or granuloma produced by the immune system in response to Mycobacterium tuberculosis. It consists of a central area of infection surrounded by epithelioid cells, giant cells, and lymphocytes.
Why other options are incorrect:
Why other options are incorrect:
- • Liquid formation: While caseous necrosis (cheese-like tissue death) in a tubercle can eventually undergo “liquefaction” to form cavities in the lungs, it is a secondary stage of the lesion rather than the primary defining symptom.
- • Both: Because “liquid formation” is a specific late-stage event and not a primary diagnostic hallmark like the tubercle itself, option (a) is the most accurate clinical answer.
BCG vaccine is for the prevention of?
- a) Brucellosis
- b) Diphtheria
- c) Botulism
- d) Tuberculosis
Explanation:
The BCG (Bacille Calmette-Guérin) vaccine is used primarily for the prevention of Tuberculosis. It is prepared from a live-attenuated strain of Mycobacterium bovis. While its effectiveness in preventing adult pulmonary TB varies, it is highly effective in protecting children against severe forms of the disease, such as TB meningitis and miliary TB.
Why other options are incorrect:
Why other options are incorrect:
- • Brucellosis: There is currently no widely used or recommended vaccine for brucellosis in humans; prevention relies on animal vaccination and pasteurizing milk.
- • Diphtheria: This is prevented by the DTP (Diphtheria, Tetanus, and Pertussis) vaccine, which contains a toxoid rather than a bacterial strain like BCG.
- • Botulism: Prevention is mostly achieved through food safety and proper canning techniques. While vaccines exist for high-risk laboratory workers, they are not used for general public prevention.
Dose of BCG vaccine for a newborn (under 4 weeks) is?
- a) 0.2–0.5 ml
- b) 0.1 ml
- c) 0.05 ml
- d) 0.2 to 0.3 ml
Explanation:
The standard dose of the BCG vaccine for neonates (newborns under 1 month/4 weeks of age) is 0.05 ml given intradermally. For infants older than 4 weeks, the dose is increased to 0.1 ml.
Why other options are incorrect:
Why other options are incorrect:
- • 0.2–0.5 ml: This is a significantly high volume for an intradermal injection and could cause severe local reactions or abscesses.
- • 0.1 ml: While this is the BCG dose for children older than 4 weeks and adults, it is not the initial birth dose.
- • 0.2 to 0.3 ml: These volumes are incorrect for BCG administration and do not follow the standard WHO or national immunization protocols.
Bacilli Calmette Guerin (BCG) contains the avirulent strains of?
- a) Human tubercle bacilli
- b) Avian tubercle bacilli
- c) Bovine tubercle bacilli
- d) A typical mycobacteria
Explanation:
The BCG vaccine is a live-attenuated vaccine derived from Bovine tubercle bacilli (Mycobacterium bovis). It was developed by Albert Calmette and Camille Guérin, who sub-cultured the strain for 13 years (230 passages) until it became non-pathogenic to humans while still providing immunity against Tuberculosis.
Why other options are incorrect:
Why other options are incorrect:
- • Human tubercle bacilli: This refers to Mycobacterium tuberculosis. While BCG protects against this, the vaccine itself is not made from the human strain.
- • Avian tubercle bacilli: This refers to Mycobacterium avium, which primarily causes disease in birds and is not used in the production of the BCG vaccine.
- • Atypical mycobacteria: These are environmental mycobacteria (non-tuberculous mycobacteria) that are not used for standard TB vaccinations.
Drugs used against tuberculosis (TB) are?
- a) Rifampicin, Isoniazid
- b) Pyrazinamide, Streptomycin
- c) Both Rifampicin, Isoniazid and Pyrazinamide, Streptomycin
- d) None of these
Explanation:
Tuberculosis is primarily treated with a combination of “first-line” antibacterial medications. The standard regimen includes Rifampicin, Isoniazid, Pyrazinamide, and Ethambutol (or sometimes Streptomycin).
Why other options are incorrect:
Why other options are incorrect:
- • Option a: While these are primary TB drugs, choosing only ‘a’ ignores the other effective medications listed in option ‘b’.
- • Option b: Like option ‘a’, these are standard treatments, but they do not represent the full list provided in the question.
- • Option d: This is incorrect because all the drugs mentioned in options ‘a’ and ‘b’ are clinically proven treatments for TB.
The greatest number of tubercle bacilli is present in?
- a) Large sized tuberculomas
- b) Miliary tuberculosis
- c) Tuberculous lymphadinitis
- d) Tuberculous cavity of the lung
Explanation:
The tuberculous cavity of the lung provides a highly oxygenated environment and liquefied caseous material, which is ideal for the rapid multiplication of Mycobacterium tuberculosis. A single large cavity can contain between 107 to 109 bacilli.
Why other options are incorrect:
Why other options are incorrect:
- • Large sized tuberculomas: These are usually solid caseous masses where the lack of oxygen and acidic pH limit the growth of bacilli.
- • Miliary tuberculosis: While it involves widespread dissemination, the individual lesions (millet-sized) contain relatively few organisms compared to a large open cavity.
- • Tuberculous lymphadinitis: These lesions generally have a lower bacterial load because the environment is less aerobic than the pulmonary cavities.
Histoid Hansen is a variety of?
- a) Tuberculoid Leprosy
- b) Borderline tuberculoid
- c) Borderline lepromatous
- d) Lepromatous leprosy
Explanation:
Histoid leprosy (Histoid Hansen) is a unique and distinctive clinical variant of Lepromatous Leprosy (LL). It is characterized by the presence of firm, well-demarcated cutaneous and subcutaneous nodules and an extremely high bacterial load (highly bacilliferous). It often occurs in patients who have relapsed after Dapsone monotherapy or due to drug resistance.
Why other options are incorrect:
Why other options are incorrect:
- • Tuberculoid Leprosy: This is the “paucibacillary” end of the spectrum where the body has high immunity and very few bacteria are present.
- • Borderline Tuberculoid (BT): This is an intermediate stage leaning toward the tuberculoid end, showing different clinical features than the histoid variety.
- • Borderline Lepromatous (BL): While closer to the lepromatous end, “Histoid” is specifically classified as a specialized form emerging from the Lepromatous (LL) pole.
Causative agent of Scarlet fever?
- a) Staphylococcus aureus
- b) Streptococcus viridans
- c) Stre. pyogens
- d) None of these
Explanation:
Scarlet fever is caused by Streptococcus pyogenes (also known as Group A Streptococcus). The characteristic red rash is produced by the release of erythrogenic toxins (pyrogenic exotoxins) by the bacteria.
Why other options are incorrect:
Why other options are incorrect:
- • Staphylococcus aureus: This bacteria causes various skin infections, pneumonia, and toxic shock syndrome, but it is not the cause of scarlet fever.
- • Streptococcus viridans: This is a group of bacteria typically found in the mouth; they are common causes of dental caries and endocarditis, but not scarlet fever.
- • None of these: This is incorrect because Streptococcus pyogenes (Option C) is the recognized causative agent.
Rheumatic fever is most commonly caused by?
- a) Str. viridans
- b) Str. pyogenes
- c) Stph. aures
- d) None of these
Explanation:
Rheumatic fever is a delayed, non-suppurative autoimmune complication following a pharyngeal infection (strep throat) caused by Streptococcus pyogenes (Group A Beta-Hemolytic Streptococcus). It occurs due to cross-reactivity between bacterial antigens and human tissues (molecular mimicry).
Why other options are incorrect:
Why other options are incorrect:
- • Str. viridans: These are commensals of the mouth and are a common cause of subacute bacterial endocarditis, but they do not cause rheumatic fever.
- • Stph. aures: While it can cause skin infections, pneumonia, and infective endocarditis, it is not associated with the specific immune response that leads to rheumatic fever.
- • None of these: This is incorrect as Str. pyogenes is the well-established causative agent.
Penicillin is the drug of choice for?
- a) Scarlet fever
- b) Whooping cough
- c) Brucellosis
- d) Cholera
Explanation:
Penicillin G (or Penicillin V) is the drug of choice for Scarlet fever because the causative agent, Streptococcus pyogenes, remains highly sensitive to penicillin. It effectively prevents complications like rheumatic fever.
Why other options are incorrect:
Why other options are incorrect:
- • Whooping cough: Caused by Bordetella pertussis; the drug of choice is a Macrolide (like Erythromycin or Azithromycin).
- • Brucellosis: This requires a combination therapy, typically Doxycycline plus Rifampin or Streptomycin.
- • Cholera: The primary treatment is rehydration, but the drug of choice for shortening the illness is usually Doxycycline or Azithromycin.
In human being str. pneumoniae causes?
- a) Septicaemia
- b) Paronychia
- c) Pneumonia
- d) None of these
Explanation:
Streptococcus pneumoniae (also known as the pneumococcus) is the leading cause of bacterial Pneumonia in humans, particularly community-acquired pneumonia (CAP). It is a Gram-positive bacterium that often resides in the upper respiratory tract.
Why other options are incorrect:
Why other options are incorrect:
- • Septicaemia: While S. pneumoniae can enter the blood and cause septicaemia (bacteremia), it is usually a complication or secondary stage following the primary infection in the lungs.
- • Paronychia: This is a skin infection around the nails, typically caused by Staphylococcus aureus or yeast, not S. pneumoniae.
- • None of these: This is incorrect as Pneumonia is the hallmark disease associated with this pathogen.
Virulence factor for Stre. pneumoniae?
- a) Capsular polysaccharide
- b) Specific soluble substance
- c) Vi-antigen
- d) Forsmann antigen
Explanation:
The Capsular polysaccharide is the most important virulence factor of Streptococcus pneumoniae. It is antiphagocytic, meaning it prevents the host’s white blood cells from engulfing and destroying the bacteria. Strains that lose their capsule (rough strains) become non-pathogenic.
Why other options are incorrect:
Why other options are incorrect:
- • Specific soluble substance (SSS): This is actually the capsular polysaccharide itself when it is released into the surrounding tissues or culture media. While related, “Capsular polysaccharide” is the standard term for the structural virulence factor.
- • Vi-antigen: This is a surface antigen (capsular polysaccharide) specifically associated with Salmonella Typhi, the cause of typhoid fever.
- • Forsmann antigen: This is a heterophile antigen. While a Forsmann-like antigen is found in the C-polysaccharide of the pneumococcal cell wall, it is not the primary virulence factor.
Conjunctivitis in a new born is caused by?
- a) Streptococcus
- b) Pneumococcus
- c) Meningococci
- d) None of these
Explanation:
Conjunctivitis in a newborn (also known as Ophthalmia Neonatorum) is most commonly and classically caused by Neisseria gonorrhoeae (Gonococci) or Chlamydia trachomatis. Since neither of these primary causative agents is listed in the options, “None of these” is the most appropriate answer.
Why other options are incorrect:
Why other options are incorrect:
- • Streptococcus/Pneumococcus: While these can cause conjunctivitis in older children and adults, they are not the “classic” pathogens specifically associated with neonatal infection acquired during birth.
- • Meningococci: Neisseria meningitidis is a rare cause of conjunctivitis; it is the Neisseria gonorrhoeae species that is the significant threat to newborns.
- • Correct Answer Info: The most urgent bacterial cause to rule out in a newborn is N. gonorrhoeae because it can lead to corneal perforation and blindness.
Influenza is belonging to?
- a) Orthomyxoviridae
- b) Retroviridae
- c) Both Orthomyxoviridae and Retroviridae
- d) None of these
Explanation:
Influenza viruses (Types A, B, and C) belong to the family Orthomyxoviridae. These are RNA viruses characterized by a segmented, negative-sense, single-stranded RNA genome and an envelope containing Hemagglutinin (H) and Neuraminidase (N) spikes.
Why other options are incorrect:
Why other options are incorrect:
- • Retroviridae: This family includes viruses like HIV. They differ significantly because they use the enzyme reverse transcriptase to convert RNA into DNA, which Influenza viruses do not do.
- • Both: A virus belongs to only one specific taxonomic family based on its genetic structure and replication method.
- • None of these: This is incorrect as Option ‘a’ is the globally recognized classification for Influenza.
Influenza virus contains?
- a) Eight segments of RNA
- b) Two strands of RNA
- c) Single RNA
- d) None of these
Explanation:
The genome of Influenza A and B viruses consists of eight segments of single-stranded, negative-sense RNA. This segmented nature is significant because it allows for “genetic reassortment” (antigenic shift), which can lead to the emergence of new pandemic strains.
Why other options are incorrect:
Why other options are incorrect:
- • Two strands of RNA: This description is more applicable to Retroviruses (like HIV), which contain two identical copies of single-stranded RNA, or Reoviruses, which have double-stranded RNA.
- • Single RNA: Many RNA viruses (like Poliovirus or Rabies) have a single, non-segmented piece of RNA, but Influenza is defined by its multiple segments.
- • Note: Influenza C virus actually has seven segments, but in a general medical context, Influenza is most commonly associated with the eight-segment structure of types A and B.
‘Reye’s syndrome’ is caused by?
- a) St.pneumoniae
- b) St.pyogenes
- c) Influenza
- d) None of these
Explanation:
Reye’s syndrome is a rare but serious condition that causes swelling in the liver and brain. It most commonly occurs in children and teenagers recovering from a viral infection, particularly Influenza or Chickenpox (Varicella), especially when aspirin (salicylates) is used to treat the symptoms.
Why other options are incorrect:
Why other options are incorrect:
- • St.pneumoniae: This is a bacterium causing pneumonia and meningitis; it is not associated with the metabolic and neurological failure seen in Reye’s syndrome.
- • St.pyogenes: This bacterium causes strep throat and scarlet fever. While it can lead to complications like rheumatic fever, it is not the trigger for Reye’s syndrome.
- • None of these: This is incorrect because Influenza is a well-documented viral trigger for this syndrome.
German measles is also known as?
- a) Rubella / 2-day measles
- b) Rubella / 3-day measles
- c) Rubella / 4-day measles
- d) Rubella / 1-day measles
Explanation:
German measles is another name for Rubella, a viral infection characterized by a mild fever and rash. It is commonly referred to as “3-day measles” because the rash typically lasts about three days.
Why other options are incorrect:
Why other options are incorrect:
- • Rubella / 2-day measles: Rubella is not commonly known as 2-day measles.
- • Rubella / 4-day measles: This is not a recognized medical term for Rubella.
- • Rubella / 1-day measles: Rubella symptoms generally persist longer than one day.
The commonest cause of rubella in newborns?
- a) Congenital rubella
- b) Postnatal rubella
- c) Expanded rubella syndrome (ERS)
- d) Both Congenital rubella and Expanded rubella syndrome (ERS)
Explanation:
Congenital Rubella Syndrome (CRS) occurs when a pregnant woman is infected with the rubella virus and transmits it to the fetus. It is the most common form of rubella-related disease seen in newborns and can cause multiple birth defects.
Why other options are incorrect:
Why other options are incorrect:
- • Postnatal rubella: Occurs after birth and is not the commonest cause of rubella in newborns.
- • Expanded rubella syndrome (ERS): A broader clinical concept but not the commonest presentation in newborns.
- • Both Congenital rubella and ERS: Congenital rubella alone is the correct and most common cause in newborns.
Mumps virus belongs to?
- a) Retroviridae
- b) Paramyxoviridae
- c) Orthomyxoviridae
- d) None of these
Explanation:
The mumps virus belongs to the family Paramyxoviridae. It is an enveloped, single-stranded RNA virus that primarily affects the salivary glands, especially the parotid glands.
Why other options are incorrect:
Why other options are incorrect:
- • Retroviridae: Includes viruses such as HIV, not the mumps virus.
- • Orthomyxoviridae: Includes influenza viruses, not mumps virus.
- • None of these: Incorrect because mumps virus belongs to the family Paramyxoviridae.
Measles is characterized by?
- a) Negri bodies
- b) Babes-Ernst granules
- c) Koplik’s spots
- d) Fever
Explanation:
Koplik’s spots are the characteristic diagnostic feature of measles. They appear as small bluish-white spots with a red halo on the buccal mucosa and usually precede the skin rash.
Why other options are incorrect:
Why other options are incorrect:
- • Negri bodies: Characteristic inclusion bodies seen in rabies infection.
- • Babes-Ernst granules: Metachromatic granules found in Corynebacterium diphtheriae.
- • Fever: Common in measles but not a specific characteristic feature, as it occurs in many infectious diseases.
Brucella causes?
- a) Pertussis
- b) Plague
- c) Brucellosis
- d) None of these
Explanation:
Brucella species are the causative agents of brucellosis, a zoonotic disease transmitted from infected animals to humans through unpasteurized dairy products, direct contact with infected animals, or inhalation of contaminated aerosols.
Why other options are incorrect:
Why other options are incorrect:
- • Pertussis: Caused by Bordetella pertussis, not Brucella.
- • Plague: Caused by Yersinia pestis, not Brucella.
- • None of these: Incorrect because Brucella is the causative organism of brucellosis.
Mediterranean fever is caused by?
- a) M. tuberculosis
- b) S. typhi
- c) C. neoformans
- d) Brucella
Explanation:
Mediterranean fever, also known as Malta fever or undulant fever, is caused by bacteria of the genus Brucella. The disease is commonly transmitted through unpasteurized dairy products or contact with infected animals.
Why other options are incorrect:
Why other options are incorrect:
- • M. tuberculosis: Causes tuberculosis, not Mediterranean fever.
- • S. typhi: Causes typhoid fever, not Mediterranean fever.
- • C. neoformans: Causes cryptococcosis, a fungal infection.
- • Brucella: Correct answer. Brucella species cause Mediterranean (Malta) fever.
Which of the following test is specific for Brucellosis?
- a) Frei test
- b) Weil test
- c) Castaneda strip test
- d) Rose water test
Explanation:
The Castaneda method (Castaneda biphasic culture/strip test) is specifically used for the isolation and diagnosis of Brucella species from blood and other clinical specimens, making it a specific test for brucellosis.
Why other options are incorrect:
Why other options are incorrect:
- • Frei test: Used for the diagnosis of lymphogranuloma venereum (LGV).
- • Weil test: Refers to the Weil-Felix test used for rickettsial infections.
- • Rose water test: Not a recognized diagnostic test for brucellosis (the Rose Bengal test is used, not “Rose water”).
Malignant pustule is caused by?
- a) Anthrax
- b) Tetanus
- c) Diphtheria
- d) None of these
Explanation:
A malignant pustule is the characteristic skin lesion of cutaneous anthrax, caused by Bacillus anthracis. It begins as a papule, progresses to a vesicle, and finally forms a painless black eschar surrounded by edema.
Why other options are incorrect:
Why other options are incorrect:
- • Tetanus: Caused by Clostridium tetani and characterized by muscle rigidity and spasms, not malignant pustules.
- • Diphtheria: Caused by Corynebacterium diphtheriae and produces a pseudomembrane in the throat.
- • None of these: Incorrect because malignant pustule is a classic manifestation of anthrax.
The commonest form of anthrax in man is?
- a) Alimentary
- b) Cutaneous
- c) Pulmonary
- d) Hepatic
Explanation:
Cutaneous anthrax is the most common form of anthrax in humans, accounting for the vast majority of cases. It occurs when Bacillus anthracis spores enter the body through cuts or abrasions in the skin, producing the characteristic black eschar (malignant pustule).
Why other options are incorrect:
Why other options are incorrect:
- • Alimentary: Gastrointestinal anthrax is much less common and results from ingestion of contaminated meat.
- • Pulmonary: Inhalational anthrax is rare but highly fatal if untreated.
- • Hepatic: Hepatic anthrax is not recognized as a common clinical form of anthrax.
The animals most frequently infected with anthrax are?
- a) Sheep
- b) Cattle
- c) Goats
- d) All of these
Explanation:
Anthrax is primarily a disease of herbivorous animals. Sheep, cattle, and goats are all commonly affected by Bacillus anthracis and serve as important reservoirs for transmission to humans.
Why other options are incorrect:
Why other options are incorrect:
- • Sheep: Frequently infected, but not the only animal commonly affected.
- • Cattle: Frequently infected, but anthrax also commonly occurs in other livestock.
- • Goats: Susceptible to anthrax, but not the sole commonly infected species.
- • All of these: Correct because sheep, cattle, and goats are all frequently infected with anthrax.
Virus causing Rabies is?
- a) Orthomyxovirus
- b) Paramyxovirus
- c) Rhabdovirus
- d) Togaviruses
Explanation:
Rabies is caused by the Rabies virus, which belongs to the family Rhabdoviridae and genus Lyssavirus. It is a bullet-shaped, enveloped RNA virus that affects the central nervous system and is usually transmitted through the bite of an infected animal.
Why other options are incorrect:
Why other options are incorrect:
- • Orthomyxovirus: Includes influenza viruses, not rabies virus.
- • Paramyxovirus: Includes mumps and measles viruses.
- • Rhabdovirus: Correct answer. Rabies virus belongs to the family Rhabdoviridae.
- • Togaviruses: Includes rubella and certain arboviruses, not rabies virus.
Rhabdoviruses belong to the family?
- a) Rhabdoviridae
- b) Togaviridae
- c) Paramyxoviridae
- d) None of these
Explanation:
Rhabdoviruses belong to the family Rhabdoviridae. This family includes the rabies virus, which is a bullet-shaped, enveloped, single-stranded RNA virus.
Why other options are incorrect:
Why other options are incorrect:
- • Togaviridae: Includes rubella virus and several arboviruses, not rhabdoviruses.
- • Paramyxoviridae: Includes measles and mumps viruses.
- • None of these: Incorrect because rhabdoviruses belong to the family Rhabdoviridae.
Rabies virus isolated from natural human or animal infection is termed as?
- a) Street virus
- b) Fixed virus
- c) Both Street virus and Fixed virus
- d) None of these
Explanation:
Rabies virus obtained directly from a naturally infected human or animal is called a Street virus. It has a variable incubation period and retains its natural pathogenicity. Repeated passage through laboratory animals produces a Fixed virus, which has a shorter and more constant incubation period.
Why other options are incorrect:
Why other options are incorrect:
- • Fixed virus: Produced by repeated laboratory passage of the street virus, not isolated directly from natural infection.
- • Both Street virus and Fixed virus: Only the virus isolated from natural infection is termed street virus.
- • None of these: Incorrect because the correct term is street virus.
